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THE ANNALS OF
APPLIED BIOLOGY

THE OFFICIAL ORGAN OF THE ASSOCIATION
OF ECONOMIC BIOLOGISTS

BDITED (BY
Prorrssor MAXWELL LEFROY, Imperial College of Science and Technology, London,
AND
Proressor B. T. P. BARKER, National Fruit and Cider Institute, Bristol
Dr S. E. CHANDLER, Imperial Institute, London
F. J. CHITTENDEN, Royal Horticultural Society’s Gardens, Wisley
Prorressor F. W. GAMBLE, The University, Birmingham
Proressor PERCY GROOM, Imperial College of Science and Technology, London

Dr A. D. IMMS, The University, Manchester

Proressor R. NEWSTEAD, The University, Liverpool

Proressor J. H. PRIESTLEY, The University, Leeds

Volume | 1914-15

CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, Manacer
LONDON: FETTER LANE, E.C.
EDINBURGH: ICO, PRINCES STREET
also
H. K. LEWIS, 136, GOWER STREET, LONDON, W.C.
WILLIAM WESLEY & SON, 28, ESSEX STREET, LONDON, W.C.

PARIS: LIBRAIRIE HACHETTE & CIE.

CHICAGO: THE UNIVERSITY OF CHICAGO PRESS
BOMBAY AND CALCUTTA: MACMILLAN & CO., LTD.
TORONTO: J. M. DENT & SONS, LTD.
TOKYO: THE MARUZEN-KABUSHIKI-KAISHA

Cambridge :
PRINTED BY JOHN CLAY, M.A.

AT THE UNIVERSITY PRESS

Me

COMEEN TS

No. 1 (May, 1914)

Editorial :

Impending Decteeaents., in Keneutate a Fralaay By Pre
F. W. GamMBLE ; ;

The Action of Bordeaux Wiebe on Plone By Pit i T. E
Barker and C. 'T. Gimincuam. (With 6 Textéfigures)

Notes on the Green Spruce Aphis (Aphis abietina Walker). By
F. V. Turosatp. (With 10 Text-figures) f

Pollination in Orchards. By F. J. CarrrenpEen } ;

Life-history of Pegomyia hyoscyami. By A. E. Cameron.
(Plates I and II and 4 Text-figures)

Caterpillars attacking Oaks in Richmond Park. By R. H.
Deakin. (Plates [IIJ-VIII)

A Bacterial Disease of Fruit Blossom. By B. ds P. Pres fen
OrTo GROVE .

On the Preparation of Gbccidas for Miersec sina Study. By
K. E. GREEN

Me 2 (ae 1914)

Preliminary Notes on Damage to Apples by Capsid Bugs. By
J. C. F. Fryer. (Plates [IX and X) 3 :

The International Phytopathological Conference, 1914. By
A. G. L. Rogers

The Host Plants and Habits of Apis rumicis Tiras ait some
Observations on the Migration of, and Infestation on Plants by
Aphides. By J. Davipson

Some Observations on the Life-history and ionamias a the
Knapweed Gall-fly (Urophora solstitialis Linn.). By J. T.
WavswortH. (Plates XI and XII and 1 Text-figure)

A Braconid Parasite on the Pine Weevil (Hylobius abietis). By
J. W. Munro. (With 4 Text-figures)

Observations on the Life-history of the American Greener:
Mildew (Sphaerotheca mors-uwoae (Schwein.) Berk.). By
K. 8. SatMon ; ‘ : : : 5 ; ‘

Potato Diseases. By A. 8. Horne. (With 8 Text-figures)

A Note on Celery Leaf-Spot Disease. By F. J. CarrrenDEN

Notes 4 é : :

}

PAGE

107

115

118

142

iv

12.
15.

Contents

Nos. 3 and 4 (January, 1915)

Some Difficulties in the Improvement of Indian Sugarcanes. By
©. A. Barper. (Plates XIII-XVI and 3 Text-figures) .

The Pea Thrips (Kakothrips robustus). . C. B. WitiiaMs.
(With 12 Text-figures) :

The Apple Sucker, with Notes on the Pear Sucker. ae PB
Awatr. (Plates XVII and XVIII and 21 Text-figures)

Insecticides from a Chemical Standpoint. By W. F. Cooprr
and W. H. Nutra. ; : : ;

Insecticides. By H. M. Lerroy. (With 1 Text-figure)

The Composition of the Coffee Berry and its Relation to the
Manuring of a Coffee Estate. By Rupotex D. ANsTEAD

The Life-history and Habits of the Greenhouse White Fly
(Aleyrodes vaporariorum Westd.). a E. HARGREAVES.
(With 56 Text-figures) ; :

Infection and Immunity Studies on the oe and Pear Scab
Fungi (Venturia inaequalis and V. pirina). By 8. P. Wixr-
SHIRE. (Plates XIX—XXII) : : :

Winter Cover Washes. By A. H. Lrrs

A Preliminary Investigation as to the Cause of Rotting of Oranges
from Brazil. By W. Ruswron. (With 1 Text-figure) .

Effects produced by Sucking Insects and Red Spider upon
Potato Foliage. By A. S. Horne and H. M. Lerroy.
(Plates XXITI-XXVIT)

Notes (with | Text-figure)

Review

PAGE

299

303

335
S51

365

370

387
403

VoLUME | MAY, 1914 No. 1

THE ANNALS

OF

APPLIED -BIOEOGY,

EDITORIAL.

THE Association of Economic Biologists was founded ten years ago
and commences herewith the publication of a journal devoted to the
special interests of its members. During this period its scope has
broadened and the Annals of Applied Biology is intended to cover the
ground in applied biology which is not now covered by special journals
such as those dealing with agricultural science, parasitology, genetics
and medical science.

Whilst the membership of the Association includes those who
contribute to these special journals, it is now intended to deal especially
with other branches of applied biology, and we are glad to be able to
issue in our first number a wide range of papers, which will soon become
still wider.

All papers which bear on the scientific problems of applied biology
will be welcome ; we have no place for purely systematic work which is
amply provided for elsewhere, nor for faunistic work as such.

The Association. The Association was founded in 1904 with head-
quarters in Birmingham and has since held meetings at which papers
on biological subjects were read and discussed. The headquarters
are now in London, and it is hoped to hold meetings quarterly, usually
in London, but with one meeting annually elsewhere.

There is room for a wider membership in the Association, which aims
at drawing together workers in applied biology, and if that membership
can include a large majority of those engaged in research and teaching,
and those in official positions, the influence of the Association could be
applied both to public opinion and to national affairs in a measure
wholly impossible in the past.

Ann. Biol. 1 L

2 Editorial

We hope to secure the support of workers in the Dominions and
Colonies. Few people realise how great is the progress made in applied
biology in the Over-seas Dominions during the last twenty years and how
vital to the success of all tropical industries is the work that is being
done in applied biology ; it has become evident in regard to medicine,
but is less realised in agriculture, horticulture, animal breeding, and
other industries in which investors at home are interested ; neverthe-
less, such industries depend for their continued prosperity more and
more on research in biology and the application of its results.

The Association will attempt to form a link between workers in
Great Britain and in the Dominions, and the support of colonial members
of the Association is as vital to success as that of their fellow-workers
in this country.

Towards effecting this, the publication of a journal may have a
great influence and we hope to attract not only the more solid scientific
contributions but also notes of progress, of interesting achievements,
of practical problems, as they present themselves to members in the
various parts of the Empire.

We have lately made a wide appeal for membership, since we believe
that only by organisation will the applied biologist be in a position to
establish his subject as one of profound importance in the future welfare
of the Empire. The recognition of the important part played by biology
is as yet very imperfect, even in the minds of the most advanced officials
of State Departments and Colonial Administrations ; large problems,
in which technical knowledge is required, are settled without the tech-
nical expert being seriously consulted and this is the fault, not of the
official mind or of the man-in-the-street’s attitude, but of the applied
biologists themselves. Medical men are organised and that so success-
fully that in a present problem, largely entomological, the medical
interest has tended to prevent all recognition of the value and need of
the entomologist’s services ; we refer to the tse-tse fly problem in Africa
but we could quote other similar cases ; at the recent Phytopathological
Congress in Rome the technical experts were outnumbered by the diplo-
mats and no country had been able to give its experts a deciding voice
in the Congress, though the questions involved were admittedly technical
and could be decided only by experts.

We see this attitude daily and every biologist in the Empire suffers
from this sooner or later; it was once a custom in India to appoint a
medical officer to any scientific post, simply because science was so
vague a conception to the senior official, educated in the classics, that

H. MAXWELL-LEFROY 3

he could not conceive subdivisions of science requiring technical expert
advice: that day is gone in India but there is still much to teach the
official, as also the man in the street, in this respect.

If then the applied biologist is to make himself felt, it will be through
an organisation comparable to those by which the chemists, the engineers
and the doctors assert themselves ; we hope to make the Association
such an organised body : the publication of the Annals will be a means
to that end and we ask all applied biologists to support it, to join the
Association and to induce others to do so too.

The Inbrary. There is at present no centre in London where the
literature of appled biology can be consulted or obtained on loan.
Societies such as the Zoological, Entomological, and Linnaean, maintain
libraries of systematic and purely scientific literature, but scarcely any
at all of the applied aspect. It is proposed to found the nucleus of a
library of applied biology and in this connection an appeal is made to
members to send : .

(1) Separates of all papers they have published so far as these are
available.

(2) Separates of those they have received which they do not speci-
ally want and duplicates.

(3) Parts or sets of any periodicals they do not need.

(4) Books they can spare.

This is an experiment in this sense, that it is not yet certain that
the library can be maintained ; but members are asked to send separates,
etc. under these conditions :

(1) All will be acknowledged.

(2) All will be kept in a room at the Royal College of Science, open
to all members.

(3) All will be card-indexed under author and subject.

(4) All will be registered with the name of the lender and under the
condition that, should the library be broken up or not maintained,
they will be returned to the lender.

(5) So far as possible, they will be available for loan, personally
or by post, on the borrower signing a receipt, and an undertaking to
return them or be liable for their return or replacement.

(6) The Association will pay postage out, the borrower postage
back.

It is probable that the foundation of a library will be of the greatest
value to members, and when the membership has increased the income
of the Association will enable the library to be added to and made of

=9

“

4 Editorial

greater value. In the present venture, no expenditure is entailed on
the Association beyond postage; the whole library will be, for the
present, on loan, but when it becomes possible, the Association will
establish a permanent library and ask all lenders to definitely donate
or resume their contributions. A library fund has been established
to which contributions of any amount are invited.

Meetings. Members resident in the United Kingdom are reminded
that the meetings will now be quarterly and before this appears the
first will have been held.

Members are informed that it is proposed to have the next meeting
after the International Agricultural Conference in London, which ends
about June 30th. We hope that all members home from the Colonies
or India will attend ; the library room kindly lent us by the Imperial
College of Science, South Kensington, is available for members and
contains the present small nucleus of our library.

H. MAXWELL-LEFROY.

IMPENDING DEVELOPMENTS IN AGRICULTURAL
ZOOLOGY.

By Proressor F. W. GAMBLE, F.R.S.

THE endowment of research in Agricultural Zoology by the Develop-
ment Commissioners is a sign of the increased interest in the possibilities
of the application of this subject to actual practice. Hitherto entomo-
logy only has been considered of value in regard to agriculture and
though other classes of animals have long been known to exert an impor-
tant influence upon the yield of crops and stock, yet no advance has
hitherto been made in their study which can compare with that accom-
plished in the case of insects. Now however the Board of Agriculture
has asked the University of Birmingham to take up these hitherto
neglected branches of zoological study with special reference to helmin-
thology and a beginning has been made both with this subject and with
the protozoology of the soils.

In the present article I propose to discuss briefly some of the problems
that lie before the investigators in this latest application of zoology to
agriculture. Taking first, the organisms of soils (other than insects)
the primary impression is the need for an ordered body of systematic
knowledge such as entomologists already possess in virtue of the longer
study and larger number of devotees which this subject has attracted.
There has been up to the present no concerted attempt in any country
to determine the biological factors of the soil, their relations to its quali-
ties, to seasonal changes, or to its fertility. Efforts have been made at
the Rothamsted Laboratory and elsewhere to determine the effects
of certain protozoa; and in Italy a movement for the study of soil
organisms is in its inception. But we have at present no estimate
based on any but exceedingly small samples, of the animal factors,
estimated either qualitatively or quantitatively, that are present in
the soil. Dr Russell and Dr Hutchinson have brought forward evidence
that the factor limiting the accumulation of one or more of the essential
substances for plant production is a biological and not a chemical one.

6 Developments in Agricultural Zoology

And Mr Goodey, working at first on their samples and more recently
at the new Birmingham Station, has determined the protozoan fauna
of certain small samples of soil, the properties of which have been tested
in other ways at the Rothamsted Station. By these and other allied
observations carried out by C. H. Martin and Lewin in this country and
by A. Cunningham in Germany, it appears that a rich fauna of ciliate,
flagellate, and amoeboid protozoa are present in certain soils ; that some
of them at least are capable of active life therein under ordinary con-
ditions ; and that they are to be seen, when raised in cultures, ingesting
masses of bacteria. Much work however still remains to be done on
these organisms both from the purely zoological aspect and from the
point of view of their effect upon soil fertility, and inasmuch as sound
results on the life-history of protozoa involve concentrated study
continued over a long period, it would be idle to expect a rapid advance
in such a difficult field of research. There can be no doubt however
that the results will be of great interest both to the science and practice
of husbandry.

Another branch of soil science which is being promoted at Birming-
ham University relates to the free-living Nematodes and to those of
parasitic or saprophytic tendencies.

That these play an important part in soil metabolism and in the
germination and growth of crops can hardly be doubted, but no data
are as yet forthcoming except for those essential parasitic species of
Tylenchus and Heterodera that occur sporadically on various cereals
and vegetables.

The case of the recent serious outbreak of disease in the rice fields
of Bengal shows how important the study of these eelworms may prove.
The rice-plant in certain districts dies off in patches or the crop may
fail altogether from the attack of Ufra disease. This term “ Ufra”
meaning “ from above” suggests that the blight is due to atmospheric
conditions, but an investigation conducted by the Agricultural Research
Institute at Pusa (Bulletin No. 34, 1913, Diseases of Rice by K. J. Butler,
M.B.) has shown that the main cause of ‘“‘ Ufra” is not atmospheric
but is a small Nematode, Tylenchus angustus, which by injuring the
epidermis of the unprotected parts of the rice-shoot causes weakening,
discolouration and ultimately the death of the plant. Moreover as this
worm multiplies rapidly and swims through the muddy fields from one
plant to another, a single focus of infection may spread over a consider-
able area in a short time. The serious nature of the outbreak lies in
the proximity of the infected district to the great rice-producing countries

KF. W. GAMBLE 6

in Northern India. On the west of this district at the head of the Bay
of Bengal, lie the extensive paddy fields of the Province, whilst on the
east is the great export rice-growing tract of the Irrawaddy Delta. The
investigation has been conducted chiefly by Dr Butler the mycologist
at Pusa, but it is to be hoped that the Indian Government will realise
the importance of having a trained helminthologist to prevent the
extension of what is perhaps the most serious blow that could befall an
oriental peasantry—the loss of the paddy crop.

There is however no need to go so far afield as India to illustrate the
importance of research on soil Nematodes, and Mr Gilbert E. Johnson,
M.Sc. of Birmingham University, who is taking up this group, has
already shown by his interesting paper on unisexual families in the
Nematode parasitic in the earthworm (Quart. Journ. Mier. Sez. June 1913)
that there are many purely scientific as well as applied questions upon
which the study of Nematodes throws light.

The part played by earthworms in regard to soil problems and
plant rearing has been very inadequately ascertained, and in this subject
further advances may be confidently expected. Enumeration of the
earthworm fauna has proceeded apace in this country of late, chiefly
through the enterprise of the Rev. Hilderic Friend and collectors inspired
by him. The result has been a marked increase in the known micro-
forms or Enchytreids, whilst a careful descriptive account of the structure
of Enchytreus pellucidus by Mr H. H. Stirrup, M.Sc. (Proce. Zool. Soe.
1913) has added much needed anatomical evidence on certain points
though it leaves the important question of the eggs and their mode of
deposition unsettled. What is wanted, however, more than anything
else with regard to this group, is an estimate of its effect upon plants
and soils.

Coming now to the parasitic helminths, there has been a great in-
crease in recent work carried on chiefly by Dr Shipley and members of
the Grouse Commission in this country, in America, Germany, Italy,
and France. This has confined itself largely to systematic and ana-
tomical features and there is a great deal still to be made out with regard
to the life-histories of even the commoner Nematodes and Platyelmia,
whilst curative or preventive measures are as yet in their infancy.
Farm stock, poultry and game in most countries are more commonly
infected with these verminous parasites than is generally supposed.
The farmer may know the fact well enough and he often finds a cheap
and effective method of ridding his stock of these pests by the applica-
tion of a vermifuge in early autumn ; but it is not always that his stock

8 © Developments in Agricultural Zoology

responds to this curative treatment, and although evidence is at present
hard to obtain except by personal visits, yet it points to the serious
incidence of husk and other round worm diseases in certain districts,
whilst the severe stomach worm disease seems at present to be waning
in extent of range and intensity. There is however a very real need of
dealing more fully with these animal parasites from all points of view
than has ever been undertaken before and to this end the Board of
Agriculture has approved the appointment of Dr Chas. L. Boulenger as
Reader in Helminthology at Birmingham University. It is to be hoped
that the other centres, such as Liverpool and London Universities
where similar work is organised and other Research Institutions where
animal nutrition and animal pathology are dealt with, will co-operate
with Birmingham in regard to the difficult common problems that arise
in connection with prevention of stock from these verminous diseases.

One general conclusion is reached on considering the future that lies
before zoological research as applied to agriculture. It is that mutual
assistance between the man on the land and the worker in the laboratory
or in the field is essential to progress. We need a careful census of the
country, a census that is of the animals and the animal-borne diseases
affecting agriculture. We need more work, far more work, on the life-
histories of the groups in question, whether indifferent, noxious or
beneficial. But more than these, there is required a real and mutual
understanding between the stock owner and the investigators and
between the investigators of different countries working at similar
problems. An organised study of animal parasites is now in progress
in most civilised countries, and renewed interest in the subject has spread
like a wave in the last few years. Schools of research are growing up
in Egypt, in Australia, Japan and China, so that a means of coordinating
the activities of such scattered workers is highly necessary. May this
new journal be effective in promoting the progress of research by en-
couraging such mutual understanding !

THE ACTION OF BORDEAUX MIXTURE
ON PLANTS.

By B. T. P. BARKER, M.A., anp C. T. GIMINGHAM, F.L.C.

(University of Bristol ; Agricultural and Horticultural
Research Station.)

In the course of experimental work involved in the investigation
of the fungicidal action of Bordeaux mixture!, a number of observations
have been made on the inter-action between the spray fluid and the
plants with which it comes into contact in the process of spraying.
Further attention has now been given to this part of the subject and as
the results help to explain various points arising in practical spraying,
it is proposed to give an account of the experiments here.

It will be most convenient to consider the work in two sections,
dealing with (a) spray injury or “ scorching” by Bordeaux mixtures,
and (b) the penetration of copper from Bordeaux mixtures into the plant.

Foliage Injury or Scorching by Bordeaua mixture.

The injury to foliage, more or less pronounced, which is frequently
found to follow the application of Bordeaux mixture, has been the subject
of a good deal of work, especially in America. As regards its possible
bearing on the question of the fungicidal action of Bordeaux mixtures,
the matter is discussed shortly in Section II of the second paper
referred to. In considering the various means by which copper might
be brought into solution on the surface of sprayed leaves, the suggestion
was then made that some importance should be attributed to the in-
fluence of exudations from injuries to the leaves; and it was further
suggested that if soluble copper is produced in this way, it would probably
show its presence by causing or intensifying scorching. This point has
been followed up in some detail.

In order to have reliable material for experimental work in this

' See Journ. Agric. Sci. 1v, p. 69; ibid. tv, p. 76.

10 Bordeaux Mixture and Plants

connection, it was essential to obtain apple foliage known to be entirely
undamaged. As is generally recognised, it is almost impossible to find
any number of apple leaves, when grown under ordinary conditions,
which are really free from minute injuries of some sort or another. It
was therefore found necessary to grow foliage specially protected from
liability to injury. With this object, a number of one year old apple
seedlings in small pots were carefully cleaned before the leaf buds

i 9

Fig. 1. Foliage undamaged and treated with “‘ no-excess-lime ’’ Bordeaux mixture.
Fig. 2. Foliage damaged with scratches and cuts and sprayed with water.

opened and each one enclosed in a muslin cage supported on a light
frame. The plants were kept in a cool greenhouse and the new foliage
put out was thus almost completely protected from the chance of damage
by bruising or by insect attacks. A few leaves on some of the plants
were slightly attacked by apple mildew, but these were always removed
before starting an experiment.

B. T. P. BARKER AND C. T. GIMINGHAM 11

When the leaves were fairly well developed, the plants were uncovered
and the following series of experiments was carried out :

Plant No. 1. Leaves covered with ordinary Bordeaux mixture
(7.e. containing large excess of lime).

Plant No. 2. Leaves first artificially damaged with scratches and
pin-pricks and then treated as No. 1.

3 4

Fig. 3. Foliage damaged with scratches and cuts and treated with “ no-excess-lime”
Bordeaux mixture.
Fig. 4. Foliage damaged with pin-pricks and treated with ordinary Bordeaux mixture.

> Bordeaux

Plant No. 3. eaves covered with ‘* no-excess-lime ’
mixture!.
Plant No.4. Damaged exactly as No. 2, and the leaves then covered

with the ‘‘ no-excess-lime ”’ mixture.

1 This expression is used to indicate a mixture of copper sulphate and lime water
in such proportions that the whole of the copper is precipitated in the form of the basic
sulphate 10 CuO, SO, (Pickering).

12 Bordeaux Mixture and Plants

Plant No. 5. Damaged exactly as No. 2, and then sprayed with
water.

On the day following the treatment, there was not the least trace of
injury or scorching noticeable on plants Nos. 1 and 3; whereas Nos. 2
and 4 showed very serious injury typical of Bordeaux scorch, and
moreover the injuries in every case had quite obviously begun at the
artificially damaged spots, and afterwards spread. The scorching was

6

Fig. 5. Foliage damaged by aphis and treated with ‘ no-excess-lime ” Bordeaux mixture.
Fig. 6. Foliage damaged by bruising and treated with ‘no-excess-lime””’ Bordeaux

mixture.

very much worse in character and more widespread in No. 4 than in
No. 2; No.5, the plant sprayed with water, showed a browning along
the extreme edges of the scratches and spots, but no spreading of injury.
Other plants belonging to the same batch as those used in the above
trials but which had been allowed to develop their foliage without special
protection in the greenhouse were covered with the ‘‘ no-excess-lime ”’
mixture and included in the series; these showed slight scorching

B. T. P. BARKER AND C. T. GIMINGHAM ~ 18

especially round the edges of the leaves. These results have been con-
firmed several times.

In another series, aphides were introduced into the muslin cage
surrounding the foliage and allowed to increase until many of the leaves
were badly infested ; the plants thus damaged were then covered with
the “ no-excess-lime ” mixture. The result was very bad scorching,
largely confined to the underside of the leaves where they were most
damaged by aphis.

The relative degrees of injury under various conditions are shown
in the accompanying drawings, the shaded portions representing
browning of the leaf.

Similar experiments with the protected foliage of apple shoots stand-
ing in water gave confirmatory results. The leaves in this case being
much less well developed were mostly entirely killed by the Bordeaux
where the artificial damage had been at all severe, but undamaged leaves
remained healthy. It was found, further, as was to be expected, that
these effects were very much more marked when the Bordeaux was put
on soon after the damaging of the leaves. In a moist atmosphere, bad
“ scorching ” followed treatment with the spray fluid up to.24 hours
after the damage had been done; if a 48 hour interval was allowed, the
effect was markedly less severe and after 72 hours it was very slight.
In a fairly dry atmosphere both out of doors and in the greenhouse,
the “scorching” following treatment 18-24 hours after the leaves
were damaged, was not very serious; although in some cases it got
noticeably worse after several days. In these experiments the damage
to the leaves was made as far as possible equally by means of pins fixed
in a cork, and the spray fluid was usually put on the leaves with a brush
so as to ensure a uniform coating.

We have then definite evidence of the importance of the presence
of artificially or naturally damaged foliage in considering the scorching
by Bordeaux mixture. The extreme difficulty of finding leaves which
have altogether escaped damage has already been mentioned ; and has
been experienced by many other workers. Crandall! in America, for
example, made a careful examination of 6000 leaves taken at random
from 60 different trees and found only 27 (less than 0°5 °%) which he
could call perfect leaves; although the appearance of the foliage on
these trees, on the whole, was good. Wallace? in his work on spray
injury by lime-sulphur preparations also emphasises the rarity of

1 Univ. Illinois Agric. Expt. Sta. Bull. 135.
2 Cornell Univ. Coll. Agric. Bull. 288.

14 , Bordeaux Mixture and Plants

uninjured leaves, and both he and Crandall and other workers have
drawn attention to the fact that, in practice, foliage which is badly at-
tacked by insect or fungus pests or otherwise badly injured is specially
liable to serious damage by scorching. Pickering also refers to the
effect of injuries in intensifying scorching?.

There is then no doubt whatever that even slight injuries to the
leaf cuticle, if they have not had time to dry up, play an important
part in determining the extent of scorching, following spraying with
Bordeaux mixtures. Summer foliage, known certainly to be un-
damaged, as far as our experiments go, shows no scorching.

In order to explain the increased scorching due to leaf injuries,
it is necessary to account for the production of copper in a soluble form.
Until lately the view has been generally accepted that atmospheric
agencies, and in particular carbon dioxide, are responsible tor the pro-
duction of soluble copper sulphate from the insoluble basic copper sul-
phate which is deposited on the leaf. Both the fungicidal action and the
scorching are attributed to the copper sulphate thus formed. It has,
however, been shown by one of us? that from the chemical standpoint this
view is not tenable ; the fungicidal action of Bordeaux mixture cannot
be put down to copper sulphate liberated by the action of atmospheric
carbon dioxide; and the experimental evidence for this statement is
equally applicable with reference to the scorching action. The authors
have further shown? that the fungicidal action of Bordeaux mixture is
very largely, if not entirely, due to an inter-action between the fungus
and the particles of the insoluble basic sulphate with which it comes in
contact ; the fungus dissolving and absorbing enough copper to kill
itself. In the same way the simplest explanation of the enhanced
scorching of damaged, as compared with undamaged, foliage is, that
soluble copper compounds? are produced by the solvent action of exuda-
tions from the injured cells and from those underlying, which are exposed
by the injury, and that these substances are then absorbed through the
thin-walled cells of the internal tissues of the leaf. It is then easy to
understand the gradual spreading of the spots from a centre which is
observed in most cases of Bordeaux scorch. Serious scorching occurring
several days or even weeks after the actual spraying is probably to be

1 11th Rep. Woburn Exptl. Farm, p. 123.

2 Journ. Agric Sci. 1v, p. 69.

3 Ibid. Iv, p. 76.

4 Soluble copper produced in such manner may, as previously suggested, also act

fungicidally.

B. T. P. BARKER snp C. T. GIMINGHAM 15

accounted for by rough weather causing damage to the foliage, or by a
serious insect attack. Again the general opinion of practical men! that
the severity of Bordeaux injury is determined by the weather condi-
tions at the time of spraying and that the injury is most serious when
rain immediately follows the spraying fits in well with the view here
suggested, since in wet weather any injuries present will heal over much
less quickly and will therefore be capable of dissolving copper during
a longer period.

In view of these considerations as to the important part played by
imjuries to the leaf surface in determining the extent of Bordeaux
scorching, it becomes interesting to enquire whether the presence of
such injuries is the sole cause or whether Bordeaux mixture does ever
cause scorching on undamaged leaves. This is not an easy point to settle
satisfactorily. It appears that, as recorded above, there is no notice-
able scorching of foliage which has been carefully protected ; and indeed
we have a good deal of evidence emphasising the impenetrability of
the undamaged leaf cuticle of ordinary healthy summer foliage. For
example, the general surface of healthy leaves stands immersion in
5 % or even 10 % copper sulphate solution remarkably well; and on
repeating many of the experiments with damaged and undamaged
foliage described above, but using 5 % copper sulphate solution in place
of the Bordeaux mixture, almost identical results were obtained. The
damaged leaves indeed “ scorched” worse with copper sulphate than
with the Bordeaux mixture, but the undamaged leaves remained
almost entirely unaffected, unless the time of contact was very pro-
longed.

The general conclusion which may be drawn from a large number
of experiments on the effects of solution of copper sulphate upon the
foliage of different varieties of apple is that, except where the leaves
are originally damaged in some way, a short time of contact with a weak
solution causes little or no immediate injury, though a longer time of
contact may initiate injury to the under surface. Even, however,

1 Confirmed experimentally by Crandall (loc. cit.) and by Hedrick (New York Agric.
Expt. Sta. Bull. 287).

* It is somewhat difficult to understand exactly what is the position taken by Crandall
with regard to this point. On p. 232 of his Bulletin, after describing some experiments,
he concludes that “ the uninjured epidermis of apple leaves was not permeable by copper
sulphate solutions”: whilst his conclusion No. 16 runs “‘.... burning quickly follows appli-
cations of copper sulphate even when the solutions are very dilute.” Possibly the latter
statement refers only to damaged foliage, in which case his observations are in full agree-
ment with those here recorded.

16 Bordeaux Mixture and Plants

after immersion for one hour in a 5 % solution or for half an hour in
a 10% solution the general surface of healthy leaves is not seriously
injured. It must be mentioned, however, that with all leaves, damaged
or undamaged, treatment with copper sulphate affected the hairs on
the under surface, resulting in slight yellowish discolouration, which on
close examination were found to be due to the staining of the cell walls.
It also hastened the death of late autumn foliage.

By coating one or other of the surfaces of the leaf with vaseline, it
was possible to compare their behaviour towards copper sulphate solu-
tion, and it was thus found that the upper surface, where quite free from
damage, possesses a remarkable power of resistance to the penetration
of the solution. Even when the liquid was allowed to dry on the Jeaves,
injury to the upper surface was confined to certain areas, usually
evidently arising from some original damage. The under surface is
more easily affected: possibly the presence of stomata (in the apple)
on the under surface of the leaf only may have some bearing on this
point.

These observations apply, however, only to summer foliage.
When similar experiments are tried in the late autumn the
results are different. The effect of covering autumn leaves, whilst
still on the trees, with ‘ no-excess-lime” Bordeaux mixture is
to cause considerable and apparently general scorching over most of
the leaf surface, accompanied by premature defoliation. When ordinary
Bordeaux mixture (containing excess lime) is used, there is more scorch-
ing than is noticed in the summer, but the action is not severe. With
5% copper sulphate solution the leaves very soon shrivel up and drop,
and the presence of copper can be traced inside the stem lower down
than the parts actually immersed!. There is in these cases apparently
a general scorching independent of the presence of visible injuries, and
of a somewhat different character to that which occurs in the summer.
The cuticularised walls of the cells are found to be stained a pale greenish
colour, in a manner similar to the leaf-hairs already mentioned.

Possibly under autumnal conditions changes take place in the nature
of the cuticle, which lead to the production and absorption of soluble
copper over the general surface of the leaf, the Bordeaux mixture thus
damaging underlying cells in spite of the really uninjured leaf surface.
On the other hand, the possibility of the presence of small injuries was
not entirely excluded in these experiments, though the foliage was chosen
for its generally sound appearance.

1 See also p. 18.

B. T.. P. BarKeR anp C. T. GimingHaM 17

The behaviour of apple foliage in the summer condition towards
Bordeaux mixture appears to be typical of that of a variety of other
hardy plants. The leaves of wallflowers, privet, and violet have been
similarly tested and in each case there has been no scorching of uninjured
foliage. It is well known, however, that very great variations in sus-
ceptibility to scorching are shown by different plants. Some are
peculiarly susceptible, and in such cases the general character of the
scorching strongly suggests that a change in the nature of the cuticle
or, perhaps, the presence of groups of uncuticularised cells rather than
local injury is responsible. It is possible that the cuticle in these
instances is normally more or less permeable, just as the cuticle of apple
leaves appears to become in autumn. Salmon’s work! on the sus-
ceptibility of. certain varieties of gooseberries to scorching injury after
spraying with lime sulphur washes of various strengths appears to bear
out this point; varieties such as Lancashire Lad, Crown Bob, and
Berry’s Early remaining unaffected by the spray when treated in early
summer, while later a wash of the same strength causes scorching.
It was also shown that certain kinds such as Valentine’s Seedling and
Yellow Rough were regularly injured, whilst others such as Whinham’s
Industry, Rifleman and May Duke escaped damage even when a wash
of more concentrated strength was used.

It may be said in conclusion that the evidence seems complete as
regards the part played by injuries to the leaves in causing scorching
of apple foliage following spraying with Bordeaux mixture; whilst
under some conditions it would seem that scorching might also occur
over the general surface of the leaf and unconnected with the occurrence
of injuries, though this is less certain. No doubt such action if it takes
place is more important in foliage such as peach and apricot where either

the cuticle as a whole or certain parts of the leaf surface appears to be
less resistant than is the case with the apple.

The Penetration of Copper from Bordeaux mixture into the Plant.

The action of the copper of Bordeaux mixture upon plants is not
confined to the surface. It is found that under certain conditions plants
which have been sprayed absorb some copper either through their foliage
or their roots.

Millardet and Gayon (Journ. d’ Agric. Prat. 1887, p. 125) were the
first to refer to the absorption of copper by leaves. They proved the

1 Journ. Bd. Agric, xv, p. 881; xx, p. 1057.
Ann, Biol. 1

bo

jt Bordeaux Miature and Plants

presence of copper in the cuticle of grape leaves which had been treated
with various strengths of copper sulphate solution : no information is
however given as to the condition of the leaves as regards injury. Rumm
(Ber. Deut. Bot. Ges. x1, p. 79) and later Crandall (loc. cit.) found no
penetration of copper from copper sulphate solutions through the cuticle
of uninjured apple leaves. Pickering on the other hand (loc. cit. p. 113)
showed the presence of copper in the ash of “ perfectly sound” apple
leaves treated with various copper solutions.

During the present investigation damaged apple foliage which has
been sprayed and which shows any signs of scorching has always been
found to contain some copper. Repeatedly, such leaves have been
examined. The procedure adopted has been first to wash the sprayed
surface in dilute acid, great care being taken to wet every portion with
a brush, then to transfer the leaves to running water for half an hour
or longer, after which they are dried and ignited and the ash tested for
copper. In the case of scorched leaves, copper is invariably found to
be present in the ash. On the other hand, with really uninjured summer
apple foliage, copper has not been detected in the ash!. Probably the
presence or absence of slight injuries is sufficient to account for the
conflicting results of other workers.

A comparison of the results of dipping healthy summer and autumn
apple foliage into 5 per cent. CuSO, is very striking. As has been men-
tioned, the summer leaves are little affected by this treatment; the
autumn leaves, however, besides being severely scorched, absorb a good
deal of copper which is passed down into the stem, killing all the interior
cells for some distance below the portion actually immersed.
Crandall has recorded a similar translocation of copper through the
stem of apple trees into which solutions of copper sulphate had been
injected through wounds. Browning of the leaves was also observed.

It would appear that there is no absorption of copper through the
normal cuticle of a healthy apple leaf. Autumnal changes, however, as
already shown, lead to a partial change in the nature of the leaf
surface, and there is a varying amount of action of Bordeaux mixture
resulting in injury and absorption of copper.

Turning now to the behaviour of potato foliage towards Bordeaux
mixtures, we find rather a different state of affairs. The cuticle appears
to be distinctly more permeable than that of normal apple leaves. On
covering potato leaves either with the ordinary or the “* no-excess-lime ”’
mixture there is certainly some absorption of copper, for it can readily

! By the ferrocyanide test.

B. T. P. BARKER anp C. T. GimIncgHAM 19

be detected in the ash of treated leaves, but on the other hand there is
seldom any noticeable injury to the cuticle.

The cuticle of potato leaves is of quite a different type to that of
apple leaves and either all the cells or some only (possibly the hairs)
are evidently capable of exerting a slight solvent action upon the copper
compounds, which gives rise to a limited absorption insufficient to cause
injury to the cells. Copper absorbed in such a manner as this appears
to be rapidly translocated and dispersed without harm to the living cells
through which it passes. Possibly the removal is sufficiently rapid to
prevent the toxic dose being reached at any one point.

Another series of experiments showed that copper can be ahaoehenl
by potatoes through their roots. A number of potato plants were grown
in pots in soil mixed with considerable quantities of various Bordeaux
mixtures, so that the tubers were actually in contact with the copper
containing compounds. Samples of foliage were taken from each plant,
dried, ashed, and the ash tested for the presence of copper.

The following are the notes obtained from this series on testing the
foliage on two occasions separated by about a month:

|
Soil treated with | Copper reaction Copper reaction
| | IL
shes A te cts r |
“* No-excess-lime ” mixture | Faint, but distinct | Strong |
|
| = . , .
| Cooper’s Bordeaux powder Very faint | Very faint
| 5 | J
| . A | ia mi Dat ]
Ordinary Bordeaux mixture Very faint—uncertain | Faint, but distinct
| Control Nil | Nil

Here again we have apparently an absorption and translocation
of copper through the plant from the roots to the aerial parts without
injury to cells during transmission. There is in this case some local
injury to the surface of the root.

Precisely the same thing was found to occur with broad beans when
these were grown with their roots in contact with the basic copper
sulphate ; an appreciable amount of copper was found to be present
in the leaves. Analysis of the foliage of control plants showed absence
of copper. The influence of the absorbed copper was not, so far as could
be observed, injurious, the amount of growth often being equal to that
of the control plants, and where appreciably less, probably this was
attributable to the disorganisation of the root system.

i)

20 Bordeaua Mixture and Plants

What the physiological effect of the absorbed copper may be is at
present uncertain. In a set of practical spraying experiments it was
noticed that in all cases (as has often been recorded) the colour of
the sprayed plants differed from that of the unsprayed, being of a darker
and rather bluish-green shade. This was especially noticeable in plants
treated with Burgundy (Soda-Bordeaux) mixture. A further point
was that the darker green colour was not confined to leaves coated
with the spray. New foliage which developed after the spraying, showed
the colour effect almost equally well. A comparison of sections of leaves
of treated and untreated plants showed that the colour change was
due mainly, if not entirely, to the difference in the nature or amount of
the chlorophyll in the mesophyll tissues. It was not possible to decide
positively, whether there was also a difference in the colour of the
cuticular epidermal walls and of the hairs.

A colour effect was also noticed in the case of the broad beans.
The foliage of the copper-containing plants was on the whole notice-
ably darker in colour, although considerable variation in this respect,
due partly at any rate to the conditions of the experiment, was met with.
In marked cases the tint of the green colour differed considerably from
that of the normal leaf green of a healthy bean plant, being of a distinctly
bluer or greyer character. Comparison of alcoholic extracts of chloro-
phyll from copper-containing and copper-free foliage by spectroscopic
examination and other methods failed to reveal any difference between
the two; and the colour of the extracts, unlike that of the leaves them-
selves, was practically identical. In making the chlorophyll extract,
however, it was noticed that in the case of the copper-containing foliage
there was considerable difficulty in obtaining complete extraction of
the colouring matter; and generally after extraction the tissues instead
of being quite colourless, contained areas of a pale purplish-black tint.
Sections of the tissues showed that this colour was due not so much to
colouring matter within the cells as to cell walis stained with this tint.

The question of the influence of the copper in potato and other
foliage on the power of resistance of the plant to fungoid attack is still

under investigation.

The results of these observations on foliage injury and the absorption
of copper by the plant from Bordeaux mixtures may be summarised as
follows :

(1) Cells with readily permeable walls (such as germ tubes of fungus
spores, root hairs, the interior tissues of leaves, etc.) exert a considerable

B. T. P. Barker anv C. T. GimMIncHAM 21

solvent action on the particles of the copper compounds with which
they may come into contact. There is rapid absorption of the dissolved
copper followed by death of the cells. In the case of injured foliage
such action results in scorching.

(2) The amount of inter-action, if any, between other types of cells
and the copper compounds is determined by the nature of the cell wall.
Direct absorption of copper by leaves of certain types takes place with
or without local injury, depending on the nature of the leaf surface.
Translocation of the absorbed copper to other parts of the plant may
follow.

(3) Copper may be absorbed through the roots of certain plants
(potatoes, beans), with local injury to the root. This absorbed copper
can be translocated to the aerial parts of the plants without injury to
the cells through which it passes.

bo
i)

‘NOTES ON THE GREEN SPRUCE APHIS
(APHIS ABLETINA WALKER).

By FRED. V. THEOBALD, M.A., etc.

DurtnG 1913 a very severe attack of the aphis described by Walker
in 1849 as Aphis abietina took place on spruce trees of various kinds.
This aphis [ have found in considerable numbers in the south of England
for many years, but I have never known it until the summer of 1913
to do any serious harm.

Since Walker’s original account given in the Annals and Magazine
of Natural History', the only references I know of it are those given by
Buckton in his Monograph of British Aphides® in 1877 and in Gillander’s
Forest Entomology in 1908%. I have also recorded it from Worksop*
in 1910 and from Kent in 1911°. P. Van der Goot® places this in his
new genus Myzaphis. I have known however of this insect since 1889
when it was abundant on the Norway spruce at Kingston-on-Thames,
and on some of the spruce trees in Richmond Park.

I can find no reference to this spruce aphis on the Continent, but I
remember finding it near Odde in Norway in 1891.

Like most aphides it is of erratic appearance. Districts in which it
is quite common one year, may suddenly become comparatively free
from it. Then after a lapse of time it may occur again in quantity.
The only years in which actual damage has been noticed however are
1846 and 1913.

It is quite possible that the damage caused by it on other occasions
may have been put down to other causes, such as unsuitable soil, drought,
etc.

' Ann. Mag. Nat. Hist. m1, Ser. 2, pp. 301-302.

* Mono. Brit. Aph. 11, p. 43, pl. xlix, figs. 3 and 4.
* Forest Entomology, p. 304.

* Rept. Eco. Zool. for year ending Sep. 1911, p. 132.
° The Entomologist, xu1v, p. 398 (1911).

8 Tijdschrift v. Ent. tv, p. 96 (1913).

Pars)

F. V. THEOBALD 23
There is no doubt it is influenced very largely by the weather. Its
destructive nature under certain weather conditions can be understood
by the notes given here and the photos showing the damage, and it may
here be pointed out that both in the 1846 and 1913 attacks, that the
previous winters were noted for their mildness and dampness. No
doubt these conditions place the Piceas in an unhealthy condition,
and that in consequence the effect of these sucking insects becomes
much more marked and at the same time the mild weather enables
the aphis to flourish right through the cold months.

Description of the Insect.

Aplerous viviparous female.
Green, oval, convex, with a darker line on each side of the body.

igs aes
Aphis abietina Walker. <A Alate female B and C Apterous viviparous females.

24 The Green Spruce Aphis

Head yellowish-green to fawn colour, with two foveae; a small pro-
minence on each side of the head at the base of the antennae.

Antennae about half the length of the body, pale yellowish-green,
darker at the tips, the first segment very wide, second small and narrow,
third longer than the fourth, the fourth a little longer than the fifth, the
sixth about as long as four and five, the basal area as long as the fla-
gellum, which is blunt ; all the segments markedly imbricated.

Fig. 2.

Aphis abieltina Walker. <A. Antenna of alate female a. further enlarged third seg-
ment. £. Antenna of apterous female. C. Cornicle of alate female.

Eyes dull red. Proboscis green, dusky at the apex, reaching to
the third coxae.

Cornicles pale yellowish-green, some with a brownish tinge, apex
in some dusky, about one-fourth the length of the body, a few lines
and large reticulations at the apex, remainder strongly imbricated.
Legs green, tarsi, tips of femora and the tibiae dusky. Cauda green,
rather long.

Length, 1 to 15 mm.

Winged viviparous female.

Green. Head large, a pale olive green to pale fawn colour;
antennae nearly as long as the body, pale brown, the third segment
with 9-12 large sensoria along its whole length, the fourth shorter
than the third, with 2-4 sensoria; the fifth slightly shorter than the
fourth, with a sub-apical sensorium, the sixth not as long as four and five
together, the basal area only a little shorter than the flagellum ; all the
segments markedly imbricated. Head with two prominent but small

F. V. THEOBALD 25

frontal processes at the base of the antennae. Kyes deep red; stem-
mata prominent.

Bios 3.
Aphis abietina Walker. Alate viviparous female and further enlarged cauda A.

Pronotum fawn coloured to green ; mesonotum greenish with darker
lobes, scutum and scutellum in some brown; venter of thorax dark.

Abdomen bright green with dark sub-median lines, really made up
of four darker spots, also traces of four pairs of darker lateral spots ;
segments caudad to the cornicles marked and somewhat darker than
the rest. Cauda pale green, pointed, moderately long.

Cornicles long, thin, straight, cylindrical, reaching beyond the cauda,
pale greenish to greenish-brown ; in some slightly darkened at the tips ;
apex with a few transverse lines and large hexagonal areas, not strongly
imbricated.

Legs pale green in some, pale brown in others, rather short ; femora
thick ; tarsi and apices of the tibiae slightly darkened. The wings are
large, much longer than the body with rounded apices; the stigma
and veins pale brownish-green to grey, subject to considerable variation
in veination ; the veination in the twa wings often being totally unlike
one another (vide Figs. 1 A and 4).

26 The Green Spruce Aphis

Proboscis green, dusky at the apex, reaching to the third pair of
legs. Cauda with three long chaetae on each side.
Length, 1 to 18 mm. Wing expanse, 5 to 5°2 mm.

il al

Fig. 4.

Variations in veination in Aphis abietina Walker.

Localities where found.

England. Alnwick, Northumberland (Gillanders) ; Great Lalkeld,
Penrith, Cumberland (Britten); Thirlmere, Grasmere, Manchester
Corporation Water Works, Westmoreland (Edwards), Windermere
(Aymer Roberts) ; near Flamborough Head, Yorks. (Theobald) ; Holmes
Chapel, Cheshire (Young); Great Staughton, near St Neots, Hunt-
ingdonshire ; Little Hadham, Herts; Widdington, Essex; Kew
Gardens, Surrey; Rudgwick, Sussex; Woking, Guildford, Worples-
don, Esher, Kingston in Surrey ; Panton, near Wragby, Lines. ; Wye and
Goudhurst, Kent; Tiverton, Devon; Fowey, Cornwall; Worksop
(Theobald) ; Culford, Bury St Edmunds, Suffolk (Henry).

Wales. Aberglaslyn and Criccieth, Merionethshire! (Theobald).

1 This aphis swarmed in Aberglaslyn in 1906. The attacked trees have since been
cut down.

EK. V. THEOBALD 27

Treland. Rathdrum, Co. Wicklow; Dundrum, Co. Tipperary ;
Kilrush, Co. Clare; Camolin, Co. Wexford.

I have been unable to obtain any records from Scotland.

Food plants.

There is no doubt that the genus Picea is the normal food plant of
this aphis, but I have taken it in numbers on Scots firs on six occasions
and once on a Weymouth pine at Wye.

Its normal food plant is probably Picea excelsa, and until recently
I have not seen it on any other species of conifer except the Scots and
Weymouth pine!

The species of Picea on which it has been recently found are the
following :

Picea excelsa, P. sitchensis, P. pungens, P. engelmanni, P. nigra,
P. alba, P. gigantea, P. rubra, P. morinda, P. orientalis, P. monstrosa,
P. omorica, P. kosteriana, P. glehire.

Apparently immune varieties.

Certain varieties are apparently immune, such as P. polita, P. hon-
doensis, P. alcoguiana and P. alaskiana and in some places P. omorica
has not been attacked.

Varied degrees of attack on different species.

Speaking generally, the Sitka spruce is by far the most damaged,
but this does not apply everywhere. For instance in the small nursery
belonging to Wye College I was unable in 1913 to find a single specimen
of this insect on the Sitkas, but Picea excelsa close to them were found
to have any number on them and a few were badly damaged.

At Kew P. siichensis, P. pungens and P. engelmannii were badly
damaged, even trees 20 to 30 feet high, P. nigra and P. alba were in
some cases damaged, others escaped. It was noticed here that the
European and Asiatic species were damaged much less, the only seriously
injured one being P. excelsa.

In a large nursery I visited at Woking I found it doing great damage
to P. pungens, P. alba and P. sitchensis and a great deal on P. excelsa.

In my garden one large P. excelsa was entirely browned by it and I
think is dead, another was partly ruined, whilst P. pungens var. kostera,

1 'T may point out here that Dr Henry in the Gardeners’ Chronicle says the aphis has not
been noticed on any genus except Picea.

28 The Green Spruce Aphis

a large needled, very glaucous form (Fig. 7) had some amount of aphis
on three specimens, but two were affected scarcely at all and the aphis
increased very slowly, the third however, which had been previously
damaged by accident, was badly infested with this insect. All the other

Fig. 5.

Sitka Spruce attacked by Aphis abielina Walker. Early stage showing
needles turning brown and falling.

English records I have are on P. excelsa. Writing from Dundrum,
Co. Tipperary, Mr A. McRae says, “I find the common spruce of all
ages, from nursery stock to matured trees of 80 years or over, are badly
infested. On matured spruce the effects are most marked on partially

F. V. ‘THEOBALD 29
isolated trees, growing on road sides or along the margins of belts and
woods, on comparatively low ground, say 300 to 400 feet altitude. T also
find the aphis in comparatively large numbers on old trees of white
American spruce, but up to the present they do not show any very
serious results. At Dundrum the Sitka would appear to succumb most

Fig. 6.

Picea excelsa showing denudation on upper portion of shoot after a year’s attack.

readily to the attack ; in the nursery, however, the Sitka are not affected
to the same extent as the spruce, but the latter are larger trees and have
been longer in stock than the Sitka.”

Writing from Avondale, Rathdrum, Co. Wicklow, Mr J. Black sent
the following list of species attacked :

P. sitchensis, badly attacked, six years planted, 8—10 feet high.

P. excelsa, attacked to some extent.

30 The Green Spruce Aphis

P. morinda, two years planted, partially defoliated.
P. rubra, P. alba, six years planted, attacked similar to ezxcelsa.
P. pungens, four years planted, attacked quite as badly as setchensis.

Fig. 7.

Picea pungens v. kosteri showing aphides but little damaged.

Single specimens attacked are as follows :
P. orientalis, slightly affected.

P. engelmannii, badly attacked.

P. kostervana, badly attacked.

P. glehire, badly afiected.

EF. Wy: "PRROBADD

P. monstrosa, badly aftected.
The only species not affected here are :

P. polita, P. omorica, P. aleoguiana and P. alaskiana.

Fig. 8.
B. Sitka Spruce completely defoliated by Aphis abietina Walker. A. First stage of attack.

Different effects produced on different varieties.

Two very marked different effects are produced by this aphis. In
P. sitchensis the damaged needles soon fall and complete defoliation

results, as shown in the photos reproduced here. In P. excelsa the

»
”

32 The Green Spruce Aphis

needles turn brown, but the majority hang on and the tree looks as if
it had been scorched by fire. In one tree in my garden the leaves
have partially kept on into the spring of 1914. The damaged needles
certainly fall, but nothing like to the same extent as in the Sitka spruce.

In P. morinda they become partly defoliated; in P. engelmannii

Fig. 9.

Picea excelsa showing a few fallen needles and young growth unattacked. a. young
srowth. 6. some nodes where needles have fallen. c. discolouring of needle.

the trees do not become defoliated, nor in kostertana ; one of the latter
attacked in my garden has every browned needle still holding on, much
more so than in ewcelsa. Partial defoliation takes place according to
Mr Black in glehire and monstrosa.

F. V. THEOBALD 33

Young excelsa do not present the same appearance as old ones when
attacked, the needles instead of turning brown are mottled, where the
aphis sucks yellow spots appear and this lasts through the winter.
Writing from the Camolin Forestry Centre, Co. Wexford, Mr A. Stewart
says “the aphis is extremely plentiful on young Sitka and Norway
spruce, but that in May not much damage had been done to the latter,
but the Sitkas are in many cases practically defoliated.”

Fig. 10
Sitka Spruce defoliated by Aphis abietina at Arndale (Dr Henry).

Mr Murphy of the Kilrush Forestry Centre, Co. Clare, found the
few thousand Sitka spruce attacked, but not badly, but that both Sitkas
and Norway spruce in the plantations were practically immune.

It thus seems that both the Norway and Sitka spruce are badly
attacked and then next comes pungens, but that there is a marked

Ann, Biol, I 3

34 The Green Spruce Aphis

difference in the appearances produced, 7.e. complete and rapid defolia-
tion in the Sitka, browning and slow defoliation in excelsa and still less
defoliation in pungens and scarcely any in the glaucous variety kos-
leriana.

Infe-history.

So far I have been unable to find any sexuparae and I have searched
carefully for four years.

I have found apterae from early January on to December. The first
alatae occurred on the 20th of March at Woking, but in small numbers.
At Wye I have never noticed any until June and in July many occurred
and went on appearing in numbers into August. After August the trees
kept under observation showed comparatively few aphis until the
end of September, when they again became fairly common and some
could always be found right into December. These winter apterae
seldom producing any living young. At this time both mature and
immature apterous viviparous females occur.

Gillanders says that it may be found in winter. Mr McRae writes
me that where infestation is serious the aphis appears to live on the trees
throughout the winter, and Mr Black also noticed that this aphis persists
throughout the year. I have vainly searched for sexuparae this year,
a year when the sexual brood of aphides has been particularly noticeable.

The apterous aphides usually occur along the needles, a single one
settling on each needle and giving rise to a colony of young, which later
spread out and do the same; where the apterous mother feeds a yellow
spot occurs, sometimes with a reddish tinge and which later darkens ;
two or three of these spots on old trees seem sufficient to kill the needle,
whilst in young ones they remain, the needles but seldom completely
dying. The aphides also wander about on the shoots and remain and
feed there.

They do not seem to attack the new growth to any extent in summer,
but in autumn and winter a few may be found on the young growths.

In October and November I counted about six apterae to every
foot of branch examined and a few small young with them. The insect
is very sluggish both when in the apterous and alate stages, but if a
branch is cut off they become active in a few hours and wander away
from the needles,

It thus appears that this insect lives normally through the winter
as apterae and that sexuparae must be very rare and are so far un-
xnown.

EF. V. THEOBALD 35

This winter, 1913-1914, I found apterous viviparous females again
right through the winter, a weekly search being made, and they now
and then produced living young.

Natural enemies.

In spite of this aphis having a very large number of natural enemies,
they do not seem to have any effect upon it when weather conditions
are favourable to it and unfavourable to the host plants. I have failed
to find any parasites or predacious insects attacking it in winter when
they might clear off the comparatively small numbers that then occur,
nor do they appear until June or July, long after the aphides have done
their worst harm.

Later in the year they are preyed upon by a number of natural
enemies. The chief amongst these are several spiders, at least two species
of Phalangidae or harvest men, and the adults of Scymnus sp. and
its larvae to a small extent. That spiders and phalangids do enormous
good there is no doubt at this time. But the most interesting enemy
this aphis has that I have seen is the long eared bat. A tall tree in
my garden was every night in July surrounded by these animals, hovering
like a large moth at the tips and sides of the top branches, and clinging
on to them. Wishing to know what they were so assiduously hunting
for, I shot one and found it was full of hundreds of Aphis abietina, not
only the alate females, but the apterae and nymphae that they must
have taken from the needles.

I bred only two Chalcids. Several Syrphid larvae were active
amongst them and Adalia bipunctata.

Treatment.

In plantations of course nothing can be done that would pay to do,
put in nurseries and where any special trees we wish to save are attacked
we can very easily destroy this pest. Paraffin jelly, nicotine and soft
soap, quassia and soft soap, soft soap alone, lime sulphur wash and such
patent washes as White’s Abol, MacDougall’s Summer Wash, and Cook’s
Tobacco Wash were tried. All with the exception of lime sulphur and
soft soap alone killed great numbers, but the best results were obtained
with Cook’s Tobacco Wash, then with nicotine and soap and slightly
below these came White’s Abol, MacDougall’s Summer Wash and
paraffin jelly, then soft soap and quassia, Soft soap alone was not

3—2

36 The Green Spruce Aphis

found sufficiently penetrating to do much good. Lime sulphur at
summer strength had no effect at all. The main thing is to give a very
fine spray applied with force and to well wet the foliage. Winter treat-
ment with strong paraffin jelly yielded excellent results and probably
will prove to be the best method of treatment.

I have to thank Dr Henry for the information sent me from

Ireland.

POLLINATION IN ORCHARDS.
By F. J. CHITTENDEN, F.LS.

I am venturing to bring the question of pollination in orchards before
this Association, because, in the first place, it is one of extreme economic
importance in the fruit-growing industry, since it touches one of the
fundamental points for consideration in planning the planting of an
orchard ; and, in the second place, the problems its phenomena raise
include many of deep biological importance. Like so many of the
questions the practical man has at present to solve by empirical methods,
and which await scientific investigation, it touches more than one side
of biological science.

Historical note. Swayne was the first, in 1823, to demonstrate by
experiment that certain varieties of pears were self-sterile, 7.e. required
the intervention of pollen from another variety in order to cause fruit
production. Peaches, old gardening literature shows, were thought to
require pollen of other varieties, but experimental evidence seems lacking
in regard to this fruit. The matter, although set out very clearly by
Swayne, was apparently lost sight of until about 1890, when Waite
re-discovered it for pears in America, and later found the same thing
was true of apples. Considerable attention has been, and is being,
devoted to the problem with these and other fruits in America, and to
a less extent in Australia and other of our great fruit-producing colonies.

Our own experiments, begun at Chelmsford in 1902, confirmed
Waite’s observations, and clearly established the fact that a large pro-
portion of our commonly grown varieties of apples and pears failed to
set fruit unless pollen from some other variety was placed upon the ripe
stigma. More recently Backhouse, and, later, Sherrard, has shown that
our varieties of plums fall into two more or less distinct groups of self-
sterile and self-fertile types. Cherries, peaches, nectarines, and probably
grapes also, apparently show the same phenomena. Hooper’s experi-
ments at Wye are confirmatory. Some work has also been done by
continental biologists upon the problem, but especially by Ewert in

38 Pollination in Orchards

Germany, and Miiller Thirgau at Zurich, who have written several papers
on “ Parthenocarpie ”’—an expressive term which we owe to France.

Meaning of Terms “ Self-sterile” and “ Self-fertile.’ The terms
“ self-sterile ” and “ self-fertile”? have been somewhat loosely applied
in connection with this subject. In the strictest sense, self-sterility
would mean that, although normal ovules were produced, without the
intervention of pollen from another variety of the same kind, they would
stop development at the egg-cell stage, and no seeds would be produced ;
conversely, in self-fertile varieties, the pollen from the same flower,
or from a neighbouring flower on the same tree, would fertilize the egg-
cell, and seeds would be produced.

We have purposely said “ another variety,” not “‘ another plant,”
because the different trees of, say, ““ Cox’s Orange Pippin” apple are
all parts of the original tree which was raised at Colne in Middlesex,
just as all the trees of ‘‘ William’s Bon Chretien ” pear in all parts of
the world (it is called “‘ Bartlett’? in America) are all parts of one,
propagated by vegetative methods. The different trees of one variety
are, although they have a certain individuality of their own, not indi-
viduals in the same sense as plants raised directly from seeds would
usually be. ‘The varieties of fruit trees are comparable with separately
raised seedlings. All the trees of the apple “ Blenheim Orange ” are,
for our purpose, but parts of one individual, all those of “ King of the
Pippins ” of another, all those of “ Ribston Pippin” of another, and
SO on.

This is the usual meaning of self-sterility in animals and in other
plants, but with the fruit-grower the term has another significance.
The important point for him is whether or not the fleshy envelope of
the seed is matured—the seed itself concerns him not at all, and we find
that a considerable number of varieties of apple and pear produce perfect
fruits, except that they are seedless, when pollen of other varieties has
no access to the stigmas. I have used the term “ self-fruitful ” for the
production of fruit without the intervention of foreign pollen, whether
seed is produced or not. Seedless apples and pears are by no means
uncommon. They may be found any year, in any orchard, produced
from summer flowers. They are common in such varieties as ‘ Lord
Derby ” and “ Golden Spire,” when these varieties are not open to
pollination by other varieties, for these are self-fruitful, though not
self-fertile. They are normal in the pear ‘“‘ Ruyshe’s Coreless ”’ and
in the apple ‘‘ No-pip.”

9

399

K. J. CarrreNnDEN 39

It is this form of fruit which is called parthenocarpic, but it is not
yet clear whether pollination of any sort is necessary for the production
of these seedless fruits. In cucumbers it certainly is not, for commerci-
ally grown cucumbers reach a large size without fertilization of any kind,
and contain no fertile seeds. The histories of many seedless fruits,
like the banana, and of the well-known seedless oranges, and other
seedless fruits, seem never to have been thoroughly worked out, though
something has been done with seedless grapes by Miiller Thirgau.
There may well be two types of parthenocarpy.

Further, it is not yet clear whether, in the case of the relatively
few apples and pears which produce seed without the intervention of
foreign pollen, the seed is produced parthenogenetically or not.

Parthenoearpic fruits are almost unknown in the plum and cherry.

Cause of Self-sterility. It is in only the rarest cases that apples or
pears have unisexual flowers. Both ovules and pollen in some two
hundred varieties of apples, and in the same number of pears, which
we have examined, are apparently properly developed. The pollen is
capable of germination in every variety, though the per cent. of ger-
mination varies greatly in different seasons. So far as our experiments
have gone, it seems that the pollen of any variety of apple is capable
of fertilizing the egg-cells of any other variety of apples, and similarly
with pears. (Backhouse has shown this is not the case in plums and
cherries.) Naturally, the enormous number of possible combinations
has not yet been exhausted. The point needs further investigation,
especially from the economic point of view, for some variety may be
better fitted to induce fruit production in some other than are other
- varieties. There is sufficient evidence, however, to show that, while
the pollen of one variety may be quite impotent when applied to the
stigmas of flowers of the same variety, yet it is capable of fertilizing
another variety and of inducing the production of viable seed. Extended
microscopic examination of the apple flower has failed, so far, to reveal
to us, either in its structure or in its development, anything to account
for this remarkable state of things, both pollen and ovule appear normal
in every way. We have been repaid in the rather time-consuming
operations this examination has entailed by the discovery of one or
two curious and possibly significant facts hitherto unrecorded, but these
facts have no bearing upon the present question. We have, here, a
very curious phenomenon, rather wide-spread in the vegetable kingdom,
of incompatibility between the gametes of a hermaphrodite flower.
Does such incompatibility exist among hermaphrodite animals? and

40 Pollination in Orchards

what can be its explanation ? A hypothesis which would fit all the facts
has, so far, evaded us, nor have we been able to form a mental picture
of what self-sterility means, and the whole question seems wrapped up
with another of the deepest biological significance, viz. what is the real
meaning of individuality ?

There is some evidence that this self-sterility is not absolute in, at
least, some varieties. That is, a variety self-sterile here, may be self-
fruitful somewhere in the range of its distribution, or in some seasons.
It seems almost that, where the variety “‘ does ”’ best, it is more likely
to be self-fruitful (whether self-sterile or not, the recorded observations
do not make clear, though our own experiments tend to show that, e.g.
in “ Cox’s Orange Pippin,” in which self-sterility is the rule, when excep-
tions occur, seed is produced). This fact no doubt explains the con-
tradictory evidence afforded by different observers on such a pear as
“ William’s Bon Chretien,’ which produces fruit without foreign pollen
in some places, not in others.

There is the further question as to whether vegetative vigour may
not be a factor in the production of the seedless fruits already alluded
to. It may be so, for we find vigorous trees of the pears “‘ Conference ”
and “‘ Durondeau ” almost invariably very fruitful, and, where protected
from foreign pollen, bearing seedless fruits, while, among apples, “ Stirl-
ing Castle ”’ very rarely fails.

It seems quite possible that the pollen of a self-fruitful variety such
as these may have the function of stimulating the development of what
may be called the vegetative part of the fruit, though it fails to effect
fertilization. This is a very commonly observed phenomenon in the
case of many orchids, even foreign bodies falling upon the stigma
causing the production of fruits (of course, usually seedless). An
interesting instance of the effect of stimulation of a rather novel character
came to my notice not long since, and it was not an isolated instance.
All the pears on a tree, except those attacked by the pear midge Diplosis
pyrivora, fell very early, failing to swell, apparently owing to defective
fertilization. Those attacked remained till the end of May, and, as is
their wont, swelled very considerably. I commend this observation
to the notice of our entomological members. The case of the absolute
effect of the stimulus of egg-laying, or of the larval presence, is not quite
conclusive, but it is certainly suggestive.

Some Econonue Aspects of the Question. Itis clear that a knowledge
of varieties dependably self-fruitful would at once show what varieties
might be planted in large blocks without fear of failure from this cause,

F. J. CHITTENDEN 41

and this is an economical method of planting an orchard, since the same
operations can be carried out simultaneously over a considerable and
consecutive area. On the other hand, with self-sterile varieties, the
knowledge of what varieties to interplant is important. It is quite
certain that, until we have much more light on the causes of self-sterility,
it will not be possible to give the authoritative advice for which the
grower is entitled to look.

We are experimenting in the gardens of the Royal Horticultural
Society, with the object of ascertaining what varieties of apple and pear
are fertile inter se, and are carrying out other lines of work on the matter,
and have just put up a large orchard house for extending our work,
but, as we have indicated, observations in other localities upon particular
points are of the utmost importance, in order that some of the questions
at issue may be solved. The wish to bring this very important matter
before the notice of those who may have the opportunity of carrying
out some work upon it, is one of my objects in writing this note.

Certain points are, of course, clear, and the plainest is that varieties
flowering at approximately the same time should be planted together.
We have given, in the Journal of the Royal Horticultural Society, lists
of varieties of apples and pears, in their relative orders of flowering,
with the object of guiding the planter on this particular pomt, and we
have there compared our own average dates of flowering with those of
the same varieties in other parts of the world. These comparisons make
it clear that approximately the same order of flowering is maintained
by the different varieties all over the world, no matter what the climate
may be, so that a list founded, upon the average for several years, drawn
up in one locality, will prove a reliable guide in any other fruit-growing
district.

Another point of economic importance lies in the relative size of
fruits produced by the aid of foreign pollen and without it. They are,
as a rule, larger when seeds are produced, and are reputed to be sweeter.

The Carrying of the Pollen. There remains another point of general
interest : How is the pollen carried ? The suspension of glass slips
smeared with glycerine a few feet on the leeward side of blossoming
apples and pears, has resulted in the capture of a very small amount of
pollen, in marked contrast to the amount of pine pollen which we have so
collected from pine trees as much as a quarter of a mile distant.

A large number of rather desultory observations have been published
regarding the insects which effect inter-pollination in the apple and pear,
and it is certain that insects are the chief agents. But some have claimed

42 Pollination in Orchards

for the hive bee a great preponderance of visits over those of other
insects, and it would be a good thing to get the matter cleared up.

The record of captures at the flowers is of relatively little value, for
that takes no note of the number of visits an individual insect may pay.
I have watched a bumble bee, Bombus terrestris, for instance, pay
48 visits to different flowers (not all on one tree) in the course of ten
minutes. Note ought also to be taken of the length of time over which
the visits may extend. The bumble bee is out earlier by far than is
the hive bee, and it goes to rest much later, but is the pollen in a fit
state to be carried during all these hours? The fishy scent of the pear,
rather like that of hawthorn, no doubt attracts numbers of Diptera,
and midges seem particularly partial to them.

Some one recently, too, pointed out the great importance of the
hairy wild bees in effecting cross pollination in orchards, and, I am sure,
it would be a productive piece of work if the investigation were taken
up seriously. The Isle of Wight Bee Disease has practically exter-
minated the hive bee in many districts, and the cultivation of the ground
in and round orchards has destroyed the nesting places of not a few of
the insects that, in all probability, effected cross pollination in the past.

A CONTRIBUTION TO A KNOWLEDGE
BELLADONNA LEAF-MINER, PEGOMYIA

HYOSCYAMI, PANZ., ITS LIFE-HISTORY

BIOLOGY}.
ALFRED EK. CAMERON, M.A., B.Sc. (Aberd.), M.Sc. (Manch.).

Board of Agriculture Scholar and Honorary Research Fellow

won =
ve aes

SEU

im the University of Manchester.

(From the Department of Agricultural Entomology,

Manchester University.)

CONTENTS.

Introduction

Synonomy of the Species and Nevnenulstiite of he Ge snus .

History of the Species
Distribution
Food Plants ; : : .
Description of the Leaf- Minor, Pegomyia hyoscyami
The adult
The egg
The larva
The puparium
Copulation, Oviposition and Ege Period

Habits of larva, duration of the various larval sian

pupal period : :
The adult period, length of life. cycle
The Buccal-Pharyngeal Apparatus .

Comparison with Pegomyia bicolor Wied. and Puonan nigri-

tarsis Zett.
Remedies in England
Natural Enemies ;
Relation to Host Pinna 2
Summary

1 Communicated by A. D, Imms, M.A., D.Se.

OF

cn on Or
WwW ee

rR

43

THE

AND

+4 Belladonna Leaf-Miner

1. Introduction.

THE first record that we have of Pegomyia hyoscyami Panz. dates
back over a century when Panzer described it in 1809 from Central
Europe, including it in the genus Musca. Previous to this however
Réaumur in the year 1737 gave an admirable account of the behaviour
of the larva, with a few structural details, which he found mining the
leaves of henbane, Hyoscyamus niger. He figured the larva, and drew
attention to the resemblance that exists between it and the larva which
he found mining in the leaves of the beet. No mention is made of the
adult insect, a fact which Vallot noted in 1849, in dealing with the
“ Pegomyie de la jusquiame.” This latter also observes that Réaumur’s
expectation that the larvae which mine the leaves of the pear would
be identical with those found in the leaves of henbane failed in its reali-
sation, for he showed that the adult insects belong to two different genera
of Diptera.

This fly has been treated of by various authors and much confusion
exists in the literature on the species, due to the fact that it has a fairly
large number of food plants. This has led many authors astray, so that
it has been described several times under various names, and in one or
two cases the same author has described it under two different specific
names. There does indeed seem to exist a distinct variety, namely that
which attacks beet and mangolds, described first by Curtis in 1847.
Much damage is done periodically to these crops both in this country
and in Kurope as well asin America. In fact so much so is this the case
that it often constitutes itself a serious menace to their successful culti-
vation. In England and in Ireland Curtis and Ormerod recorded damage
from various parts of the country, and Carpenter more recently has
notified its ravages from Ireland, as also Farsky on the continent and
Chittenden in America.

It was with the idea of verifying some points in the life-history of
the species and also of unravelling the tangled skein of the nomenclature
that I took the opportunity presented to me of rearing the species on
Atropa belladonna, the Deadly Nightshade, which I believe to be the
first record of its being bred from this plant. By means of facilities
offered at Holmes Chapel Agricultural College Farm, I was enabled to
compare it with the var. betae which was obtained from the mangold
crop there, and I am also indebted to Professor Carpenter of the Royal
College of Science for Ireland for several specimens kindly given to me.
In addition I took the opportunity of making a comparison of the larval

A. E. CAMERON 45

characters of P. hyoscyami with those of Pegomyia bicolor Wied. and
of Pegomyia nigritarsis Zett. The results of this comparison have
been incorporated in this paper. The research was carried out in the
Laboratories of the Department of Agricultural Entomology, Victoria
University, and in the Experimental Laboratory, Fallowfield. It affords
me great pleasure to express my gratitude to Professor 8S. J. Hickson
for the various facilities readily granted to me, to Dr A. D. Imms for
many useful suggestions made when the work was approaching com-
pletion and to Mr J. T. Wadsworth, who photographed the specimens
for text-figures 2, 3 and 4,

2. Synonymy of the Species and Nomenclature of the Genus.

The Katalog der Paldarktischen Dipteren gives the following list of
names which at one time or another were supposed to apply to valid
species, and are included therein as synonyms of P. hyoscyami.

P. hyoscyami Panz., P. atriplicis Gour., P. chenopodii Rond., P. con-
formis Fall., P. cunicularis Rond., P. effodiens Rond., P. egens Meig.,
P. exilis Meig., P. Gouraldi R.-D., P. haemorrhoa Pand.

Var. Pegomyia betae Curt., P. dissimilipes Zett., P.femoralis Brischke,
P. spinacia Holmer.

In America, Lintner, in 1881, described the species under the name
of Pegomyia vicina.

The generic name has not remained constant and the species has
been included by various authors at various times in the genera Musca
(Panzer, Fallen), Anthomyia (Meigen, Schiner, Rondani), Anthomyza
(Zetterstedt), and Chortophila (Rondani). According to Stein (1905),
Robineau-Desvoidy in his paper on the Myodaires (1830, 595) estab-
lished the tribe Pegomyidae for a number of Muscidae which are dis-
tinguished from the Anthomytiidae by the more or less red colouration
of the body, by the small squamae and because in the larval stage they
subsist on the parenchyma of leaves. Rondani did not assume the genus
Pegomyia, but from a consideration of the size of their squamae he
disposed of the species in the genera Anthomyia and Chortophila. Meade
in 1883 re-adopted the name Pegomyia including under it all Antho-
mylids with naked, or at least pubescent antennary bristle, with the
anal vein continued to the wing margin and with partly red colouration
of the legs and abdomen. His species are classified into two sections,
in the first of which there are four included, P. betae, P. conformis,
P. hyoscyami and P. haemorrhoum, the last of Zetterstedt. The first

46 Belladonna Leaf-Miner

three of these are however synonyms for one and the same species.
Pandellé (1907) considered Pegomyia as a sub-genus of Anthomyia
giving the colour of the body as of sub-generic value, which is by no
means satisfactory. Stein (1906), although admitting that the estab-
lishment of Pegomyia as a separate genus is quite artificial and untenable
stricto sensu, yet adopts it in his scheme of classification. His reason
for so doing is that the species included in the genus possess at least
one plastic character in addition to colour, namely the quite regular
absence of the cruciate bristles (Kreuzborster) in the female sex. In
the few exceptions the presence of these bristles forms a very good specific
character. In scrutinising the extent of the genus it is observed that
Stein considered as belonging to Pegomyza, all Anthomytids which have
the antennary bristle naked, or at least slightly pubescent, eyes naked,
always three dorso-central bristles behind the transverse suture, the
anal vein continued to the margin of the wing and the tibiae yellow in
at least the greater part.

3. History of the Species.

According to Westwood (1840) the larvae of P. hyoscyami are stated
as devouring the parenchyma of the leaves of various plants, living
between the two surfaces, but the author records no definite food plants.
Zetterstedt in 1846 described the adult and quotes Wahlberg as having
found several of the larvae in the parenchymatous tissue of the leaves
of Hyoscyamus niger just before the plant flowered. Curtis in 1847
first recorded the var. Anthomyza betae as mining in the leaves of mangold-
wurzel and quoted a short description of the larva. The author also
described the adult male, the female being unknown to him. In his
account the antennae and palpi are stated to be wholly black whereas
the former have the basal segment more or less red and the latter have
only the terminal segment black, the two basal segments being yellow
as Meade later described. A doubt is expressed as to the extent of the
damage caused by the maggots and a suggestion made that cattle
eating the leaves containing them may be injuriously affected. In
the following year (1848) Scholtz, in a paper on leaf-mining insects, has
the following: ‘‘ Anth. betae mihi (der Anth. exilis Meig., versicolor
Meig., und mitis Fbr. verwandt) minirt nach meinen Beobachtungen in
grossern Plitzen, die oft das ganze Blatt einnehmen, und zwar gesellig
die Blatter von Beta trigyna.”’ The author must have been unaware

A. E. CAMERON AT

that the name had been previously employed and the species described
by Curtis.

In 1851, Goureau described the adult which he named P. alrrplicis G.
and called attention to the resemblance of the larvae to those found by
Réaumur in the leaves of henbane. He reared his specimens from larvae
which he found on the leaves of orache, Alriplexr hortensis, and hence
he named the fly “la Pegomyie de l’Arroche.” The description of the
larva is scanty, and that of the pupa, although brief, is the first record
we have of this stage in the life-history of the species. Further he
recorded and described a Braconid parasite which emerged from the
puparium of the fly, and this he named Alysia picta. For the first
time we meet with rather an interesting statement in this author’s
paper where he says that “la Pegomyie de lArroche” also attacks
beetroot. This is a matter which will bear investigation as I am inclined
to think that the species occurs in distinct “ biologic species,” each of
which has its own food plant, and my experiments, although not by any
means exhaustive, tend to support this fact. Guérin-Méneville in the
same year (1851) described P. atriplicis R.-D. and states that in
Goureau’s collection this species is wrongly named P. hyoscyami, which
he says is a distinct species. They are probably one and the same,
as also the P. Gowraldi R.-D., which he also describes, seemingly from
one immature specimen.

Nordlinger (1855) deals with the “‘ Runkelfliege ” (Musca (Anth.)
conformis Fall.) and makes some very interesting observations on the
life-history. He was the first to note the ornamental network on the
chorion of the egg and he also attempted to determine the duration of
the various stages in the development. Perhaps of most importance
is his discovery of two broods of flies per year with perhaps a third in
favourable climatic conditions. Comment is made on the backward
growth of beet plants which are severely infested and on the difficulty
of applying remedial measures. Taschenberg (1880) practically takes
Nordlinger’s description of the fly as well as his account of the life-
history. He states that the development of the larva occupies a few
weeks which, besides being rather indefinite, is inclined on the side of
iength. To compensate for damage caused by the pest he suggests
that there should be no stinting in the amount of seed sown, a method
which would have had little practical significance in combatting the
enemy.

Schiner (1862) and Rondani (1864) give descriptions of hyoscyamz, the
latter employing the generic name Chortophila, and the only observation

48 Belladonna Leaf-Miner

that he makes of the larva is that he has on a few occasions seen it
feeding between the two epiderms of the leaves of Hyoscyamus niger
(henbane).

Kaltenbach (1874) records the larvae of Anthomyia conformis Mg.
from Chenopodium album and C. murale. He also records the larvae
of A. betae Scholtz from mangolds, those of A. hyoscyami Mg. and
A. mgritarsis Zett. from Hyoscyamus niger. From henbane too he
reared adults of A. hyoscyami R.-D., which he believes to be distinct
from the A. hyoscyami of Meigen.

Farsky (1879) carried out some interesting experiments to determine
the time occupied in the development of the egg, larva and pupa, but
as the material was kept in glass-houses at a temperature much in excess
of what would have normally prevailed outside, he recognised that the
results were somewhat vitiated. For some reason or other which he
could not explain he failed after several attempts to rear adults from
first-brood larvae. With regard to the damage committed to beet
crops, Farsky proved by direct experiment that those plants, the leaves
of which had been mined, gave a markedly poorer yield when compared
with that of unattacked plants. On an average he reckons that the
beet plants which have been laid under toll by the pest have their polari-
sation affected adversely to the extent of two to four per cent. As
preventive measures he advocates, like Nérdlinger, an abundant sowing
of seed with conditions kept fairly humid in the young stages of the
plant’s growth, and charcoal dust is said to be effective, but only to a
small extent, in keeping the pest under control. Searching for the eggs
on the leaves and their consequent destruction on being found is also of
great utility.

Brischke (1880) in a most useful paper entitled ‘“‘ Die Blattminirer
in Danzig’s Umgebung,” describes Anthomyia femoralis as a new species
which he reared from Chenopodium album, but, except that the antennae
are stated as being black, the description tallies with that of hyoscyami,
with which it is agreed to be synonymous. The food plants of the
polyphagous hyoscyami and its synonym conformis are also listed.
Brischke attempts a rough classification of leaf-mining insects according
to the mode of excavation of their galleries and the deposition of their
excrement in the same.

Two Swedish entomologists, Holmgren (1880) and Tullgren (1905)
have described the species from spinach, Spinacia oleracea, the former
under the name of Anthomyza spinaciae (“ Spenatflugen ’’), the latter
employing Zetterstedt’s name, Anthomyia dissimilipes. Besides spinach

A. EK. CAMERON 49

Tullgren reared the fly from Chenopodium album, As remedial measures
against the larvae, he advocates spraying the plants with a paraffin
emulsion of the following composition ; 10 litres of paraffin, $ kilogram
of soft-soap to 100 litres of water. Another method which he thinks
might prove effective against the puparia in the soil is to spread the
latter with soot, guano or superphosphate. Probably neither of these
methods would prove very effective in combatting the pest.

In 1905 Professor Carpenter in Ireland reported the prevalence and
ravages of P. betae in that country. In his account of the life-history
he suggests the probability of there being four larval moults resulting in
five stadia. As far as my own observations are concerned with P. hyo-
scyami, I think I may pretty safely say that there are not more than four
stadia. The removal and burning of all affected leaves, as the author
states, is an effective but laborious method, where large crops are in-
volved, of temporarily minimising the ravages of the pest. Another
and more practical method which he advises, consists in the application
of a stimulating manure which, with a copious rain supply, would have
the effect, at least in the young stage, of forcing the growth of the plant
and strengthening it, the better to endure the attack of the maggots.
As the author further observes, the affect on the yield of a mangold
crop is most accentuated when the injury has been severe during the
period when the young foliage has recently burst forth.

In America Chittenden (1903) deals briefly with the beet or spinach
leaf-miner, Pegomyia vicina Lintn., and asserts that infestation of
cultivated crops is often traceable to the negligent harbouring of weeds
such as lambs-quarters which, the author says, fulfil the function of
breeding-reserves on which the fly can always rely in times of need.
As the fly is said to show a decided preference for spinach the author
proposes its use as a trap crop in sugar-beet fields. Otherwise the
methods of control are similar to those suggested by Professor Carpenter
whose source of information is Chittenden’s memoir.

4. Distribution.

This species is widely disseminated throughout Europe and is pro-
bably to be found wherever beet, spinach and mangolds are cultivated.
Vassiliev (1913) records it from Russia and it is perhaps more prevalent
in Northern (where these crops are more generally grown), than in
Southern Europe Its ravages have been recorded from all over Great

Ann. Biol. 1 4

50 Belladonna Leaf-Miner

Britain and Ireland and wherever mangolds are grown in this country
it makes its presence felt.

In the collection of the British Museum (Natural History) there
are specimens from the following localities in England :

W. Haddon, Rugby (W. Page); Newmarket, Walton-on-Naze,
Slapton, 8. Devon, Penzance (G. H. Verrall) ; Hastings (EK. N. Bloom-
field).

A better idea of its range is derived by consulting the reports of
Miss Ormerod and Theobald, to which reference is made later.

In America its activities are practically confined to the New England
States, and it has been recorded from Michigan. It also extends into
Canada as Lochhead (1903) reports.

5. -Food Plants.

The food plants of the species are distributed principally amongst
the two orders Chenopodiaceae and Solanaceae. Brischke records it
from a single example each of the Cruciferae, Stellaria media, and of the
Polygonaceae, Polygonum persicaria. According to Goureau, Scholtz,
Nordlinger, Kaltenbach, Brischke, Tullgren and Holmgren, the following
are the host plants in Europe of P. hyoscyami and its synonyms.

Pegomyia hyoscyami Panz., Mg. Chenopodium murale (nettle-leaved goose-
Hyoscyamus niger (henbane) foot)
Pegomyia betae Scholtz, Curtis Beta vulgaris (beet)
Beta trigyna (beet), Hungary, Asia Minor Polygonum persicaria (spotted persicaria)
Beta vulgaris (common beet) Pegomyia Gouraldi Rob.-Desv.
Beta vulgaris var. hybrida (mangold Atriplex hortensis (orache)
wurzel) Pegomyia femoralis Brischke
Pegomyia atriplicis Gour., Rob.-Desv. Chenopodium album (white goosefoot)
Atriplex hortensis (orache) Pegomyia dissimilipes Zett.
Beta vulgaris (beet) Spinacia oleracea (spinach)
Pegomyia conformis, Mg., Fall., Nord., Zett. Pegomyia spinaciae Holmgr.
Stellaria media (chickweed) Spinacia oleracea (spinach)

Chenopodium album (white goosefoot)

Jablonowski (1909) makes two significant statements with regard
to the food habits of the larvae of P. hyoscyame. If the natural food
plants should by any chance fail the larvae may complete their develop-
ment on a diet consisting either of manure or humous matter, and also
on decaying leaves of any kind. This is a point of much importance
as, in cases of exigency, the species is always more or less ensured of a
means of subsistence. Referring to the larvae the author says (p. 310) :
“Gibt es fiir sie keine Wirtpflanzen mehr, so kann sie sich auch in
diesem Falle helfen: findet sie kein ihr entsprechendes Blatt, so

A. K. CAMERON 51

lebt sie auch im gediingten, oder im sehr humosen Boden (dies ist
dann die Anthomyia cunicularis Rond).” Later (p. 313), he says:
“ Falls aber die eigenen Bliitter der Riibe unzulanglich wiiren, finden
sich wohl in der Nihe andere faulende Blatter, welche ihr eben-
falls zusagen. Die Fliegenmade bleibt in der einen, oder der anderen
Weise doch immer am Leben und kann sich spiiter in grésserer Anzahl
vermehren.”

6. Description of the Leaf-Miner, Pegomyia hyoscyami.
The adult (Pl. I, figs. 19, 20, 21, 22).

The following account has been borrowed and translated from Stein’s
paper on the genus Pegomyia, “ Die mir bekannten europiischen
Pegomyia-Arten,” a very exhaustive and systematically arranged piece
of work. The author points out that although enjoying a fairly wide
distribution, thé species cannot be designated a common one. The
numerous synonyms applied to it are accounted for by the fact that the
colour of the adult varies according to the life-history of the maggot,
but in spite of this variation the plastic characters are so constant as
to admit of the species being recognised with a fair amount of certainty.
Stein distinguishes two varieties, hyoscyami Panz., the true species,
light-coloured, and the darker form, be/ae Curt.

“The eyes, not very large, are almost equally broad above and
below and are separated by a distinct stripe and the orbits. Frons pro-
jecting, cheeks small carinate, jowls rather broad, posterior aspect of
the head convex below, bedusted all over silver-grey, on the cheeks
close to the basal segment of the antennae a quite distinct, blackish,
somewhat iridescent spot. Vertex as well as the median stripe generally
blackish-red, also in some cases of a lighter shade, according to the age
of the individual. Antennae incurving just below the middle of the
eyes, shorter than the face, black, second segment more or less red,
bristle naked, rather thickened at the base, palps thread-like, yellow,
the terminal third segment black. Thorax, scutellum and abdomen
in the lighter coloured form varying from pale to yellowish-grey, the
former without perceptible striping ; acrostichal bristles somewhat more
closely set than the dorso-central, pre-alar small. The abdomen is
sub-cylindrical, sometimes somewhat depressed and viewed obliquely
from behind a small, pale brown median stripe is recognisable; the
rather swollen hypopygium as well as the ventral lamellae (belly) is

42

52 Belladonna Leaf Miner

often of a reddish colour, rarely the entire abdomen is of a brick red
colour. Legs yellow, anterior femora with a more or less distinct,
longitudinal streak, tarsi black, pulvilli and claws rather elongate.
The investment of bristles does not present any special characteristic,
only it might be noted that, of the bristles on the outer side of the pos-
terior tibia, the one beneath is usually quite long. Wings pale yellowish,
without costal spine, third and fourth longitudinal veins parallel, pos-
terior cross vein steep and straight, the equally-sized squamae whitish-
yellow, halteres yellow.

In the darker form the thorax and abdomen are of a more brownish
colour and on the former there is seen posteriorly the faint trace of three
somewhat dark longitudinal stripes. The abdomen as viewed from
behind is thickly bedusted, pale brown and a fine dark dorsal line is
relatively quite distinctly recognised ; it is often interrupted at the
posterior margin of the segments. The rather strikingly spherical
hypopygium is bedusted just like the abdomen, sometimes overspread
reddish, the ventral lamellae reddish. The colour of the legs varies ;
either only the anterior femora brown or also the middle and posterior
femora completely or at least on their upper surface, although sometimes
very indistinct.

The eyes of the female are more roundish, the broad frontal stripe
reddish-yellow, sometimes somewhat obscured, the entire head either
pale brown or reddish, palpi generally thickened at the extremity,
club-shaped. Thorax grey or brownish-grey with the trace of a fine
median stripe; sternopleural bristles 12, the lower posterior but con-
siderably smaller than the upper, often only hair-like. In the matter
of colour, the abdomen again very variable, either pale brown or brick
red, sometimes a dusky red with the posterior margins of the segments
a pale brick red. But in all cases there is faintly seen, when looked
at quite obliquely from behind, a fine brownish or reddish longitudinal
line. The legs are rarely entirely yellow, generally the anterior femora
with a more or less evident longitudinal streak.”

Length 58-6 mm. Wing 5° mm.

The egg. (Pl. 1,.tig. AL).

The eggs are pure white, elongate oval, 0°87 mm. long x 0°31 mm. ;
surface not glistening, with a delicate sculpturing or pattern of irregular
hexagonal areas on that side of the chorion distal from the leaf ; surface
attached to the leaf, plain ; micropyle in a small depression at the apex.

~s)

A. K. CAMERON 53

The larva (Pl. I, fig. 2).

Larva, newly hatched, about 1°0 mm. in length, almost transparent,
with mouth apparatus, tracheae and alimentary canal distinctly visible
through the cuticle. Anal spiracles sessile with two slits apparently
communicating, shaped like a semi-inverted w, thus e. Fleshy tubercles
on the ultimate segment not very distinct. Anterior thoracic spiracles
absent. Immediately before the first ecdysis the larva has increased
its length to 1°6 mm.

The second instar larva (PI. I, fig. 6), smooth, with a pair of pro-
thoracic spiracles, one on each side of the post-cephalic segment and
each divided into seven lobes. Posterior stigmata situated on the
oblique dorsal position of the ultimate segment with two slits (PI. I,
fig. 7, p.sp.) just as in the first-stage larva, but constriction between
the two now more accentuated, slightly elevated. Paired tubercles
of the last segment are four in number (PI. I. fig. 7), with rather a large
but inconspicuous pair of flat adanal lobes (a./.). On completion of
the second stadium, the larva has almost doubled its size, now measuring
2°8-3 mm. in length. Following another ecdysis, the larva enters
the third stadium when, except for size, it resembles in all respects
the fully mature larva. Length 6 mm.

The full grown larva (PI. I, fig. 2) averages about 7°5 mm. long and
18 mm. broad, with thirteen segments of which twelve are evident,
of a dull yellowish colour, much wrinkled. On the cephalic segment
immediately posterior to the mouth hooklets are situated the minute
two-jointed antennae (PI. I, fig. 4, a.), and slightly posterior to these
again and placed somewhat nearer to each other, is a pair of sensory
spots (s.p.). The prothoracic spiracles (figs. 2, 4, pt.sp.) quite distinct,
with the number of lobes increased to eight. Definite areas on each
segment bear minute, closely-set locomotory spines, arranged lineally
in rows; on the first two segments posterior to the head the spinous
areas are not so definite, but these bear anteriorly three or four regular
rows of spines encircling the segments. Ultimate segment has the pos-
terior aspect divided into two distinct areas, a dorsal oblique and a
ventral truncated, bearing in all seven pairs of small tubercles (PI. [,
fig. 3) arranged as in figure. The pair lying immediately below the
spiracles in the stigmatic field are slightly internal to the circumference
of the circle formed by the others. Posterior spiracles (p.sp.) sub-sessile,

54 Belladonna Leaf-Miner

with three apertures clearly delimited, of which the two placed more
dorsally are about half as far apart as the median and ventral.

There would appear to be much individual variation both in the
size and structure of the mature larva. For instance Farsky (p. 111)
states the size to be 7 mm. long and 1°7 mm. thick, and Professor Car-
penter (p. 290) gives the length as being 8-10 mm. The latter also
states that the prothoracic spiracles have eight to ten branches whereas
I have only been able to observe eight in the full grown larvae. A
possible explanation of such variations as being an expression of differ-
ences in the nature of the host plants, readily presents itself to our minds,
and while Farsky’s larvae were reared from beet leaves and Carpenter’s
from the leaves of mangolds, mine fed on the leaves of belladonna.
It may be that we get distinct “ biologic species ”
the food plants which they patronise.

In a note which I have from Professor Carpenter, dated October 12th,
1912, the writer realises the probability of variation in definite species
of dipterous maggots, but states also an interesting case of convergence
where, if one takes a large series of larvae of Lucilia Caesar and Calli-
phora erythrocephala, distinctions which apparently hold good amongst
a small number lose their value. His attention was drawn to this fact
by Dr R. Stewart MacDougall.

of flies according to

The puparium (Pl. I, fig. 13).

Puparium measures 4°8-5 mm. in length, greatest breadth about
14-15 mm. Shape rectangular oval, narrowing sharply both ante-
riorly and posteriorly, sides slightly smuate in outline, but not so
markedly as in the puparium of P. bicolor (fig. 14). The rounded contour
of the last segment interrupted by the slightly projecting posterior
spiracles. Anterior spiracles less prominent with a lateral outward
inclination. Scarcely a trace of the posterior tubercles of the larva.
Segments distinct, demarcated by narrow striate bands of lineally and
serially arranged spines, characteristic of the larval cuticle, as shown
in the figure. The whole puparium as if lightly scarred or wrinkled,
a condition due to the general contraction that occurred in the trans-
formation from the larva. Colour at first pale ochreous yellow, gradually
deepening through shades of red, reddish-brown to dark brown and
brownish-black.

A. EK. CAMERON 55

7. Copulation, Oviposition and Egg Period.

The Anthomyiidae are very restless active flies, and in captivity
they seem to be endowed with such exuberance that they rarely become
accustomed to the narrow confines of a wire-gauze breeding cage, such
as was used throughout in the experimental rearing of P. hyoscyami.
In many ways these roomy cages, as manufactured by Voss, commend
themselves for observational purposes, built as they are of stout sheet
iron, with sides of wire gauze, back wall and sloping roof of iron and
with a glass panel front. On one side there is a hinged door and basally
a detachable, well-fitting tray of zinc for containing soil, into which the
fully mature larva of the species in question burrows previousto pupating.
A potted plant of belladonna (the host plant of P. hyoscyami) was intro-
duced into the cage and periodically watered to maintain its freshness
and ensure its growth. The stout heavy basal part of the cage may be
detached from the upper, lighter portion by the removal of two small,
bent, iron rods, one on each side, fitting closely into hollow projecting
iron cylinders placed alternately on the upper edge of the basal and
the lower edge of the upper part. When in position these rods fix the
two parts of the cage firmly together.

Copulation takes place after the lapse of a number of days from the
time of exit of the female from the pupa case. This interval is deter-
mined by one or more factors, such as the constitution of the female,
the kind of nutrition and the amount of food, the time of year, and
the prevailing weather conditions. For instance in the breeding cages
kept in the insectary which had free access to daylight and where the
conditions were, as nearly as possible, similar to those in the open,
the flies were never observed to copulate when the sky was overclouded.
Indeed, in the summer and autumn of 1912, owing to some reason or
other, copulation never occurred in the cages and consequently no eggs
were laid. Never yet has it been my good fortune to observe the act
of pairing outside, but on Aug. 26th, 1913, the behaviour of the flies
in this respect was noted for the first time and the accompanying sketch
(Text-fig. 1) drawn from life.

As represented in the figure, the male stands above the female with
its fore tarsi applied to the thorax and resting on the shoulders of the
wings which are kept divaricate. The middle tarsi of the male embrace
laterally the fifth abdominal segment of the female, whilst the hind tarsi
encircle the extremity of the latter’s abdomen. The femora and tibiae

56 Belladonna Leaf-Miner

of the middle and hind legs of the male are hunched up, the femora
ascending backwardly and the tibiae descending forwardly making a
sharply acute angle with the femora. The head of the male extends
forward above the level of the scutellum. The ventral side of the male’s
thorax rests upon the dorsal region of the female’s abdomen, and the
concave ventral surface of the male abdomen arches round the convex
dorsal surface of the female’s in such a manner that the hypopygium (the
modified ninth abdominal segment) of the male with its claspers and
intromittent organ extends under the extremity of the female abdomen
and is closely applied to the latter for purposes of coition.

The act of pairing continues for about half an hour and even longer,
and, if disturbed, the female endeavours to liberate itself by pressing

d
XQ
g >.

Fig. 1. Pegomyia hyoscyami in copulation. The investing bristles are omitted. x 12,

with its posterior tarsi against the tarsi of the male, in its attempt to
loosen them.

Martelli (1908) in his paper ‘“‘ Altre Notizie Dietologiche della Mosca
delle Olive,” p. 93, describes copulation in Dacus oleae. The position
adopted by the male of this species is quite different from that of
P. hyoscyami owing to the female’s having a long, exserted ovipositor,
which is general in the Trypetidae. In this case the anterior tarsi
of the male embrace laterally the first abdominal segment of the female,
while the others rest upon the ground.

Oviposition does not always take place immediately after copulation,
and indeed all evidence points to the necessity of an interval of one or

A. K. CAMERON ay

more days. The female lays the eggs (Text-fig. 2) superficially on the
under side of the leaf (only once have I observed the eggs on the upper
surface), generally in neat, parallel rows, the eggs of any one row being
closely applied to each other laterally and seemingly held together by
a kind of cement which also serves to attach the eggs to the leaf surface.
A good idea of what is meant will be obtained from the figure. The
number of eggs in any one row as well as the number forming an
egg-group varies. All sorts of combinations may be got. The number
may be as low as one or two and there may be as many as fifteen or
twenty, and even more. On the same leaf, apparently depending on

Fig. 2. Eggs of Pegomyia hyoscyami on under surface of a belladonna leaf. x9.

its size, there is often more than one group of eggs and rare cases of three
or four are recorded. The flies seem to show a preference for the leaves
of the top shoots, but later on in the season the radical leaves become
quite as badly attacked.

The eggs hatch in from four to five days, but as long an interval as
five to six days has been recorded. Farsky (p. 109) states the period
to be six to eight days in the case of the synonym, P. conformis, and

58 Belladonna Leaf-Miner

Chittenden (p. 51), quoting Howard, gives it as three to four days in
the case of the synonym P. vicina. The time will vary according to
the weather conditions and temperature, and to the degree of exposure
of the eggs on the various leaves. In the laboratory where a tem-
perature of 70° F. was maintained, the eggs hatched usually after the
short interval of three days.

In order to get an approximately accurate idea of the duration of
the egg period, the belladonna host plant was kept under close obser-
vation in the open. As soon as a leaf was noted with eggs newly deposited,
a tag-label bearing the date was attached to the stem immediately
below the leaf petiole and numbered. From time to time the leaves
thus marked were closely examined. A fairlv exact idea was thus
obtained of the time occupied in the development of the embryo within
the egg. Some of the results are appended in Table I :

TABLE I. Pegomyia hyoscyami and its oviposition.

Number of Date of Number of Eggs Date of Hatching Number of

Experiment Oviposition in a Group of First Egg Days
1 24th June 4 29th June 5
2 24th 6 30th a 6
3 25th .,, 12 Ist July 6
4 26th ,. 8 30th June 4
5 aafiey pp 11 3rd July 6
6 28th ,, 4 4th ,, 6
1 28th _., 13 Sel os 5
8 28th ,, 9 Sie © Be 5
9 29th ,, 8 4th ,, 5

10 30th —,, 7 4th ,, . 4

It must be observed that the larvae generally hatched in the cool of
the evening, and in a few cases the emergence of the larva occurred
during the night. In these latter the time could only be guessed at, but
with quite a close approximation to the truth since an indication would
generally be got of the time that the larva had abandoned the egg, from
the progress which it had made with its gallery beneath the epiderm.
The eggs of any one group do not hatch synchronously, but the variation
in time is often only one of minutes. As long as twenty-four hours
between the hatching of the first and last eggs have been noted. Later
in the season, towards the end of September, a single case where the
eggs took eight days to hatch was recorded.

The number of eggs which any one individual will deposit cannot

A. K. CAMERON 59

be definitely stated, but a reference to my notes reveals the case of one
female which laid first eleven eggs and then proceeded to deposit two
more groups of twelve and nine. The probability is that even then
she had not finished. Perhaps forty would be a very low estimate.
In an examination of a fertilised female about one hundred and forty
ova, of which twenty-two were ready for oviposition, were discovered
in the egg-tubes and uterus.

Habits of larva, duration of the various larval. stadia,
pupal period.

The behaviour of the larva within the epiderm of the leaf has been
fully dealt with by Farsky (pp. 109-110) in the case of P. conformis
mining beet leaves and what is said there holds good for the larvae
of P. hyoscyami in belladonna leaves. Réaumur has also given a de-
tailed description for the larvae mining in the leaves of Hyoscyamus
niger, and my observations practically agree with theirs.

The young larva makes its exit from the egg by a small circular
aperture at the micropylar end. Operations on the leaf epiderm are
immediately commenced with a view to an entrance ‘to the underlying
mesophyll layers, but at this time its actions are not characterised by
excessive energy. The egg-shell collapses when the larva has abandoned
it, and a small quantity of frass, the excrement of the tiny maggot
as it burrows into the leaf, isleft behind. It would appear that an ecdysis
occurs on the exit of the embryo from the egg. In all cases where
evacuated eggs were examined, a very thin, transparent, delicate
membrane was persistently found adhering to the internal walls of the
chorion. The whole process of the larval emergence is a progressive
one. The larva, by eating its way into the parenchyma, makes a
gallery for itself, increases its size, and by bodily extension, rends the
egg-shell longitudinally and ventrally. The migration from the egg to
the parenchyma is stated by Farsky (p. 109) to occupy a whole day,
if the weather conditions are favourable; if adverse, the operation
occupies two to three days, whilst excessive moisture induces abortion.

Where a large number of eggs are present on one leaf, it is often
impossible for all the emerging larvae to find subsistence thereon, and
consequently many are sacrificed. On several occasions it was observed
that when two or three batches of eggs were deposited on a single leaf,
only a few larvae succeeded in attaining maturity. Should a com-
paratively long interval elapse between the times of emergence of the
larvae from the different egg-bundles, those which hatch earliest stand

60 Belladonna Leaf-Miner

the best chance of completing their development. If, in the course of
their activities, they undermine the mesophyll layers beneath a bundle
of unhatched eggs, the larvae issuing from the latter do not attempt
to enter the leaf where the epiderm has been loosened, but they search
about for a part that is fresh and untouched. Often they die before
they succeed in fulfilling their mission, and, indeed, sometimes the eggs
do not hatch at all. The exact reason for this it is not easy to find.
Perhaps it may be that they merely undergo desiccation owing to the
discontinuance of the respiratory functions of the injured part of the
leaf. The incurrent and excurrent streaming of moisture-bearing gases
through the leaf-stomata, which would, in the natural course of events,
maintain an atmosphere sufficiently humid for the successful develop-
ment of the embryo in the egg is totally checked, with fatal results.

No definite information has been previously given of the duration
of the various larval stages of which there are undoubtedly three, and
the statements also of the different authors of the length of the complete
larval and pupal stages are apparently in disagreement. But this
seeming inconsistency is quite comprehensible when one considers that
the times may vary in multi-brooded species depending on the season,
according as it is the first, second or third brood, and further because
of the climatological conditions which prevail in different countries
as well as in different districts of the same country.

As indicated previously in the description of the larva, there are at
least two moults and three distinct stadia. Carpenter (p. 290) suggests
the probability of there being four moults, but I have not been able to
verify this additional one which he assumes as intervening in the last
larval stadium. During the month of June the larva completed its
development in about ten days. Later in the year, during September,
as many as twelve days were required. Where incidental circumstances
are favourable, the times of the various larval stages are approxi-
mately twenty-four hours for the first, forty-eight hours for the second
and seven days for the third.

It is interesting to note the time occupied by the larvae of the
different stages in making an entrance into a fresh leaf when placed upon
its surface. In some cases they get to work rapidly. Often they keep
wandering restlessly here and there. The following are three authen-
ticated cases, the facts of which were noted on June 23rd.

(1) Three larvae recently emerged were removed to a fresh leaf.
After a few sluggish efforts to pierce the epiderm, which occupied an
hour, they gave up the attempt. Even when a tiny puncture was

A. E. CAMERON 61

made for them with the point of a needle they achieved no progress
and finally died in about an hour and a half.

(2) A larva in its second stage was similarly treated. After moving
about actively for about a quarter of an hour, it seemed to find a spot
to its liking. Working vigorously it first made a small slit in the epi-
derm which it enlarged to a circular aperture by an unflagging series
of to and fro, semi-rotatory movements of its mouth hooks. In two
hours and twenty minutes it had disappeared completely from view
in the gallery which it had eaten out.

(3) A larva of the third stadium, recently moulted, accomplished
the same performance in the comparatively short space of twenty-five
minutes.

The pupal stage extends over a period of about two or three weeks,
and sometimes longer. Nordlinger (1885) believes the pupal stage
occupies fourteen days, whilst Taschenberg (1880) gives as low an esti-
mate as ten days, which is in accord with the ten to twelve days cited
by Jablonowski (1905). The insects hibernate in the soil as puparia.
Several larvae, collected during October, assumed the resting condition
on the 20th of this month, and from one of the puparia which were kept
amongst damp sand in a cool-house, an adult emerged on May 24th
of the following year, representing the elapse of one hundred and four-
teen days.

The adult period, length of life-cycle.

When the fly is ready to emerge it bursts open the retaining pupa-case
anteriorly by means of the pressure of the exserted ptilmum and makes
its exit through the resulting T-shaped cleavage. The animal does not
at once assume its final, natural colour. The thorax is pale, cinereous,
whilst the legs and abdomen are pale yellowish. Having finally rid
itself of the puparium, the imago remains resting for a time during which
the ptilinum is periodically inflated. This action together with a
peristaltic movement of the abdomen, is associated with an apparent
growth in size of the fly and also with the expansion of the wings hitherto
neatly folded up and closely applied to the body. The wings take
about three minutes to expand completely, the extremities unfolding
first. All the time the colour is becoming darker.

There is then a period of apparent rest when the various regions
of the body assume their normal shape, and the cuticle hardens. The
wings are slightly raised and become more transparent. The frontal

62 Belladonna Leaf-Miner

region of the head loses its flexibility, and becomes more or less rounded.
There is then a period of contraction when the fly remains motionless.
The abdomen shortens gradually until it has attained its natural size,
whilst the head and thorax also become visibly smaller. By this time
all the parts have assumed their fundamental colours. The complete
operation occupies about an hour.

The adults live for about two weeks but, in confinement, when fed
on a solution of sugar, they will live for as long as three weeks.

From a consideration of the foregoing remarks on the life-history
of P. hyoscyami, a fairly definite idea may be got of the time that elapses
for the various stages of development in the north of England during
midsummer :

DAYS

Time intervening between the issue of the adult and oviposition 4
Egg period... = Si ais se as ae =i) home)
Larval period

First stadium... at e .. 24 hours

Second _ ,,’ a ” ae .. 48 hours 10

Third - a a si te adavas
Pupal period .. Ee Ae a wi es sie oc ll

Average time for one brood .. Sy. - ys ae

There are at least three broods per annum, but there is a good deal
of overlapping of the various stages owing to differences in the times of
emergence so that eggs, larvae, pupae and adults are all found to occur
simultaneously from June to September.

8. The Buccal-Pharyngeal Apparatus.

The complete masticating apparatus of the mature larva of P. hyo-
scyami (PI. I, fig. 15) consists of a number of paired sclerites, the members
of each side articulating with one another to form a united whole. In
the younger larval stages the form of the apparatus is essentially similar
to that of the fully-developed larva, the difference being one of degree
and not of kind. Each moult sees a strengthening of the chitinous
structure.

The strong tooth-like hooks which are seen projecting when the
larva is feeding are the mandibular sclerites (md.s.) provided ventro-
laterally with four small teeth and with a blunted dentate process

A. E. CAMERON 63

ventro-posteriorly. Basally each is perforated by a tiny pore. The
dentate sclerites which articulate ventrally with the posterior halves
of the mandibular sclerites of the larva of Anthomyia radicum, as Hewitt
figures (Pl. II, fig. 7, d.s.), are here absent. Articulating posteriorly
with the mandibular sclerites are the hypostomal sclerites (/.s.) united
to each other by a slender rod, not evident in a lateral view. Hach
individual of this pair somewhat resembles a short dirk. From the
angle formed by the handle and the blade there proceeds a delicate,
slender rod (7.s.) which articulates with the broad, ventral, posterior
process of the mandibular sclerite. The proximal extremities of the
two hypostomal sclerites articulate, one on each side, with the distal
ends of the cephalo-pharyngeal sclerites (c.p.s.) which have each a slight
anterior, ventral, ploughshare-like continuation joining on to the hypo-
stomal sclerite of its side. The cephalo-pharyngeal sclerites are broadly
and deeply embayed posteriorly, thus forming a dorsal (d.p.) and a
stout ventral process (v.p.). The latter is provided posteriorly with
a dorsally directed blunt process. The dorsal arm of the cephalo-
pliaryngeal sclerite is itself bifurcate, so that a slender ventral process
directed posteriorly underlies the broader dorsal process. Finally the
perforate sclerite (pf.s.) situated dorso-anteriorly between the cephalo-
pharyngeal sclerites, serves to unite them. In the figure it would appear
to be quite detached. This displacement is caused by the pressure of
the cover-slip on the mounted preparation from which the drawing was
made. Midway between the ventral arms of the cephalo-pharyngeal
sclerites there is situated a carinate sclerite of very slender proportions.

In Carpenter’s figure of the mouth apparatus of the mature larva
the cephalo-pharyngeal sclerite is represented as having quite a
pronounced rectangular continuation anteriorly, where it articulates
with the hypostomal sclerite. This gives one the impression of a fore-
shortening of the latter. In reality the suture is placed rather more
posteriorly and the apparent continuation of the cephalo-pharyngeal
sclerite belongs to the hypostomal.

9. Comparison with Pegomyia bicolor Wied. and
Pegomyia nigritarsis Zelt.

The two allied species P. bicolor and P. nigritarsis mine the leaves
of Rumex obtusifolius and Rumex crispus in their larval stages, and
their life-histories are practically identical and concurrent with that of
P. hyoscyami, As imagos all three species have the same general facies

64 Belladonna Leaf-Miner

so that it 1s of interest to find that the larvae can be quite easily dis-
tinguished as also the puparia. It is almost impossible to find any
distinguishing feature in the eggs of the three species. In each case
the chorion has the same hexagonal pattern, but generally the sculp-
turing is more delicate on the eggs of hyoscyami (Pl. I, fig. 1) than on
those of the other two, bicolor and nigritarsis. We realise however
that this character is insignificant and unimportant, inclined as it is to
much variation.

The following table is a résumé of the distinctive characters of the
larvae, by which the three species may be separated and recognised
in the larval condition :

Larval Character P. hyoscyami P. bicolor P. nigritarsis
Integument.. .. Wrinkled Smooth, tough Smooth

No post-cephalic Post-cephalic ven- Absent
ventral tubercle tral tubercle pre-

(‘‘ foot ’’) sent (fig. 8, a.p.)
Colour .. ee se ADIL yellowish- Yellowish, iridescent Dull white

white
Length .. ae se fs) etuaal 10 mm. 9°5 mm.
Anterior spiracles .. S8lobes(PI. I, fig.5) 25-30 lobes (Pl. I, 16-25 lobes

fig. 11)
Palmate Ellipsoidal Semi-ellipsoidal

Posterior spiracles .. Sub-sessile (Pl. I, Porrect, prominent Slightly projecting

fig. 3, p.sp.) stigmatic projec- (PI. I, fig. 12, p.sp.)

tion, 2-segmented
(BIS Tehigs 83.9:
p.Sp-)

3 apertures broadly 3 apertures, elongate 3 apertures, elongate
oval, equidistant, oval, acuminate; oval, the largest
of equal size (Pl. equidistant (Pl. I, dorsal, separate ;
I, fig. 3) fig. 9) twice the distance

between the dorsal
and the median as
between the median
and the ventral
(Pl. I, fig. 12)
Tubercles of Ultimate 7 pairs (PI. I, fig. 3) 38 pairs—adanal 6 pairs, of which 2a
Segment te lobes (Pl. I, fig. 9) | and 3a placed pos-
teriorly (PI.I,fig.12)

Antennae and WSense- Sense-organs not so Sense-organsalmost Sense-organs have

organs Bic .. widely separate as adjacent, antennae — same distance apart
the antennae (Pl. I, separate as antennae; situ-
fig. 4) ated nearer the an-

tennae than is the
case in bicolor

Nathan Banks (1912) describes and figures only twelve lobes to the
prothoracic spiracles of bicolor, but careful examination of bona-fide
specimens has always shown the presence of at least twenty-five lobes.

A. E. CAMERON 65

As the puparium, which represents the shrunk larval integument,
retains the external characters of the larva in greater or less degree,
though not always so prominent, the same distinctions thus hold good
for the resting, as for the active, larval stage.

The mouth apparatus is of the same general formation in all three
species, with the component sclerites practically similar in shape.
They only differ in quite small details almost negligible for purposes
of classification. A comparison of the cephalo-pharyngeal sclerites
of hyoscyami and bicolor shows that the upper subtended process of the
dorsal arm is relatively broader in the latter species (PI. I, figs. 15, 16
and 17, d.p.). In bicolor the angle formed by the hypostomal and inter-
stitial sclerites is more acute than is the case in hyoscyami, which is 45°.
Further, the mandibular sclerites of bicolor bear dorso-posteriorly a
small, backward-curving denticular process (PI. I, fig. 17, d.p.), absent
in those of hyoscyami, which aids in forming a concavity for the arti-
culation of the distal extremities of the hypostomal sclerites. Again
the teeth or denticles borne by the mandibular sclerites of hyoscyami
arise more laterally than those of bicolor. The relation of parts is practi-
cally the same in bicolor and nigritarsis.

These generalisations have been made on the evidence of numerous
specimens carefully examined, but I quite realise that the characters
may not be absolutely stable. In some cases as will be seen from the
foregoing remarks, the distinction of the species has a negative basis,
depending on the presence of some detail in one species which is absent
in another, This is often very useful for classificatory purposes, but
either the specimens must be examined fresh or precautions taken that
those examined have been well preserved.

10. Remedies in England.

Miss Ormerod collected much valuable information about the in-
festations of the mangold fly, which was incorporated in her reports
of the years 1880-95. Severe attacks were recorded periodically from
all parts of England, Ireland and Wales, from Cumberland and West-
morland in the north, where the species was first recognised about
1876 as a serious pest of mangolds in this country, to Devon and Cornwall
in the south-west. The years 1880 and 1891 were notable for the great
amount of damage done to this crop which was in many cases practi-
cally sacrificed to the ravages of the leaf-mining maggot. The same
author also noted that the incidence of the fly was generally associated
with the use of farmyard manure as a crop stimulant, especially when

Ann. Biol. 1 5

66 Belladonna Leaf-Miner

applied in the spring, immediately previous to the sowing of the seed.
Autumn manuring, as soon after the harvest as possible, is therefore
advised, a course which Jablonowski (1909) also recommended in the
cultivation of the beet. The manure is thus given a chance to decay and
sink well into the soil during the winter months with the result that
the fly is not attracted by it to the same extent as it would be by
fresh dung.

The greatest and most lasting damage is usually committed by the
mangold maggot at the seedling stages of the plants soon after they have
been singled out. Thus a system of manuring which forces on the
growth of the crop beyond this susceptible period, proves of much
advantage in staving off ultimate disaster. To accomplish this Miss
Ormerod found that the application of sodium nitrate in the proportion
of about -two-hundredweight to the acre produced desirable results.
The only drawback is that, unless there be sufficient rain to wash the
fertiliser down to the roots, its value as a stimulating agent is vastly
reduced and almost negligible. Dressings of salt, potash and super-
phosphate introduced to the soil along with the seed have often proved
beneficial. Where clean culture is practised and where the crop is
grown in situations favourable to growth the loss incurred from the
ravages of the maggot is not very appreciable. When neglected, the
crop simply perishes from exhaustion in consequence of the leaves being
killed off by the maggots more rapidly than the plant can replace them.

Spraying the infected crops with paraffin emulsion is another method
which was brought to Miss Ormerod’s notice (1885, p. 68) as an efficient
remedy. The insecticide is made up in the proportions of 8 parts of
water to 1 part of soft soap with 43 parts of paraffin added to the first
two of these ingredients which have been previously mixed and boiled.
A homogeneous mixture is thus obtained, and 1 part of the emulsion
combined with 4 parts of water is said to prove quite effective in
killing off the maggot.

Theobald also deals with the occurrence of the fly in this country
in his reports 1909-11, and the same methods of combatting its attacks
are recommended as those given by Miss Ormerod. This author also
states that deep ploughing after an attack of the maggot will bury the
puparia in the soil, thus rendering the emergence of the fly to the surface
a difficult one. But I should imagine that where the soil is inclined to
be heavy, forming clods instead of a fine tilth, the adults will generally
succeed in making their way up, so that this method would only prove
of utility in the case of light soils,

A. E. CAMERON 67

In carrying out experiments with the maggot which mines in the
leaves of the belladonna, I found that an emulsion consisting of nicotine,
paraffin and soft soap with water would at least check virulent attacks,
and, if applied to the plants early in the season, it proved an excellent
preventive against the fly ovipositing. The fully developed larvae
did not seem to experience much inconvenience from contact with the
insecticide, which is prepared as follows: to four parts of soft soap
two pints of paraffin are added, and the mixture brought to the boiling

Fig. 3. Belladona plant used in breeding experiments of Peyomyia hyoscyami.
Appearance after attack.

point. A small quantity of boiling water is then stirred in, and the
whole then well mixed until a good emulsion is obtained. Four ounces
of 95 % pure nicotine are then added. After thoroughly mixing the
volume is increased to 100 gallons by the addition of more water. If
poured into a drum and kept well corked the mixture can be stored and
used at any time. The insecticide should be administered as a fine
spray by means of a nozzle of the improved Vermorel or other makes,
care being taken that both the upper and under surfaces of the leaves

5—2

68 Belladonna Leaf-Miner

are drenched. It penetrates the epiderm where the latter has become
detached from the parenchyma and is most effective against the larvae
of the younger stages. The hest results are achieved if the nicotine-
paraffin-emulsion is delivered to the plants just before the flies may be
expected to oviposit as it wards off the adults. Frequent sprayings
should be made in order to keep the pest under control. The cost works
out at about 3s. 9d. per 100 gallons of the mixture.

11. Natural Enenuies of the Belladonna Leaf-Miner.

Three species of parasitic Hymenoptera were reared from the puparia
of hyoscyami. Of these two are Braconids belonging to the genus
Opius and one of them is Opius nitedulator Nees ; PI. I, fig. 23 represents

Fig. 4. Opius nitidulator Nees. Parasite of Pegomyia hyoscyami. Also parasitised
puparia of Pegomyia showing the ragged edges where the parasites have emerged.

the fully developed larva of the latter dissected out from the puparium
of its host. The third is a Proctotrypid, probably a hyperparasite of
one or other of the two species of Opius, or perhaps of both. It was com-
paratively rare. The percentage of parasitism is rather high and, as
the season advances, increases in intensity until the beginning of Sep-
tember, when it suffers a diminution.

Examination of larvae and puparia collected towards the end of
this month and during October revealed very few parasites, a fact which
may be associated with the diminution in temperature experienced in
the autumn. This is borne out by the fact that the parasites are not so

A. E. CAMERON 69

prevalent when the first brood of the leaf-miner is on the wing as during
the occurrence of the two subsequent generations, showing that the
hibernating pupae had not been heavily attacked.

Continued spells of cool, damp weather are believed to have the effect
of reducing the number of parasites, but this was certainly not very
marked during the wet summer of 1912. The percentage was only
slightly less than that of the following year, when more favourable
conditions prevailed. This fact will be seen by consulting Table IT,
which shows the number of parasites that emerged from infested leaves
collected in the field and kept either in breeding jars or cages in the
laboratory :

Taste II. Pegomyia hyoscyami and its parasites at Fallowfield,
Manchester, in 1912 and 19138.

Month Locality Experiment No. of Pegomyia No. of parasites °% of parasites
leaves were No. emerged emerged to total insects
collected emerging
July 1912 Fallowfield 1 86 18 17
Aug. ,, 3 2 24 6 20
Sept. ,, = 3 37 21 36
Total .. bc 3c 147 45 23°4
July 1913 Fallowfield 1 36 6 14
Aes ue 2 88 27 23
Sept. ,, Rs 3 41 32 43
Total .. be ee 165 65 28°2

12. Relation of Pegomyia hyoscyami to its Host Plants.

Random statements are often made by entomologists of the migra-
tion of herbivorous insects from one host plant to another, and, although
there are well-authenticated cases of certain species becoming serious
pests by deserting common weeds to infest cultivated crops which are
closely related, I am not at all convinced that this transition always
takes place with that abrupt suddenness which many authors assume.

To determine whether adults of P. hyoscyami, reared from larvae
which had fed on belladonna leaves, would oviposit on the leaves of
mangold wurzel, a large number of fertilised females were confined in
breeding cages along with fresh mangold plants, but the results were
purely negative. In no single instance were eggs deposited. These
experiments were repeated with fertilised females reared from mangold

70 Belladonna Leaf-Miner

feeding maggots and liberated in cages containing potted plants of
belladonna. Again the results were quite negative. From the slight
evidence thus obtained one would not be prepared to jump at a general
conclusion, but it may just be possible that within the limits of a single
polyphagous species, certain well-defined “ biologic ” species may be
established, each of which shows a marked tendency towards one of
their food plants. Consequent on this preferential adoption of a host,
slight variations may arise such as in the colour, a fact which at one
time led to the establishment of the variety betae as a species distinct
from hyoscyami. As has been already noticed the imagos of hyoscyam,
the larvae of which have had henbane and belladonna for food plants,
are distinctly lighter in colour when compared with those the larvae of
which have fed on the leaves of beet and mangold.

At Dartford in Kent, where henbane and belladonna are grown
on a large scale for the sake of their alkaloid bases, it has been found
that, whereas in some years as much as 80 per cent. of damage is done
to the former crop by the maggot, the latter remains unaffected, although
in close proximity. It would appear that the fly has become thoroughly
established on the henbane to the exclusion of the allied belladonna.
Of course, it may be that some definite organic substance specific to
henbane and not present in belladonna is chemotropic to the fly,
which would account for its ovipositing on the one host rather than on
the other. When henbane is absent belladonna proves quite attractive.

Much interest, again, is derived from the question why P. hyoscyami
should select members of the widely different families of Chenopodiaceae
(beet, mangold) and Solanaceae (henbane, belladonna) as its host
plants. Is it possible that they all exert the same sort of chemical
stimulus inducing the one species to oviposit on any of them? Dr
Triigardh (p. 116) says: “If the food of the larva consists of several
species of one and the same genus, or of different genera within one
or several families, then it is an organic union, or group of such, common
to all these, to which the species reacts positively.” Again he says
(bid.): “ The odour of organic matters [to which the flies orient them-
selves and are attracted‘| is due to the occurrence of certain specific
chemical combinations, e.g. organic acids, amines, terebines, phenols,
glycosides, ete. which are characterised by a certain structure and strati-
fication of the atoms.” One can easily perceive the validity of the
argument where one is confined to a consideration of a single vegetable

1 The italics are mine (A. E. C.).

A. KE. CAMERON ‘A

family, but in the present case of the two families Chenopodiaceae and
Solanaceae, it lays itself rather open to attack, unless one extends the
content of “specific chemical stimulus” to mean not merely that
exerted by any one organic substance, but rather by certain of them
which have similar groupings of their component atoms (7.e. specific
kind of chemical stimulus). Such for instance are the nitrogen bases
of which betaine, guanine, hyoxanthine in the beet, atropine in the
belladonna, and hyoscine and hyoscyamine in henbane, all possessing
marked physiological or toxic properties, are well-known examples.
But it must not be inferred that these substances are attractive to
P. hyoscyami, for there is no direct proof on this point, but, hypotheti-
cally, their presence in these different plant species would satisfactorily
explain the varied food habits of the larva.

Since completing this paper, Dr Imms suggests to me the possibility
of betae being one species confined to the Chenopodiaceae and hyoscyami
a second species confined to the Solanaceae. The possibility of their
being physiological species, which have undergone more or less morpho-
logical separation, appears to him as well as to myself, on the sum total
of evidence, to be quite a feasible and justifiable proposition.

SUMMARY.

The species P. hyoscyami has been recorded at various times by
various authors, and it has often been described under different names,
partly because of its having been reared from a fairly wide range of
food plants. The belladonna leaf-miner is the larva of this species,
found during the summer throughout Europe, United States of America
and Canada.

The injury to the plant consists in the destruction of the paren-
chyma which the maggot greedily devours, the leaves assuming a
blistered appearance in consequence. The leaves thus attacked quickly
flag and wither during dry weather. In this way excessive damage to
the various food plants often results in their total loss, heavily affecting
the agriculturist pecuniarily where they are grown as cultivated crops.

Other food plants besides belladonna are mangolds, beet and henbane.

The number of the larvae in one leaf varies with the size of the latter
and, roughly speaking, directly as the size.

The ravages are periodic and often quite localised, resulting in
diminished yields of the products of the different crops attacked. The

72 Belladonna Lea f-Miner

top shoots are most heavily infested early in the season, but later the
radical leaves are most attacked.

Hibernation occurs in the pupal condition about two inches below
the surface of the soil near the food plants.

The number of broods vary. There are at least three in latitude.
The broods are not separated sharply off-from each other. There is a
good deal of overlapping so that all stages occur in the field during the
greater part of the season.

The eggs are deposited superficially on the back of the leaf in groups
consisting of parallel series varying in number. The incubation period
is about 5 days.

The larvae feed uninterruptedly and complete their metamorphosis
in 10 days under the most favourable circumstances. The larvae of
the first two broods sometimes pupate in the leaf, generally making
their way to the margin to do so. The pupal period of the first two
broods is about 17 days.

The average period for one complete life-cycle is about 36 days.

Two closely related species, P. bicolor and P. nigritarsis, attack com-
mon weeds such as dock. Their life-histories are, in all details, almost
similar to that of P. hyoscyami. Structurally, there are some interesting
differences, especially in the larval stages.

According to the different food plants which it affects, hyoscyami
may be divided up into at least two “ biologic ” species, one of which
would seem to confine its energies to a few members of the Cheno-
podiaceae, the other to Solanaceae, and within these two families
preferences to different species are shown. But in the absence of the
one favoured food plant, another, not ordinarily so attractive, may be
selected.

Species of the Chenopodiaceae and Solanaceae have in common
certain specific organic substances belonging to the group known as the
alkaloid bases. They probably serve as an attraction to the fertilised
females to oviposit on the leaves of the plants which contain the active
principles concerned.

Experiments showed that mangold-reared adults would not oviposit
on belladonna and vice versa. This restriction to one kind of plant is
indirectly advantageous to the agriculturist in that strains of flies reared
on belladonna confine themselves probably to this species or one closely
related, such as henbane, and do not attack mangolds.

The young plants are more easily killed than the more advanced
ones.

»

A. E. CAMERON 73

Natural control of the pest is secured by the parasitism of two species
of Braconids on one or both of which a Proctotrypid is probably hyper-
parasitic.

The degree of parasitism ascends to a climax at the end of August
and beginning of September, and then suddenly diminishes.

Frequent hand-picking of attacked leaves and their destruction
provides a ready and effective means of killing the maggot and unhatched
eggs. This method is only practicable where the crop is a small one.

Dressings of stimulating, chemical manures in the early stages,
strengthens the plants so that they maintain themselves the better
against the injurious effects of infestation.

Farmyard manure which attracts the flies should where used be
applied in the autumn to give it the chance of decaying before the adults
appear in the spring.

Deep-ploughing in the autumn serves to bury the hibernating
puparia which lie near the surface, thus rendering the emergence of
the adults in the spring a matter of comparative difficulty.

Paraffin emulsion is not so effective in killing the maggot as this
same emulsion with nicotine added.

BIBLIOGRAPHY.

Banks, N. (1912). The Structure of Certain Dipterous Larvae with Particular
Reference to those in Human Foods. U.S. Department of Agriculture, Bureau
of Entomology, Washington, Technical Series, No. 22, p. 30, Pl. VI, figs. 110, 112.

Boucué, P. Fr. (1834). Naturgeschichte der Insekten besonders in Hinsicht ihrer
ersten Zustiinde als Larven und Puppen. Berlin, 216 pp., 10 pls (A. mites Mg.,
p- 66, A. rumicis Bché, pp. 209-210).

Braver, F. (1883). Die Zweifliigler des Kaiserlichen Museums zu Wien. ILI.
Systematische Studien auf Grundlage der Dipteren-Larven nebst einer Zusam-
menstellung von Beispielen aus der Literatur iiber dieselben und Beschreibung
neuer Formen. Denkschr. der Kais. Akad. der Wiss. math.-naturwiss. Classe,
Wien, vol. xtvu, p. 71.

BriscHKe, ©. G. A. (1881). Die Blattminirer in Danzig’s Umgebung. Schrift.
der naturfors. Ges. Danzig, vol. v, pp. 233-290, figs. 1-5 (A. femoralis Brke,
p- 275).

CaMERON, FE. A. (1913). General Survey of the Insect Fauna of the Soil, ete. Journ.
Econ. Biol., vol. 111, pt. 3, p. 186.

CaRPENTER, G. H. (1905). Injurious Insects and other Animals observed in Ireland
during the year 1904, XIV. Econ. Proc. Roy. Dub. Soc. vol. 1, pt. 6, pp. 289-291,
2 pls (XxIIl, XXIV).

74 Belladonna Leaf-Miner

CHITTENDEN, F. H. (1903). A brief Account of the Principal Insect Enemies of the
Sugar Beet. U.S. Dept. of Agriculture, Division of Entomology, Bull. No. 43,
pp. 50-52, 1 fig. (The Beet or Spinach Leaf-Miner, P. vicina Lintn.).

Curtis, J. (1874). Observations on the Natural History and Economy of a Weevil
affecting the Pea-crops, and various Insects which injure or destroy the Mangold-
wurzel and Beet. Jour. Roy. Agric. Soc. Eng., vol. via, pp. 399-416, 1 pl.
(Anthomyia betae. The Mangold-wurzel Fly, pp. 411-413).

Farsky, F. (1879). Die ersten Stiénde zweier Runkelriitben-Fliegen, II. Die
Runkelfliege Anthomyia conformis Nordlinger (Fall.). Verh. d. k.-k. zool.-bot.
Ges. in Wien, vol. xxtx, pp. 107-114, 1 pl.

Gourkau, M. Le Col. (1851). Mémoire pour servir 4 histoire des Diptéres dont les
larves minent les feuilles des plantes et 4 celle de leurs parasites. Ann. d. I.
Soc. Ent. de France, vol. 11, pp. 131-176 (Pegomyia atriplicis G., pp. 163-166,
pl. 7, No. xv1, Pegomyia mitis Macq., Pegomyia rumicis R.-D., pl. 7, No.
XVII).

GurRIN-MENEVILLE, M. F. G. (1851). Descriptions de plusieurs espéces de Myo-
daires dont les larves sont mineuses des feuilles de végétaux; par M. J.-B.
Desvoidy, D.M. Revue et Magasin de Zoologie, 2nd Ser., T. mt (P. atriplicis
Rob.-Desv., P. Gouraldi Rob.-Desv.).

Hewirt, C. G. (1907). On the Life-History of the Root Maggot, Anthomyia Radicum
Meigen. Jour. Econ. Biol., vol. 11, pt. 2, pp. 56-63, 1 pl.

Hotmaren, A. E. (1880). Bladminerande Fluglarver pa vara Kulturvixter. Entom.
Tidskr. pa foranstallt. af Entom. Féren. i Stockholm, vol. 1, pt. 2, pp. 88-90.
(Spenatflugan, Anthomyza spinaciae Holmgr., Rédbetsflugan, Aricia betae
Holmer.)

JABLONOWSEI, J. (1905). Die tierischen Feinde der Zuckerriibe, 399 pp., 75 figs.,
Budapest. Die Runkelfliege, chap. x1, pp. 303-315, figs. 61-63.

KaALTENBACH, J. H. (1874). Die Pflanzenfeinde aus der Klasse der Insekten. Stutt-
gart (A. conformis Mg., pp. 504-505, A. betae Scholtz, p. 510 ibid., A. hyoscyami
Mg., p. 456 ibid., A. nigritarsis Ztt., p. 456 ibid., A. bicolor Wied. p. 519).

LocHHEAD, W. (1903). Insects of the Season. Ann. Rep. Ent. Soc. Ont., No. 34,
pp- 31-36 (P. vicina).

LunpBecKk, W. (1900). Diptera groenlandica. Vid. Medd. f. d. naturhist. For.
i Kjpbenhavn, Sjette Aartis, p. 287.

MarTetxt, G. (1909). Altre Notizie Dietologiche della Mosca delle Olive. Boll. d. Lab.
d. Zool. Gen. e Agr. d. R. Scuola Superiore d Agricoltura in Portici, vol. tv,
p. 93 (Accopiamento).

Mrape, R. H. (1883). Annotated List of British Anthomyiidae. Hnt. Monthly
Magazine, vol. xx, pp. 9-14; ibid. vol. xxtv, p. 58.

Metagen, J. W. (1826). Systematische Beschreibung der bekannten europiiischen
zweifliigeligen Insekten, vol. v, p. 182 (Anth. hyoscyami Mg.), p. 180 (A. conformis
Fall.), p. 181 (A. egens), p. 184 (A. ewilis).

Nirpuraer, H. (1855). Die kleinen Feinde der Landwirthschaft oder Abhandlung
der in Feld und Haus schiidlichen oder listigen Kerfe, sonstigen Gliederthier-
chen, Wiirmer und Schnecken, mit besonderer Beriicksichtigung ihrer natiir-
lichen Feinde und der gegen sie anwendbaren Schutzmittel. pp. 556-560
(Die Runkelfliege, Musca (Anth.) conformis Fall.).

~

A. E. CAMERON 75

OrmeErop, E. A. (1880-95). Report of Observations of Injurious Insects and
Common Crop Pests with Methods of Prevention and Remedy. London.
Réaumur, R. A. F. (1737). Mémoires pour servir & Phistoire des Insectes. Paris,

Imprim. Royale, vol. tm, pp. 42 et 532, tab, 47 (Pégomyie de la jusquiame).

Ropineau-Desvorpy, A. J. B. (1830). Essai sur les Myodaires, p. 598.

Ronpant, C. (1866). Anthomyinae Italicae Collectae Distinctae et in Ordinem
Dispositae. Ati della Societa Italiana di Scienze Naturali, pp. 68-217.
(Chorlophila chenopodii Rond., C. cunicularia Rond., C. perforans Rond., C. hyo-
scyami Mgn., C. effodiens Rond.)

Sontner, J. R. (1862). Fauna Austriaca: Die Fliegen. Wien, vol. 1, 674 pp.

Scnorrz, H. (1848). Zwischen der Ober- und Unterhaut des Blattes Minirlarven.
Ent. Zeit. Breslau, vol. 11, pp. 10-11.

Srrm, P. (1906). Die mir bekannten europiiischen Pegomyia-Arten. Wiener
Entom. Zeitung, vol. xxv, pp. 47-107. Wien.

Stirr, A. (1903). Die Runkelfliege (Anthomyia conformis Fall.). Wiener land-
wirtsch. Zeit. Wien, vol. Li, p. 423.

TascHenBerG, E. L. (1880). Praktische Insekten-Kunde, IV. Die Zweifliigler,
Netzfliigler und Kaukerfe. Bremen, pp. 123-125.

THEOBALD, F. V. (1909-11). Report on Economic Zoology. London (Annual
Reports).

TrAqgArpu, I. (1913). On the Chemotropism of Insects and its Significance for
Economic Entomology. Bull. Hnt. Research, vol. tv, pt. 2, pp. 113-117.

Tutteren, A. (1905). Om Fluglarver pa Spenat. Upp. i Prakt. Entom. med
Statsbid. Utgif. af Entom. Féren. i Stockholm, pp. 76-80 (Anthomyia (Pegomyia)
dissimilipes Zett.).

Vatiot, J. N. (1849). Eclaircissements relatifs 4 plusieurs passages des Mémoires
de Réaumur. Mém. Acad. sc. Dijon, pp. 81-111.

Vasstuigv, E. (1913). The Entomological Section of the Report of the Experi-
mental Entomological Station of the All Russian Society of Sugar-Refiners
for 1912. Kiev. pp. 12-13 (Résumé in Rev. App. Ent., vol. 1, Ser. A. pt. 12,
1913, p. 487).

Westwoop, J. O. (1840). An Introduction to the Modern Classification of Insects.
London, vol. 0, p. 571.

ZETTERSTEDT, J. W. (1846). Diptera Scandinaviae disposita et descripta, Lund,
vol. v, pp. 1791-2.

EXPLANATION OF PLATES | AND II.

[For purposes of reproduction it has been necessary to reduce the size of the figures
by ith. The magnifications given refer to the author’s original drawings. ds. ]

Fig. 1. Dorsal aspect of the egg of Pegomyia hyoscyami. 80.

Fig. 2. Mature larva of P. hyoscyami. %10°5. pt.sp. prothoracic spiracle.

Fig. 3. Posterior aspect of ultimate segment of same to show the position of the tubercles
and the posterior stigmata (p.sp.). an. anus (highly magnified).

Fig 4. The three first segments of same, ventral aspect. 15. s.p. sensory papilla ;
a. antenna; md.s. mandibular sclerite ; pt.sp. prothoracic spiracle.

Fig.

Fig.

Fig.

Fig.
Fig.
Fig.
Fig.

Belladonna Leaf-Miner

. 5. Prothoracic spiracle of mature larva (very highly magnified).
. 6. Larva of second stadium. x 23.
. 7. Posterior aspect of ultimate segment of same to show the tubercles and posterior

stigmata (p.sp.). 34. an. anus; a.l. adanal lobes.

. 8. Mature larva of Pegomyia bicolor, %10°5. pt.sp. prothoracie spiracle; p.sp.

posterior spiracle ; a.p. anterior ventral protuberance (“‘ foot ’’).

. 9. Posterior aspect of ultimate segment of same, showing arrangement of tubercles

and posterior spiracles (p.sp.). X11. a.l. adanal lobes; an. anus.

. 10. Larva of second stadium of same. X27. p.sp. posterior spiracles.
. ll. Prothoracic spiracle of mature larva of Pegomyia bicolor (highly magnified).
. 12. Posterior aspect of ultimate segment of mature larva of Pegomyia nigritarsis.

Tubercles are numbered; 2a, 3a placed more postero-laterally than the others.
p.sp. posterior spiracle ; an. anus.

. 13. Puparium of P. hyoscyami—ventral view. 7.
. 14. Puparium of P. bicolor—ventral view. 8.
. 15. Buccal-pharyngeal apparatus of mature larva of P. hyoscyami—rvight lateral

aspect, drawn from preparation previously treated with potash and mounted in
canada balsam (camera lucida). 40. md.s. mandibular sclerite; 7.s. interstitial
sclerite; h.s hypostomal sclerite; c.p.s. cephalo-pharyngeal sclerite; pf.s. perforate
sclerite: d.p. dorsal arm of cephalo-pharyngeal sclerite ; v.p. ventral process of cephalo-
pharyngeal sclerite; a. antenna.

g. 16. Buceal-pharyngeal apparatus of P. bicolor (the preparation similarly treated

to the previous). X18. Lettering as in Fig. 15. pt sp. right prothoracic spiracle.
The two subtended arms of the dorsal processes shown, one of which belongs to the
left cephalo-pharyngeal sclerite.

17. The same dissected out and more highly magnified. For significance of lettering
refer to Fig. 15 (camera lucida). d.p. denticular process.

18. Left wing of adult female of P. hyoscyami. X26. an. anal lobe; al. alula ;
as. antisquama; aux. auxiliary vein; 1-6 first to sixth longitudinal veins; c.v.
costal vein; h.v. humeral vein; cr.v. anterior cross-vein; a.cr.v. anterior basal
cross vein; p.cr.v. posterior basal cross vein; c.c. costal cell; s.c. subcostal cell.
m.c. marginal cell; sm.c. submarginal cell; p.c.}, p.c.°, p.c.’, first, second, and third
posterior cells ; d.c. discal cell ; 6.c.1, b.c.*. first and second basal cells ; a.c. anal cell.
19. Left anterior leg of adult female of same, to show arrangement of the bristles.
x19. t. trochanter; f. femur; JZ. tibia; ¢a. tarsus.

20. Middle left leg of same. 29°5. Lettering as in Fig. 19.

21. Posterior left leg of same. %26°5. Lettering as in Fig. 19.

22. Adult female of P. hyoscyami. X15.

23. Mature larva of Opius nitidulator, X16. Drawing made from specimen
dissected out from a puparium of P. hyoscyami.

Figures 16, 18, 19, 20. 21 were drawn with the aid of the Zeiss-Greil drawing apparatus
by means of which most exact reproductions are obtained.

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Pegomyia hyoscyami.

THE CATERPILLARS ATTACKING THE OAKS OF
RICHMOND PARK, WITH AN ACCOUNT OF
AN EXPERIMENTAL SPRAYING WITH LEAD
CHROMATE.

By R. H. DEAKIN.

Tue oak trees of Richmond Park have suffered very extensively
of late years from the attacks of caterpillars.

I have not personally seen the damage done in previous years, but
from all accounts the trees last year (1912), as also the year before, were
almost stripped of foliage, presenting as a result the appearance of dead
trees. A secondary growth of foliage then occurs. The period of maxi-
mum damage is said to have occurred in June, the time doubtless
varying with the weather conditions in the spring. Impressed by the
serious nature of the damage, the authorities at Kew Gardens com-
municated with the entomological department of the Royal College
of Science, and Professor Lefroy, under whose guidance I have been
working, took the matter up.

It was decided that one section of the oaks in the park should be
kept under observation and sprayed and for this purpose Ham Cross
Plantation, consisting of some 400 large oak trees planted in 1825, was
chosen.

This plantation, presenting a very compact area of trees, has been
very severely attacked in previous years.

I first visited the plantation in the third week of April. Some half
dozen trees were already breaking into leaf and on these minute cater-
pillars were observable.

From this time onwards the number of caterpillars and the accom-
panying damage to the leaves increased rapidly, and it became possible
to collect the different forms for the purpose of breeding out the moths.

The two commonest caterpillars were soon seen to be those of Tortrix
viridana, the leaf-roller moth, and Cheimatobia brumata, the winter

78 Caterpillars on Oak

moth. The caterpillars of these two forms of moth far outnumbered
the rest of the species present. The leaf-roller was likewise somewhat
more numerous than the winter moth.

The moths bred out were identified in the British Museum.

The following is a list of the species identified, the geometers being
identified from their caterpillars.

Noctuidae. Calymma trapezina L.

Geometridae. Oparabia dilutata Bkh.

Hybernmia defoliaria Cl.
Cheimatobia brumatu L.

Tineina.

Sparganothidae. Batodes (Capua) angustiorana Hw.

Olethreutidae. Syrlonota ocellana Schiff.

Gy pnosoma dealbana Frol. (¢ncarnana Hw. nec Hb.)

Tortricidae. Tortriz viridana L.

Tortriz (Pandemis) ribeana Hb.
Archips (Cacoecia) podana Sc.
Archips (Cacoecia) xylosteana L.
Archips (Cacoecia) lecheana L.

Coleophoridae. Coleophora lutipennella Z.

C’. trapezina was not very numerous, only a few caterpillars being
found. The moths hatched out at the beginning of June. These
were the largest caterpillars found on the oak, but owing to their small
numbers can hardly be classed as pests.

O. dilutata was also scarce. One caterpillar of this species was
found parasitised, presumably by a Tachinid, the egg of the fly adhering
to the dorsal surface of the caterpillar. Unfortunately the adult was
not bred out.

Although nothing like so numerous as either, Hybernia defoliaria
ranks next in importance after C. brumata and T. viridana. Being of a
fair size and of an active disposition it causes considerable damage to
the leaves. C. brumata was very numerous and a large proportion of
the damage must be attributed to this caterpillar. The caterpillars
of this species disappeared about the beginning of June, pupating in
the ground below the trees. The use of grease bands to catch the
fertilised female as she climbs the tree to lay her eggs should help to
keep this pest in check.

Of the Microlepidoptera, none of the species identified are sufficiently
numerous to be considered as pests with the exception of Tortrix viridana.
Archips lecheana L. occurred pretty frequently and was successfully

R. H. DEAKIN 79

bred out from a dark greenish-black caterpillar, yellowish-green ventrally
and laterally and on the dorsal surface of the last two or three abdominal
segments. Head dark brown with two black bands. Prothorax deep
black. The caterpillar of Archips podana Se. is almost an inch long
when fully grown. The colour before the last moult is greenish-blue,
with four spots of lighter colour on the tergum of each segment. Head
reddish-brown.

Tortrix ribeana was bred from a caterpillar characterised by the size
and prominence of the dorsal spots, these being white and the rest of
the body pale green. Head with three or four longitudinal brown stripes.
This moth was first hatched out on June 3rd.

Coleophora lutipennella Z., is quite common on the oak, the cater-
pillar living in a tube and boring under the epidermis of the leaf—this
resulting in a dead brown patch on the surface. The caterpillar of
another Tineid moth, Lvthocolletis sp., was found to be very common
during June, many leaves being covered with areas of dead epidermis
due to the mining of the caterpillar.

Gypnosoma dealbana Frél., Tam told, has not previously been recorded
from the oak.

By rolling up the leaves and eating the area so enclosed, 7. viridana
causes considerable damage. I was never successful in finding the eggs
in the spring, but judging from the position of the young caterpillars
on the early buds of the oak, the eggs themselves cannot be very far
from these buds, if not actually on them. I believe the eggs of 7. viri-
dana have never been observed and described. The larvae are full
grown in three to four weeks and pupate under the rolled up leaves.
By the 4th of June almost all the caterpillars of 7. viridana on isolated
oaks in the park had pupated, those on the Ham Cross Plantation being
slightly later. The period of pupation lasts roughly a fortnight and by
the 15th of June many moths were found hidden in the lower branches
of the oaks.

About this time I observed on the trees a considerable number of
minute pale coloured caterpillars of the leaf-rolling type. The original
brood of 7. viridana had so far as is known all by now pupated, and
the question arose, Is this a second brood of 7’. wiridana. The cater-
pillars had the characteristic appearance of those of 7’. viridana and their
occurrence when the original brood had apparently all pupated seems
to support the idea of a second brood.

Moths kept in captivity were found in copulation and one female
later laid eggs on the back of an oak leaf, about June 12th. The eggs

80 Caterpillars on Oak

were rounded, slightly flattened and of a yellowish-brown colour. They
were about ‘75 mm. across and occurred singly or in twos or threes buried
in scales from the abdomen of the moth and in some cases with bunches
of scales sticking out like bristles.

Although unfortunately not absolutely established I think there is
little doubt that a small caterpillar found eating the epidermis of the
- leaf some days after the eggs were laid had hatched out from one of these
same eggs.

Other eggs however failed to develop, so that this question of a
second brood remains somewhat doubtful as I was unfortunately obliged
to give up the investigation at this critical period. Most writers say
nothing of the existence of a second brood. Judeich and Nitsche in
their Lehrbuch Forstinsektenkunde (1895) believe there is but one genera-
tion, but mention other German investigators who believe that two exist,
and that the second hibernates as a pupa from which the moths appear
in April, the second brood of moths in the year appearing in June and
July. One of these investigators (Feussner,on 7’. viridana, Zeitschrift
fiir Forst u. Jagdwesen, vi, 1874), found larvae and pupae, which he
believed to be 7. viridana, in leaves spun together, the time being the
end of September. He was unsuccessful however in rearing the moth
from them.

The importance of this question 1s obvious as it concerns not only
the second brood and hence the lability of the oaks to a second attack
but also the way in which the first brood makes its appearance in the
spring.

Should it be found that the foliage undergoes a second attack, by
leaf-rolling caterpillars, and I believe it has been observed that the
attack does occur in two stages, then the problem of this second brood
should be easy of solution. A large sawfly larva was found to be
fairly common on the oak and under conditions favourable to its
increase might develop into a pest.

Natural Checks.

Large numbers of rooks and starlings were noticed in the tops of
the oaks of the plantation, doubtless feeding on the caterpillars.

The wild birds in the park have been artificially fed during the winters
of 1910-11 and 1911-12. Last winter being an open one, much less
feeding was done and Mr Pullman, the park superintendent, suggests
that the tits and other small birds, being dependent on the natural supply

R. H. DEAKIN 81

of food, may have done something to account for the comparatively
small amount of damage, which this year has been done to the oaks by
the caterpillars. Unless however 7’. viridana hibernates as a pupa, which
might serve as food for the birds, these could do little good in the winter
unless indeed they eat the eggs of 7’. viridana and C. brumata.

Parasites. Oparabia has been mentioned as being parasitised by
a Tachinid fly.

No case of parasitism on the winter moth larva was observed.

Only a small percentage of leaf-roller caterpillars were parasitised.

At the beginning of June 60 pupae were collected from the trees and
from these 43 moths hatched out. Twelve pupae died but were not
parasitised. The remaining five were parasitised, two by an Ichneumon
(Pimpla arctica), one by a Braconid (Meteorus laeviventris (Wesm.) and
two by Tachinid flies one of which was hatched out and identified as
Thrytocera (pilipennis Fin. °).

This gives a percentage of about eight parasitised caterpillars
The 60 pupae were not actually identified as 7’. viridana, but since all
the moths which appeared were of this species there is little doubt that
the parasites appeared from this species also, but this requires con-
firmation. A caterpillar of 7. viridana was also found with four bright
green hymenopterous larvae attached to the hinder part of the thorax.

The caterpillar’s condition was quite normal, it was apparently
about to pupate.

The larvae which were about one-eighth of an inch long when full
grown, existed on the still living caterpillar for three days and then left
it and spun rough webs on the sides of the vessel in which they were kept.
They failed however to continue their development.

Artificial Methods of Control.

Two days, May 6th and 7th were spent spraying the trees of the Ham
Cross Plantation, it being hoped to cover the leaves with a stomach
poison whilst the caterpillars were still young. The spray used was
made from a paste of the following composition :

Lead chromate 20 or 50 %

Soft soap 10-25 %
Gelatine ‘6-15 %
Water 9:4-23°5 %

I believe this is almost the first time lead chromate has been used
in this country as a stomach poison for insect pests. The supply used
Ann, Biol. 1 6

—_

82 Caterpillars on Oak

was an experimental lot, and cost £5 per ewt. One pound of the paste
was used to about 30 gallons of water, this giving | lb. of lead chromate
to every 60 gallons of spray.

Messrs Merryweather of London supplied us with a 3h.p. petrol
driven pump with sufficient metal piping and flexible tubing to reach
right across the plantation. Six jets were available and with the pump
working at full pressure each jet was spraying about one gallon per
minute. (See Plates III, IV, V.)

About twenty students and others from the college were present
to do the spraying, and mix the material.

Considerable time was spent in moving the engine and laying out
the mains; rain delayed matters, and only about eight hours during
the two days were actually spent in spraying.

The water was supplied in water carts by the park authorities, and
a second petrol pump was used to pump it into the galvanised iron
tanks in which the spray was mixed. ‘Two of these tanks were used,
each holding about 30 gallons of water, and as one was being emptied
the spray was made up in the second. One pound of paste was softened
in a bucket with warm water from the engine and diluted down to 30
gallons. In this way the solid matter was obtained in a very fine state
of suspension, forming an admirable spray to work with. No trouble
was experienced due to the paste settling to the bottom of the tanks.

During the two days some 1700 gallons of spray were used, practi-
cally every tree being reached. The pressure however was quite in-
sufficient to drive the spray to the tops of the oaks. On the second day
a fire escape was provided and with its help many of the tallest trees
were thoroughly sprayed all over (Plates VI, VIL). The days chosen
for the spraying were the only ones available, and there is little doubt
that at least a week later would have been better as then the trees
would have presented a much larger area of foliage. Moreover the
leaves being more fully grown would not so readily have caused the
breaking of the film of spray (viz. solid matter from the spray) by their
expansion, as actually was the case. On the other hand the caterpillars
would have been older and hardier at this later date.

The attack of caterpillar has, throughout the park generally, been
very slight this year and the damage up to the end of June inconsiderable,
though one or two trees were noticed which either on account of cater-
pillars or for some other reason never from the beginning appeared to
have the normal amount of foliage and presented a very bare appearance.

Nor can it be said that the Ham Cross Plantation fared better or

R. H. DEAKIN 83

worse than the rest of the oaks in the park. Had the attack been as
bad as last year’s, doubtless a contrast would have been apparent
between those trees which were thoroughly sprayed and trees outside
the plantation which were not touched. The growth of the leaves was
very rapid during the favourable weather which followed the time of
the spraying, and the coating of spray, observable for some days and
quite unaffected by exposure and rain, finally disappeared owing to the
expansion of the leaf. Rain fell while the trees were being sprayed
and to some extent this must have affected the deposition of the spray.
Caterpillars fed on sprayed foliage either died at once or became starved
and finally perished, so that no doubt remains as to the efficacy of the
poison.

The question of the falling off in the severity of the attack this year
is an interesting one. The possibility of birds influencing this, has
already been touched upon.

It is possible that last season the parasitic enemies of the chief
caterpillar pests were very numerous, thus lessening the numbers this
year. The caterpillars appeared however to be numerous enough,
especially those of T. virrdana. It may be that the dry sunny weather
of May and June this year (1913) so favoured the rapid growth of the
oak foliage that this easily kept ahead of the attack of the caterpillars,
the growth of foliage being greatest when the caterpillars were most
numerous and dangerous.

It can readily be understood that if the growth of the foliage is
delayed by unfavourable weather the caterpillars will gain the upper
hand and the foliage already present will disappear and the tree will
assume the bare appearance typical of years of bad attack. The weather
last year (1912) I believe was favourable for the trees till the beginning
of June when the weather became colder and damper. If the cater-
pillars were still active at this time, they may have caused the stripping
of the trees, on the cessation of the fine weather.

I should like to take this opportunity of thanking Professor Lefroy
for the advice and assistance which he gave me during this investiga-
tion, and Mr Pullman, the park superintendent, for his advice about
the trees and caterpillars.

[Mr Deakin’s observations were put an end to by his appointment
as assistant to the Government entomologist, British East Africa.
The almost entire absence of any visible effects of caterpillar attack
anywhere in Richmond Park in 1913 destroyed the value of our experi-
ment as no plantation in the park was affected. But it showed that

6—2

84 Caterpillars on Oak

trees could be sprayed in England as elsewhere, and that the cost was
not excessive. For approximately 400 trees, 1700 gallons were used
or 56 lbs. of lead chromate paste.

Our thanks are due to Messrs Merryweather who provided the
machinery and ladders ; their apparatus worked admirably, even though
we had hundreds of yards of main, branch and rubber pipes out at a
time: the whole work was done by students except the actual control
of the petrol-driven motor. The illustrations attached speak for them-
selves.

To the courtesy of the Office of Works, we owe the opportunity
to make this experiment; it is unfortunate that no result was obtained.
H. M. LErroy. |

85

A BACTERIAL DISEASE OF FRUIT BLOSSOM.

By B. T. P. BARKER, M.A. anp OTTO GROVE.

(University of Bristol: Agricultural and Horticultural Research Station.)

In the Gardeners’ Chronicle of May last year an announcement was
made by one of us that several cases of blackening of pear blossoms,
commonly supposed to be due to frosts or cold winds, had been traced
to the action of a bacterium. For several seasons past the blackening
of the blossom followed by the death of the flower has been observed
in the plantations of this institution at Long Ashton, the severity
of the attack varying from year to year, but on the whole showing a
tendency to increase. In the spring of 1913 the disease was much more
marked than at any time previously ; and although the trees of most of
the varieties grown there were heavily laden with blossom, the crop was
a failure, certain varieties being especially severely attacked and failing
to produce more than half a dozen or so mature fruits per tree on good
sized trees ten or twelve years old. Until then no particular attention
had been given to the disease, the damage being attributed to the action
of frost and cold winds according to the generally accepted view. Mr
J. W. Eves, at that time pomologist at this station, observed during the
course of pollination work on pears early last April that in many in-
stances the pistils of unopened flowers were already badly discoloured,
and was impressed with the general resemblance of the features of the
disease to an attack by a parasitic organism rather than to damage
caused by unfavourable weather conditions. He accordingly submitted
to us typical diseased blossoms for examination, selecting cases where
frost could not possibly be held responsible for the damage. In the
case of the first flower examined a large semi-transparent gelatinous-
looking colony of bacteria was readily seen under the low power of the
microscope situated on the surface of the discoloured disc of the flower.
From this colony streak and plate cultures on beerwort gelatine were
at once made, and in these in the course of two or three days abundant
growth was obtained. The cultures in all cases proved to be pure, only

86 Disease of Fruit Blossom

one type of organism, a rod-like bacillus, developing. After the necessary
trials to test purity, stock cultures were made, and material from these
was taken for use in infection experiments. The latter gave positive
results quickly and without any difficulty, the characteristic discoloura-
tion of the flowers following a few days after infection.

It was thus soon demonstrated that the disease was bacterial in
nature ; and a detailed study of it was begun. Our work is still incom-
plete, the limited duration of the flowering season curtailing infection
experiments and other observations on the flowers themselves in a living
condition ; but it has been thought desirable to publish a preliminary
account of the disease rather than to defer it until the results of the
current season’s work are available. The present paper is concerned
primarily with the general characters of this disease, which, so far as
we are aware, has not hitherto been recorded, and a description of the
causal organism.

The Characters of the Disease.

The nature of attack and the result vary considerably in individual
flowers; but the two following forms are perhaps the commonest.

In the one case the sepals are the first parts of the flower to show
signs of attack. Their tips turn grey and then begin to blacken.
When weather conditions favour the disease this blackening soon spreads
to the whole of the calyx and in due course down to and along the flower
stalk. The infection of the latter quickly leads to the death of the whole
flower bud. This mode of attack is common with young, unopened
flower buds. The flower bud blackens and shrivels up. In moist
weather it soon falls from the blossom truss ; but under drier conditions
it withers and dries up, remaining attached to the flowering shoot or
spur for weeks or even months. It is not uncommon to find in late
summer whole trusses of these blackened mummified blossoms still
on the spur. In cases where the whole of the blossoms of a truss are
affected, the consequences as regards the future history and fruiting
capacity of the spur bearing the truss are serious. The whole truss of
blossom eventually dies and falls off, leaving the spur as a bare stump
devoid of foliage. This stump may eventually die back entirely to the
point of its attachment to the branch carrying it; and in such cases,
if numerous, the future fruiting capacity of the tree is seriously restricted
for several seasons at least, until new growth and fresh fruit spurs
have had time to develop, on account of the large stretches of barren

-

B. T. P. BARKER AND O. GROVE 87

branches thus created. In less severe cases the apical portion of the
spur is alone affected, dormant buds in due course breaking to form
fresh growths ; but even in such instances some time must elapse before
the spur is once more properly furnished with fruit buds. The variety
Catillac seems particularly susceptible to the disease in this form ; and
trees of this sort at Long Ashton are laden with spurs showing this
type of damage in all degrees.

In the other case the first signs of trouble appear in the receptacle
of fully opened flowers as minute greyish-black spots. These rapidly
increase in size until they finally coalesce. In a short time the entire
receptacle is blackened and the disease spreads to the ovary. As a
consequence the fruit fails to set properly and sooner or later drops from
the spur as in the type of attack previously described. The main differ-
ence between these two forms of attack is that in the case first described
the initial points of infection occur in the external whorls of the flower,
the disease catching the eye therefore at a very early stage, whereas in
the second instance the attack begins on an internal structure of the
flower and may escape observation entirely, the failure of the fruit to
set properly being attributed wrongly to imperfect fertilisation.

In both cases the description given applies to examples in which the
disease spreads comparatively rapidly through the floral structures ;
but under some conditions the extension of the disease proceeds more
slowly. Before it has made serious headway the fruit may have set
and even have swelled to the size of a pea or larger before the injurious
effect puts a stop to further development. Sooner or later, however,
the death of the young fruit generally results, although in a few cases
signs of attack have been noticed on quite large fruits ; and it is possible
that at times an affected fruit may actually reach maturity without
serious damage. Such cases are probably infrequent if the disease once
establishes a footing. The rapidity of the spread of the disease in an
infected flower appears to vary considerably, depending largely upon
climatic conditions. Cold, wet weather seems to favour its develop-
ment and, conversely, warm dry weather restricts it. Further reference
to the influence of various conditions will be made later.

In addition to these two typical forms of attack a variety of other
types has been observed. In some cases the stigma is first affected,
becoming unhealthy and discoloured in appearance. The blackening
extends thence downwards through the style to the ovary, the whole
pistil eventually turning completely black and failing to develop into a
fruit. In other cases small blackened areas appear first on one or more

88 Disease of Fruit Blossom

of the petals. The remaining parts of the flower may or may not be
attacked in due course. In the latter event the affected petals fall as
the flower ages, and the young fruit may then develop normally.

While attacked flowers at times remain attached to the fruit spur
for a comparatively long period, even when the disease has obtained a
strong hold, it is very common to find flowers which fall at the slightest
touch, although the external signs of disease are limited to a few small
black spots on the receptacle. A slight shaking of the tree suffices to
cause blossoms in all stages of development to fall in showers. Young
fruits which appear to have just set are particularly liable to come off in
this manner. Examination of the internal parts of the flower in such
cases generally shows that the ovary is more or less completely
blackened.

The disease spreads very rapidly from flower to flower; and, if it
makes its appearance when the tree is just beginning to blossom, it may
spread to nearly all the flowers on the tree during the three to four weeks
over which the latter is carrying open blossom.

While the disease in its most serious form is concerned mainly with
the flowers, other parts of the tree are attacked. The young leaves
which appear during the blossoming season frequently show small
black spots or areas, very similar in general character to the blackened
spots which occur at the points of infection on the petals. Serious
damage to the foliage does not generally result, the spots remaining
small and eventually drying up and falling out. The leaves developing
around the blossom trusses on the fruit spurs are usually most severely
attacked. The disease on the foliage generally starts at the tip of the
leaf, but occasionally at some point along the margin.

The fruit spurs of the tree are also often attacked ; and it is possible
that this feature of the disease may prove to be the most serious. Refer-
ence has already been made in passing to the fruit spur attacks when
describing the course of the disease of the blossom trusses: and it has
been shown that after the death and fall of the flowers of the truss the
spur is left as a barren stump, which sometimes dies back as far as the
point of its attachment to the branch carrying it, but occasionally sur-
vives and produces lateral growths which develop in due course into
either shoots or branch spurs. In both cases the tissues of the spur
are attacked by the bacillus. When death of the spur results, apart
from the loss of the spur by the tree no evil effects may follow ; but if
the spur survives, the infected tissues harbour the organism throughout
the summer and winter and may prove to be responsible for an outbreak

B. T. P. BARKER AND O. GROVE 89

of the disease the following spring through the lateral buds which were
formed after the original attack. On cutting transverse sections through
such a spur just below the point of attachment of the diseased
flower truss a number of small brown spots are seen, both inside
and outside the cambium. In longitudinal section these appear as
brown lines, which at times extend back $—1 inch or more into the woody
portion of the spur. The bacillus is present in these affected portions ;
and proof is now forthcoming that it remains in a living condition there
over the winter. It seems likely, therefore, that new crowths from such
spurs are also infected. The affected portions of the tissues of the spurs
do not increase in size to any considerable extent ; and no serious damage
to the surrounding tissues results immediately, except in the severe
cases where the whole body of the spur dies back. Possibly in the latter
event the death of the spur may be due not so much to the organism
in question as to fungi, such as Nectria ditissima or Sclerotinia fructigena
which have the opportunity of infecting the spur at the point of
severance of the blossom truss. At present no decisive evidence either
way has been obtained ; but, as will be seen later, infection experiments
with the bacillus on woody branches have shown little serious damage,
and the balance of probability therefore points to the action of other
organisms in cases where the spur dies back.

In the foregoing description of the disease reference has been confined
to its characters on the pear as host. There is reason to believe, however,
that a number of other plants are also susceptible to attack. A bacterio-
logical examination of discoloured parts of flowers of apples, cherries,
gooseberries, and plums has been made, and in many cases there has been
found in the diseased areas a bacillus in practically a pure state, which
on isolation has proved to be the same organism as that occurring on
the diseased pear flowers. It has also been found on the tissues of the
flowers and leaves of various other plants in parts showing discolouration.
Since at present, owing to our attention having been given mainly to
the disease on the pear, very few infection experiments have yet been
made on the other plants mentioned, the evidence connecting the bacillus
with the disease in the latter cases is not absolutely conclusive ; and
pending further investigation it is not proposed here to do more than
‘call attention to the fact of the occurrence of the organism in association
with affected parts on other kinds of plants.

There appears to be a marked difference in the susceptibility of differ-
ent varieties of pears to attack. The organism has been isolated from
diseased flowers of practically all the varieties grown in the plantations

90 Disease of Fruit Blossom

at this institution, including the following kinds: Beurré d’Aman-
lis, Catillac, Vicar of Winkfield, Louise Bonne de Jersey, Conference,
Bellissime d’Hiver, Dr Jules Guyot, Williams’ Bon Chrétien, and
Pitmaston Duchess. Of these sorts the two first named are much more
badly attacked than the remainder; and most of the trees of those
kinds, although covered with blossom, produced very few fruits in 1913,
some indeed failing to yield a single pear. After examination of the
older fruit spurs of the trees of all of the varieties named, it is evident
that also in years prior to 1913 the two varieties in question have suffered
more severely than the other kinds.

In the case of apples discoloured flowers of Beauty of Bath, Bramley’s
Seedling, Allington Pippin, Devonshire Quarrenden, and Duchess of
Oldenburgh have been examined, and from each sort the bacillus has
been isolated. There is not sufficient information available yet to show
if some varieties are more susceptible than others. Few kinds of plums
have yet been examined ; but cultures of the bacillus have been obtained
from the Victoria variety and the Myrobella plum. Only two cases of
cherry blossom have been examined, viz. the Norwegian cherry and a
kind sent through the Board of Agriculture without name. In both
instances the organism was isolated.

There is little doubt from the specimens of fruit blossoms examined
last year that the disease is very widely spread. Not only was it re-
peatedly found in the immediate neighbourhood of Bristol, but also in
many other parts of the country. The bacillus has already been isolated
from affected pear flowers sent to us from Devon, Teddington, Wolver-
hampton, Stroud, Ross, and Offenham ; and from apple blossom sent
from Berkeley, Ledbury, Elsenham, Essex, and Hailsham. The
occurrence of the organism over so wide an area suggests the probability
of a general distribution throughout the midland and southern counties
at least; and the fact that it has been isolated from a number of plants
other than pears and apples, in which blossom or foliage damage was
slight, raises the question of its pathogenic character in all cases.

It undoubtedly is responsible for the disease of pear blossom in the
forms already described, since branches of pear trees carrying unopened
and undamaged blossom have been brought on under greenhouse con-
ditions and have in due course borne flowers which have developed the
disease both after artificial inoculation with the bacillus and in many
cases without deliberate infection. Also abnormally late blossoms
produced in the open in June have been found to be affected. In such
instances the possibility of frost damage has been excluded, care having

B. T. P. BARKER AND O. GROVE 9]

been taken to ascertain that the flowers showed no sign of such damage
before being selected for the experiments under cover. On the other
hand many cases occur under outdoor conditions in which it is difficult
to decide whether the damaged blossom has been affected by the organ-
ism or by frost, the type of damage appearing to the naked eye very
similar in either case. Again in other instances there is no question of
the damage being due to frost. In this connection it may be noted that
the blackening or browning of the pistils in unopened or partially opened
buds can be caused by frost even when the other parts of the flower are
quite unaffected. Striking cases of this kind have been observed this
spring on the Myrobella plum. ‘The bacillus having been isolated from
frosted blossoms, from flowers with blackened pistils which may or may
not have been caused by frost, and from undamaged fully expanded
flowers of the Myrobella, it is evident that for this plant at least the
organism is not always pathogenic. At the same time the tissues of
the discoloured pistils have been swarming with cells of the bacillus
in some instances. Further investigation is necessary before such points
can be satisfactorily cleared up.

When the disease was at its height last year in the fruit plantations
at this institution one of its most striking features was the rapidity with
which it spread from flower to flower. Definite proof was forthcoming
that this was due mainly, if not entirely, to the agency of bees and other
insect visitors to the flowers. A number of bees were caught in sterilised
test-tubes, while they were actually working among trusses of pear
blossom. They were transferred to Petri dishes containing a layer of
sterile malt extract gelatine, and were allowed to walk over the surface
of the latter. In fifty per cent. of the cases examined it was found that
colonies of the bacterium with the typical characters to be described
later developed in the footprints of the bees after an interval of three or
four days. The course of the bees across the plate was most strikingly
mapped out by the line of colonies. It is interesting to note that per-
fectly pure cultures were obtained in some cases in this way, no
other organism developing on the plates.

There is no doubt therefore that the dissemination of the disease is
largely due to insect visitors to the flowers. Infection is carried by them
from diseased to healthy blossoms, which become inoculated either
through the stigmas or the points of the viscid receptacle with which
the feet of the insects come into contact. It will be seen later that
infection can take place by merely superficial inoculation with the
organism in this manner.

92 Disease of Fruit Blossom

Probably the start of an outbreak at the beginning of the flowering
season occurs in two ways. In the first place it seems likely that in
cases where blossom is produced on a spur the tissues of which are
already infected with the organism, some of these blossoms are infected
at the time of their formation through the spur tissues. In the second
place, since the organism has been found in the soil of fruit plantations,
it is likely that insects or wind convey infection from that quarter in
many Cases.

In the light of present knowledge the organism seems to be a form of
very wide, if not general, distribution in this country, occurring at times
in the soil of fruit plantations and possibly having a natural habitat in the
soil. It is frequently found in flowers, especially such as rosaceous species,
where a prominent nectar-secreting disc, on which it appears to thrive,
is present ; becoming parasitic in some cases, notably the pear, perhaps
being aided in obtaining entry to the tissues through frost or other
damage. It is carried from flower to flower by bees; and finally, in
the case of the pear at least, is capable of gaining access to the tissues of
the fruit spurs and remaining in an active state there throughout the year.

Infection Experiments.

These experiments have been mainly carried out on pear blossom,
flowers of the varieties Catillac, Beurré d’Amanlis, Louise Bonne de
Jersey, and Vicar of Winkfield being for the most part used. The
number of flowers infected was very large, and the infection was in
nearly all cases successful.

The usual procedure in these experiments was to select young healthy
shoots bearing blossom in an unopened or comparatively unopened
condition, any individual flowers showing traces of natural infection
being removed. After infection the shoots were kept in the laboratory
or greenhouse at ordinary temperature in covered glass vessels, the
atmosphere of which was kept moist by the water in which the cut
ends of the shoots were placed. The mode of infection varied. In some
cases drops of water containing the bacteria were simply placed upon
various parts of the flower by means of a sterilised platinum loop, care
being taken to avoid injury to the tissues of the flower. In other cases the
culture was applied with a fine needle, the tissues being slightly pricked.
It may be added that in all infection experiments pure cultures of the
organism were alone used, the usual precautions against foreign infection
being taken by the use of sterilised instruments and other necessary

B. T. P. BARKER AND O. GROVE 93

details. It was found that although infection was obtained by both
methods, the disease set in much more readily when the tissues were
punctured. By the latter method the flowers formed small moist drops
in three to four days after infection at most of the injured spots, and on
the fifth day distinctly grey coloured slimy colonies could be seen. After
six to seven days the affected areas were black and exactly like the
natural ones. Microscopical examination of the tissues of these regions
showed a heavy growth of the organism, and the latter after isolation
in pure culture again presented all the characters of the original type.
It is noteworthy that in practically every case tested the bacillus in
question was the only one isolated from the affected tissues. In due
course the blackening spread to other parts of the flower in the manner
already described in connection with the disease under natural conditions.
Control experiments in which the flowers were punctured with a sterile
needle, but not inoculated with the organism, gave in the large majority
of cases negative results. Some discolouration occurred at the point
of injury, but nothing further resulted. Where the control experiments
in a few cases showed a development of the disease at such points, it
is probable that the organism was already present on the flower at the
time of injury. There is evidence to show that the bacillus is at times
present on the surface of perfectly healthy flowers.

The infection experiments in which the tissues of the flowers were
uninjured yielded less striking results, although in the great majority
of cases the disease eventually developed.

Owing to the extent of the disease on the trees at Long Ashton last
spring, the selection of unaffected blossom trusses for infection experi-
ments was difficult. Many instances of the disease developing without
artificial infection on selected trusses apparently quite healthy occurred ;
and although there is no question of the success of the infection experi-
ments, there were occasions when it was difficult to decide as to natural
infection also playing a part.

Infection experiments were also made on flowers on trees growing
in the open plantations at this institution. These were less satisfactory
than those already recorded. In the first place it was almost impossible
to distinguish between the results of artificial and natural infection,
the latter being so common, when the infected trusses were not enclosed
in paper bags ; and secondly, when paper bags were used, a large number
of artificially infected trusses remained healthy, the controls behaving
similarly. Probably this was due to the effect of bagging on the flowers.
While at present we know little as to the influence of external conditions

94 Disease of Fruit Blossom

on the disease, the available evidence indicates that the disease is
encouraged by a comparatively low temperature and a damp atmo-
sphere and conversely is checked by hot and dry weather. The conditions
within the bags approximate to the latter type.

Since it was discovered that the tissues of the fruit spurs of pears
were frequently attacked by the organism several infections were made
in young shoots of apples, pears, plums, and gooseberries, by means of
needle punctures. Control punctures with a similar sterile needle were
made at the same time. The two sets of shoots were compared at
monthly intervals, and it was found that, although the inoculated punc-
tures were full of the living bacteria, so much as to show that some
multiplication had taken place, the organisms had not spread appreciably
in the tissues nor caused more than a minimal amount of local damage.
Macroscopically the infected shoots differed in no way from the controls.

A few infections on Catillac pear fruits when they had nearly attained
their maximum size were also made by puncture. No serious results
ensued.

Isolation, Description, and Cultural Characters of the Bacillus.

As already mentioned, microscopical examination of the tissues of
the discoloured areas of the flowers, leaves, and fruit spurs showed them
to be swarming with cells of a rod-like bacterium. The detection of
the organism was generally difficult and frequently impossible when
material for examination was selected from the centre of the blackened
patches owing to the alterations in the diseased cells of the tissues.
The formation of granular substances and the abundance of compara-
tively opaque and darkened cell contents prevented satisfactory identi-
fication of the presence of the parasite. It 1s indeed probable that the
latter dies off in those places. When, however, portions of the tissues
at the periphery of the discoloured spots bordering on healthy unattacked
cells were examined, there was generally no difficulty in finding the
bacteria in abundance and in a most active condition. There appears
to be a zone of the bacteria along the periphery of the affected areas,
where fresh cells are being attacked, which advances with the spread
of the discolouration ; while behind, where the cells of the host have been
killed, the parasite has migrated or died off.

The isolation of the organism from the peripheral portions of affected
areas was simple. Plate cultures of malt extract gelatine infected from
such regions gave colonies of the bacterium in the course of four or five
days. Many independent series of plate cultures have been made from

B. T. P. BARKER AND O. GROVE 95

different flowers, leaves, and fruit spurs, and in the great majority of
cases the characteristic colonies of the organism have developed. It
was rarely that other organisms appeared on the plate cultures ; and
in such cases the foreign form was nearly always Monalia fructigena,
the “‘ brown rot” fungus. It is not uncommon to find flowers attacked
at the same time both by this fungus and the bacillus.

The isolation of the bacterium was especially easily effected from
flowers showing newly developed small, black spots on the receptacle.
By touching these spots with the point of a sterilised needle, and making
streaks with the latter over the surface of a sterile plate of the nutrient
gelatine, pure cultures were very often immediately obtained. From
older, dried up material, the growth is not so quickly developed.

Pure stock cultures of the organism were kept on various nutrient
substrata and in liquid nutrients. In most cases the organism retained
its vitality for several weeks at least and did not lose its parasitic powers,
infections on fresh flowers and leaves giving positive results. In due
course, however, on most of the media tested it eventually died off ;
but cultures on potato blocks have retained their vitality and parasitic
abilities for over eight months.

The bacillus is a rod 2-4 x5-8 in dimension. Although
satisfactory stained preparations of the flagellae have only been obtained
in one or two instances after repeated trials, there seems no doubt that
the cells are lophotrichic. The flagellae, two or more in number, are at
least four to five times as long as the cells themselves. The organism
stains well with the usual stains, and especially so with gentian violet.
It is also stained by Gram’s method.

It grows well in malt extract solution (sp. gr. 1040), glucose-peptone
water (5%, glucose, 1% peptone), and in neutral and slightly acid
(+ 0°15 % normal) bouillon.

The bacillus is highly motile in young cultures, showing quick pro-
gressive movements. The motility depends greatly upon aeration.
This is very well shown in ordinary coverslip preparations made from
colonies or young plate cultures, the bacillus coming to rest in about
two minutes at the centre of the slide, the movement being progressively
more active in the cells passing outwards towards the edges of the
slip. At the latter region or in the neighbourhood of air bubbles
movements continue for about 20 minutes. It then ceases and agglu-
tination takes place. After all have come to rest, if the slip is lifted for
a few moments and then replaced, nearly all the cells are found in
an active state of movement.

96 Disease of Fruit Blossom

The cells are mostly single or in pairs, seldom in long chains. No
endospores have been observed in any cultures. Involution forms are
produced very readily, especially at temperatures of 25-30° C., and in
old cultures. These involution forms attain often a length of about
100 # and are irregularly swollen. The optimum temperature for growth
. 1s about 18° C.

In bouillon at 15-18° C. a slight cloudiness is formed in 24 hours,
and a good growth obtained after two days; after four days there is
an appreciable deposit and a slight thin film on the surface of the liquid.
At 25° C. growth is a little slower, and at this temperature after 48 hours
the cells gradually increase in size and begin to lose their motility.
Small chains and involution forms are then soon developed, and after
four to six days the organism has completely changed its original form.
It grows out into long threads and large, irregularly swollen and often
very granulated forms. Movement is then practically stopped.

At a temperature of 18° C. the cells do not change their form or lose
their motility until the cultures are getting old.

If involution forms from a six-day old culture are placed in fresh
bouillon and kept at a lower temperature, the new cells quickly begin
to assume the normal size and motility.

In two months old bouillon cultures, the cells collect at the bottom
of the vessel, forming a disc of somewhat gelatinous character, and the
liquid is left perfectly clear.

With bouillon gelatine stab cultures show feeble development after
24 hours. After 48 hours there is good growth with crateriform lique-
faction ; after six days the liquefaction is stratiform, and after eight
days all the gelatine is liquefied and a flocculent deposit formed. Streak
‘cultures after 48 hours show strong liquefaction, there being a broad
concavity in the gelatine and a cloudy liquid and white, flocculent
deposit in the tube.

In plate cultures of gelatine media colonies are extremely character-
istic after four days. The submerged colonies are small and white,
the surface colonies are liquid with smooth edges, round, 6-8 mm. in
diameter, concave, moist and glistening, semi-transparent, often with
small white nuclei in the centre and concentric rings of granular matter

beyond, and with whitish margins. Under the microscope the surface
colonies show a flocculent deposit and a margin forming a double
ring.

The liquefying action is very pronounced ; and in a plate culture
the whole gelatine is generally liquefied in about eight days, even if

B. T. P. BARKER AND O. GROVE Q7

the plate originally contained only 8-10 colonies. A plate culture in
the liquid state has a pronounced smell of ammonia

In bouillon agar at 18° C. stab cultures give feeble growth in three
days, spreading out on the surface. Streak cultures form in three days
a flat, glistening, smooth-edged, whitish, spreading growth. In plate
cultures the colonies are visible after 48 hours. The surface colonies
after three days are small, round, raised, glistening and whitish, later
spreading out over the surface. Submerged colonies are white and remain
very small,

On potato a raised, yellowish-white, broad, smooth-edged growth
is formed after eight days at 18°C. On parsnip and carrot a feeble
growth is observed after five days. On turnip no development takes
place.

In sterilised milk a good growth is obtained. No curdling takes
place in eight days at 18° C., but the milk is eventually very slowly
peptonised.,

No fermentation takes place in 2 °% solutions of saccharose, maltose,
glucose, laevulose, or lactose, to which 1 °% peptone was also added,

Old cultures in glucose-peptone solution exhibit a pronounced
greenish fluorescence. This has not been observed in the case of any
other media.

There is no indol reaction given in eight-day old cultures.

From these characters it appears that the organism is a species of
Pseudomonas. So far it has not been identified with any hitherto
described form ; but on account of its wide distribution and occurrence
in the soil it is possible that it may be known to soil bacteriologists as
one of the ammonia-forming types.

Ann. Biol. 1 7

98

ON THE PREPARATION OF COCCIDAE FOR
MICROSCOPICAL STUDY.

By EK. E. GREEN.

1. Introductory Notes.

Havine been asked by several correspondents to describe the best
method of preparing Coccidae for critical study, | have thought it might
be useful to publish an account of the technique that I have adopted
in my own work. I do not set it up as being the best method, as I have
not experimented to any extent in other directions ; but I have gradually
arrived at a procedure that appears to produce satisfactory results which
compare favourably with examples of mounting that I have received
from other working entomologists. I am, however, confident that useful
modifications and improvements could be effected by anyone conversant
with the processes employed in modern laboratories. I must also confess
that I work largely by rule of thumb and have not reduced my processes
to exact measures of time and quantities. I find, indeed, that the
essence of success depends upon minute variations in the treatment
employed—to be learned by actual experience alone.

2. Appliances und Reagents.

I will first give a detailed list of the appliances and reagents that I
have found necessary or convenient :

Any good compound microscope, with modern objectives.

A dissecting microscope (preferably an erecting binocular).

An Abbe-Zeiss camera lucida.

A reliable stage micrometer.

Fine-pointed forceps.

Small scalpels.

Dissecting scissors.

Two or three fine camel-hair brushes.

EK. EK. GREEN 99

Some “snipe-points” (the terminal feather of a snipe’s wing)
mounted in small porcupine quills.

Setting needles. These should be the smallest and finest obtainable.

A small (narrow) section lifter. A piece of stout silver wire, ham-
mered flat at one end and turned up at a slight angle, serves the purpose
admirably.

Evaporating dishes (24 in. diam.).

Several flat-bottomed watch glasses.

Short test-tubes (1 in. diam.).

Kxcavated glass blocks. These may take the place of the watch
glasses, as they are most useful for the reception of such reagents as
oil of cloves, distilled water and various strengths of aleohol, in which
the objects have to be steeped for various periods. They will stand
steady on the stage of the dissecting microscope.

Glass pipettes with rubber teats.

A small glass table, with a mirror below, is of great convenience
when transferring objects from one medium to another.

The following reagents will be required :

A strong solution of potassium hydrate (liquor potassae).

Alcohol, 70 %, 90 %, and absolute.

Fuchsin (acid), strong aqueous solution.

Picric acid, saturated solution in alcohol,

Glycerin, dilute.

Oil of cloves.

Canada balsam, dissolved in xylol.

Distilled water.

3. Preparation and Mounting of Specimens.

Coccidae do not necessarily require any prolonged process of pre-
liminary preparation. They may be treated in the fresh condition
without any difficulty. On the other hand, material that has been
kept in alcohol or other liquid preservatives, or that has remained dry
for many years, will respond to treatment with complete success—pro-
vided that it has not been allowed to become mite-eaten or infested with
fungus.

Naked species, such as Lecanium, are the simplest subjects and may
be best utilised to illustrate the process. The general procedure is the
same for all Coccidae; but slight modifications (to be noticed later)
will be necessary in particular cases.

100 The Preparation of Coccidae

Let us suppose that we have some dried leaves or twigs infested with
a species of Lecanium. Detach a few of the insects by means of a needle
or fine scalpel, taking care not to injure the margin in so doing. Select
examples of different stages of growth, and take more than will be actu-
ally necessary for the final mount. Some of them are sure to be imper-
fect and may be discarded during the later stages of the preparation.
Place the selected specimens in a small evaporating dish, together with
a tiny fragment of pumice stone (to prevent too violent ebullition).
Add about two teaspoonfuls of strong potash solution and heat over a
spirit lamp for from two to five minutes, agitating the vessel slightly
and regulating its distance from the flame so as to keep the liquid simmer-
ing rather than actively boiling. If it is necessary to prepare several
different species at the same time, specimens of each may be isolated
in small test-tubes (with the requisite amount of potash), plugged with
cotton wool and placed erect in a small saucepan containing water, the
whole being boiled together. The specimens must be examined at
intervals and removed so soon as they begin to show signs of clearing.
The right moment can only be learned by experience. If not treated
long enough, there will be subsequent difficulty in removing the contents
of the body _ If treated for too long a time, the cuticle will become too
tender and will tear or break up during subsequent manipulation.

During this process, note any colour given off by the objects. Certain
species colour the liquid pink-—or even crimson ;. others give off a
greenish, brownish, or inky stain. A knowledge of such characteristics
may be of assistance in differentiating between closely allied species.

Remove the prepared specimens, by means of the section lifter, to
distilled water. Here, by a process of osmosis, further clearing will
take place and part of the contents of the body will pass out into the
water. I find it convenient to leave the objects in this medium for
24 hours, and I use the excavated glass blocks for their reception.

At this and all subsequent stages care must be taken to label the
specimens in such a manner that they may be identified with the material
from which they have been taken. This label should be transferred
from vessel to vessel at each subsequent transference of the specimens.
Failure to observe this precaution may lead to most unfortunate mis-
takes.

Before further treatment, note the form of the insect which will
often have become distended to its fullest extent, when it may show
characters that will be lost under subsequent compression. For in-
stance, the lateral tentacular processes characteristic of the living

EK. E. GREEN 101

Diaspis boisduvallii usually disappear entirely when mounted in balsam.
The peculiar form of the Zachardia insect is best shown (and figured)
at this stage.

It should also be noted whether the bodies contain well developed
ova or embryos. The presence of such will settle conclusively the stage
of the insect, in doubtful cases.

On the following day the specimens should be transferred to clean
water, when the remaining contents of the body may be easily removed
by manipulation with fine needles, assisted by the mounted snipe feathers.
If the body is not already ruptured, a small opening should be made at
one point, through which the liquid contents may be gently worked
out. Small aggregations of wax, fatty globules, or partially solid matter
may be removed by inserting a fine point through the artificial aperture.

The specimens are next transferred to and washed in 70 % alcohol
for a few minutes. They are now mounted temporarily on a glass
slide in a drop of dilute glycerine, under a glass cover slip, for preliminary
examination. After which, a few drops of fuchsin solution are run in
with a pipette, and the slide is put by for another 24 hours.

Then add a few drops of picric acid solution and leave for five or
ten minutes, to fix the stain.

Remove the cover glass ; flood the slide with alcohol, to redissolve
the partially crystallised picric acid, and transfer the objects to a bath
of 70 % alcohol, where the glycerine and superfluous stain can be washed
out, together with any small fragments of the body contents that may
have been overlooked during the earlier process. Such omissions can
now be readily detected, as they will have absorbed a deeper stain.

When the removal of the stain has proceeded to the right point,
the objects may be washed in absolute alcohol, preparatory to their
removal to a bath of oil of cloves, though [ have not found any ill effect
following upon their direct transference from 70 °% alcohol. They may
be allowed to remain in the oil for about 10 minutes, after which they are
finally mounted in canada balsam.

If the same receptacles and media are used on subsequent occasion
great care must be taken that every specimen has been removed. Con-
fusion and erroneous determinations have occasionally arisen through
the accidental inclusion in the finished mount of one or more specimens
inadvertently left over from a previous operation.

After arranging the objects neatly in the centre of the slide, I place
a sufficiency of balsam on the underside of the cover glass and lower it
gently on to the specimens. I used, at first, to find that the balsam,

7—3

102 The Preparation of Coccidae

when spreading itself under the cover glass, would disarrange my
neatly disposed specimens, and even carry some of them away to the
extreme margins. I now prevent this inconvenience by pressing the
objects on to the glass with a small piece of thin smooth blotting paper.
This absorbs the remaining oil of cloves and makes the objects adhere
closely to the glass. | Before adding the balsam and cover glass, the
mount should be examined for the removal of any small fibres that may
have detached themselves from the absorbent paper. Several specimens
should be mounted on one slide, some showing the dorsal and others
the ventral surface uppermost.

When dealing with strongly convex species, it is often advisable to
slit the dorsum, as otherwise it will not lie flat on the slide. In such
cases the venter should be separated from the dorsum and disposed so
that the two surfaces can be examined side by side.

Species that are densely coated with wax, such as Ceroplastes, should
have the waxy covering removed before the insect is boiled in potash.
This can usually be done with a fine scalpel, without injuring the insect;
or the wax may be dissolved in carbon bisulphide. Boiling in oil of
cloves will have the same result.

The larger species of Monophlebus and allied genera are often so
dense that satisfactory mounts cannot be made of the complete insect.
It is better to divide them horizontally, separating the venter from the
dorsum completely. If the insects have been preserved in alcohol,
this section can be effected before boiling in potash. But, with dried
examples, it is necessary to boil them for a short time, until the skin is
softened, before attempting the operation. The object is then replaced
in the potash and boiled until the two halves come apart and the soft
inner tissues separate from the derm, leaving the latter quite clean.

The species of Tachardia (lac insects) are embedded in dense resinous
gum which may be softened or completely dissolved by immersion in
strong alcohol, before treatment.

Coccidae of the family Diaspidinae are concealed beneath composite
scales consisting of the larval exuviae supplemented by secretionary
matter. To obtain the insect itself, the scale must be lifted or turned
over when the creature will be found either free or lying in the hollow
of the overturned scale. If there is any difficulty in extracting the
insect, the whole scale may be boiled in potash, when the secretionary
matter is decomposed and the insect and pellicles freed. Some of these
pellicles should be stained and mounted with the insect itself, as they
often afford useful characters for the differentiation of closely allied

E. E. GREEN .- 22

species. In the absence of male puparia it is often difficult to decide
whether a certain species should be included in the genus Aspidiotus
or Diaspis. Examination of the larval and nymphal pellicles of the
female will usually decide this point, for in Aspidiotus the dorsal half
only of the pellicle is present in the scale, whereas in Diaspis the venter
remains attached and will be found beneath the posterior extremity of
the pellicle.

In the genera Aonidia, Fiorinia and Leucaspis, the adult female is
completely enclosed within the nymphal pellicle, and it will be necessary
to break this open (with a fine needle) to obtain the actual insect.

Insects of the genus Asterolecanium require very careful handling.
The derm is exceedingly thin and delicate. A very short immersion
in boiling potash is sufficient to soften the tissues and decompose the
contents of the body. I find it best to place the complete scale in the
potash and continue the boiling only until the secretionary matter is
dissolved, when the insect—now freed from its covering—should be
immediately transferred to distilled water.

The treatment must be modified when dealing with adult males of
any of the smaller species. Boiling in potash results in the hopeless
crumpling of the wings and their entanglement with the other limbs.
For such delicate objects a more prolonged immersion in cold potassium
hydrate is preferable.

The procedure may be roughly summarised as follows:

(1) Boil in potash for a few minutes, or immerse in cold potash
for a longer period, until the contents of the body are completely
softened.

(2) Soak in distilled water for 24 hours.

(3) Press out the softened contents, and clean the surface parts.
(4) Mount temporarily in dilute glycerine.
(5) Stain with fuchsin, for 24 hours.
(6) Fix stain with picric acid for 5 or 10 minutes.
(7) Wash and remove superfluous stain in 70 % alcohol
(8) Wash in absolute alcohol.
(9) Place in oil of cloves for 10 minutes.
(10) Mount finally in canada balsam.

104 The Preparation. of Coccidae

4. Preservation of Unmounted Specimens.

A few hints for the preservation and storing of unmounted material
may be of use.

Desiccation is the method usually adopted and—for a general
collection—is certainly the most convenient ; though, where it is desired
to retain the exact form of the fresh insects, it may be advisable to
preserve duplicates in alcohol or dilute formalin.

A very large number of species, e.g. all the Diaspidinae and the flatter
forms of Lecanium, may be treated like botanical specimens, 7.e. dried,
together with the leaves to which they are attached, between absorbent
paper. But the pressure employed should be light—merely sufficient
to keep the leaves flat. I frequently have material submitted to me
for determination, where no pressure at all has been employed, with
the natural consequence that the leaves are so curled or shrivelled that
the task of examination is greatly aggravated. In such cases it is
necessary to break up the whole material and to examine it very closely
or valuable specimens may be overlooked. A leaf that has been dried
flat may be completely examined with the maximum of convenience
in the minimum of time. Thin slices of bark, or rind of fruits, may be
treated in the same way. ‘Twigs bearing specimens may be cut up into
convenient lengths and dried without pressure. In any case, super-
fluous and useless parts should first be removed, to facilitate subsequent
examination and save space. Leaves bearing hemispherical or highly
convex species may be dried flat without pressure by pinning down the
edges. Species that are not habitually attached to their host plant,
such as many species of Pseudococcus, Orthezia, etc., are best removed
and dried separately, after which they may be kept in small glass tubes
plugged with cotton wool, or, better still, in the small gelatine capsules
supplhed by chemists for the reception of various drugs. Specimens
dried in situ should be wrapped in soft paper and placed in small envelopes
upon which the full data should be written. Capsules or tubes should
be placed in similar envelopes. The envelopes themselves may be
conveniently stored in white cardboard boxes which should be made
to order and should be of various sizes which must be multiples of the
smallest unit. The sizes that I have adopted in my own collect?on are :

EK. E. GREEN 105

The drawers of my cabinet have an inside measurement of 17 16
<2 inches deep, each of which will hold six rows of 30, 15, 8 or 4 boxes,
according to the size. With the exception of the largest size, the boxes
stand edgeways in the drawer.

Each box should be reserved for a single species only, but may con-
tain several gatherings of that species. The name of each species should
be clearly indicated on the cover of its particular box. The various
genera will naturally be grouped in their respective families, but it will
be found convenient to arrange the species alphabetically, under their
respective genera. A small quantity of finely powdered naphthalin should
be placed in each box, and renewed periodically. If preferred, naph-
thalin dissolved in petrol or benzine may be employed. A few drops of
this liquid will spread over the bottom of the box and, upon evapora-
tion, will leave a fine deposit of naphthalin which has the advantage
of not shifting its position when the boxes are placed on edge.

Specimens preserved in a liquid medium (for which alcohol of about
80 % or formalin diluted to about 3°% may be employed with satis-
factory results) must be kept in tightly corked tubes. These do not
lend themselves so conveniently to arrangement in the general collection.
They must be stored in separate racks, or in boxes fitted with compart-
ments for the purpose.

Glass slides with microscopical preparations can be stored in any
of the various forms of boxes or cases designed for the purpose. I use
cases made in book form, each case containing 50 slides, with an index
on the inside of the cover. Such cases can be arranged like volumes on
book shelves.

Surplus material should always be retained, for purposes of exchange.
Great convenience and economy of time will be experienced if such
duplicates are at once portioned out and placed in labelled envelopes,
ready for distribution when required, instead of being stored in bulk.
When an application for specified duplicates is made by some corre-
spondent, the time required to go through a large collection, separate
out the required material, do it up in packets and label it, 1s often greater
than can be given at the time. The task is therefore postponed for
some more favourable opportunity which may be indefinitely delayed.
I keep all my duplicate material in small labelled envelopes which are
stored (alphabetically) in tin boxes made especially to fit them. Any
species can then be found instantly and is ready, without further
attention, for distribution.

106 The Preparation of Coccidae

5. The Importance of Exact Measurements.

Finally, I should like to say a few words on the importance of exact
measurement in critical comparisons. For this purpose a camera
lucida is almost indispensable. Take, for instance, the determination
of the antennal formula. Direct measurement of such minute parts
is extremely difficult ; but, if enlarged camera drawings are made, they
can be compared and measured with the greatest facility. Neither the
eye alone, nor freehand drawings can be trusted implicitly. Body
measurements alone are not of much value between closely allied species,
as individuals from a single colony often vary considerably in size,
and such variability is still more marked betwee examples collected
on different plants. But the more densely chitinous parts—antennae,
limbs, anal lobes, ete.—are much more constant. After the final moult
these organs do not increase in size, though the body of the insect may
more than double its original dimensions.

THE ANNALS OF APPLIED BIOLOGY.

VOED I, NO. 1

General view of the machine showing main pipe.

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NO, 1 PLATE IV

‘ home

[ Photo by Clarke Hyde

The motor pump,

THE ANNALS OF APPLIED BIOLOGY. VOL. |, NO. 1 PEATE,

See nae -
ts

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[ Photo by Clarke &: Hyde
Mixing wash.

THE ANNALS OF APPLIED BIOLOGY. VOL. |, NO.

PLATE

Using telescopic ladder.

VI

THE ANNALS OF APPLIED BIOLOGY, VOL. |, NO. 1 PLATE VII

Spraying the tallest trees.

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THE ANNALS OF APPLIED BIOLOGY. VOL. I, NO. 1}

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Lifting the motor.

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VIII

VoLuME I JULY, 1914 No. 2

PRELIMINARY NOTES ON DAMAGE TO
APPLES BY CAPSID BUGS.

By J..C._¥.. FRYER, #4...

Entomologist to the Board of Agriculture,
Fellow of Gonville and Caius College, Cambridge.

(With Plates IX and X.)

Tuat plant bugs of the family Capsidae can be responsible for a
serious form of injury to apples has been recognised in this country for
several years. Cases have been recorded by Theobald[1] and by
Collinge [2] while complaints have been received from time to time by
the Board of Agriculture from fruit growers in various parts of the
country. On the continent brief references can be found to the Capsidae,
notably to the genus Lygus, in most works on economic zoology, but the
precise form of injury here dealt with does not seem to have been gener-
ally recognised. In America members of the Capsidae are well known
as pests to both apples and pears and, though with the exception of
Lygus pratensis Fab. the species there are not those found in Europe,
yet the type of injury produced seems to be much the same. In this
connection attention may be drawn to the papers of Taylor [3] on
Lygus pratensis, of Crosby [4] on Heterocordylus! malinus Reut. and
Lygidea mendaa Reut., and of Caesar [6] on the two latter species and on
Neurocolpus nubilus Say. and Paracalocoris colon Say. where full accounts
may be found both of the insects and the injuries they produce. It will
suffice to point out here that at least one author, Caesar, has found some
difficulty in showing which of the various species found on apples are
actually responsible for the damage and that while Crosby in the U.S.A.
lays most of the blame on H. malinus and L. mendaxz, Caesar in Canada
attributes the injury primarily to NV. nubilus and P. colon, treating the
two previous species as of secondary importance. The difficulty in
the identification of the actual cause of the damage has also been felt

1 An allied species, H. flavipes Matsuma damages apples in Japan. Nitobe [5}.
Ann. Biol. 1 8

108 Capsid Bugs and Apples

in England and this paper is intended partly to throw more light on this
question—though it has for its primary object the attraction of more
attention to the subject at large, since the actual loss which may result
from the attacks of Capsids is very serious.

As in the case of most plant bugs (LZ. pratensis is sometimes an
exception) the primary cause of the damage is a puncture made by the
bug in feeding. The juices of the plant are drawn up through this
wound and either on account of the direct loss of sap or possibly from
the injection of some irritant poison the surrounding tissues are more or
less injured, the extent of the injury varying with the condition and
portion of the plant attacked. In the case of apples the injury takes
place very early in the season, probably before the blossom opens, when
the tissues of the developing fruit and foliage are soft and in a state
of rapid growth. The bugs responsible have then but recently been
hatched and are very small; they appear to feed equally on the
young fruit, foliage and young shoots, all of which suffer to some
extent, though the injury to the fruit is the serious feature. The
puncture of the bug appears to cause a definite check to the sur-
rounding tissues so that, as the fruit grows, some parts develop more
rapidly than others and a badly shaped, distorted apple is formed. When
the check is very severe all growth ceases near the wound and as the
remainder of the fruit swells rapidly a crack appears and may extend
the whole length of the apple. A further feature often present is a
more or less extensive discolouration or “ russetting,” which seems to
arise from the abnormal development of the damaged cuticle. Finally
the surface of the fruit may show a number of small pimples which so
far as is known at present are the result of the unhealthy healing of the
punctures. In the young fruit the actual puncture is readily seen but
later it becomes obliterated and there is not as a rule any discolouration
in the flesh of the apple as described by Caesar in the Canadian attack.
It will be noticed that some of these forms of injury may also appear
from other causes and are not infrequently attributed to some climatic
action, as for instance to cold winds or excessive moisture. Although
it seems probable that Capsid injury is more common than is generally
supposed, at the same time it is obvious that all checks to the developing
tissues of the fruit would be likely to produce very similar results so
far as the mature fruit is concerned.

The injury to the foliage is perhaps more definitely diagnostic of
an insect attack. As in the case of the fruit the puncture affects the
surrounding tissues so that an attacked leaf shows numerous brown

J. QGuboPRyer 109

spots, usually near its base, where the proboscis of the bug has pene-
trated. The leaf is frequently undersized and badly shaped and when
it becomes old the small patches of dead tissue round each puncture may
falt away, producing a very ragged condition. Distortion of the young
shoots has been noticed by Theobald and this feature of the attack was
also observed in 1913. All damage to both fruit and foliage is completed
early in the season and though the bugs continue to puncture the foliage
little harm seems to ensue.

The sum of the damage detailed above is very considerable. The
injured fruit is almost unsaleable and cases were visited where 30 %-
50 % of the crop was stated to have been affected, and in this estimate
no account was taken of fruit so damaged that it fell off before reaching
maturity. A further serious feature of the attack is that it seems to
preserve a high intensity for several years consecutively in the same
orchard and is not like the many diseases which vary within wide limits
year by year.

In distribution, this Capsid attack is very local and is not known to
be widespread in any district ; at present it is known to occur sporadi-
cally in Kent, Suffolk, Nottingham, Worcester and Hereford.

As regards the different varieties of apple it is not possible yet to
say that any kind is either immune or specially susceptible, since facts
obtained from one affected orchard were negatived by observations in
the next. It certainly appeared that the trees in the affected orchards
were not in a good state of health. Mr G. P. Berry, of the Board of
Agriculture, examined all the affected orchards and he was able to
confirm this view. A number of soil analyses were therefore made in
the hope of obtaining further light in this direction, but the work was
fruitless for the soils in most cases showed no marked deficiencies in
composition or other disability adequate to explain the apparent low state
of health. It is still felt however that this side of the problem offers
material for investigation since a tree not in a flourishing condition would
naturally be less able to withstand the Capsid punctures than a healthy
tree.

Turning next to the problem of the species of Capsid responsible
for the damage, a few notes may be given on a somewhat cursory survey
of four of the affected orchards, all of which are of large size and have
suffered greatly from the disease for several seasons consecutively. An
ordinary Bignell beating tray was used to obtain specimens and attention
was paid to insects which were present in large numbers or belonged to
a species to which the damage had previously been attributed. These

8—2

110 Capsid Bugs and Apples

species are (1) Lygus pratensis Fab., (2) Psallus ambiguus Fall., (3) Atracto-
tomus mali Mey., (4) Plesiocoris rugicollis Fall., (5) Orthotylus marginalis
Reut. The first of these, L. pratensis, may be dismissed at once from
the enquiry since only one or two specimens in all were found in the
affected orchards. Its mode of injury too, as described by Collinge and
Taylor, differs from that actually observed, and consists in a dimpling
of the fruit. ZL. pratensis is a species which hibernates as an adult,
and lays eggs in the early spring ; occasionally these eggs are laid under
the cuticle of the young apple, and as the fruit grows a dimple is formed,
which persists until the fruit is mature. In the case of this species,
therefore, the injury is not always the result of the punctures made
by the bug in feeding.

As regards the other species just mentioned, their distribution in
the affected orchards may be seen from the accompanying table. In
the same table a few selected unattacked orchards are given to show
which species may be present in an orchard without producing injury.

Psallus Atractotomus Orthotylus Plesiocoris

ambiguus mali marginalis rugicollis

Suffolk affected
Worcester affected
Worcester affected
Worcester unaffected
Nottingham affected ..
6. Hertford unaffected ..
Cambridge unaffected

oe

i
bd bd bd Dd bd Dd Pd
OoOnWoOon On

COOK MK HS
COOOKMH

Note. In No. 3 O. marginalis was scarce. In No. 4 two specimens only of O. mar-

ginalis were obtained. In the other cases the “‘ X ” implies that the species was exceed-
ingly abundant, the ‘‘O” that it was absent

Taking these species singly it will be seen that P. ambiguus was
found abundantly in all orchards and can hardly be the cause of the
damage. It is a small brown or red species which is usually very common
on apples everywhere.

The second species, A. mali, was considered by Theobald to be
responsible for injury in Kent; in the present case it was absent from
two affected orchards, present in the other two, but also present and in
large numbers in an unaffected orchard. It is not therefore considered
here to be a markedly injurious species. In colour and shape it somewhat
resembles P. ambiguus, but may at once be known by its small size
and thickened antennae. The third and fourth species, P. rugicollis and
0. marginalis, may be considered together. Both species were present
in two of the affected orchards and in each of the other cases of attack

: J. Os FeoPRYER 111

one or other was present. Further they were absent from the un-
affected orchards with the exception of one in Worcester where O. mar-
ginalis was recorded as present from two specimens only. It therefore
appears that one or both of these species are responsible for the injury,
and this opinion is strengthened by an experiment carried out by the
proprietor of an affected orchard in Worcester. This experiment
consisted in excluding the larvae of these species from a number of
trusses and also in enclosing them with others. The trusses from which
the bugs were excluded developed sound fruit, while the apples enclosed
with them sustained typical capsid damage. It is hoped to repeat
this experiment with P. rugicollis and O. marginalis separately, in order
to confirm suspicion as to their both being responsible for damage—
in the meantime they must be left to share the responsibility between
them. In colour O. marginalis and P. rugicollis differ from Psallus and
Atractotomus in being green or yellowish-green ; they closely resemble
each other superficially and may easily be confused in the field. The
presence of a rounded ridge or collar towards the anterior margin of
the pronotum will always distinguish P. rugicollis from an Orthotylus,
while in addition the former species is broader and stouter than the
latter, characters which give it a somewhat different appearance. Both
species are on Theobald’s list of suspects, in his articles on the subject, in
the Journal of Wye College, which also contains a quotation from Schoyen
to the effect that these species are harmful to apple and currant in
Sweden. Of neither species is the life history known. Mr EH. A. Butler,
who was consulted on the subject, kindly gave the information that
both species were usually found on willow or alder, though Reuter, who
described O. marginalis, mentions apple as one of its food plants. Further,
in Mr Butler’s experiences, these species appear rather late in the season,
larvae being found in June and July, and adults at the end of the latter
month and in August. In the cases now under consideration, P. rugi-
collis was adult in Suffolk on the 13th June and one or two pairings
were then observed. O. marginalis was adult in Worcester on the
24th June, but many specimens were still immature, and it appears
to be a later insect than P. rugicollis. Both species, however, must
have hatched towards the end of April and there is thus a considerable
discrepancy between the observations here recorded and those of
Mr Butler. The possibility of two broods naturally suggested itself
but this is considered as most unlikely by authorities on the Hemiptera.
Examples sleeved on apple trees in June failed to produce a second
brood, and up to the present no eggs have been discovered, and their
exact situation is unknown. It is assumed temporarily that apple has

112 Capsid Bugs and Apples

somewhat recently been adopted as a food plant, and that this change
has brought about an alteration in the time of appearance of the insects.
However this may be, it is evidently useless to speculate on the biology
of these species without further observations and this paper may be
concluded by a reference to the very meagre notes on “ treatment ”
which have been gathered.

Since the damage is done soon after the insects leave the egg it is
evident that any treatment by means of spraying must be carried out
at exactly the right time, and the spray must of course be one which
kills by contact. Crosby, in America, found that paraffin emulsion,
whale-oil soap and lime sulphur were of little service. Preparations
of nicotine and soft soap gave fairly good results and were recommended
with the caution added that the trees must be very thoroughly drenched
with the wash. The spray was to be applied both before the blossom
opens and after it falls. In England, a wash of this nature has been
found partly successful, but in one case no benefit whatever resulted,
the reason given being that the bugs hatch out over a long period. In
this case, both species were present and if O. marginalis is later in
appearing than P. rugicollis, it is probable that this explanation is
correct. The possibility of a winter wash against the eggs is hardly
worth considering, for apart from the failure of winter washes against
insect eggs in general, it will probably be found that the eggs of these
bugs are deeply imbedded in the bark of the twigs, quite out of the reach
of all sprays. The problem of dealing with these bugs in some ways
resembles that of the apple sucker (Psylla mali) and is likely to be as
difficult. At present, therefore, the only treatment which can be
suggested is a spray of soft soap and nicotine, or possibly soft soap
and quassia, but success will depend on a nice estimation of the exact
time to apply the wash, and the thoroughness with which the application
is made. Cases such as this bring out clearly the need for further
experiments in insecticides, especially in “‘ contact ”’ insecticides, with
the object of finding an efficient substitute for the expensive nicotine

and if possible of increasing the number of reagents from which to
choose.
REFERENCES.

1. THropatp. Wye College Journal. Reports on Economic Zoology for the years
1910 (p. 108), 1911 (p. 115), 1912 (p. 24).

2. Coxttiner. Journal of Economic Biology, vol. vit. p. 64.

Taytor. Journal of Economic Entomology, vol. 1. p. 371.

CrosBy. Cornell University Bulletin 291.

See reference 4 above.

6. Cansar. Hntomological Society of Ontario, 1912, p. 102.

mR ge

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NO. 2

Apples to show distortion and cracking due to punctures by
Capsid bugs. Natural size.

PLATE

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NO. 2 PEATEs

C. D. EE.

Fig. A. Plesiocoris rugicollis. Fig. B. Orthotylus marginalis. Fig. C. Lygus pratensis.
Fig. D. Atractotomus mali. Fig. EB. Psallus ambiguus. Each specimen x 3.

THE INTERNATIONAL PHYTOPATHOLOGICAL
CONFERENCE, 1914.

By, A. GCG. l. ROGHES
Horticulture Branch, Board of Agriculture and Fisheries.

Tue International Phytopathological Conference which was opened
at Rome on the 24th February last and was brought to a conclusion
on the 4th March, is the outcome of a long agitation. According to
the Report prepared by M. Louis Dop, and circulated to the "Delegates
before the Conference began, the first proposal for international action
was made by Professor Eriksson as far back as 1880. Similar proposals
were made from time to time at different International Congresses, but
with little result, except that at the Seventh Congress of Agriculture,
held in 1903, a special Committee on plant diseases was formed, and
the Zeitschrift fiir Pflanzenkrankheuten started as their official organ,
under the editorship of Professor Sorauer. The publication is, however,
international only in the sense that papers from authors of any nation-
ality are accepted, and the Governments of the chief states are in no
way involved. The first real step towards international action was
taken in 1905, when the Institute of Agriculture was founded at Rome,
and the subject of plant diseases definitely included among the subjects
with which it was competent to deal. Further progress was made when
the French Government were invited by a resolution passed at the
International Congress for Comparative Pathology at Paris in 1912,
to take the initiative by calling an International Phytopathological
Conference at Rome. Invitations were sent out for a meeting in 1913,
but the notice given was inadequate, and the meeting was postponed
till 1914. The Conference which has just been concluded is therefore
very largely due to the action of the French Government, and certainly
the initiative was taken by the French delegates throughout the pro-
ceedings. M. Develle, a former Minister of Agriculture, was elected

114 Phytopathological Conference

President of the Conference at the opening meeting, and M. Louis Dop,
the permanent representative of France at the International Agricultural
Institute, took a prominent part in the direction of business. The chief
credit, however, belongs to the French technical delegates, headed by
M. Mangin, whose persistence and readiness in debate, coupled with
his fertility in devising expedients for overcoming difficulties, carried all
before him. The prominent position occupied by the French delegates
in the Council chamber, and the fact that the discussion was carried
on in their native language, and in accordance with the usage of their
Parliamentary procedure, no doubt gave them a great advantage over
other delegates, an advantage, however, which they never abused.

As many as 30 States were represented, and the Conference was
informed that certain other countries accepted the principle of an
International Convention in advance. The only notable sovereign
state unrepresented was the United States of America but no
delegates were sent by South Africa, Australia, New Zealand, or
any of the smaller colonies. The instructions given to the three
English delegates were simple. We were not authorised of course to
commit our country to any binding agreement, but this was the less
important because it was made very clear at the beginning of the
debate that no delegate had such powers, and that no proposal would
be made which would not be submitted for the approval of our Govern-
ment through the Foreign Office, for subsequent ratification by pleni-
potentiaries appointed for the purpose. We were authorised, however,
to accept on behalf of the Board, the principle of a Convention, and
to press for three cardinal points: (1) that plants coming from a nursery
that had been inspected and found free from important diseases, should
be allowed entry if accompanied by an official certificate of health,
and that it should not be necessary that each consignment should be
specially examined ; (2) that the certificate should specify the diseases
for which the nursery had been examined, and (3) that consignments
accompanied by the official certificates should not be detained at the
frontier for re-examination by the officials of the country of destination.
It was thought that if we could secure these points, the hindrances
to trade, which had in recent years grown up in so many countries, would
be removed, and that a wide field for the development of English
commerce in plants would be opened. As events turned out, we had
singularly little difficulty in getting these principles conceded. The
first two points were pressed for by the delegates of other countries,
and were agreed to without opposition, and though the delegates present

A. G. L. Rogers 115

would not agree to surrender entirely the right of examination on arrival,
the first delegate of England pressed our claim so skilfully that an
assurance was understood to be given that the right would rarely be
exercised if it was found that the inspection in this country was
thorough and the consignments were found to be healthy. It is
most improbable that any further concession would have been gained
by pressing the claim any further.

The Convention which was ultimately drafted, and signed by all
the delegates present, may be summarised as follows. Adhering States
pledge themselves to form at once, if they have not already done so,
an official service of inspection of all nurseries, glasshouses and other
establishments offering plants for sale. They shall be prepared to issue
phytopathological certificates, control the movement of plants, and the
methods of packing and means of transit of the same, organise a
service for the suppression of dangerous diseases, and otherwise fulfil
the usual functions associated with a phytopathological department of
State. No State can adhere unless this is done at once. But it must
also undertake to create within two years, if it has not already done so,
one or more institutes for enquiry and research, obviously so that the
Administrative Department may be supplied with the best scientific
and technical advice possible. The State must pledge itself to issue
certificates with all consignments of plants sent abroad and to receive
consignments accompanied by such certificates from other adhering
States, and better terms must not be given to States that do not adhere
than to those that do, while States with common borders may make
special arrangements with each other with regard to the movement
of plants. All this is elemental, and no Convention would be possible
without some such agreement. But the really important point of the
Convention consists in the way in which this system is to be applied.
It was agreed with very little discussion that the Convention should
not apply to certain kinds of plants. Grain, seeds, potatoes, onions
and general farm produce—articles de grande culture—to use the exact
words, are excluded. Presumably, States may make their own regulations
as regards such produce, but it was generally felt, I think, that 1t would
be inadvisable in most cases to make any regulations at all. Most
delegates felt that the service at present in force in their own country
would be incapable of such a system of inspection, as would make
the certificates of any real value. Vines also were excluded as being
dealt with under the Berne Convention, to which every State that
joined the Rome Convention would be expected to adhere. On the other

116 Phytopathological Conference

hand, a vigorous stand was made for the inclusion of cut flowers and
bulbs of the flowering kind, a matter which is likely to give some countries
a good deal of trouble. Finally, an important discussion took place
on the diseases for which inspection is to take place. A single certificate
of health was felt to be insufficient ; a list of diseases prepared by the
Conference too fruitful a subject for dispute; and after a short debate
it was unanimously decided to leave each country to prepare its own
list of the diseases against which it wished to be protected. The pre-
paration of this list will be a matter of extreme difficulty, and may have
an important bearing on the nature of phytopathological research.
But the really important article is that which lays down the rules on
which the list is to be prepared. This article was drafted by a special
Sub-Committee though modifications were introduced when the report
was presented to the Committee and, as far as my recollection serves,
at the final sitting of the Conference. It prescribes that the list is to
be as restricted as possible, that no pests are to be included whose
host plant is not to be found in the country of destination, and that
the common pests whose distribution have been widespread in almost
every country for many years are to be excluded. This in itself would
be sufficient to keep the list from being unduly long, since few people
could be found who would object to the inclusion of such pests as could
properly fall within the category left open. But in order to emphasise
the limitations two further definitions were proposed. On the motion
of one of the Danish delegates it was decided that the pests must be
capable of being easily conveyed by living plants or parts of such plants,
and on the suggestion of one of the English delegates it was agreed
that the pests must be epidemic in character, and destructive or at
least injurious to the plant. It was explained that destructive meant
destructive to the life of the plant, and that injurious meant destructive
to the commercial value of the crop, or to that part of the plant for the
economic use of which the plant itself is cultivated. This article would
prevent such a pest as Nectria ditissima being included, though it
appeared on several of the provisional lists presented by delegates
present at the Conference, since it is not only of old standing and general
distribution but it cannot be said to be destructive to the tree or to the
crop it bears. There are plenty of apple trees in this and other countries,
which have been cankered for many years and yet continue to bear
a serviceable crop of fruit.

The proposed Convention is not a very drastic affair, and it is quite
as likely to be attacked on the ground that it does not go far enough

A. G. L. Rogers 117

as on the score that it goes too far. But for many reasons, I think it
is a great step in the right direction. It establishes the principle of
international action in the first place, and of international unity in
the second. It implies direct administrative effort to control dangerous
plant diseases, and it checks excessive and unreasoning restrictions.
It is based on the principle of mutual trust, and the procedure con-
templated is the productive method of the eradication of disease at
home in place of the present wasteful system of inspection of foreign
consignments. It will, I hope, promote trade and not hinder it. It
will benefit both the nurseryman and the consumer. These considera-
tions cannot be overlooked by administrators and pure economists. But
on this occasion it is natural that other questions should be asked.
Scientists may well demand whether it will promote the cause of
learning, and encourage research or if it will by establishing adminis-
trative rules and procedure, which will tend to become stereotyped and
inelastic, hinder the application of new scientific discoveries and become
a bar to progress. It is difficult to forecast the future. We all know
how the wisest laws, if maintained after the need for them has ceased,
prove instruments of reaction, and it is impossible to say that no flaw
will ever be found in this Convention, or that it will never be open to
criticism. There are some people who object to State action in such
matters on principle, and others who do not believe that regulations
can check the spread of disease. Such persons will no doubt view the
whole idea of a Convention with disapproval. But to those who are
prepared to accept the principle that epidemic diseases can be checked by
State action, and probably by State action alone, I would point out that
this is the first time that any Convention, so far as I am aware, has
made it an essential part of the obligations of each adhering State,
that scientific research must be associated with administrative action :
that this Convention gives economic biology and phytopathology a
status they never had before, and both directly and indirectly offers
a new field for scientific research.

118

THE HOST. PLANTS, AND HABITS OF -2r ais
RUMICIS LINN., WITH SOME OBSERVA-
TIONS ,ON, THE .MIGRALION) OF, AND
FESTATION OF, PLANTS BY APHIDES!.

By J. DAVIDSON, M.Sc., F.E.S.
(Research Scholar in Agricultural Zoology, Board of Agriculture.)

INTRODUCTION.

Tue following experiments are the first of a series of experiments
and observations on the habits and life-history of the Aphididae, which
the author hopes to carry out, with the hope that our knowledge of the
migratory habits of these insects, and the infestation of plants by them,
may be increased.

The results obtained this season do not afford sufficient data upon
which to base any definite explanations of these problems. Many of
the observations, however, have suggested certain lines of enquiry.

In the latter part of this paper, the author has briefly discussed
some of the factors which may underly the questions of the migration
of Aphides and the infestation of plants by them.

Some tentative suggestions as to the nature of these factors have
been made, with the hope that deeper enquiries into the habits of this
important family of insects may be stimulated. These suggestions are
based upon observations made in connection with these experiments.

In September, 1912 (op. cit. below), Theobald published an interesting
paper dealing with the habits and life-history of Aphis rumicis, in which
this author describes a double life-cycle for this species. In one cycle
ova are produced by the sexuparae, in late Autumn, on Rumex plants.
These ova hatch out in Spring, and subsequently winged migrants are
produced on the Rumex plants. These migrants go, about June, to

1 The species of Aphis used is the black aphis found in spring on Huonymus europaeus

(Aphis euonymi). It is now considered as one of the many synonyms of Aphis rumicis,
vide Theobald, F. V. (1912), Journ. Bd. of Agric. vol. xx, No. 6, Sept. 1912, pp. 466-476,

J. DAvipson 119

Broad Beans, which plants they heavily infest throughout the Summer.
In Autumn the winged migrants from the Broad Beans return to Rumex,
sexuparae being produced in late Autumn, and subsequently ova being
laid on the Rumex plants.

In the second life-cycle, ova are produced by the sexuparae on
Euonymus in late Autumn or Winter, which hatch out in Spring. The
winged migrants subsequently produced migrate to Poppies in June,
which plants they heavily invest as Aphis papaveris. In some years,
when the number of Aphids produced is abnormal, some of the migrants
go from the Poppies to Mangolds and many plants of the Chenopodi-
aceae family. In Autumn the winged migrants return to Euonymus
where sexuparae are produced and ova laid.

The aphids taken from these different plants showed no structural
differences, although they differed slightly in size or colour on the
different host plants.

It seemed to the present author that, if these two parallel life-
histories for Aphis rumicis were stable, the question of the influence
of the host plants on aphids is an important factor. The two life-
cycles seemed to show that the preceding host plant upon which a
generation of aphids is produced, has a determining influence on the
species of plant subsequently selected by the winged migrants.

Theobald found that winged viviparous females taken from Kuony-
mus lived on Broad Beans, and gave rise to the “ bean black fly,” but
from field observations he was unable to trace whether the winged
migrants from HKuonymus went to Broad Beans.

This seemed to the present author to be a very important question
in connection with the two life-cycles described for Aphis rumicis. It
intimated that the two parallel life-cycles might be merged into one by
crossing from Kuonymus to Broad Beans, and from Rumex to Poppies.
If the two life-cycles proved to be absolutely constant and separate,
a very important feature would be established, namely the establish-
ment of two biological species (A. ewonymi and A. rumicis), both
resembling each other in structure but differing physiologically in habits.

As the results obtained in these experiments will show, Aphis ewonymi
will heavily infest Broad Beans, and Aphis euonymi reared on Rumex
will heavily infest both Broad Beans and Poppies. Thus the two life-
cycles may be merged into one. The life-history, however, has not
been completed, as owing to leaving England in September, I have
been unable to trace the history of the sexuparae. However, the plants
are still under observation, and the ova will be looked for in due course.

120 Food Plants of Aphis rumicis

In concluding this general introduction, it may be added that the
experiments, series B and C, have been carried out as far as possible
under natural conditions.

The plants in the pots in series A, did not in some cases flourish
as well as might have been expected, owing to the dry summer.

Experiments. Series A, B and C.

The aphis species used in series A, B and C, is the Black Euonymus
Aphis (A. euonymz). All the aphids used in the first two series were
reared from a small colony found in January (27. 1. 1913) on a small
Euonymus bush in a garden near Richmond. In this way one was
quite certain that the same species of Aphis was being used throughout,
and further one knew exactly the history of the different generations
produced as the various plants were infected.

The original colony on Kuonymus was taken to the College green-
house, and the plant covered with a muslin bag. When winged forms
were produced, a clean Kuonymus plant was infected.

The experiments have been made in three series, A, B and C, and
have been carried out at Acton Lodge, Brentford, Middlesex, the experi-
ment orchard for the Department of Economic Entomology, Royal
College of Science, London. My sincere thanks are due to Professor
Maxwell-Lefroy for the kind and generous way in which he has given
me every facility for carrying on the work.

The notes and observations given under the various dates will show
the results obtained.

Experiments. Series A.

The various plants indicated below, were infected with winged
viviparous females in every case, except in the case of Rumex, No. 2,
the aphides being transferred by means of a fine camel hair brush.
The plants were raised in pots from seed and kept covered with muslin
bags so that they were quite proof against external infection. During
rainy weather the plants were kept in a partly closed frame, but other-
wise they were kept in the open as much as possible. Observations
were made from time to time and notes made as given below.

It will be seen in experiments, series A, that the chief food plants
of A. rumicis have been infected from different hosts; thus, plants
Nos. 1, 2, and 3, were infected with aphids bred on KEuomymus, plant B.
Similarly plants Nos. 4, 5 and 7 were infected with aphids bred on
plant No. 1, and so on.

J. DAVIDSON 121

NoTES AND OBSERVATIONS ON PLANTS IN SERtrEs A.

Plant No. A. Euonymus europaeus.

Found infected with a small colony of A. rumicis, at Richmond, 27. 1. 13 and
transferred to College greenhouse. The colony developed, and about the middle
of February, many winged viviparous females were produced. These swarmed
over the plant which became heavily infested. At the end of February, the aphids
swarmed over the plant in vast numbers. Many of them died off. The winged
forms crowded round the muslin bag, as though wanting to escape, and dissatisfied
with the plant. Many of the young shoots of the plant were killed, and the aphids
alldied. The plant was kept covered till May 23rd, on which date there were no living
aphids present. It was then reinfected with Aphis ewonymi, from some Euonymus
trees in Acton Lodge garden, and they produced several small colonies on the young
growing shoots of this plant.

It should be noted that owing to a hard frost occurring early in February, the
greenhouse was heated at night so as to make sure that the aphids would not die.
This doubtless hastened the production of winged forms.

Plant No. B. Euonymus europaeus.

This plant was infected from No. A, about the third week in February, with
three winged viviparous females. They produced colonies of apterous females.
Winged viviparous females (2nd generation) appeared on this plant on April 27th.
By the 20th May, the aphids were very numerous on this plant, and both the apterous
and viviparous females were actively running over the plant, on the stakes supporting
the muslin bag covering it, and crowding over the muslin, as though wanting to escape.
By the end of the first week in June, many of the aphids were dying off. The aphids
were much smaller than the members of the original colony, this no doubt produced
by the fact that they were not feeding on the plant. Some specimens of the winged
forms, which I preserved at this stage, show that the abdomen is small and shrunken
in appearance. The apterous forms were also small, and present in extraordinary
numbers. Contrary to their usual sluggish habits, they were actively running over
the stakes supporting the muslin cover.

On May 5th, I put one apterous viviparous female from B on a clean branch
of a small Euonymus bush, and on another branch I put a winged viviparous female
from B. These both produced lice in 3 days, and although the numbers produced,
even after a month, were very few, yet the individuals looked fat and healthy.

Plant No. 1. Rumex sanguineus.

5. 5. 13. Infected from Euonymus B, with 4 w. viviparous 9’s.
7. 5. 138. A few aphids produced.

22. 5. 13. Many colonies present; collected round the apex of the young shoots,
also several colonies along the mid-rib of the leaves. Some of the
apterous forms are a smooth, shiny, jet black, colour, but many of
them are covered with a mealy bloom.

26. 5. 13. A few winged forms produced.

122

24.

16.

28.

24.

28.

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lice

. 13.

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Food Plants of Aphis rumicis

The aphis infests the stem in vast numbers, almost along the whole of
its length, also beneath the leaves along the mid-ribs. They are big,
healthy individuals, the winged forms being much larger than those
present on Euonymus B. Most of the winged forms are actively
walking on the muslin cover as though wanting to escape.

Enormous numbers of winged forms are now present, crowding round
the top of the muslin cover, and not on the plant at all. It is
noticeable that during the progress of the infestation, the colonies
of apterous forms first collected at the apex of the young growing
stem, and gradually extended towards the base, until the whole
stem was covered. Many also along the mid-rib, and main veins
of the leaves.

Plant dead, all the aphids dead.

Plant No. 2. Rumex sanguineus.

Infected from Euonymus B with four apterous viviparous females.

Several aphids produced.

Several colonies present on this plant, also nymphs of winged forms
produced. Colonies present on mid-rib beneath the leaves.

A few winged forms produced.

Now fairly heavily infested, but numbers not so great as in case of No. 1 ;
there are fewer winged forms present.

Aphids not nearly so numerous as in No. 1; chiefly collected at top of
the stem, but one colony forming half-way down. <A few winged
forms present, walking on the muslin cover. Several colonies
beneath the leaves, on the mid-rib and veins.

Plant fairly heavily infested ; numbers of w. v. 9’s, which are crowding
round the top of the muslin cover. Infestation not so heavy as No. 1.

Plant heavily infested, vast numbers of winged forms actively crawling
over the muslin cover. Many apterous forms clustered along the
length of the stem, and beneath the leaves, along the mid-rib, many
of these very small.

Plant dead, aphids all dead.

Plant No. 3. Broad Beans.

Infected from Euonymus B with five w. v. 9’s.

A few aphids produced, but it would appear that the w. viviparous
females from B are weak and are not producing happily. Rein-
fected with 3 w. v. 9’s from B.

Only a few aphids present. Reinfected with four w. v. 9’s from Euony-
mus Bb,

Many colonies produced, situated on the upper part of the stem and in
axils of the leaves. A few nymphs of winged forms present. Aphids
big and healthy.

Winged forms present.

14,

24.

27.
31.

24.

28.

24.

31.
18.

28.

CERISE

13.
13.
13.

DOHMH

a. des

7 J. dd.

dato:

Ann

13.

. Biol. 1

J. DAVIDSON 123

Plants fairly heavily infested ; many winged forms gathered at the top
of the muslin cover.

Infestation heavy ; many winged forms crowding in vast numbers on
the top of the muslin cover.

Plant smothered with aphids; many dead; plants very sickly, leaves
curled and of a dirty brownish colour.

Plant No. 4. Broad Beans.

Infected from Rumex No. 1, with four w. v. 9’s.

Only a very few aphids produced, winged mothers dead. Reinfected
with five w. v. 9’s from Rumex No. 1.

Note. It is possible that the w. v. 9’s taken from the Rumex were old,
and had already laid a number of lice on that plant.

Many aphids present which are collected along the upper part of the
stem. Winged viviparous females present.

Aphids numerous along upper part of stem. Many winged forms present,
some settled beneath the leaves, but many collected in the top of
the muslin cover as though wanting to migrate.

Heavily infested, great numbers of winged forms collected in top of
muslin cover, aphids distributed all over the stem, and beneath the
leaves.

Plants smothered with aphids; many winged forms dead; plants look
sickly.

Plant No. 5. Rumex sanguineus.

Infected from Rumex No. 1, with four w. v. 9’s.
Many colonies going on this plant, but it became diseased, and the leaves
died, so the aphids were transferred to another Rumezx plant.

Plant No. 6. Shirley Poppies.

Infected from Euonymus B with four w. v. 9’s.

Several apterous viviparous females present, and one fairly large colony.

Several small colonies produced, but reproduction seems slow in numbers.

A few small colonies present beneath the leaves and on the stem, but
numbers small.

A fairly good number of aphids present, along the mid-rib of leaves and
on the stem, and flower stalks.

A good number of aphids distributed generally over the plants, which
look sickly, and flowers almost over ; several winged forms produced.

Many winged forms present; plants fairly heavily infested.
9

124

14. 7.

24. 7.

24, 7.

28. 7.

25. 6.
28. 6.

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13.

13.
13.

Food Plants of Aphis rumicis

Plant No. 7. Shirley Poppies.

Infected from Rumex No. 1, with five w. v. 9’s.

Several large apterous females present beneath the leaves, along the
mid-ribs ; very few in number.

Several colonies present, beneath leaves, and on the stem.

Plants are rather poor specimens ; there are a few individuals collected
along the stem, and beneath the leaves, but numbers small.

Several colonies along the stem and flower stalks, and beneath the leaves,
along the mid-ribs.

A few winged viviparous 9’s produced.

Several winged forms collected at the top of the muslin cover, as though
wanting to escape. Many nymphs of winged viviparous 9’s on
the plants. Poppies in flower.

Infestation fairly heavy.

Plant No. 8. Papaver rhoea.

Infected from Rumex No. 2, with ten w. v. 9’s.

Several aphids produced.

Several colonies going well beneath the leaves.

Plenty of colonies present along the flower petioles, and beneath the
leaves ; winged viviparous females produced, and several nymphs
of winged forms present.

Plants are healthy ; many aphids on the flower stalks, and beneath the
leaves ; not very many winged forms produced.

Infestation moderate.

Plant No. 9. Red Beet.

Infected from Rumex No. 2 with ten w. v. 9’s.

The plants Nos. 9, 10, and 11 are not growing well, and have wilted
considerably owing to lack of water, so that the aphids seem to have
died off. Reinfected with five w. v. 9’s from Rumex No. 5.

A few isolated individuals present.

Several large apterous viviparous females present, collected on the under-
side of the very young leaves.

The apterous viviparous females are collected on one small young leaf ;
they are large and healthy individuals, but up to the present do not
appear to be increasing very much in numbers on these plants. No
nymphs of winged forms or winged forms produced as yet.

Plant No. 10. Mangolds.

Infected from Rumex No. 2 with ten w. v. 9s.
One living winged form left, but owing to lack of water the plant has
wilted, and aphids have not taken.

Only one or two individuals present. Have reinfected with five w. v. 9's
from Rumex No. 5.

14.
24.

30.

Salles
13.

= Ae.

13.
13.
= 13.
wiles
. 13.

dss

Sis s

13.
als.

» 13:
. 13.
ais.

. 13.
13.

. 13.

TS,
re
AS,
1S:

13.
. 13.

. 13.

J. DAVIDSON 125

A few individuals present.

A few small colonies present on one young leaf, numbers few, four fat,
healthy apterous females.

Aphids few in number; no winged females yet.

Plant No. 11. Sugar Beet.

Infected from Rumex No. 2 with eight w. v. 9’s.

Plant has wilted owing to lack of water; a few young aphids present.

Reinfected this plant with five w. v. 9’s from Rumex.

One colony going well beneath one young leaf, the individuals being
healthy ; a few individuals also present on the older leaves.

About 30 individuals present, collected chiefly on the underside of the
leaves, along the veins.

Aphids chiefly collected on one young leaf, which is curled, but a few
colonies on the older leaves. Winged forms produced, and nymphs
of winged 9’s present.

Aphids look healthy, but numbers up to the present are small.

Plant No. 12. Onions.

Infected from Broad Beans No. 4 with five w. v. 9’s.
No aphids present, have left the plants and died.

Plant No. 13. Red Beet.

Infected from Broad Beans No. 4 with five w. v. 9’s.

A few aphids produced.

One winged mother alive, but not many individuals produced, so rein-
fected with five w. v. 9’s from Broad Beans No. 4.

A few small colonies formed on the young leaves.

Several big healthy apterous females present beneath the young leaves ;
a few nymphs of winged viviparous females produced.

Infection heavier than in case of No. 9, but numbers not great; winged
forms produced.

Plant No. 14. Shirley Poppies.

Infected from Broad Beans No. 4 with eight w. v. $’s.

Several aphids produced.

Several colonies going well beneath leaves, on the veins; also a few
individuals on the flower-stalks.

Poppies in flower ; several colonies present beneath the leaves, and on the
flower-stalks.

Winged viviparous females produced.

A fair number of aphids present, distributed along stems and flower-
stalks; winged viviparous females present.

Many winged forms produced ; infestation is moderately heavy.

9—2

126

24. 7.

2457;

28. 7.

27. 7.

10. 8.

bo
oo >
DD

13.
13.
13.
- 13.

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- 13.

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13.

13.
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balers

yalisss
13.
13.
sas.

13.

13.

13.
13.
13.

Food Plants of Aphis rumicis

Plant No. 15. Shirley Poppies.

Infected from Broad Beans No. 3 with five w. v. 9’s.

A few small colonies present on the veins beneath the leaves.

Several small colonies going on the veins beneath the leaves.

Aphids seem to be chiefly beneath the leaves; several nymphs of winged
viviparous females produced.

Several of the leaves curling owing to aphid colonies. below ; nymphs of
w. viviparous females present.

Aphids only in moderate numbers.

Plant No. 16. Shirley Poppies.

Infected from Broad Beans No. 3 with five w. v. 9’s.

A few colonies present on the veins beneath the leaves; Poppies just
coming into flower.

Several colonies on the flower-stalks and beneath the leaves; Poppies
in flower.

A moderate number of aphids present ; many winged forms produced ;
aphids infest the stem and flower-stalks, and also collect along the
veins beneath leaves ; Poppies still flowering.

Plant No. 17. Swedes.

Infected from Broad Beans No. 3 with five w. v. 9’s.

A few aphids produced.

One colony of three or four individuals present.

A few isolated individuals going on the leaves, but numbers very few,
and no colonies forming.

Plant No. 18. Red Beet and Sugar Beet.

Infected from Broad Beans No. 3 with five w. v. 9's.

Several aphids produced.

A few colonies present beneath the leaves, on the veins, on both plants.

Numbers very small, but several healthy apterous forms on underside
of the young leaves of both plants.

Nymphs of winged forms produced ; several small colonies of healthy
individuals present beneath young leaves.

Aphids big and healthy but not many produced ; chiefly collected on the
very young leaves, but a few on older leaves; nymphs of winged
forms present.

Plant No. 19. Red Beet.

Infected from Shirley Poppies No. 6 with five w. v. 9’s.
A moderate number of young aphids present.
Not very many individuals present as yet.

14.

24,

13.

J. DAVIDSON 127

The following plants were also infested as follows.

Ral Se

. 13.

Plant No. 20. Broad Beans.

Infected from a Euonymus tree growing in Acton Lodge garden with
four w. v. 9’s.

Many aphids now going well on the plants, along upper half of stem,
and some along mid-ribs beneath leaves.

Winged females produced.

Aphids heavily infesting the plants along the stems. Many winged
forms present, which are walking over the muslin bag as though
wanting to escape.

Plants heavily infested ; very many winged forms crowding on the muslin
cover.

Bean plants almost dead; leaves curled and brown; many aphids
dead.

Plants dead; all the aphids dead.

Plant No. 21. Shirley Poppies.

Infected from Euonymus tree growing in Acton Lodge garden with
four w. v. 9’s.

Several apterous forms present beneath the leaves.

Several colonies present on the stem and leaves, along the mid-ribs ;
aphids big and healthy.

Aphids fairly numerous, along flower-stalks and beneath the leaves.

Winged viviparous females produced.

Many winged forms produced; Poppies in flower; several colonies
going well.

Infestation moderate ; aphids dying off; plants sickly.

Poppies looking very sickly ; aphids nearly all dead. The soil used was
poor and plants did not do well.

Plants dead.

Plant No. 22. Onions.

Infected from Rumex No. | with eight w. v. 9’s.
No aphids present; have died off.

Plant No. 23. Red Beet.

Infected from Rumex No. 1 with eight w. v. 9’s. These plants were
grown in the open garden, and at the time of infection were covered
with a muslin cage. Although I searched carefully and found no
aphids on the plants, one could not be absolutely certain that some
individuals from the neighbouring infected Beans had not infected
them. The plants in the pots did not, generally speaking, grow as
healthily as those in the open garden, and I wanted to see the effect
on these plants which were growing well. Soon after infecting them
the winged forms made their way up to the top of the muslin bag,
but a day or so after they seemed to settle on the plants.

128 Food Plants of Aphis rumicis

28. 6. 13. A few colonies present on the underside of some of the leaves.

28. 7. 13. Several colonies present beneath the leaves; nymphs of winged vivi-
parous females present; some of the leaves are crinkled along the
veins showing a slight damage due to the aphids ; there are however
not very many aphids produced, and the infestation is only moderate.

Plant No. 24. Onions.

18. 6. 13. Infected from Euonymus tree growing in Acton Lodge garden with four
w. v. 9’s.
28. 6. 13. Aphids all dead.

Experiments. Series B.

In this series of experiments, the writer wished to find out if the
winged migrants from EKuonymus showed any preference for particular
plants, if a choice of food plants were given.

It was desirable that the aphids should, as far as possible, be under
natural conditions. At the same time it was necessary to ensure against
infection from other plants, and that the plants should be grown under
conditions which enabled constant observations to be made.

For these reasons, a wooden framework, 33 feet long, 6 feet wide,
and 5 feet 6 inches high, was erected over a plot of ground in Acton
Lodge garden. This was covered with very fine muslin which was
carefully fastened down to the woodwork so that insects could not
get in or out. The tent was divided into three compartments by
muslin partitions, so that the insects could not pass from one compart-
ment to the other.

Karly in April the plot of ground surrounded by the tent was heavily
fumigated with carbon di-sulphide. At the end of this month several
food plants which had been raised in pots from seed were placed in the
tent, and in addition, some seeds of Broad Beans, Shirley Poppies,
Mangolds, etc. were sown.

In Compartment 4, the following plants were grown: Broad Beans,
Shirley Poppies, Papaver rhoea, Mangolds, Red Beet, Sugar Beet,
Swedes, Onions, Rumex sanguineus, Nasturtiums.

In Compartment B, Broad Beans, Shirley Poppies and Papaver
rhoea.

In Compartment C, Broad Beans and Rumex sanguineus.

Kach compartment was entered by a door which opened from
outside into each compartment separately.

At the beginning of June (3. 6. 13), Euonymus bushes which had
been infected in May with Aphis rumicis from the Euonymus bush B,

J. DAVIDSON 129

referred to in series A, were placed in the tent. These bushes had been
kept covered with muslin, and although the number of aphids produced
on the bushes by this date was very few, several healthy colonies were
present on them. The plants in the tent were carefully examined
before the infected bushes were introduced, and were found to be quite
free from aphids. They were very clean and healthy, and owing partly
to shade afforded by the muslin, and partly to the effect of the fumiga-
tion, they were making splendid growth.

Owing to the colony of Aphids on the Euonymus bush placed in the
Compartment C not developing, no infestation of A. rwmicis occurred
in this compartment, consequently no results were obtained.

After the Euonymus bushes were placed in the tent, the plants were
kept under close observation and notes made from time to time. These
notes are given below, with the dates when the observations were made.
They show the results obtained, and indicate the progress of the infesta-
tion of the different plants by the winged migrants from the Kuonymus
bushes.

The following plan shows the arrangement of the food plants in the
different compartments.

Compt. C Compt. B Compt. A

Door Door Door

General plan indicating the general arrangement of the food plants in the tent.

P.=Shirley Poppies; B.=Broad Beans; R.B.=Red Beet; S.B.=Sugar Beet; H#.=in-
fected Euonymus bush; M.=Mangolds; S.=Swedes; R.=Rumex sanguineus ;
N.=Nasturtiums; P.R.=Papaver rhoea; On.=Onions.

Compartment A.

3. 6. 13. Euonymus bushes infected from Euonymus A, placed in the tent.
28. 6. 13. Some winged viviparous females have now migrated from the Euonymus
to Broad Beans, and a few colonies of lice are produced on these plants.
3. 7. 13. Aphids now infesting the Broad Beans in fair numbers, and many colonies
are present on the flower-stalks and tips of the young shoots.

130 Food Plants of Aphis rumicis

A few small isolated colonies present on the veins beneath the leaves of
the Rumex plants, but very few in numbers. One Rumex plant which
is producing a tall flowering head has a number of colonies on it.

The other plants not infected.

14. 7. 13. The aphids are heavily infesting the Broad Beans, and appear to have all
left the Euonymus bushes.

A few isolated, small colonies on the Rumex leaves. I found one winged
viviparous female on the Poppies, but no colonies forming yet on
these plants.

Many winged viviparous females are produced, and a number are walking
on the roof of the tent as though wanting to escape.

A few aphids present on the leaves of the Red Beet, but numbers very
few.

Other plants not infected.

22. 7. 13. The Broad Beans are very heavily infested, although some of the plants
still have plenty of young growth to afford food for the aphids.
Many of the young pods are heavily infested with the aphids, and
the colonies have extended to about half-way down the stems in some
cases. Many colonies also beneath the leaves, and the winged
females present on these plants chiefly settle below the leaves,
although several are also on the stem.

A few colonies are now forming on the Poppies being chiefly collected
along the flower-stalks, but some also on the stems and beneath the
leaves.

There are a few colonies on the Red Beet and Sugar Beet, but very few in
number. Some of the Red Beet leaves are crinkled along the veins,
which seems to be due to the action of the aphids.

Several of the Rumex plants have a few colonies, consisting of a small
number of individuals, present on the underside of the leaves.

I found one or two small colonies of apterous forms present on the
Euonymus bush, but the aphids seem to have practically all left
these plants.

There are no aphids on the Swedes, Nasturtiums and Onions.

10. 8. 13. The Broad Beans in many cases are almost smothered with aphids, the
underside of many of the leaves being almost covered with them.
They are also in great numbers on the young pods. The terminal
shoots of these plants are brownish in colour and dying off.

The Shirley Poppies are now fairly heavily infested, and there are many
winged viviparous females and nymphs on them. The aphids are
to a great extent collected along the flower-stalks, towards the flower-
heads, but also some along the stems and beneath the leaves.
There are several colonies also present on the Papaver rhoea
plants.

There are a few isolated colonies, small in number, present on the Red
Beet and Sugar Beet ; and a very few aphids on the Mangolds, but
in this latter case only a small isolated colony on a very few

* leaves.

10. 10. 13.

3. 6. 13.

oe te ho.

14. 7. 13.

eee he Loe

10. 8. 13.

10. 10. 13.

3. 6. 13.

Bode Io:

14, 7. 13.

HORS. 13.

10. 10. 13.

J. DAVIDSON 131

Several small colonies present beneath the leaves of the Rumex sanguineus
plants. There is a great deal of Rumex present so that the colonies
are widely distributed.

There are no colonies forming on the Swedes.

The Broad Beans, Poppies, and Nasturtiums have all died down. Beet,
Mangolds and Swedes are growing well, and look healthy. Aphids
seem to have all disappeared, having died off, and only an isolated
individual to be seen here and there.

Compartment B,

Euonymus bush infected with Aphis rumicis from EKuonymus B placed
in this compartment.

Winged viviparous females have been produced on the infected Euonymus
bush, and several winged forms have migrated to the Broad Beans
where they are forming colonies.

Broad Beans now fairly heavily infested, and a few small colonies are
also going on the Poppies.

The Broad Beans are heavily infested. Colonies forming rapidly on the
Shirley Poppies. The aphids have all left the Euonymus bush.

The Broad Beans and Shirley Poppies are now heavily infested. Papaver
rhoea plants also attacked, and many of the leaves are curled and
clustered together owing to the aphids. The Shirley Poppies are
especially infested along the flower-stalks.

The Poppies and Beans have now died down. The aphids seem to have
all disappeared, having died off. An isolated winged form here
and there on the dead plants. No aphids on the Euonymus bush,
which is growing fast.

Compartment C.

Euonymus bush infected with Aphis rumicis from Euonymus B, placed
in this compartment.

The colony is very small, and does not seem to be making any progress.

One small colony on the Rumex plants. The aphids on the Euonymus
bush are small in size and numbers, and do not appear to be going
well.

No aphids on the Broad Beans. The aphids present on the Euonymus
bush are not making any progress.

No aphids on the Euonymus bush. <A few winged viviparous females
present on the Broad Beans, but only a few small colonies formed.

The Broad Beans have died down.

132 Food Plants of Aphis rumicis

Experiments. Series C.

This series of experiments consists of observations made on plants
grown in the open garden at Acton Lodge. Many different kinds of
plants and vegetables were cultivated in various parts of the garden,
and weeds were also allowed to flourish in order that observations might
be made on the migration of the winged forms of Aphis rumicis from
Euonymus.

On May 24th, three small Kuonymus bushes found near Richmond,
heavily infested with Aphis rumicis (ewonymi), were introduced into
the garden at Acton Lodge. There were great numbers of winged forms
on these bushes at this time.

The following notes recorded below will show how the aphids became
distributed to many of the plants growing in the garden. The dates
given do not denote the exact date when the plants became infected,
but the date on which the observations were made. It may be noted,
however, that in the case of the Broad Beans, Aphis rumicis was not
found on these plants until the date given below. The infestation
of these plants occurring so quickly after the introduction of the infected
EKuonymus bushes (one bush was placed close to a row of Broad Beans)
leaves little doubt that the infection came from EKuonymus. By the
middle of June, practically all the aphids had left the infected Euonymus
bushes.

Date Host Plant Remarks

24. 5.13. Huonymus europaeus.. Three bushes heavily infested with Aphis rumicis,
introduced into Acton Lodge garden; many
winged viviparous females present. These had all
migrated by the 30th May, and by the middle of
June the bushes were quite free from aphids.

25. 5.13. Broad Beans.. .. Many winged females present and several colonies
forming.

29. 5.13. Broad Beans.. .. Many colonies now developing on these plants.

29. 5. 13. Huonymus europacus Found several winged viviparous females on some

large Euonymus bushes in Acton Lodge garden,
and colonies are being produced on these bushes.

1, 6.13. Spinach 2 .. Several plants infected and colonies forming on them,
along the stems and flower-heads.
1. 6.13. Parsnips Ss .. Some old Parsnip plants which are running to seed

are now infected, and colonies forming in the
flower-heads.

to
far)
=
“

Rumex, sp... .. Several plants now infected, one plant near the Broad
Beans being especially heavily infected.

13.

13.

13.

13.

6.

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13.

. 13.

els:

Gels

alo.

13.
3. 13.
13.

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. 13.

. 13.

ais:

243!

alley

sulla

Searlet Runner Beans

Spinach.

Red Beet

Onions ..

Red Beet

Sugar Beet
Mangolds

Atriplex hortense

Peas
Carduus sp.

Tomatoes

Scarlet Runner Beans

Asparagus

Capsella bursa-pastoris

Chenopodium album ..

J. Davison 135

Aphis rumicis forming colonies on the tips of the
young shoots, and a few colonies beneath the
young leaves.

A few plants near the infested Broad Beans are now
fairly heavily infested.

A plot of Red Beet plants near the Broad Beans have
now severa! colonies on them, and some of the
leaves are crinkled along the veins which is pro-
bably due to the presence of the aphis. The
colonies are forming along the veins beneath the
leaves, but only a few leaves infected. Another
plot of Red Beet at some distance from the Broad
Beans is not infected.

A few individuals are present on a few plants; they
seem to wander to the top of the leaves. Found a
few lice produced on these plants, but in a few
days the aphids disappeared from the plants.

Several plants infected. The aphids have collected
chiefly on the very young leaves, near the base
of the mid-rib, and along the veins. These plants
are however only slightly infected.

Only a few aphids present on these plants.

A very few leaves with one or two small colonies
present.

These plants are now growing tall, and several
colonies of aphids are present along the young
parts of the stems.

A few small colonies present on the young terminal
shoots.

A few of the plants in a large plot of thistles are
heavily infested along the stems.

A few individuals generally distributed over these
plants, but the aphids do not seem to be forming
colonies.

Several plants fairly heavily infected, the aphids
forming colonies on the young terminal shoots,
and some along the mid-ribs beneath the leaves.
There are several small colonies present on the
leaves of the Dwarf French Beans.

These plants have now grown big and bushy, and
many colonies of Aphis rwmicis are present on
them; nymphs of winged females are produced.

Several Shepherd’s purse plants are infected, the
colonies forming along the apex of the stems at
the base of the flower-stalks.

There are many small Chenopodium plants fairly
heavily infested. The colonies are present chiefly
along the veins of the leaves, which make the
leaves curl. Several nymphs of winged females

produced.

134 Food Plants of Aphis rumicis

4.7.13. Urtica sp. = .. Asmall species of nettle, about a foot high, is infected.
The colonies are forming along the apex of the
stem and along the mid-rib of the leaves, causing
the terminal leaves to cluster together ; nymphs
of winged females are present.

4.7.13. Dahlias &3 .. One Dahlia plant has two or three large colonies of
big apterous females on it. The aphids are col-
lected along the flower-stalks, towards the base
of the flowers.

18. 8. 13. Nasturtiums .. .. These plants are growing beneath the Dahlias. The
aphids have now left the latter plants, and there
are several colonies present on the Nasturtiums.

— 9.13. Chenopodium sp. .. A few of these plants are still infested with aphids.

— 9.13. Urtica sp. He .. A few aphids still present on these plants.

GENERAL CONCLUSIONS.

a

The general results obtained in these experiments have already been
indicated in the notes given about the various plants.

It is seen that, in the experiments, series A, as the different genera-
tions of winged migrants were produced they were transferred to
different host plants. It was thought the previous plant host upon
which the aphids were produced might have an influence on the degree
of infestation of the succeeding host plants to which the winged migrants
were transferred. The results obtained do not, however, give sufficient
evidence of this. It will be necessary to carry out this experiment
with a large number of plants, the number of aphids produced on the
different plants in a specified period of time being counted. Further,
it will be necessary to find the variation in the number of aphids produced
on different plants of the same species, for the purpose of comparison,
before definite conclusions can be drawn.

The Euonymus bush A (series A) became heavily infested with
Aphis euonymi in February by the rapid reproduction of the original
small colony. The bush had been put into the greenhouse and the
sheltered conditions no doubt favoured this rapid reproduction.

The EKuonymus bush B which was infected with winged viviparous
females from A did not become heavily infested until several weeks
had elapsed, although by the middle of May it was almost smothered
with the aphids.

The third set of Euonymus bushes which were infected from EKuony-
mus B early in May had only a few small colonies on them by the
beginning of June. On the third of this month they were placed in
the muslin tent and although winged forms were produced towards

J. DAVIDSON 135

the end of June the numbers of aphids produced on these bushes were
very small. In fact the colony on the Kuonymus bush placed in the
compartment C of the tent made little or no progress, so that results
were not obtained for this compartment.

Now if we compare these results with what happened in the tent
when the winged migrants settled on the Broad Beans, we find that in
two or three weeks these latter plants became very heavily infested
by the rapid reproduction of the aphids feeding on them.

Also in series A the Rumex plants, Broad Beans, and Poppies infected
from EKuonymus B with winged viviparous females became heavily
infested in a few weeks.

The plants in series A were all infected with winged viviparous
females, with the exception of Rumex No. 2, which was infected with
apterous viviparous females. Winged forms were used because it is
the winged migrants which infect new host plants. It will be seen,
however, that the apterous viviparous females from Kuonymus flourished
and reproduced in great numbers when transferred to Rumex sangquineus,
winged migrants being produced in due course.

A noticeable feature throughout the experiments was the migratory
tendency of the winged viviparous females. Soon after the winged
generation was produced on the various plants, the winged forms showed
a desire to migrate and collected in vast numbers at the top of the
muslin bags which covered the plants. They seemed active and restless,
and apparently not feeding on the host plant on which they were pro-
duced. However, many undoubtedly produced “lice” on the host
plant, and several could usually be found sitting beneath the leaves,
but the majority of the winged forms crowded round the top of the
muslin cover, even when the host plant was still in a healthy condition.
When the top of the cover was opened they immediately took flight.

It would appear from these observations that the winged females
demand a change of host plant, and it is for this reason that certain
plants which may be heavily infested early in the summer suddenly
become free from aphides, owing to the production of winged migrants
which, when they are produced, tend to leave the original host plant.
In the case of Aphis euonymi I found hundreds of young nursery Euony-
mus bushes smothered with these aphids in May, whereas a few weeks
later the bushes were almost free from them. Two or three of these
bushes were kept under close observation. On May 23rd, they were
heavily infested with Aphis ewonymi, many winged forms being present.
A week or so later the bushes were almost free from these aphids, and

136 Food Plants of Aphis rumicis

the winged migrants had gone to Broad Beans, on which plant they
were reproducing rapidly.

This brings us to the important question, What are the factors
underlying the production of winged forms and the consequent migra-
tory habits of Aphides ? The migratory instincts of the winged females
may underly the desire to escape from the original host plant, but it
may be that a change in the constitution of the cell sap of the host
plant, which affords the food of Aphides, has an influence on the pro-
duction of winged forms and the consequent migration of the Aphides
from the original host plant.

In the case of the Euonymus bushes A and B (series A), when these
bushes became very heavily infested, being practically smothered with
aphids, both the winged viviparous females and the apterous forms
became surprisingly active and ran over the bushes and muslin cover
in a most restless manner as though wishing to escape. Moreover,
they became considerably reduced in size, both apterous and winged
forms being very much smaller than those produced on the Broad Beans
and Rumex plants. In the latter stages of the heavy infestation of the
Broad Bean plants, the aphids on these plants were also much smaller
than in the early stages of infection. It may be that owing to the
pathological condition of the plants induced by the heavy infestation,
the aphids were unable to obtain sufficient food, but there is the fourth
question of the change in the constitution of the cell sap brought about
by the heavy infestation of the plants.

Woodworth, C. W. (1908)!, who made some observations on Aphis
brassicae, states that when a plant wilts the birth rate decreases and
suggests that the failure of plant lice to develop winged forms under
favourable conditions is due to the rapid development of the rest of
the body. He refers to a paper by Clark in the Journal of Technology,
Vol. 1 (which, unfortunately, I have been unable to consult), who
obtained winged forms of Macrosiphum rosae in the first generation,
by rearing the aphids on rose-cuttings grown in sand wetted with a
solution of magnesium salts.

During the summer of 1913, I carried out a number of experiments
with Macrosiphum rosae, on rose-trees grown in soil treated with definite
quantities of various inorganic salts. I regret that owing to the extra-
ordinary numbers of aphids that were produced, and the confusion
resulting from this, that the experimental error is too great to allow

! Woodworth, C. W. (1908), Entom. News, Philad. 1908. x1x, pp. 122-3.

J. DAVIDSON 137

of conclusions being drawn from them. It is intended to repeat these
experiments, making the necessary alterations to avoid error.

During the summer of 1911 a young apple tree infected with Schizo-
neura lanigera Hausm. was kept under observation in a greenhouse.
The aphids reproduced in great numbers, the leaves began to wilt, and
the tree looked very sickly. In the later stages of the attack, winged
viviparous females were produced in vast numbers, and most of them
left the tree and collected on the woodwork of the greenhouse. Later,
all the leaves on the plant died, and although there were several “ living ”
branches the aphids practically all died off.

The winged forms of Schizoneura lanigera are not common in England,
and it would seem that the heavy infestation produced some change
in the constitution of the cell sap, which induced the production of
winged migrants. When a plant becomes so heavily infested that the
leaves begin to wilt and the green parts are smothered with aphids,
the normal green surface of the plant which carries on the processes
of photosynthesis is considerably reduced in area and as a result the
constitution of the cell sap is probably changed.

It is a well-known observation that aphids prefer the young growing
shoots of the plants they attack. They readily select the parts of the
plant which afford the best supply of sap.

In early summer, rose-trees frequently become infected with Macro-
siphum rosae, the aphids collecting on the young stems and terminal
shoots, where they reproduce in great numbers. Later on in the season,
the trees are often quite free from these aphids.

During the summer of 1913, one rose-tree in Acton Lodge garden
was kept covered with a muslin cage. The tree was covered early
in the summer and infected with Macrosiphum rosae. The colonies
increased in great numbers on the young terminal shoots, and along
the petioles of the flower buds, and soon the plant became very heavily
infested, vast numbers of winged forms being produced. Many of the
leaves died and the young terminal shoots looked very sickly. Later
on practically all the aphids died off. The tree then began to make
new growth later in the summer. These young shoots soon became
infected and the aphids reproduced in great numbers on them.

It was noted in the case of the rose-tree experiments mentioned
above, that at first the aphids collected on the young terminal shoots,
or along the petioles of the flowers, just beneath the buds. When
the flower buds were cut off, the aphids very soon left the petioles
and went to another part of the plant. Gradually as the numbers

138 Food Plants of Aphis rumicis

increased, they distributed themselves beneath the leaves, along the
mid-ribs, and secondary veins, and, finally, practically the whole plant
in many cases became smothered with the insects. At this stage, both
the apterous and viviparous forms became active and restless and ran
over the plant as though wishing to escape. Many of them left the
plants and died on the soil in the pots. _

From these observations, it would appear that at different periods
of the growth of plants, a change in the quality or constitution of the
cell sap occurs which renders it unsuitable for the aphids. Further,
the pathological condition of the plants, induced by heavy infestation,
no doubt causes considerable changes in the constitution of the cell sap.

When Broad Beans are infected with Aphis rumicis, the young
terminal shoots are first infested, the aphid colonies gradually extending
down the stem, and on the veins below the young leaves.

From an examination of sections through the stems and leaves of
some plants, which were infested with aphids, one sees that the stylets
are forced through the epidermis and pass intracellularly between the
cells of the plant tissues towards the phloem cells of the vascular bundles.
The stylets often pass in a very irregular manner between the cells
of the cortex, and are not forced into the plant in a direct straight
line.

From a recent study of the mouth parts and mechanism of suction
in Schizoneura lanigera, which the author has recently carried out, it
has been shown that the plant juices pass up to the pharynx through
a very minute suction canal formed by the partial fusion of the two
internal stylets!. This canal is extremely minute in transverse section,
and it is highly probable that the ascent of the sap through it is largely
due to capillarity.

This is an important point for consideration. It is obvious if the
surface tension of the cell sap is such that it cannot ascend up the
minute capillary tube the aphids would be unable to obtain food. It
is probable that in young growing shoots the stylets can be more easily
forced into the plant tissues, but there is the question of the difference
in the supply and constitution of the cell sap in young, actively growing
parts of a plant. It is not improbable that in the case of small plants
heavily infested with aphids, the cell sap is rendered toxic, or at any
rate distasteful to the insects.

I have indicated that the individuals living on a plant very heavily
infested with aphids become gradually smaller, and apparently derive

! This paper will shortly appear in the 7'ransactions of the Linnean Society.

J. DAVIDSON 139

no nourishment from the host plant. This was seen in the case of the
aphids on Euonymus, and on Broad Beans. It would be interesting
to know if the pathological condition of the plants had an effect on the
surface tension of the cell sap.

In the paper on the mouth parts of Schizoneura lanigera, referred
to on the preceding page, there is described a “ taste organ,” which is
situated near the entrance of the suction canal into the pharynx. It
is very probable that by means of this organ the aphids are able to
appreciate changes in the quality of the cell sap, although owing to the
extreme minuteness of these mouth parts it 1s almost impossible to
demonstrate its function practically. That the aphids become restless
and dissatisfied with their hosts at different periods of the plant’s growth,
or when the plant is heavily infested, has been seen throughout these
experiments as is indicated in the observations given.

As is seen in the case of the tent experiments, Aphis rumicis, under
favourable circumstances, will select its host plant. Thus in the Com-
partment A, Broad Beans became first infected, then the Shirley Poppies
and the other plants only became infected to a very slight degree.

Davis (1909), found that Aphis maidis Fetch, showed a decided
preference for broom corn plants over Indian corn and Sorghum!.

It is an interesting feature of aphid habits, that one species may
infest a number of different species of plants. This is the case with
the species at present under consideration (Aphis rumicis). It is readily
seen, however, that although this particular species of Aphis may live
on a number of different species of plants, some of these plants are
subject to a greater infestation than others.

It was observed that while Broad Beans infected with Aphis euwonyma
from Evonymus europaeus became rapidly infested by the reproduction
of the aphids, Red Beet infected from Broad Beans did not become so
heavily infested, although the few aphids produced appeared to be
healthy.

Again, in all cases where Broad Beans and Shirley Poppies were
infected with this species, the former plants became heavily infested
sooner than the latter.

Further, it was noted that certain plants in the garden of Acton
Lodge were infected with Aphis rumicis. On many plants, such as
Broad Beans, Rumex sp. and Chenopodium album, the colonies repro-
duced in great numbers and in most cases gave rise to a more or less

66

1 Davis, J. J. (1909), “ Biological studies of three species of Aphididae,” U.S.D.A.
Bur. Ent. Techn. Ser. No. 12, pt. vi, p. 146.

Ann. Biol. 1 10

140 Food Plants of Aphis rumicis

heavy infestation. On many other plants, however, although aphids
were present, the colonies were small. The individuals looked healthy
and happy, but the numbers produced were small, and the plants really
never became heavily infested.

This would seem to show that the cell sap of certain plants affords
a suitable stimulus for certain species of aphids, resulting in rapid
reproduction of young, while on some other plants, although the cell
sap may afford a suitable food for the specific aphids, the stimulus
derived from it does not induce such a rapid reproduction of young.

There is the question that the quality of the sap in any particular
species of plant may be subject to change according to the soil conditions
in which it may be growing. I have not any particular reference to
hand, but I believe work has been done, showing that by treating
certain plants with chemical substances they may be rendered immune
to a specific fungus attack. Mangolds and Beet have been recorded
from time to time, both in this country and in France and Germany,
as subject to infestation by Aphis rumicis. In some seasons, on the
other hand, these plants may be more or less free from infestation.

In connection with this point, there seem to be two points for
consideration. Firstly, whether the presence in the neighbourhood of
these crops of food plants for which Aphis rumicis shows preference,
afforded sufficient food for the aphids and so prevented an overflow
to the Mangolds and Beet. Secondly, whether any special manurial
treatment of the soil rendered the crop more susceptible to attack.

It would be interesting during such an outbreak, to tabulate the
food plants found in the immediate neighbourhood. It does not seem
at all unfeasible that in a very bad season, a “ catch crop” might be
sown; for example with Aphis rumicis, the aphids evidently prefer
Broad Beans and Poppies if these plants are present.

Malanquin and Moitié (1913)! record heavy attacks of Aphis papa-
verts in 1911 on the Sugar and Cattle Beet in the North of France.
They record the presence of the Aphis also on Spinach, Rhubarb,
Poppies and Beans. These authors add that this Aphis leaves the
seed plants about the middle of July because they do not afford sufficient
food and go to the Sugar and Cattle Beet.

Davis (op. cit. p. 132) observed with Aphis maidi-radicis that when
food supply was scarce, the tendency was for winged forms to be
produced.

99

' Malanquin, A. and Moitié, A. (1913), “‘ Le Puceron de la betterave dans le nord de
la France,’ La Vie Agricole, u, No. 24, pp. 696-699.

J. DAVIDSON 141

Throughout my experiments it was observed that, when the plant
had finished its young active growth, or became heavily infested with
aphids, the changes resulting either in the quality or quantity of the
cell sap (or both) seemed to induce the production of winged forms,
which wanted to migrate to other plants.

It may be that in the case of the Compartment A in the tent, the
Shirley Poppies and Broad Beans afforded sufficient food, and thus the
Mangolds and Beet did not become heavily infested.

Gaumont (1913)! records a heavy infestation of Beet by Aphis
evonymé in the South of France during 1911.

Theobald (1912, p. 471, op. cit.) records migration flights of Aphis
rumicis in the South of England during 1911. Poppies became very
heavily infested, and then when these became “seedy,” masses of
winged migrants were distributed over many different plants, but only
on Dahlias, Beet, and Mangolds did they flourish to any great extent.

It would seem that under natural conditions winged migrants
of Aphis rumicis are produced on the host plant, and they take flight,
being carried partly by their own powers of flight, partly by the wind,
to many different species of plants. On some plants such as with
Onions in these experiments, they soon die off, on others they live
happily, and form small colonies, while on others they reproduce in
enormous numbers and heavily infest the plants. In the latter case,
it would appear that the cell sap is best suited for the particular species
of Aphis and affords the necessary stimulus for the rapid reproduction
of young.

It remains yet to be proved whether the stimulus derived from the
cell sap of the previous host plant has any influence on the degree of
infestation of the succeeding host plant.

Some seasons are much more favourable than others for the distribu-
tion of aphids. The present season of 1913 has been a particularly
favourable one for Aphis “ blight?.” Winged aphids are very fragile,
and, if the weather conditions are wet and severe, the winged migrants
are unable to withstand the journeys from plant to plant.

In favourable seasons the distribution of aphids over a district from
plant to plant may be very extensive.

1 Gaumont, L., (1913), ‘‘ Le Puceron de la betterave,” Revue de Phytopathologie, 1,

No. 1, April 20th, 1913, pp. 12-13.
2 Gardeners’ Chronicle, London, 7th June, 1913, p. 377.

142

SOME OBSERVATIONS ON THE LIFE-HISTORY
AND BIONOMICS OF THE KNAPWEED GALL-
FLY UROPHORA SOLSTITIALIS LINN.

By J. T. WADSWORTH,
Research Assistant, Department of Agricultural Entomology,
University of Manchester.

(With Plates XI and XII and 1 Text-figure.)

CONTENTS.
PAGE
Introduction : ; : : : : : 142
Description of fly aha siaaciivation : ‘ : : ‘ : ‘ 143
Geographical distribution . : : : : P : ‘ : 145
Historical . ; 5 : . : : ; : : : : 146
Food-plants ‘ ‘ : ‘ : g : ; ‘ 147
Life-history, description of ovipositor, and method of oviposition . 148
Descriptions of ova, larvae, and pupae. : 152
Effects of larvae on production of seeds in pelled fieivar: hewn of
Centaurea nigra L. 2 : : : : : ; : 160
Parasites. 2 ‘ : : é : : : ; 163
Remarks on gall- fonsslian: and on other inhabitants of the flower-
heads . ; : : : : ; : : ‘ é : 164
Summary . ’ ‘ : : é : : : é c : 165
Bibliography ‘ : : : : : : : : : 166
Explanation of plates é : : : : : : ‘ . 168
Introduction.

In September 1911, whilst collecting seeds of wild plants at Prestatyn,
North Wales, I found galls in many of the flower-heads of the small
knapweed, Centaurea nigra L., and these on further examination were
found to contain dipterous larvae.

On counting the seeds contained in a few of the galled flower-heads,
and comparing the numbers obtained with the numbers present in
ungalled heads, it was seen that considerably fewer seeds were present
in the former than in the latter It therefore seemed probable that

J. T. WapswortH 143

the dipterous larvae present in the flower-heads, by inducing gall-
‘formation, caused a reduction in the number of the seeds normally
produced by this troublesome and useless weed, which is very common
in many pastures and meadows.

A number of the infected heads were brought to Manchester, and
kept until the following spring, when, towards the end of June, imagines
commenced to emerge from the galls, and continued to do so during
the ensuing three weeks.

The fly was recognised as a Trypetid and specimens for determination
were submitted to Mr J. E. Collin, of Newmarket, to whom I am indebted
for naming them; they belong to one of the common species of Try-
petidae, viz. Urophora solstitialis L. Mr Collin also informed me that
so far as he knew the larvae and pupae of this species had never been
scientifically described.

Early in July some young flower-heads of the knapweed were
gathered and a few fertilised female flies were placed on them in a covered
glass jar. The females deposited eggs freely, and in eight days from
the date of oviposition free larvae were observed within the flower-heads.
It was thus apparent that the flies would breed freely in captivity,
and Professor Hickson suggested that I might undertake a study of
the life-history of this species.

The work was carried out in the Department of Agricultural Ento-
mology of the Victoria University, Manchester, and I wish here to thank
Professor 8. J. Hickson for his kindness in providing me with opportu-
nities by which I have been enabled to undertake this research ; to
Dr A. D. Imms my thanks are also due for valuable suggestions and
advice given during the later stages of its progress, and to Professor
F. E. Weiss for permission to use apparatus belonging to the Botanical
Department. My indebtedness to others who have assisted me in
various ways, is acknowledged in the text.

Description of fly and classification.

The fly was described by Linnaeus (1758) under the name Musca
solstitialis; since then it has been frequently referred to and more
fully described, under various names, by several entomologists. Loew
(1844) discussed the characteristics of this species very fully, and he
recognised and described five well marked size and colour varieties.
In his monograph Die europaischen Bohrfliegen (1862) the same author
gives a full description of the species, together with the synonomy ;

144 Knapweed Gallfly

the description given by Schiner (1864) is more complete however, and
of this the following is a slightly abbreviated translation.

‘Wings yellowish-white, with brown bands, of these the first and
second are always widely separated at the anterior border. Body
glossy black ; thorax with a brownish-yellow dusted appearance, and
with the usual yellow side-stripes as in Ur. stigma; scutellum yellow,
blackish at the sides. Ovipositor much longer than the abdomen, and
swollen from the base to the middle. Head yellow, posterior aspect
black or brown; facial aspect paler, frons distinctly brighter in the
centre, sometimes rusty-yellow. Antennae, proboscis, and palps,
reddish-yellow ; proboscis lobes rather narrow, and much elbowed
backwards. Legs yellow, in most specimens the anterior femur with
a black stripe on the outer border, less frequently a similar stripe is
present on the mid and hind femora; terminal tarsal joints brown.
Wings with a yellowish-white tinge; at the base and towards the
anterior border as far as the stigma, a deeper yellow, with four lighter
or darker brown moderately straight cross bands. The first lies near
the wing base, is frequently indistinct, and reduced, but always present ;
it extends backwards at the most into the anal cell, and is always
widely separated from the second band. The second proceeds from
the point of the brownish-yvellow stigma over the discal cross-vein,
almost completely straight to the posterior wing-border; the third
arises at the anterior wing-border in front of the apex of the marginal
cell and proceeds moderately straight over the posterior cross-vein to
the posterior wing-border ; the fourth is usually narrowly continuous
with the third anteriorly, and borders the wing-tip just beyond the
fourth longitudinal vein. The clear area between the second and third
bands is at least double the width, or frequently only just wider than,
the bands themselves. Examples are found in which the bands are
very much faded, their position, however, is always distinctly recogni-
sable. Discal cross-vein a little beyond the middle of the discal-cell ;
3°1—6°2 mm.”

Bezzi (1910, 1913) has recently proposed that the family name
should be Trypaneidae instead of Trypetidae, by which name this
family of acalypterate flies has been known so long. He divides the
family into two sub-families, the Dacinae and the Trypaneinae; the
latter is divided into three tribes, Ceratitininae, Myiopitininae, Try-
paneininae. The second tribe contains only three genera: Myiopites
(Stylia), Asimoneura, and Urophora.

Among other characteristics of the tribe Myiopitininae are the

J. T. WapDSWwoRTH 145

following: ‘‘ the species are found exclusively in temperate countries,
being wanting in the tropics; the larvae live only on plants of the
family Compositae, and often make galls” (Bezzi).

The genus Urophora was proposed by Robineau-Desvoidy in 1830,
one of many that he formed out of the large genus Trypeta of Meigen,
and from this date onwards the name of the species Urophora solstitialis
Linn., has been accepted by most entomologists.

The following is a list of the principal synonyms of the species as
given in Loew’s monograph.

Urophora solstitialis Linn. (1758) ¢ and 9.

Musca solstitialis Linnaeus, Syst. Nat. x. 601,98. Faun. Suec. 1. 1879. Syst. Nat.
xan, 999) 127.

Musca Dauci Fabricius, Mant. Ins. 1. 353, 118. Ent. Syst. Iv. 358, 187.

Musca solstitialis Cederhjelm, Prod. 318, 1006.

Dacus Dauci Fabricius, Syst. Antl. 277, 22.

Dacus hastatus Fabricius, Syst. Antl. 276, 15.

Trupanea Leucacanthi Schrank, Faun. (Boic.) mr. 141, 2507.

Tephritis solstitialis Fallen, Ortal. 6, 5

Trypeta solstitialis Meigen, Syst. Beschr. v. 324.

Trypeta pugionata Meigen, Syst. Beschr. 330.

Urophora solstitialis Walker, Ent. Mag. 1. 7 (ex parte) Macquart, Suit. Dipt. 11.
457, 9.

Trypeta solstitialis Loew, Germ. Zeitschr. v. 355,

Geographical distribution.

Urophora solstitialis has been recorded from nearly all the countries
of Europe ; a list of these records is given by Schiner (1858). Mr J. E.
Collin informs me that it is common and widely distributed in England ;
Fitch (1872) records it from Suffolk ; Wingate (1906) from Hesleden,
Durham ; Connold (1901) from Hastings, Sussex. I have collected the
galled flower-heads containing larvae of this species at Prestatyn,
North Wales, and also at Port Erin, Isle of Man; and Dr A. D. Imms
collected a few galled-heads at Llwyngwril, Merionethshire. Professor
J. W. H. Trail of Aberdeen very kindly sent me the following list of
localities in Scotland where galled heads containing the larvae have
been obtained: Aberdeenshire and Kincardineshire, especially in the
valley of the Dee ; near Dunkeld and elsewhere in the valley of the Tay,
from Glen Falloch, and from Loch Lomond in Perthshire ; in these and
in other localities the galls are abundant. I am indebted to Professor
G. H. Carpenter of Dublin for a note on its occurrence in Ireland ;

146 Knapweed Gall-fly

it has been recorded from Ballyvaughan, Co. Clare; Westport, Louis-
burgh and Clare Island, Co. Mayo. Professor Carpenter further remarks
that probably the species is widely spread in Ireland.

It is worthy of note that specimens belonging to the genus Urophora
have been recorded only from the old world. In the Katalog der Paldark-
tischen Dipteren (1905) twenty-nine species of this genus are recorded
from Europe and Northern Africa ; seven of these are listed as British
(Verrall) and one species, U. spoliata Hal., has not been found elsewhere.

Historical.

Records of detailed observations on the life-history of this species
appear to be very scanty, although a few well-known entomologists
have studied closely allied forms. Thus Goureau (1845) described the
larva and pupa of U. cuspidata Meig., and Dufour (1857) those of
U. quadrifasciata Meig. Until comparatively recently the former was
regarded as synonymous with U. solstitialis (Schiner, H. Loew);
Becker (1902) however, who examined Meigen’s type of U. cuspidata
in the Paris Museum, considers that U. cuspidata Meig. is distinct from
U. solstitialis L. The most complete account of the larva and pupa
of a species of the genus Urophora was given by Mik (1897) who described
those of U. cardwi L.; the larvae of this species induce galls on the
stems of Cirsium arvense L.

Boie (1848) obtained U. solstitialis in hundreds from galled flower-
heads of Carduus crispus L.; they emerged from June 8 to July 12.
From several thousand pupae only three or four flies emerged in autumn,
and his opinion was that this species gave rise to a single brood only,
unless exceptional conditions prevailed.

In a paper devoted to the natural history of the Trypetidae, Frauen-
feld (1857) refers to this species among others ; he states further, that
it produces swellings in the receptacles of all the plants that it infects,
and he gives a list of its food-plants.

There is a brief paragraph by Kaltenbach (1874) on this species,
he gives the names of three hymenopterous parasites reared by Goureau
from U. cuspidata, as parasites of U. solstitialis. He assumed, however,
that the two latter were one and the same species.

Fitch (1872, 1879) refers to it in two short notes ; it is also referred
to by Connold (1901) and by Swanton (1912). Connold gives a short
description of the galls together with photographs of these and of the
larva and pupa.

J. T. WADSWORTH 147

Food-plants.

As regards the food-plants Schiner (1858) remarks that :

‘“* The larvae live in the flower-heads of Carduus nutans L., erispus L.
and acanthoides L.; they are also found in those of Cirsiwm lanceo-
latum L., Centaurea scabiosa L. and montana L., and on other Cynaroi-
deae”’; F. Low (1866) recorded Centaurea paniculata L., as a food-plant
of the larvae, and Fitch (1872) recorded this species from galled flower-
heads of Serratula tinctoria L., collected in Suffolk. In a later paper
(1879) this observer remarks that in 1872 he added to the list of [ British]
gall-making Trypetidae, Urophora solstitialis L., “‘ which deforms the
ovary of the common knap-weed (C. nigra) into a hard, woody, but
only tactilely noticeable gall.”

This is the first record which I have been able to find of the occur-
rence of this species on Centaurea nigra. Curtis (1860) refers to U. sol-
stitialis under the name Tephritis solstitialis as being abundant on thistle
blossoms during the summer, he does not state, however, that he bred
the fly from thistles. Connold (1901) and Swanton (1912) both give
C. mgra as the food-plant of the larvae of this species; Prof. Trail
informs me that in Scotland C. migra alone is known as the food-plant.

It is noteworthy that none of the continental authorities, whose
writings I have been able to examine, record Centaurea nigra as one
of the food-plants of these larvae ; on the other hand, with the single
exception of Fitch’s record of Serratula tinctoria referred to above, all
the records of its occurrence in this country that I have been able to
consult, state that Centaurea nigra is the food-plant of the larvae here.

Many of the recorded continental food-plants are equally common
in this country, whilst Centaurea nigra is common on the continent,
and it is worthy of remark that there appears to be this difference in
the habits of the larvae here and abroad.

The larvae of a closely related species, Urophora quadrifasciata, are
recorded as feeding in the flower-heads of Centaurea nigra (Loew,
Schiner); and according to the account of Dufour (1857) the life-
history of this species and the effects produced by the larvae on the
host-plant, are very similar to those of U. solstitialis.

There was just the possibility therefore, that I might be dealing
with this species (U. quadrifasciata). Through the kindness of Mr J. E.
Collin, I have had the opportunity of examining two continental speci-
mens of U. quadrifasciata from Bigot’s collection, and there is no doubt
that the specimens reared here from Centaurea nigra are distinct from

148 Knapweed Gall-fly

the continental specimens of U. quadrifasciata that I examined. Possibly
in this country U. solstitialis feeds also in the flower-heads of various
species of thistles, and its occurrence in these food-plants may have
been overlooked.

U. quadrifasciata differs from U. solstitialis in the following charac-
ters. Its average size is smaller. The thorax appears almost black
owing to the very slight yellow powdering (Bestiiubung) on the surface ;
all the femora are black also. The ovipositor is not much longer than
the abdomen. The four cross-bands on the wings are very broad, dark,
and sharply defined ; the first band is united with the second, and the
third with the fourth at the anterior border of the wing.

Life-history, description of ovipositor, and method of oviposition.

A supply of galled flower-heads was gathered in September, 1912,
and one or more of these were examined from time to time in order
to find out when pupation commenced. The first indication of change
was observed on April 29th, the following spring; in one gall, two
larvae were found whose skins were just hardening and changing to
a darker colour. On May 3rd, ten individuals were found in one gall,
and in nine of these the puparium was hard and definitely formed,
whilst the remaining one was still in the larval state. From this date
onward pupae were invariably found and in increasing numbers; the
latest date on which I found unchanged larvae was May 29th. On
June Ist imagines appeared; we may therefore say that the pupal
state lasts from four to five weeks.

From June lst imagines emerged every day until July 3rd; after
this date very few emerged and only at intervals of several days, and
the last fly emerged towards the end of July. The period of emergence
thus extended seven weeks, but the greatest number of flies emerged
during the month of June.

The flower-heads from which the flies were obtained were kept
inside a cool room during the winter, and in April they were taken
into the warmer laboratory. Outside in the open fields, development
would probably be slower and the flies would emerge later. In the
open, however, flies are on the wing in mid-June.

The number of males and females that emerged between June 3rd
and July 3rd, 1913, was counted in order to ascertain the proportion
of the sexes to each other. Between these dates 152 male flies and
130 females was obtained. In the early part of June, many more

J. T. WADSWORTH 149

males than females emerged, but towards the end of the month, this
disproportion in the sexes was decreased. Fitch observed that the
males emerged before the females, but he only obtained twelve females
and eight males; the numbers he dealt with are therefore very small.
If the results obtained above should be confirmed by subsequent count-
ings of greater numbers, they might be explained by supposing that
the greater numbers of males produced and their early emergence are
provisions for ensuring that as far as possible, all the females shall be
fertilised.

Four days after emergence, two pairs of flies were observed in
copulation, and another pair copulated five days after they emerged
(June 5th and 6th). Probably several days intervene between copula-
tion and oviposition, the exact length of time that elapses between these
two acts was not determined.

When the female is ready to oviposit she selects an unopened bud ;
the bracts of this, however, are just beginning to open. If the flower-
bud is suitable for the purpose, she is observed to move over it in various
directions; at the same time the ovipositor is frequently protruded
and inserted at various points between the bases of the scales; she is
evidently selecting a suitable place for the insertion of her ovipositor.
As soon as this is found she settles down, her head pointing towards
the apex of the bud ; the first joint of the ovipositor is then bent almost
at a right-angle to the abdomen, and pushed between the bases of the
lowest and outermost scales ; whilst in this position the ova are placed
within the flower-head.

If a flower-head which contains eggs is severed vertically into two
halves, and carefully examined, the eggs will be found either in the
space between the upper surface of the florets and the overlying bracts
(Fig. 2) or between the florets themselves. In order to understand
how the eggs are placed in these positions, the ovipositor, during the
process of oviposition, may be rapidly severed from the abdomen with
a sharp pair of fine scissors, and its position in the flower-head observed ;
or in a fortunate section of an infected flower-head the tunnel made
by the passage of the ovipositor may be seen (Fig. 13). Evidence has
been obtained by both these methods, and in order to explain the
process of oviposition in a more complete manner, a short description
of the ovipositor is inserted here.

The female fly possesses the usual corneous, pointed, three-jointed
ovipositor which is characteristic of the three closely related families
of acalypterate muscids, Trypetidae, Ortalidae and Lonchaeidae (Bezzi).

150 Knapweed Gall-fly

The first segment of the ovipositor (which appears as the terminal
segment of the abdomen) is about 2°7 mm. long ; it is swollen anteriorly,
being about 0°6 mm. across in this region, and it becomes narrower in
the posterior portion; near the distal end it is about 0-25 mm. in
diameter. The walls are strongly chitinised and it is covered with
numerous hairs.

The second or middle segment of the ovipositor is about 2:3 mm.
in length, by 0-15 mm. wide along its whole length, and consists of
a transparent flexible membrane in which a great number of small
chitinous sclerites are partially embedded. This segment is capable
of protrusion and retraction, like the finger of a glove.

“Satan”

Fig. 1. Extended ovipositor of U. solstitialis from left side, x 15. 1, Ist segment of the
ovipositor ; 2, 2nd, flexible segment; 3, 3rd, piercing segment

The third and last segment is the actual piercing portion of the
ovipositor ; it is composed of chitin, is about 2-3 mm. long, and except
at the extreme narrow tip is about 0-07 mm. in diameter. There are
two sharp-cutting blades at the sides of the tip. This segment contains
the terminal portion of the oviduct, which opens to the exterior near
the tip. During the passage of the ova this segment probably expands
slightly.

The ovipositor is extended by pressure, presumably by muscular
compression acting on some of the body-fluids. If the swollen portion
of the ovipositor is compressed with a pair of forceps, the flexible and
piercing segments are readily everted, and they always assume a curved

J. T. WaApDSWORTH 151

position which they retain as long as the pressure is applied. The
significance of this curvature will be apparent if we consider the structure
of the flower-head and the act of oviposition.

As is well known, the young florets of composite flowers are protected
by an involucre which is composed of numerous bracts or scales. In
the flower-head of C. nigra these bracts arise just below the level of the
receptacle, and this is the region selected by the fly for the insertion
of its ovipositor.

During oviposition the blunt end of the first segment of the ovi-
positor is placed between the lower scales as described above, and whilst
in this position the piercing portion is forced into the tissue of the
receptacle. The piercing segment passes downwards and inwards
towards the vertical axis of the flower-head, and gradually bends
upwards until the tip of the ovipositor finally reaches the space between
the tops of the young florets and the overlying bracts. The ova are
usually placed in this space; less frequently, however, they are to be
found between the young florets. In the latter case the flower-heads
are probably older than in the former case, and the florets are longer ;
consequently the ovipositor is not sufficiently long to reach the space
wherein the eggs are usually laid.

Goureau, who correctly described the external appearance and
movements of the ovipositor in U. cuspidata, believed that the ovipositor
was pushed between the florets of open flowers, and that the eggs were
then placed on the receptacle of the flower-heads. A similar opinion
was also held by Dufour who observed some phases of the life-history
of U. quadrifasciata. The latter observer, in addition, supposed that
the eggs were placed inside the tissue of the receptacle, and further,
he believed that the presence of the eggs, and possibly the injection
of an irritating fluid at the same time as these were laid, induced “ une
irritation nutritive du réceptacle transformé alors en placenta”; in
other words induced the formation of the gall.

Although the observations of these entomologists refer to species
other than the one considered here, yet, as these species are all so closely
related to each other, and their larvae also feed in similar flower-heads,
it is almost certain that on this point the opinions of these observers
were erroneous.

From evidence obtained by opening the flower-heads after ovi-
position and counting the eggs, and also by counting the number of
larval chambers in galled heads, I believe the number of eggs usually
laid at one time varies from one to four; where more than four eggs

152 Knapweed Gall-fy

or larval chambers are present they are probably the result of two or
more separate acts of oviposition.

The ovaries of two females were dissected out and the eggs counted
in order to determine the number of eggs a female fly is capable of
producing. From the ovaries of a female which had laid no eggs,
108 apparently mature ova were obtained, as well as a considerable
number of immature ones from the ovarian tubules; the ovaries and
oviduct of another female yielded 105 ova; this fly had, however, laid
a few eggs. We may safely say that a female of this species is capable
of laying at least 100 eggs, and if the immature ova ripen as the season
advances, then probably considerably more.

Descriptions of ova, larvae, and pupae.

The ovum of U. solstitialis is elongate and usually crescent shaped,
with its widest diameter across the centre; the amount of curvature
varies, however, examples are met with at times that are almost straight ;
from the central area the egg tapers towards each end, but more abruptly
towards the posterior end which is poimted, than to the anterior or
cephalic end which is rounded, and terminated by the prominent
micropyle. Bezzi (1913), who discusses the metamorphosis and bio-
nomics of the Trypaneids in general, states that the eggs are “ rounded
at the two ends”; the egg of this species is therefore exceptional
in this respect.

The ova have a glistening white appearance, and when present
are readily observed in the flower-heads ; the ‘shell or chorion is very
thin and quite smooth, and exhibits no sculpturing or pattern on the
surface.

In size the ova vary considerably : a number of ova laid by one
female varied in size from 0°87 x 0-15 mm. to 1-04 x 0-17 mm.; ova
taken from the same fly measured about 0-9 x 0-12 mm. The largest
ovum observed measured 1-3 x 0-15 mm.; the average size is about
1-1-02 x 0-15 mm.

Just before deposition the fertilised ovum completely fills the space
within the chorion, but shortly after oviposition the embryo commences
to diminish in length ; in three ova measured one hour after oviposition
there was a shrinkage of 0-18 mm., 0-2 mm. and 0-3 mm. respectively,
and within twenty-four hours of oviposition the embryo contracts to
about two-thirds of its former length. (Fig. 7.) A space thus appears
at each end between the embryo and the chorion.

a

_ Ce = —

J. T. WapswortH 153

The length of time that elapses between oviposition and hatching,
varies somewhat; probably temperature is the controlling factor.
In July 1912, larvae were obtained in eight days from the date of
oviposition, whilst in June 1913, the shortest time recorded between
these two events was eleven days.

The larvae, after hatching, may be found creeping on and between
the florets ; possibly they feed on these for a short time, but very soon
they bore their way through the walls of the corollae and travel down
the corolla tubes to the developing ovules. The corollae that contain
larvae may be readily distinguished from those that are uninfected.
Small circular or elliptical apertures with discoloured margins are visible
on florets that contain larvae, and in the majority of cases these apertures
are about one-third the length of the floret from the top. Usually
each infected floret contains only one larva, but occasionally two
larvae may be found, and in one example I found four larvae within
a single floret. I have never observed more than a single fully-grown
larva in the completed larval chamber; it is therefore probable that
where more than one young larva enter a floret all except one eat
their way out again and enter other florets. On reaching the base of
the corolla tube the young larva bores into the developing ovule and
by its activities in this position induces the formation of the gall.

The recently hatched larva measures about 0-5 x 0-1 mm. and has
a glistening white appearance; it is cylindrica] in shape and slightly
thicker at the anterior than at the posterior end. There are two pairs
of very small papillae on the anterior segment placed just above the
mouth hooks; the lower pair, nearest the mouth, are the sense-organs
or palpi, and the upper pair are the antennae (Mik). The pharyngeal —
skeleton is well developed and very similar in shape to that of the fully
grown larva, with the obvious difference that it is very slender and
slightly chitinised. At the posterior end of the body the spiracles
are visible under a high magnification, as two light-brown spots, and
each spiracle possesses three apertures.

The larvae do not grow very rapidly at first; two larvae fourteen
days after hatching measured only 0-6 x 0-12 mm., and a larva five
weeks old measured 1-3 x 0-4 mm. During the following two or three
weeks growth is very rapid; two larvae that were about eight weeks
old (Aug. 13th) measured 3-5 x 1-5 mm., and 3 x 1-8 mm. respectively.
The posterior surface of the last segment in both these larvae was
becoming dark in colour and strongly chitinised ; in larvae preserved
early in September these characters are fully developed, and in addition

154 Knapweed Gali-fly

the area round the mouth is changing to a reddish-brown colour, and
undergoing chitinisation. A series of fine grooves which radiate in
a backward direction from the mouth are very apparent about this
stage. These grooves or striations are present on younger larvae
(Aug. 22nd) but in order to see them it is necessary to strip off the cuticle
from the anterior part of the body and examine it under the microscope ;
this area is not chitinised in larvae at this stage ; in those larvae, however,
where this area has become chitinised the grooves can be much more
easily seen. A series of small channels at the sides of the oral lobes
in the larva of Musca domestica L. is described and figured by Hewitt
(1908). The grooves referred to above may correspond to those of the
house-fly larva.

The first appearance of the chitinised area round the mouth aperture
probably coincides with the nearly completed feeding period. From
mid-September to early October the majority of the larvae are fully
fed, and they remain head downwards in the larval chambers until
pupation commences in the following spring; the larvae reverse their
position just before pupation. During the period of feeding, and the
growth of the gall, an opening of the larval chamber to the exterior
is maintained, and this opening 1s sufficiently wide to allow the imago
to emerge; this opening is situated at the apex of the chamber and
is much narrower than the basal part in which the larva hibernates.

The fact that the larva remains head downwards with the strongly
chitinised posterior segment uppermost and stretched across the larval
chamber where it fits very tightly, suggests the explanation that this is
a contrivance for avoiding or preventing the attacks of parasites or other
predaceous enemies during the prolonged hibernating period. This
suggestion is made by Connold and is, I think, a very probable one.
He, however, states that pupation takes place in October. Of course,
this may be so in the South of England, although I doubt it.

The larvae of U. cardui remain head downwards during the winter
(Mik), and Goureau notes that the larvae of U. cuspidata also remain
in this position until pupation commences. In Dufour’s account of
the life-history of U. quadrifasciata there is no mention of this peculiarity ;
it may be inferred, however, that the larvae of this species hibernate
in a similar manner to those described.

I have never been able to convince myself that frass is present in
the larval chambers. In the galls of Cirsium arvense caused by larvae
of U. cardui, Mik found in the upper portions of the larval chambers
‘“*Excrementen in der Form von lichtbraunen Kriimchen ” ; possibly

~

J. T. WADSWORTH 155

the larvae of U. solstitialis derive the greater portion of their food from
the sap liberated by rupture of the cells which line the larval chamber.
If this assumption is correct, then the absence of frass might be ex-
plained, as in this case practically all the food would be absorbed.

The evidence obtained leads to the conclusion that there is only
one brood produced each year. Karly in September, 1912, I obtained
young larvae from flower-heads gathered at Prestatyn and then thought
that possibly two broods were produced in one season ; as I have never
found pupae or empty puparia during the months of August, September,
and October, the conclusion arrived at is that the young larvae obtained
in September, were the progeny of late-emerged flies and that there
is only one brood produced each year in this part of the country. Goureau
states that in France U. cuspidata gives rise to two broods in favourable
seasons.

The life-history of Urophora solstitialis may be briefly summarised
as follows :

Egg stage. 8-12 days, from end of June, during July and early
August.

Larval stages. Feeding period three months or less; from early
July to early October.

Hibernating stage of larva. About seven to seven and a half months,
from early October to mid-May.

Pupal stage. About 4-5 weeks. From mid-May to end of June.

Imago. Length of life uncertain, probably at leasta month. (I have
kept them alive for three weeks.) They emerge from mid-June to end
of July and early August.

There is a certain amount of overlapping in the times given above
owing to the extended period of emergence of the imagines.

Description of the mature larva.

There is considerable variation in the size of the fully fed larvae ;
thus, three examples taken from one gall in November measured
28x15; 35x 1-7; 4x2 mm. respectively; the average size of
five large larvae was 4-4 x 2 mm.

Naturally the variation in size is also exhibited by the pupae as will
be seen from the measurements of these given further on. A probable
explanation of this variation is that the smaller individuals develop
from eggs laid by late-emerged flies and consequently the feeding period
is much shorter than in the case of those which develop from eggs laid

Ann. Biol. 1, 11

156 Knapweed Gall-fly

earlier in the season ; it is also possible that where several larvae, say
eight to ten are feeding together in one flower-head, there is not sufficient
nourishment to enable them all to reach a large size.

The larvae are ellipsoidal in shape; the anterior end is bluntly
pointed and the posterior end sharply truncate, and the greatest width
is across the anterior third of the body (Fig. 9). With the exception
of a very few extremely small hairs on the posterior surface of the last
segment, the body of the larva is completely smooth and free from
bristles or spines ; Bezzi (1913) in his very useful account of the Try-
paneidae states that “the under surface [of Trypaneid larvae] bears
transverse rows of small black spines directed backwards,” and further,
that ‘‘ the anal end is somewhat impressed, contoured by a variable
number of fleshy points or tubercles, some of which bear also chitinous
spines.” Neither of these characters is present in the fully grown
larvae of this species, nor according to Mik in those of U. cardwi; in
his description of the larvae of this species he says they showed “ keine
Spur von Dornchen ” and “ die Larve ist also volhig kahl, glatt ” ; as
far as can be judged from the descriptions of the larvae of U. cuspidata
and U. quadrifasciata given by Goureau and Dufour, the larvae of these
species possess neither spines nor anal tubercles. The larvae of these
four species differ therefore from the majority of Trypaneid larvae in
these two features, which, according to Bezzi, are possessed by Try-
paneid larvae in general.

In colour the fully grown larva is pale creamy white, except at the
ends ; the two anterior segments are reddish brown, and the posterior
segment is pale yellow round its anterior border, merging into a very
dark chestnut-brown, almost black, colour on its posterior surface ;
the two areas surrounding the spiracles are lighter in colour.

The segmentation of the larva is well defined except at the anterior
end; Bezzi states that the number of segments in Trypaneid larvae
generally is usually fourteen. I have been able to distinguish only
thirteen segments in these larvae, and Goureau regarded the larvae
of U. cuspidata as probably possessing twelve segments, excluding the
head; there may be a fusion of two segments in the cephalic region
of these Urophora larvae. On the ventral surface of the middle segments
there are indications of creeping-pads (Kriechschwielen).

The mouth appears as a slit whose long axis is dorso-ventral ; the
antennae and sense-organs are difficult to make out on fully grown
larvae, in fact I have never been able to make them out satisfactorily ;
probably they are retracted into the body together with the cephalo-

J. T. Wapsworzei 157

pharyngeal apparatus when chitinisation of the oral segment takes
place. They can be observed on larvae about 7-8 weeks old, but they
are very minute, measuring about 12 in length and 8 in diameter ;
in larvae of this age there can be seen in addition, a number of small
papillae bordering the dorsal and dorso-lateral lobes of the mouth.
The fine radiating grooves which surround the mouth have already
been referred to.

The complete cephalo-pharyngeal skeleton consists of three pairs
of sclerites and an unpaired V-shaped sclerite. The mandibular
sclerites or “ great hooks’ each possess a prominent anterior tooth,
a smaller median tooth, and a basal tooth or spur, and each sclerite
is perforated near the base by a small aperture ; Hewitt (1907) described
a similar perforation in the corresponding sclerites of the larva of
Anthomyia radicum L. The mandibular sclerite articulates with the
intermediate or hypostomal sclerite, which in U. solstitiahs appears
to be fused with the posterior or cephalo-pharyngeal sclerite ; in this
latter sclerite there is a deep indentation posteriorly between its dorsal
and ventral prolongations, and these again are frequently bifurcated.
With careful observation a membrane can be observed surrounding
each prolongation extending some distance behind them; a corre-
sponding membrane is figured by Mik in U. cardui.

A V-shaped sclerite is situated beneath the hypostomal sclerites ;
each free end of the V articulates with a ventral projection of the
hypostomal sclerite on each side, and the apex of the V is placed near
the bases of the two mandibular sclerites (Fig. 8). It may be called
the sub-hypostomal sclerite. The examination of a number of prepara-
tions of the cephalo-pharyngeal apparatus reveals numerous slight
variations in size, shape, and amount of chitinisation of these structures ;
these variations are more especially noticeable in the posterior sclerite.
Interposed between the mouth and the mandibular sclerites there is
found another strongly chitinised body; this only becomes apparent
towards the close of the feeding period, and probably consists of the
closely apposed and chitinised sides of the oral lobes.

In appearance and structure, the anterior and posterior spiracles
are very similar to those of U. cardui figured and described by Mik ;
he described the anterior pair as being situated on the second segment
(of the pupa). In U. solstitialis the anterior pair are placed dorso-
laterally on the third apparent segment, and near its posterior border,
about 0-3 mm. apart (Fig. 11). They are yellowish-brown in colour
and do not project above the surface of the body ; each spiracle consists

11—2

158 Knapweed Gall-fly

of three short papillae joined together at the base; a slightly elliptical
aperture is situated at the apex of each papilla, and these lead into the
spongy felted-chamber (Filzkammer) which is in communication with
the longitudinal canal. In some preparations I have been able to
distinguish a membrane between the inner boundary of the felted-
chamber and the longitudinal tracheal canal, and this is perforated
by a small aperture 4 in diameter (Fig. 15).

The posterior segment bears the anus and the posterior spiracles ;
it is wider on the ventral aspect, where the anus is situated in the mid-
ventral line, than on the dorsal and lateral aspects. A shallow horse-
shoe shaped depression is present on the posterior surface of this segment
at a short distance from its dorsal and lateral borders, and a slight
depression, situated just dorso-median to the posterior spiracles, is
also apparent. The surface is marked with a number of very fine grooves
or lines which run in various directions ; round the spiracles they are
arranged concentrically. A number of small darker-coloured areas may
be observed on various parts of this surface, particularly on the ventral
portion ; they indicate the points of attachment of muscles (Fig. 12).

The posterior spiracles are situated slightly nearer the dorsal than
the ventral aspect, as in the larva of U. cardui, and they are about 0-7 mm.
apart. They are larger than the anterior spiracles and darker in colour ;
anatomically they are very similar to these but the apertures are more
definitely elliptical in shape and are arranged ina radiate manner. They
project very slightly from the body surface (Fig. 14). In one instance
a variation in the number of apertures in the left posterior spiracle of a
larva was noticed ; this spiracle possessed four apertures instead of the
usual number three.

In concluding this description of the larva, the small number of
lobes or papillae of the anterior spiracles as compared with the number
on the anterior spiracles of many other Trypaneid larvae may be noted ;
Banks (1912) describes nine Trypetid (Trypaneid) larvae whose anterior
spiracles each bear a large number of lobes varying from about fifteen
in Ceratitis capitata Wied. and Rhagoletis pomonella Walsh, to thirty-eight
lobes in Dacus ferrugineus Fab. ; whereas in the larva of U. solstitialis
and U. carduz (Mik) three lobes only are borne on each anterior spiracle.

J. T. WADSWoRTH 159

Description of the pupa.

The pupae vary considerably in size as may be expected from the
great variation in size exhibited by the larvae; among ten selected
for measurement the largest measured 4:3 x 2 mm. and the smallest
2-8 x 1-4 mm., the average size of the ten pupae was 3-6 x 1-7 mm.
In shape they are cylindrical, obtuse or bluntly pointed at the anterior
end, and obliquely truncate dorso-ventrally at the posterior end ;
during pupation there is little or no alteration in length but the pupa
is more parallel-sided than the larva (Fig. 10).

The colour varies from light yellow to dark reddish-brown ; the
majority, however, are of the lighter colour, and in all specimens the
first three or four segments and the last one are much darker in colour
than the intermediate ones. These anterior and posterior segments
vary in colour from reddish-brown to dark chestnut-brown or black.
On the surface of the puparium a number of anastomosing wrinkles
are seen which vary in direction in different parts of the same; they
are more or less parallel to the segmental grooves on the dorsal and
ventral aspects of the middle-segments, but at the sides they run
obliquely. These wrinkles are darker in colour than the smooth portions
of the puparium, and represent wrinkles of the larval skin which become
more apparent through shrinkage undergone during pupation.

At the anterior end the radiating grooves which run in a backward
direction from the mouth are very noticeable, and the anterior spiracles
are visible under a good lens as two brown spots in the position described
in the larva.

The posterior aspect exhibits the same features as in the larva and
requires no further description ; there is a variable amount of wrinkling
around the margin of the last segment, but well-marked ridges similar
to those figured by Mik on the posterior surface of the pupa of U. cardui
are not apparent. The pupae have a dull glistening appearance ;
Mik described the appearance of the pupa of U. cardui as ‘‘ etwas
seidenglanzend.”

Connold’s figure of the pupa of U. solstitialis is incorrect ; the object
figured resembles a syrphid larva.

160 Knapweed Gall-fly

Effects of larvae on production of seeds in galled
flower-heads of Centaurea nigra ZL.

In order to obtain some definite information concerning the effects
of the Urophora larvae on the production of seeds, a number of plants
were collected and a series of counts made. Perfect accuracy is not
claimed for the results obtained, as, owing to various circumstances,
the conditions were such that a high degree of accuracy could not be
expected. The plants were collected on Oct. Ist, 1913, that is to say,
late in the season, when many of the seeds had certainly escaped, in
addition to those probably taken by seed-eating birds. As the plants,
however, were collected within a space of about twenty square yards,
it may be assumed that these factors affected all the plants in this area
in a more or less similar manner. Fifty plants, single shoots cut off
at the ground-level, were selected, and these bore 147 flower-heads ;
twenty-four of these, however, were immature and therefore disregarded.
Of the remaining 123 heads, seventy-four or 60-1 per cent. contained
galls, whilst forty-nine or 39-8 per cent. were ungalled. Nine of the
galled heads contained no seeds, and these for the purpose of calculation
were neglected ; from the remaining sixty-five galled heads 1077 seeds
were obtained, averaging 16-5 seeds per head.

Twenty-five of the forty-nine ungalled heads were rejected for
various reasons; ten contained no seeds whatever, whilst the seeds
in the remaining fifteen were more or less eaten by seed-eating lepido-
pterous and free living dipterous larvae.

From the twenty-four ungalled heads that were considered countable,
755 seeds were obtained, averaging 31-4 seeds per head. Thus showing
a reduction of nearly 50 per cent. (31-4 — 16-5) in the number of seeds
produced in the galled heads, compared with the number produced in
ungalled heads. The number of seeds (31-4) per head obtained from
these particular heads is very low, and would be misleading if one were
to assume that this was the average number obtainable from normal
well-grown flower-heads of Centaurea nigra.

It may be explained that the soil on which the above plants were
grown was very poor and stony, and the specimens were gathered late
in the season when some of the seeds had escaped, as stated above ;
these considerations may help to explain the small average number of
seeds per head.

By way of contrast may be quoted the number of seeds obtained
from some flower-heads of the knapweed gathered by Prof. Hickson,

J. T. WADSWORTH 161

near St Bees, Cumberland, early in September of the same year. These
results give a more accurate idea of the number of seeds present in well-
developed flower-heads of this weed.

From twenty-seven flower-heads 2045 seeds were obtained ; averaging
75-7 seeds per head; one flower-head contained 103 seeds, whilst the
smallest number found in one head was sixty-two. A collection of
flower-heads was also made at Port Erin, Isle of Man, early in September,
and one head yielded the very high number of 109 seeds.

These figures indicate the large number of seeds that may be ripened
in a fully-developed flower-head of this plant, and it may be of some
interest to make an estimate of the number of seeds that a single plant
of this species is capable of producing.

Several plants of the knapweed were grown for experimental pur-
poses last summer, in my garden at Northenden, in Cheshire, and one
of them gave rise to several particularly lusty shoots; one of these
bore fifty-one flower-heads, and if it is assumed that each head ripened
only thirty-one seeds (the average number obtained from heads gathered
at Prestatyn) we obtain the number 1581 seeds producible on one single
shoot. A vigorous plant growing in good soil would give rise to at
least three or four shoots, so that several thousands of seeds may be
produced on one plant. Long (1910, p. 175) remarks that “ knapweed
(Centaurea nigra li.) known under a variety of names as Hardheads,
Hardhack, Blackhead, is a too common weed of pastures and meadows,”
and in view of the above estimate of its seed productivity, this is not
surprising. Were it not for the fact that several insect larvae and
birds feed on its seeds it would be even still more abundant.

A germination experiment was also made to test the difference,
if any, between the seeds ripened in galled heads and those in ungalled
heads, with regard to their vitality or germinative power.

A large number of seeds irom the ungalled flower-heads collected
in October were taken and mixed together; after rejecting all seeds
that showed evidence of injury, 7.e. indications of having been partially
eaten by other insect larvae, 100 seeds were separated without exercising
any selection. These were placed on moist blotting paper in a seed-
germinating apparatus, and kept at a temperature of 26° C. From these
seeds eighty-nine seedlings were obtained, equivalent to 89 per cent.

In a similar manner 200 seeds were selected from the galled flower-
heads that were collected on the same date and these were placed in
the germinating apparatus at the same time. That is to say, both lots
of seed were collected at the same time and place, and germinated under

162 Knapweed Gall-fly

similar conditions. Of these seeds only fifty-seven germinated, equiva-
lent to 28-5 per cent.

The percentage of germination in the seeds tested from galled
flower-heads was thus reduced 60-5 per cent. owing to the presence
of Urophora larvae in the receptacles of the flower-heads ; probably
the nourishment that normally goes to the developing seeds, becomes
diverted to the growing larvae and also to the formation of the thick-
walled woody gall.

This experimental result coincides with the indications given by
the appearance of the seeds usually obtained from galled flower-heads ;
many of these seeds are shrivelled, and smaller than the majority of
those collected from ungalled heads.

Thus in addition to a reduction in the number of seeds produced
in the galled flower-heads, the number of seeds capable of germination
is also reduced. Taking into consideration the smaller number of
seeds obtained from infected flower-heads, and also the reduced vitality
of those actually ripened, as indicated by the above experiments, it
may be stated that the presence of the larvae of Urophora solstitialis
in the flower-heads of Centaurea nigra reduces the number of effective
seeds in these infected heads at least fifty per cent.

Although the Trypaneidae or fruit-flies are justly regarded as
injurious from the economic standpoint because many of them are
very destructive to various cultivated fruits and to vegetable life in
general, yet those species whose larvae feed on, or in, the stems, leaves,
flower-heads and seeds of the weeds of cultivated land, may be regarded,
from the agricultural point of view, as beneficial. The result of the
activities of their larvae is that the plants fed upon are affected adversely,
and in many cases, as in the case of the species considered in this paper,
the production of seeds is directly checked; the distribution of the
weeds attacked is therefore restricted, even if only to a moderate extent.

The question occurs as to whether destructive weeds could be
appreciably reduced by encouraging certain species of insects which
attack the seeds thereof. It is hoped that the present paper will suggest
to others the possibilities for further research and experiment in this
field of enquiry, which is fully worthy of attention from the economic
entomologist.

J. T. WaDsSwoRTH 163

Parasites.

Three species of Chalcids and one Braconid emerged from the
flower-heads in May 1912 and 1913, but in very small numbers ;_ pre-
sumably some of these were parasitic in the Urophora larvae. The
Chalcids have not as yet been identified ; Mr Claude Morley, however,
has kindly named the Braconid, it is Bracon minutator Fab., and probably
parasitic on the lepidopteron Parasia metzneriella Stt. Brischke (1882)
records this parasite from the larvae of Sesia (Bembecia) hylaeiformis
Lasp. (not a British species) ; Marshall (1885) states that Elisha bred
two females of this Braconid from the lepidopteron Argyrolepia zephy-
rana Tr. It therefore appears probable that Bracon minutator is
parasitic on lepidupterous hosts. Under the description of Bracon
variator Nels., Marshall says “It is doubtful whether this Bracon is
a parasite of certain small curculios (Cionidae) or of flies of the genus
Trypeta ”’ and further on he states that “ Giraud records B. nigripedator
Nees, from Urophora solstitialis L.; and Fitch once obtained a Bracon,
now lost, from galls of Centaurea inhabited by the same fly.”

With regard to these records of parasitic hymenoptera obtained
from flower-heads of C. nigra and other composite plants, 1 would
remark that unless it is proved that dipterous larvae and pupae alone
are present therein, it is incorrect to state definitely that they are
the hosts of the parasites obtained, inasmuch as a single flower-head
may contain the larva or pupa of a lepidopteron in addition to those
of diptera.

Kaltenbach states that Hurytoma aterrima Schr. (verticillata) is
parasitic on U. solstitialis, and probably also Trigonoderus amabilis Walk.
and Semiotellus (Semiotus) diversus Walk. Walker (1833-37) records
these three Chalcids from near London but does not give their hosts.

Mr C. Morley (1908), from a quantity of dried heads of Centaurea
nigra gathered in March, 1907, beneath fir-trees, obtained both sexes of
a Pteromalus in May, and numerous Bracon minutator ¢ in April; he
also obtained one specimen of Pimpla sagax Htg. on April 26th, and
of this specimen he says (p. 81) “‘ Its host was undoubtedly Urophora
solstitialis, many of which emerged during the following June; unless,
of course, its presence there were purely accidental and its true associa-
tion were with the overhanging conifers, in which case it would surely
have shown itself in the jar in the course of the preceding month.”
In view of the fact that with one exception, viz. Anthonomus pomorum lL.
all the recorded hosts of this ichneumon are lepidopterous, and as the

164 Knapweed Gall-fly

larvae of at least three species of lepidoptera have been recorded from
Centaurea nigra, the evidence adduced by Mr Morley that U. solstitialis
is a host of Pimpla sagax is hardly conclusive. It seems more probable
that the single specimen obtained by him either emerged from a lepi-
dopterous host, or that its presence in the flower-heads was accidental,
as he indeed suggests.

Five hymenopterous larvae, probably of a Chalcid, were obtained
from 259 larval chambers examined in October, 1913, equivalent to
two per cent. Each of these larvae occupied a chamber that had
previously contained a Urophora larva. In one case there was direct
evidence that the hymenopteron had fed on the dipterous larva, as the
parasitic larva was inside a portion of the cuticle of the Urophora larva
and had evidently been feeding on the latter. From material in hand
I hope to be able to breed out a further supply of these Chalcids, to
get them identified, and to obtain the percentages.

Remarks on Gall-formation and on other inhabitants of the
flower-heads of Centaurea nigra.

The process of gall-formation in the flower-head of the host plant
exhibits some very interesting features. To determine whether the
formation of this gall is induced mechanically by the feeding habits
of the larva, or whether the latter secretes an irritant fluid which causes
the abnormal growth, would require further observations. The tissues
of the receptacle near the ovule attacked commence to swell up shortly
after the larva begins to feed, and in a comparatively short time the
size and shape of the future hibernating chamber of the larva are marked
out in the gall, although the larva is far from its full size. In a longitu-
dinal section of a gall that contained a larva about four weeks old and
1-3 mm. in length, the outline of the future hard-walled chamber could
be clearly distinguished. A thin layer of woody tissue is developed
within the hypertrophied tissue that the larva is feeding on, and a thick
layer of soft nutritive tissues is left within this woody layer and the
space occupied by the larva (Fig. 5); this nutritive layer is connected
at the base of the chamber with the vascular system of the plant.

During the period that elapses between this stage and the attainment
of the fully fed one, the larva gradually eats away this layer of soft
tissue, until finally when the growth of the larva is complete the layer
of soft tissue has been absorbed and the hard wall of the chamber
reached (Fig. 6); meanwhile the wall becomes more lignified and

J. T. WADSWORTH 165

harder, and the tissue between adjacent chambers that have fused
together also becomes drier and harder, and in this manner the hard
plurilocular gall is produced (Figs. 3 a and 4).

The interesting fact revealed during this process is that the stimulus
produced by the presence of the larva in the embryonic tissue of the
developing ovule, and in the hypertrophied receptacle, induces a reaction
of the plant to form a structure that is possibly protective to the plant
itself, but which is also at the same time exactly suited to the require-
ments of the fully-grown larva, forming as it does a very efficient means
of protection to the larva during the prolonged period of hibernation.

Several larvae, pupae, and imagines of Parasia melzneriella Stt.
were obtained from the flower-heads during this investigation ; 30%
of the heads examined were found to contain these lepidopterous larvae.
By far the greater number of larvae were found in chambers that had
originally been made by Urophora larvae, and it is a subject for further
investigation to find out what becomes of the original occupants of these
chambers.

Eleven larvae of an unidentified dipteron were found feeding on the
ripening seeds ; they were found in 9 per cent. of the heads examined.
Small orange-coloured larvae of a Cecidomyid were very abundant,
almost every flower-head examined contained several specimens.

A lepidopterous larva which differed from that of P. metzneriella
was found feeding on the seeds in 25 per cent. of the flower-heads
collected by Prof. Hickson at St Bees ; as the moth has not yet emerged,
I have not been able to identify the species to which it belongs.

The larvae of two species of Coleophora, C. alcyonipennella Koll.
and C. conspicuella Z. are recorded from Centaurea nigra. The larvae
found at St Bees may belong to one of these two species.

SUMMARY.

1. A description of Urophora solstitialis L. and an account of its
systematic position and geographical distribution are given, together
with an abstract of the work of previous observers on this species.

2. A list of its British and continental food-plants is given; the
records of the latter show that on the continent the larvae feed on
various species of thistles, and on three species of Centaurea, but not
on Centaurea nigra, whereas with the exception of one record of their
occurrence on Serratula tinctoria, the larvae in this country are recorded
as feeding exclusively on Centaurea nigra.

166 Knapweed Gall-fly

3. The life-history, ovipositor, and method of oviposition are
described, and descriptions and figures of the ova, larvae, and pupae
are given. The life-history is summarised on p. 148.

4. It is shown that owing to the formation of galls induced by
larvae of U. solstitialis in the flower-heads of this weed a reduction in
the number of seeds is effected amounting to about 50 per cent. in the
heads examined. The germinative capacity of the seeds produced in
these galled heads was also adversely affected. In the germination
experiment described 60-5 per cent. fewer seeds germinated from galled
flower-heads of C. nigra than from ungalled ones. At a moderate
estimate the number of seeds rendered non-effective in galled flower-
heads of C. nigra is placed at 50 per cent. It is pointed out that Try-
paneids, whose larvae adversely affect the weeds of cultivated land,
may be regarded as beneficial.

5. A short account and discussion of the recorded parasites of
U. solstitialis is given.

6. Some interesting features observed in the process of gall-forma-
tion are referred to, and a few notes are added on some other insect
inhabitants of the flower-heads of C. nigra.

BIBLIOGRAPHY.

Banks, NaTHAN (1912). The structure of certain dipterous larvae with particular
reference to those in human foods. U.S. Dept. of Agric. Tech. Series, No. 22.

Brecker, T. (1902). Die Meigen’schen Typen der Sogen. Muscidae acalypterae
(Muscaria holometopa) in Paris und Wien. Zeitschr. Hym. Dipt. 1.

Bezzi, M. (1911). Restaurazione del genere Carpomyia (Rond.) A. Costa. Boll.
del Laborat. di Zool. Gen. e Agr. Portici, vol. v, pp. 3-33.

Bezzi, M. (1913). Indian trypaneids (fruit flies) in the collection of the Indian
Museum, Calcutta. Memoirs of the Indian Museum, Calcutta, vol. 1, No. 3.

Borg, F. (1847). Zur Entwickelungsgeschichte mehrer Trypeta-Arten. Stettin.
entom. Zeit. vol. VI, pp. 326-331.

Borg, F. (1848). Idem. Jbid. vol. 1x, pp. 81-84.

BriscuKke, ©. G. A. (1882). Die Ichneumoniden der Provinzen West- und Ost-
preussen. Schrift. d. naturfors. Ges. Danzig, vol. v, pt. 11, pp. 121-183.

Connotp, E. T. (1901). British vegetable Galls. London.

Curtis, J. (1860). Farm Insects. London.

Durour, L. (1857). Mélanges entomologiques. Article 1, Urophora quadrifasciata.
Ann. Soc. ent. France, 3° série, T. v, pp. 53-58, 1 pl.

Frrcw, E. A. (1872). Urophora solstitialis Linn., a gall-maker. Entomologist,
London, vol. vi, p. 142.

Frron, EB. A. (1879). Trypeta reticulata, and general notes on the British gall-making
Trypetidae. Ibid. vol. xu, pp. 257-259.

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168 Knapweed Gall-fly

FRAUENFELD, G. (1857). Beitraige zur Naturgeschichte der Trypeten nebst
Beschreibung einigen neuen Arten. Sitzungs. Kais. Akad. Wiss. Wien,
Bd. xxu. pp. 523-557, pl. 1.

Gourrav, M. le Col. (1844). Notes pour servir a histoire des insectes qui vivent
dans le chardon penché (Carduus nutans). Ann. Soc. ent. France, 2° série, T. 3,
1845, pp. 75-102, pl. 1.

Hewirr, C. Gorpon (1907). On the life-history of the root-maggot, Anthomyia
radicum Meigen. Journ. Econ. Biol. vol. 1, part 2, pp. 56-63.

Hewitt, C. Gorpon (1908). The structure, development, and bionomics of the
house-fly, Musca domestica Linn. Part u. Quart. Journ. Micr. Sci. vol. Lu,
pp. 495-545.

KALTENBACH, J. H. (1874). Die Pflanzenfeinde aus der Klasse der Insecten (T'rypeta
solstitialis). Stuttgart, p. 379.

Linnaeus, C. (1738). Systema naturae. Tenth ed., p. 601. 98.

Lorw, H. (1844). Kritische Untersuchung der europaischen Arten des Genus
Trypeta Meigen. Germar’s Zeitschr. fiir die Entom. Leipzig, pp. 312-437.

Lorw, H. (1862). Die europaischen Bohrfliegen (‘Trypetidae). Wien.

Lone, H. C. (1910). Common weeds of the farm and garden. London.

Low, F. (1866). Zoologische Notizen, Erste Serie, p. 949. Verh. der k.-k. zool.-
bot. Ges.e« Wien.

MarSsHALL, Rev. T. A. (1885). Monograph of British Braconidae. Part 1 Trans.
Ent. Soc. London.

MeiceEn, J. W. (1826). Syst. Beschr. der bek. europ. zweifl. Insek. vol. v, p. 324.

Mix, J. (1897). Zur Biologie von Urophora cardui L. Wien. ent. Zeit. vol. xvt,
pp. 155-164, 2 pl.

Mortey, C. (1908). British Ichneumons, vol. u1, p. 81. London.

Scurner, J. R. (1858). Verzeichniss der Pflanzen auf denen Trypetenlarven gefun-
den worden sind. Verh. der k.-k. zool.-bot. Ges. Wien, vol. vItt.

Scutner, J. R. (1864). Fauna Austriaca: die Fliegen, Wien, vol. 1.

Swanton, E. W. (1912). British Plant Galls. London.

VERRALL, G. H. (1901). A list of British Diptera. Cambridge.

WALKER, F’. (1833). Monographia Chalcidum. FHurytoma verticillata. The Entom.
Mag. p. 23.

WALKER, F. (1835). Idem. Semiotus diversus. Ibid. p. 294.

WaLKER, F. (1837). Idem. Trigonoderus amabilis. Ibid. p. 40.

Wincate, W. J. (1906). A preliminary list of Durham Diptera. Trans. Nat. Hist.
Soc. Northumb., Durham, etc.

EXPLANATION OF PLATES.

PLATE XI.

1. Urophora solstitialis. Female, x5; ovipositor partially extended.

Fig. 2. Vertical section through young flower bud of Centaurea nigra, showing eggs Ov.
of U. solstitialis in situ. 24 hours after oviposition. x 9.

. 3. A. Ungalled receptacle of C. nigra. x 2.

B. Galled ss oy ¥ +

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NO. 2

J.T. W. phot.

Urophora solstitialis.

PLATES |

~Ov.

THE ANNALS OF APPLIED BIOLOGY, VOL. I. NO. 2. PLATE XIl.

J.T.W. del. Cambridge University Press.
UROPHORA SOLSTITIALIS.

J. T. WapswortH 169

Fig. 4. Vertical section through three galled flower-heads of C. nigra showing the cham-
bers in which the larvae hibernate during winter, and where pupation takes place.
The left hand one contains a pupa. x 2.

Fig. 5. Vertical section through a galled flower-head of C. nigra; the section shows the
hard woody walls of two chambers ; the right chamber contains a section of a larva
and shows the thick layer of nutritive tissue that is separated from the remainder of
the receptacle when the woody layer is developed. The section is slightly tangential,
and the larva is younger than the one in Fig 6. x65. JL. section of larva.

Fig. 6. Section similar to Fig. 5 containing an older larva in the left, chamber, the nutri-
tive layer has been almost eaten away by the larva, and the woody wall reached.
x5. JU. section of larva.

PLATE XIil.

Fig. 7. Egg of UW. solstitialis. 24 hours after oviposition. 50; m. micropyle.

Fig. 8. Cephalo-pharyngeal skeleton of mature larva from the left side. x 120. ms.
mandibular sclerite ; h.s. hypostomal sclerite ; c.s. cephalo-pharyngeal sclerite with
deep indentation between dorsal and ventral processes which exhibit further bifurca-
tions ; s.4. sub-hypostomal sclerite ; m.e. membrane surrounding each process of
the cephalo-pharyngeal sclerite.

Fig. 9. Mature larva, ventral aspect. «10. The larva was slightly lifted upwards
anteriorly bringing into view the mouth-slit and the anterior spiracles. a. anus.

Fig. 10. Puparium, ventral aspect. x10. a. anal scar.

Fig. 11. Anterior view of mature larva. x45. p.b. posterior border of third segment.
L.sp. left anterior spiracle. m.s. mouth-slit with the dark chitinised sides of the
oral-lobes. m. posterior margin of the chitinised area surrounding the mouth.

Fig. 12. Posterior view of last segment of mature larva. x50. l.m. lateral margin
oflast segment hs.d. horse-shoe shaped depression. dm.d. dorso-median depression.
l.p. left posterior spiracle. 7.m. indications of muscle-attachments which appear as
dark areas on the surface.

Fig. 13. Vertical section of flower-bud of C. nigra showing the passage p. made by ovi-
positor during the process of oviposition. 5. The ovipositor had passed on both
sides of the third floret from the left-hand side, as indicated in the drawing.

Fig. 14. Right posterior spiracle of mature larva viewed from above. x 200. fc.
felted-chamber (Filzkammer).

Fig. 15. Left anterior spiracle of nearly mature larva viewed from above. x 200.
f.c. as Fig. 14.

Nore. In figs. 14 and 15 the felted-chamber (f.c.) is displaced laterally. In the larva
the chamber is directly beneath the spiracular openings.
Figs. 7, 8, 11, 12, 14, and 15 were drawn by the aid of the Zeiss-Greil drawing apparatus.

170

A BRACONID PARASITE ON THE PINE WEEVIL,
HYLOBIUS ABIETIS.

By J. W. MUNRO, B.Sc. (Agr.), B.Sc. (Arb.), Evry.

Tue following notes are the result of observations made on pine
weevils and parasites collected in a plantation on the estate of Banchory
Devenick near Aberdeen. The-plantation in question was formed in
the spring of 1911, a year after the removal of the old crop which was
a pure wood of Scots pine. The stumps and roots of this old wood afford
ideal breeding places for the pine beetle (H. piniperda) and the pine
weevil (Hylobius abietis), and they are to be found in considerable
numbers.

Fig. 1. Larvae of H. abietis. x6.

The work of the pine weevil is familiar to all interested in forestry.
It is harmful only in the adult state and does considerable damage by
gnawing the tender bark of young conifers causing them to wilt and die.
Where conifers are not to be got it will readily attack birch, mountain
ash, and oak.

J. W. Munro 171

In the larval stage Hylobius is harmless. The adult deposits her
eggs in or under the bark of the stumps of various conifers but prefers
Scots pine. The larva on hatching out, commences to tunnel between
the bark and the sapwood, and when full grown pupates at the end of
this tunnel, either in a cavity or hook gallery in the sapwood, or in a
cavity in the bark. The tunnels are filled with frass, consisting of tiny
chips of wood bitten out by the larva and passed through its body.

Fig. 2.

a,b. Larvae of B. hylobii. x12. (a after first moult. 5 after second moult.)

c. Pupa of B. hylobii. x 12.

The whole of the larval life is passed in such a tunnel. In the spring
of 1912 I noticed a few tiny cocoons lying in one of these tunnels but I
attached no importance to them at the time. In July of last year,
however, I found several weevil larvae apparently in the resting stage,
which were attached by a small legless maggot feeding externally on

Aun. Biol. 1. 12

172 A Parasite on the Pine Weevil

them. I collected a number of weevil larvae both attacked
and immune, and also a number of the attacking maggot. In
some cases the weevil larvae were sucked quite flat and in
a few days all those which had been attacked were in this con-
dition. Accordingly I supplied the parasitic larva with more grubs
and found that they readily fed on them, crawling two or three inches
to reach their new prey.

These parasitic larvae measured somewhat over } inch in length,
and were covered with very short reddish brown hairs. Unfortunately
I was unable through lack of proper instruments to make a close exami-
nation of them and I could not make out the mouth parts. Observation
showed, however, that they fed through the skin of their host and were
purely external parasites. In September the parasites ceased feeding,
and a few days after they moulted and became more definite in shape,
and I assumed then that they were Hymenopterous. A fortnight later,
on September 25th, they commenced spinning silky cocoons and in a
few hours they were completely hidden. All through the winter I
examined a few of these cocoons every week, but no alteration in the
external appearance of the enclosed larvae was visible until February
20th, when in two out of five cocoons I found pupae. Nine days later
the first imago emerged which I recognised as a Braconid of some sort.
At the date of writing, April 14th, flies are still emerging from the later
gathered cocoons.

Dr MacDougall informs me that three years ago he obtained a
Braconid parasite on Hylobius, but in such a battered condition as to
be unrecognizable. So far as I have been able to ascertain I know of no
other British record of a Braconid on Hylobius. In Ratzeburg’s Ichneu-
mon der Forstinsekten, however, there is a short account of the rearing
by Nordlinger of 40 29 and 4 33 from the larvae of H. abielis. I may be
permitted to quote Ratzeburg’s account. “‘ Nordlinger bred 40 99 and
4 33 from this species (Hylobius abietis) each of whose larvae supports
about ten parasites. The cocoons of the latter are firm, oat-shaped
and papyraceous, woven among their hosts frass and dead bodies, and
often constructed at the end of the beetles’ tunnels beneath fir bark.”
This description agrees in every respect with my own observations and
accordingly I looked up Ratzeburg’s description of the species which he
calls Bracon hylobii. It again agrees with the insects I have bred out,
and as I have been unable to identify my specimens with any of the
Bracons in the South Kensington collection, or with those described by
Marshall, I think it highly probable that the species I have reared are

J. W. Munro {73

B. hylobii. Tf so they are a species new to Britain, and in order to be
sure of this I have sent specimens for identification to Dr Szepligeti in
Budapest.

Ratzeburg’s description of the species is as follows: “ B. hylobii.
13-2 mm. Outer and inner discoidal cells equally long. Second
cubital ceil a little larger than the first. Antennae of 2 31 jointed.
The ovipositor as long as the abdomen and tending to curve upwards.
Head approximately as broad as the thorax. All the legs and the
greater part of the first half of the abdomen reddish brown. In the
? only the middle of the first segment is black. In the male the first

Rig. 3. B. hylobi 3. x15.

ring may be almost quite black and.the last or posterior half of the
abdomen in both sexes is quite black. The thorax and head black
except in certain females when part of it is brownish.”

Ratzeburg expresses doubt as to making it a species, but he considers
that the shape and size of the discoidal cells entitle it to that distinction
from its near neighbours B. immutator and B. spathiformis.

Messrs Elliott and Morley in their Hymenopterous parasites of the
Colioptera refer to Ratzeburg’s species but do not quote his description.
These references are the only two I have been able to obtain on the
subject?.

1 Brischke, C. G. A. Die Ichneumoniden der Provinzen West- und Ostpreussen.

Schrift. Naturfors. Gesell Danzig Neue Folge, v, 1882, p. 135 (records the ¢ of Bracon

hylobit but makes no comments thereon). 5
12—2

174. A Parasite on the Pine Weevil

The degree of parasitism by B. hylobi on the pine weevil may be of
interest. In winter 1911 I observed no cocoons. In the spring of 1912,
two years after the old crop was removed and presumably in the second
year of the beetles’ occurrence there, I observed a few cocoons, while in
1913 and 1914 every third pupating chamber was occupied by them.
This represents parasitism in the third and fourth years of the pest of
over 30 per cent.

I think I do not exaggerate when I suggest that Bracon hylobu
Ratz. may prove of considerable value in combating the pine weevil,
which is every year becoming more and more common in newly formed

"at

{

Fig. 4. B.hylobit 9. x15. .
plantations, especially in Scotland. The parasite is, in all probability,
fairly common where Hylobius is found. The fact that it has hitherto
apparently been unrecorded does not imply that it is scarce. The
persons most interested in Hylobius, the forester and the factor, are
interested only in the adult beetle when it begins its attacks on their
plantations, and any measures they may take against it are as a rule
confined to the trapping and collecting of the adult. The larvae are
rarely considered, and though they were disturbed and examined, the
forester is neither sufficiently interested nor sufficiently educated to
pay any attention to the cocoons, or larvae of a parasite, though he
found them.

J. W. Munro 175

Parasites have already been used with success in combating other
destructive insects ; notably Professor Lefroy’s introduction of Rhogas
Lefroyi into the Punjaub, to combat the boll worm, and more recently
Pierce and Townsend have shown that Hymenopterous parasites play
a very important part in controlling the cottonboll weevil in the States.
Pierce found that of 2800 weevils, 591 were parasitised, and that of
these, in 525 cases the parasite was a Braconid. In 1911 Pierce and
Hunter began experiments on the rearing and distributing of the parasites
but I am not aware whether a report on these has yet been published.

As to the possibility of using B. hylobii in combating H. abietis, I
have not yet obtained a sufficient knowledge of the former’s life-history
to make any definite statement, but such observations as I have been
able to make lead me to believe there are no special difficulties to over-
come. If B. hylobii is fairly or reasonably common, and there is no reason
to suppose it otherwise, there should be little difficulty in obtaining
batches of its cocoons, or numbers of its larvae to breed from. The
larvae of Hylobius, too, can readily be kept alive if they are not removed
from the roots on which they are feeding. I have reared several weevils
by removing the smaller roots containing their larvae and keeping
these sufficiently moist. The parasite itself is easily reared inasmuch
as I bred one batch in an ordinary collecting tube in which I placed a
weevil grub as food.

Out of about 70 cocoons, I have obtained no hyperparasites on the
Braconid. This again is favourable. The parasite too is evidently
hardy. The plantation from which my specimens were obtained is a
bleak hillside near the coast and over 600 feet above sea-level. It is
often swept by cold North and Kast winds.

Another interesting fact is that B. hylobii attacks the weevil larva
in its resting stage, at a time,when the latter is practically inactive.

The greater increase in numbers of the parasite as compared with the
weevil is also interesting. Every weevil grub attacked gives rise to at
least five adult parasites. Of these according to Nordlinger’s figures,
90 per cent. will be females, but from my own observations 60
per cent. is a more probable relation.

Assuming that every weevil grub parasitised gives rise to five adults,
three of which are females, and that as in the present instance,
30 per cent. of the weevil grubs are attacked in the winter 1913-14,
then out of 100 weevil grubs we should get 70 Hylobius adults and
90 female Braconids in spring 1914. If we assume further that the
rate of increase of Hylobius and of Bracon in a given year is the same, say

176 A Parasite on the Pine Weevil

ten, and that the proportion of males to females in the two insects is the
same, then we should have in the winter 1914-15, 420 weevil grubs and
540 Braconid. This would, therefore, entail the complete destruction
of the weevil. These figures are of course purely hypothetical. Now
it is by no means improbable that the Braconid is more prolific than
the weevil, and also that the proportion of females to males in the Bra-
conid is greater than in the weevil. These, however, are points which
must be cleared up before the practical value of Bracon hylobw as a
factor in controlling Hylobius can be fully demonstrated.

177

OBSERVATIONS ON THE LIFE-HISTORY OF THE
AMERICAN GOOSEBERRY-MILDEW (SPHAERO-
THECA MORS-UVAE (SCHWEIN.) BERK.?

By E. 8S. SALMON, F.LS.,

Reader in Mycology, University of London ;
Mycologist to the South Eastern Agricultural College, Wye, Kent.

THe rule among the species of the Erysiphaceae—to which the
American gooseberry-mildew belongs—is a life-cycle consisting of the
production of a conidial stage during the growing-period of the host-
plant, and the production before the advent of winter of a perithecial
stage. In the conidial stage the spore is a naked, short-lived conidium ;
in the perithecial stage the spore is an ascospore which remains living
for several months within the ascus inside the thick-walled perithecium.

While this is the usual life-cycle, some striking exceptions occur,
particularly in cases where a species has found its way into a new
continent.

When the vine-mildew (Uncinula necator (Schwein.) Burr.) invaded
Europe, no perithecial stage was found associated with it for the first
47 years®, the mildew existing during winter in the conidial stage in
a more or less dormant condition. Appel has shown that before winter
patches of hibernating mycelium are found on the stem of the vine ;
these produce conidia the next season. These hibernating patches have
thicker-walled hyphae, and more numerous and larger haustoria.
Although the perithecial stage of U. necator has been found within recent
years on a few occasions in different years in France, Germany, and
elsewhere, it appears that the production of perithecia—which are
formed abundantly in America, the native home of this mildew—only
takes place exceptionally in Europe—possibly under abnormal weather
conditions.

1 Paper read at the Meeting of the Association of Economic Biologists, on April 17,

1914,
2 Salmon, E.S. A Monograph of the Erysiphaceae (Mem. Torrey Bot. Club, 1x, 1900).

178 American Gooseberry-Mildew

A very similar case is that of the oak mildew. About 10 years ago
oak “ scrub,” and to some extent oak trees also, in England and in many
parts of the Continent, became for the first time attacked by a species
of the Erysiphaceae in the conidial stage. It received many names
(e.g. Oidium alphitoides, O. quercinum, etc.) at the hands of mycologists
belonging to that class which has sufficient time only to add to synonymy.
In 1911, the discovery in France of the perithecial stage of this mildew
on some autumnal shoots of the oak, proved its identity with an endemic
American form of Muicrosphaera alni (Wallr.) Salm., which occurs
commonly on species of Quercus in the United States. Here, again,
quite exceptional seasonal conditions would seem to be necessary for
the formation of the perithecial stage of this mildew when introduced—
as presumably has been the case—into Kurope from America. No
perithecia have been found in this country and certainly as a general
rule the oak-mildew passes the winter in the conidial stage in a more
or less dormant condition.

A third case is the mildew which attacks the foliage of that very
useful ornamental shrub Huonymus japonicus. This mildew first
appeared in England, and also on the Continent, about 15 years ago,
and only the conidial stage is known!. It is possible that it is a form of
Erysiphe Polygoni endemic to Japan on Huonymus japonicus, and that
it has been imported with that shrub from Japan into Europe. The
mildew exists in Europe during the winter months on the evergreen
leaves in dormant or nearly dormant hibernating mycelial patches,
which on the advent of a warm spell of weather soon produce conidia.

What now are the facts with regard to the life-cycle of the American
gooseberry-mildew (Sphaerotheca mors-uvae (Schwein.) Berk.) in this
country, since its introduction into Europe from America about 1900 ?
Has its normal life-cycle been interfered with in any way as the result
of new factors such as change of climate or different ‘‘ constitutional ”
characters of its host-plants ? There is, I think, some reason for thinking
that it has. There is no evidence that there is any hibernation of the
conidial stage. The perithecial stage—or at least the outward signs
of it—is formed abundantly on the surface of the young shoots of the
gooseberry. It has been assumed from the first—-and quite rightly so
under the circumstances—that the continuance from year to year of
this new and most destructive pest was everywhere ensured by this
abundant production of the perithecial stage. Some facts which I have

" Salmon, E.S. Fungus Disease of Huonymus japonicus (Journ. Roy. Hort. Soc., XX1x,
p. 434 (1905)).

EK. S. SALMON 179

lately observed, however, show the necessity for close investigations to
be made to ascertain to what extent the perithecial stage which is
formed at different times during any one season remains living through
the following winter and is the cause of the first spring outbreaks. The
facts lately observed would seem to show that there is a real danger—
if the American Gooseberry-mildew Orders are carried out by officials
without the guidance of a mycologist—of fruit-growers being prosecuted
and fined for not removing from gooseberry bushes the mildew in a dead
condition.

In August last year, and during the present spring, I have observed
the various details connected with the dehiscence of the ripe perithecium
and the discharge of the ascospores—a process which I have not before
succeeded in observing and one which, I believe, has escaped other
investigators. The details will be described in the next number of the
Journal of Agricultural Science (now in the press'). The dehiscence of
the ripe perithecium was observed to take place in material collected last
August, a few hours after the perithecia had been supplied with moisture ;
similar material collected in November last and kept dry in the laboratory
through the winter, proved when examined in February, March, and
April, to be alive, the perithecia dehiscing when supplied with moisture.
The dehiscence, which occurred either almost at once—the shortest time
being 14 hours—or after an “incubation” period of several days
—took place at temperatures from about 5° C. to 27° C.

This living material was useful in affording a comparison with
examples of the perithecial stage obtained from bushes in the open in
the spring, 7.e. after it had “‘ wintered.” In all cases, so far, such “ over
wintered’’ material, which has been obtained from N., Mid., and E. Kent?,
proved in February or later, to be dead. In such material the perithe-
cium on being pressed open usually exudes drops of an oily nature ;
the ascus is not turgid, and is often more or less crumpled ; the asco-
spores are filled with some oily material, staiming pink with alkannin.
No development can be induced on “ incubation ”’ at those temperatures
which cause living perithecia to dehisce and discharge their spores,
and it is clear that such perithecia are dead.

It seems clear, therefore, that some amount of the perithecial stage
of the American gooseberry-mildew which is produced in this country
either does not reach maturity or does not survive the winter.

1 Salmon, E. S. Observations on the Perithecial Stage of the American Gooseberry-
mildew (Journ. Agric. Sci., v1, p. 187, May, 1914).

2 Most of this material was kindly sent to me by Mr F. G. Cousins, Inspector for
American gooseberry-mildew for Kent.

180 American Gooseberry-Mildew

It is possible, but I think very unlikely, that in these cases where an
examination in the spring showed only perithecia with dead asci that
all the mature (living) perithecia had fallen previously to the ground.
It seems far more probable that this material had never reached that
stage of development at which the perithecia can remain alive through
the winter. If so, the reason for this failure to mature may be due to
the influence of new factors which the mildew encounters in this country
—such as the “ constitutional’ characters of European varieties of
gooseberries, or to the weather conditions obtaining in this country in
the late summer or autumn. It may possibly prove to be the case that
it is only the perithecial stage which is formed early in the season,
reaching maturity about July or August, that is really dangerous, and
that later-developed perithecia do not survive the winter.

It would of course be unwise to generalise from observations made
so far on material obtained in one season only ; but there seems clear
evidence that both the fruit-grower and the official administrators of
the American Gooseberry-mildew Orders have a new fact to reckon with,
viz. the natural death, before the spring, of some amount of the peri-
thecial stage of the American gooseberry-mildew.

Postscript. Since the above was written, I have had the opportunity
of examining further “ over wintered ” material of S. mors-wvae collected
at the end of April and during May.

The first lot of material collected at the end of April, was kindly
obtained for me by Mr Gibson (Inspector for American Gooseberry-
mildew for Surrey) from Farnham, Newdigate, and Witley. Thirty-
four shoots bearing patches of the perithecial stage were sent ; these were
all closely examined. ‘Twenty-two shoots bore patches of deep-brown
persistent mycelium, which on examination proved to be either quite
barren with no perithecia, or with just a few (dead) perithecia. The
appearance of the barren patches suggested that no perithecia had
ever been formed (i.e. that the development of the winter stage had
been stopped), and not that the perithecia had fallen out from them,
since the densely interwoven mycelial patches showed—in many cases
at all events—no signs of having been worn thin or disintegrated under
the action of weather conditions ; in a few cases the mycelial patches
may have been partly worn away as the result of “ weathering.” On
more than 50 per cent. of these diseased shoots there was a completely
barren, although dark brown, mycelium.

In the remaining twelve examples perithecia had been produced
abundantly on the shoots, but in no case was a living ascus found inside

K. S. SALMON 181

any perithecium. In several cases the perithecia had apparently never
reached full development, since the ascus was not the normal size ;
in those cases where a full-sized ascus was present, it was without excep-
tion shrunken and obviously dead, and the ascospores, which contained
oil drops, were evidently undergoing a process of degeneration.

On May 4 a commercial gooseberry plantation of “ Berry’s Early ”
near Rodmersham, Kent, was visited at a time when the American
gooseberry-mildew was just beginning to appear for the first time this
season. A number of bushes were found with the (conidial) “* summer-
stage ” of the mildew developing—mostly on the young, green berries.
In a considerable number of cases—perhaps in the majority of cases—
the affected berries were in close proximity to portions of last year’s
shoots which were badly infested with the (“‘ over wintered ”’) perithecial
stage. On microscopical examination, however, of nine of these shoots
—1.e. where mildewed berries occurred close to the winter-stage formed
in 1913—~all the perithecia appeared to be dead, the ascus being either
shrivelled or empty, or when containing ascospores the ascus was not
turgid, and the spores were full of oily degeneration-products. The
perithecium on being pressed open usually exuded drops of some oily
substance.

On other branches of the bushes which bore the mildewed berries,
and also on other adjoining bushes where no mildew occurred yet, the
perithecial stage of 1913 could be found not uncommonly on some of
the young shoots (although all the bushes had been “ gone over ”’
twice in the process of “ tipping’’). As in the above-noted cases, the
perithecial stage consisted of the dark brown persistent mycelium, often
considerably worn away by “ weathering,” and hundreds of closely
ageregated perithecia. Thirty-two of these shoots with the perithecial
stage were examined and not one perithecium could be found with a
living ascus. The experiment was made of incubating some of this
material at 27° C. but no change resulted.

On May 6 a commercial plantation of “ Cousin’s Seedling,’ near
Sandwich, Kent, was visited. This plantation was so virulently attacked
by the mildew in 1913 that practically all the young shoots on every
bush became infested with the perithecial stage, and this also was
developed on nearly every berry—the whole crop was lost, not a single
berry being fit to pick. An examination on May 6 showed that the
disease was just re-starting for the season ; from 40 % to 50 % of the
bushes (250 in number) bore a few berries with small patches of the
(conidial) ‘‘summer-stage”’ on them. In a few cases young shoots
more or less plentifully infested with the perithecial stage of 1913 were

182 American Gooseberry-Mildew

closely adjacent to these mildewed berries. Nine of these shoots were
microscopically examined, but no perithecium containing a living ascus
was found. Inthe majority of cases the ascus was empty and shrivelled ;
in the few cases where ascospores occurred, the ascus was not turgid,
and the spores were full of oily contents and evidently undergoing a
process of degeneration. In a very few cases the perithecium contained
the spores of the parasitic fungus Ampelomyces quisqualis (Cicinnobolus
Cesati), but it was clear that the mildew had not been parasitised to any
appreciable extent. With regard to the bushes generally, the mildewed
berries were found either on branches from which all the young wood
(which had probably been diseased) had been cut away, or on spurs
on quite old wood.

Since there is no evidence that in these cases these primary infections
had been caused by ascospores from the “ over wintered ”’ material
still present on some of the shoots, the explanation must be looked for
in another direction. There are two ways by which infection by asco-
spores could have occurred. As I have pointed out!, perithecia may
begin to fall to the ground in August from infested berries and, to a less
extent, from infested shoots. With regard to this particular plantation,
all the berries (as noted above) became very badly infested ; they were
not removed by the grower until late in August—by which time not only
must thousands of perithecia have fallen to the ground, but many of
the infested berries had fallen or been scattered by birds; there must
therefore have been a heavy infestation of the soil. If, however, the
primary infections which were taking place in May had been caused by
ascospores arising from the soil, one would have expected to find the
majority of the mildewed berries on the lower branches of the bush,
which was certainly not the case ; the infected berries being nearly always
on the upper branches.

The second way by which infection could have been caused is as
follows. The “ tipping,” 7.e. the removal of the infested shoots, was not
done until the end of October or beginning of November; by this time
a considerable mass of perithecia must have dropped from the perithecial
patches. Many of these perithecia would doubtless lodge in the crevices
of the bark, or between the bud-scales, ete., and assuming that these
perithecia were mature ones capable of remaining dormant through the
winter, these would on liberating their ascospores infect the adjacent
berries. This theory, to which on the whole I incline, would account
for the fact that the berries in the upper part of the bush were first
attacked.

1 Journ. Agric. Sci., v1, p. 187 (1914).

183

POTATO DISEASES.
By A. 8. HORNE:

OvER seventy years have elapsed since C. EH. P. von Martius! set to
work to investigate potato disease in Germany and M. J. Berkeley? began
his observations on the potato murrain, contributed to the Journal of
the Royal Horticultural Society in 1846. These early observers recog-
nised that potato disease consisted of several distinct maladies some of
which they attributed to fungal organisms, but their knowledge of the
diseases and fungi was of necessity incomplete. Von Martius noticed
several diseases, notably Stockfaule (gangréne séche or dry-rot), con-
sidered to be due to one of the Mucidineae—Fusisporium solani ;
Krauselkrankheit (la frisole or curl), and Rande (gale), prevalent in
the calcareous lands of Thuringia, Bavaria and in Austria. Payen®
records in 1853 that Rhizoctonia violacea, the cause of the disease known
in France as mort du safron of the lucerne and sanfoin, could also attack
the potato.

The disease known in France as the maladie de la pomme de terre,
in Britain as the potato murrain, was regarded by Montagne, Morren,
Berkeley, Lindley, Payen and others as due to the fungus Botrytis
infestans known later as Phytophthora infestans. The means of com-
batting the malady adopted in Payen’s time were attention to the soil
and drainage, the choice of varieties that appeared to have the best
chance of escaping the disease, in the preparation of tubers to be used
as seed—tubers to be planted should be exposed to dry air and light
for some days before planting, whilst a wash of copper sulphate solution
sunilar to that used for grain at that time was recommended—the rotation
of crops, and the effect of autumnal planting was studied. It remained
for De Bary (1861—1876) to present the first clear account of the life-
history of Botrytis infestans and to finally settle its position among

1 ©. E. P. von Martius in Die Kartoffel Epidemic der letzen Jahre oder die Stockfdule und
Rdnde der Kartoffeln 1842.

2M. J. Berkeley in Journal of the Royal Hort. Soc., 1, p. 9 (1846).
3 Payen in Des Maladies des pommes de terre, Paris, 1853.

184 Potato Diseases

fungi. About the year 1885 the remedy bouillie bordelaise—bordeaux
mixture—used in the first instance and chiefly owing to the efforts of
Millardet, to combat the vine mildew in France, was adopted for other
plants and amongst others the potato. Under the name Stockfaiule
(gangréne séche), Martius probably confused the dry-rot disease, now
known to be due to Fusarium, and the old potato disease or murrain
caused by Phytophthora infestans. This is not surprising since Fusarium
rot almost invariably supervenes after the attack by Phytophthora.
Krauselkrankheit, frisole or curl corresponds to the modern Blattroll-
krankheit or leaf-roll, but the name Kréauselkrankheit appears to be
now used more frequently for a type of curl with crinkled leaves. Curl
is a disease of very long standing on the mainland of Europe and in this
island but it has caused much consternation on the Continent during the
last decade and has recently become a new potato problem for investi-
gators in the United States. Records of its occurrence in Britain are
to be found in the memoirs of the Caledonian Horticultural Society! of
one hundred years ago. The gale, or canker disease as it should now
be styled, is still prevalent in Europe and has been detected recently in
South Africa® on potatoes forwarded to Rhodesia from Britain, and in
America. The true nature of the canker organism, Spongospora solani,
was established by Brunchorst? in 1886.

The most important additions to the list of British potato diseases
since Berkeley’s time are the maladies known as tumour and sprain.

The occurrence of tumour in Britain can be traced back as far as 1878
but the cause of the disease was not known until 1896, when an intra-
cellular parasite was discovered by Schilberszky in material said to have
been received from Upper Hungary and named by him Chrysophlyctis
endobiotica. Chrysophlyctis was thrice described within the space of a few
weeks in England in 1902, was chronicled as a Shropshire scourge in 1908
and scheduled under the Destructive Insects and Pests Act of 1907 in
the same year.

Sprain, recorded by Frank? under the name Buntwerden or
Hisenfleckigkeit in the list of diseases enumerated by him in Kampfbuch
in 1897, and only recently definitely separated as an entity from the
tangle of things insufficiently understood, is in all probability of long
standing in Great Britain.

1 Thomas Dickson in Mem. Caled. Hort. Soc., 1 (1814).

2 J. B. Pole-Evans in Trans. Dept. Agric. Farmer's Bull., No. 110 (1910).
* J. Brunchorst in Bergens Musewms Aarsberetning (1886).

4 Frank in Kampfbuch gegen die Schddlinge unserer Feld friichte (1897).

A. S. HornNE 185

Various bacterial diseases of the potato have been described during
the last twenty-five years. In 1890 Prillieux and Delacroix! recorded
a bacterial disease attacking the stem of the potato. Other bacterial
maladies were subsequently described by Erwin F. Smith? in the United
States (1896); Iwanoff*, in Russia (1899); Harrison’, in Canada
(1906) and by Miss Dale® (1912). The disease known as black-leg or
Schwarzbeinigkeit, which is of sporadic occurrence in Great Britain, has
been attributed to various bacteria by different investigators. Frank®
isolated a bacterium which he called Micrococcus phytophthorus (1899) ;
Appel? (1902 and 1904), Bacillus phytophthorus, which is possibly
identical with Frank’s organism; C. J. J. van Hall§, in Holland (1902),
B. atrosepticus ; Pethybridge and Murphy®, in Ireland (1911), Bacillus
melanogenes. Harrison’s disease possibly belongs to this group.

On the American continent considerable attention is being given to
two comparatively recently described fungal diseases—potato wilt, due
to Fusarium oxysporium, described by Erwin F. Smith and Deane B.
Swingle!? in 1904, which is widespread in America, but, according to
W. A. Orton!!, absent from Europe; and Verticillium wilt, due to
Verticallium alboatrum, described by Reinke and Berthold!* in 1879,
present in America and Europe. Verticillium wilt has recently been
recorded in Ireland by Pethybridge?®.

Potato collar-rot caused by the Basidiomycete, Hypochmis solani
Pnill. and Del. occasionally occurs in Britain.

The problem of potato scab has become an increasingly important
one in the United States. The American scab is said to be caused by
an organism isolated by Thaxter! (1890) who named it Oospora scabies

1 Prillieux and Delacroix in Comptes rend., cx1 (1890), p. 208.

2 Erwin F. Smith in U.S. Dept. Agric. Div. Plant Path, Bull., 12 (1896).

3 Iwanoff in Zettschr. f. Pflanzenkrankheiten, 1x (1899), p. 129.

4 Harrison in Centralblatt fiir Bakt., u, Abt. xvm (1906), p. 34.

5 Elizabeth Dale in Annals of Botany. xxv1 (1912), p. 138.

§ Frank in Centralblatt fiir Bakt., a, Abt. v (1899), p. 98.

? Appel in Arb. a. d. biol. Abt. a. Kais. Gesund, 1 (1902), p. 373; 1 (1904).

8 C. J. J. van Hall in Bijdragen tot de Kennis der baktericelle Plantenziekten, Diss.,
Amsterdam (1902).

® Pethybridge and Murphy in Proc. Roy. Acad. xx1x, sec. B, No. 1 (1911).

10 Erwin F. Smith and Deane B. Swingle. U.S. Dept. Agric. Bur. Pl. Ind. Bull., 55 (1904)-

u W. A. Orton in U.S. Dept. Agric. Bur. Pl. Ind. Bull., 64 (1914).

12 J. Reinke and G. Berthold. Die Zersetzung der Kartoffel durch Pilze. Berlin (1879) _

13 G. H. Pethybridge in Jour. Dept. Agric. and Tech. Instruc. Ireland, xu, No. 3
(1913), p. 23.

14 R. Thaxter in Conn. Agr. Expt. Sta. Rept. (1890), p. 81.

186 Potato Diseases

(Mucidineae), but G. C. Cunningham! (1912) suggests its transference
to the genus Streptothrix (Schizomycetes) and H. T. Giissow? refers it
to Actinomyces. B. F. Lutman? (1913) has described the pathological
anatomy of this scab. To what extent the British scab is due to
Oospora scabies has yet to be determined.

A disease recently described by the writer? and named bruise, owing
to the occurrence of greyish or black areas in the flesh of potato tubers
which renders them unfit for culinary purposes, appears to be of a physio-
logical nature and is perhaps often occasioned by growing potatoes in
poor or insufficiently cultivated land. :

Besides the fungal and physiological maladies, there are of course
several pests on the animal side. The Colorado beetle scourge of the
United States is fortunately not prevalent in these islands. The tuber-
boring wire-worm, however, is frequently troublesome. The very
much neglected subject of insects injurious to the potato foliage has been
recently studied by Professor H. Maxwell Lefroy and the writer and
the results obtained will be soon communicated to these Annals.

I propose now to consider as far as possible in correct perspective
only those problems, the insect question excepted, that are of con-
siderable economic importance at the present time in Great Britain.

Tumour.

The disease caused by Chrysophlyctis endobiotica—the tumour
organism—has claimed considerable attention during the last few years,
firstly owing to reports of an alarming kind relative to the virulence
of this parasite and fear lest it might spread and eventually ruin the
potato-growing industry ; and secondly, owing to the stringent measures
taken by other countries, alarmed by reports of the prevalence of
the disease here, against the importation of British-grown potatoes.
According to the Report? issued by the Intelligence Division of the Board
of Agriculture and Fisheries, 1911-1912, the actual loss occasioned to
the potato harvest here is very slight indeed, since the report states :
‘There are probably scarcely five hundred acres in all England which
are under cultivation for potatoes as a field crop which are liable to
be affected while even in these the proportion of diseased tubers is

' G. C. Cunningham in Phytopathology, a (1912).

* H. T. Giissow in paper read before Assoc. Econ. Biol. London. {Faster, 1914.)
* B. F. Lutman in Phytopathology, mt (1913), p. 255.

* AS. Horne in Jour. Roy. Hort. Soc. xxxvu, p. 40.

® Board of Agric. and Fish. Annual Rept. Intellig. Div., Pt. 1 (1913), p. 24.

A. 8. Horne 187

generally trifling.” Owing to the regulations adopted by other Govern-
ments, however, the indirect loss to potato-growers is very considerable.

The question of the degree of virulence possessed by this organism
needs searching analysis and the following points may be enumerated in
this connection :

(1) ‘Tubers planted in experimentally infected soil have produced
without fail plants bearing diseased tubers (M. C. Potter).

(2) Diseased tubers have been produced year after year,
irrespective of the kind of season, in soil once infected (M. C.
Potter).

(3) Several varieties of potato were affected when planted in
Potter's experimentally infected soil.

(4) The Report issued by the Intelligence Division, 1911-1912,
states that in spite of the exceptionally dry season in 1911, the disease
in all the badly affected places was as manifest as ever even though it
was not observed in the less badly attacked districts.

(5) According to the Report, some varieties are practically
immune to Chrysophlyctis.

It may be gathered from the Report that the disease is largely
confined to cottage and allotment gardens. Now in gardens of this
type, frequently ill-kept, where potatoes are grown year after year
without rotation, canker also exhibits its worst form, rendering
potatoes worthless and unsightly (see Journal of the Royal Horticultural
Society, vol. XxXvut, figs. 101, 102). Is Chrysophlyctis, in this country,
really more virulent in character than the canker parasite, Spongospora
solani, or is the supposed greater virulence merely apparent owing to
the absence of sufficient information on the canker side ?

The life-history of Chrysophlyctis is moderately well known, never-
theless several important problems remain to be solved, such as (1)
the exact nature of the bodies penetrating the tissue and the method of
penetration ; (2) the mode of existence for a prolonged period in the soil ;
(5) the conditions which favour or inhibit infection.

It is known that the fungus forms resting bodies (sporangia) in the
tubers which when returned to the soil are capable of passing the winter
there and may perhaps rest for years in the soil without losing the power
to germinate. These sporangia are therefore a prolific source of
infection and it is important to realise that infection can be brought
about by their means in the following ways :

1. By planting diseased tubers.

2. By planting not-diseased tubers removed from infected soil.

Ann Biol. 1. 13

188 Potato Diseases

3. By planting not-diseased tubers that have been in contact
with diseased or not-diseased tubers from an infected soil.
4. By transference of soil from an infected area by some means
or other, even though actual disease be not present in that area.
Every possible precaution should of course be taken to prevent the
dissemination of these infective bodies, and the destruction of all
diseased material is a reasonable and sound requirement.
Questions naturally arise as to how the disease can be fought in situ
and the following issues need urgent attention :
1. The possibility of devising some treatment for sound tubers
raised on infected soils.
2. The experimental treatment of infected soils.
3. Extended experimental work with varieties possibly immune.
The subject of resistance to Chrysophlyctis is an extremely important
one. A high degree of resistance for certain varieties is claimed in the
Report issued by the Intelligence Division and it is stated therein that
the varieties when planted on infected land in several districts proved
highly resistant. This matter needs keen attention under more searching
experimental conditions in different localities and seasons.

The Phytophthora problem.

Although Phytophthora infestans is still the cause of the greatest
financial loss through actual damage to the potato harvest in Great
Britain, and in spite of the mass of literature that has arisen in connection
with this subject, several important matters still need urgent attention.
Of these, the manner in which the infection of the potato crop is
occasioned each year, will be first considered.

Marshall Ward! held the view, by analogy with the behaviour of
many rust fungi, that the mycelium of the fungus could remain dormant
in the tuber through the winter and bring about infection in the following
season :

‘“ More commonly however the tubers are beginning to ripen when
the hyphae reach them and the mycelium goes to sleep—passes into a
dormant state—-between the cells of the ripening tuber.”

. is not necessarily restricted
to mean mycelium hibernating in tubers showing disease, but admits
the presence of mycelium in healthy tubers. Hence Marshall Ward

b

The expression “ dormant mycelium ’

1 H. Marshall Ward in Diseases of Plants, p. 75.

A. S. Horne 189

advised that potatoes should never be saved for seed from plants of a
diseased crop.

Massee! adopted and elaborated this theory claiming that outbreaks
of Phytophthora and epidemics over wide areas are due to hibernating
mycelium. He was led to the peculiar view of the wholesale migration
of mycelium from the parent tuber to its own offspring:

“The great bulk of disease is due to hibernating mycelium against
which no remedy is known.” “I have proved by repeated experiments
that when a diseased tuber is planted, the mycelium from such tuber
passes into the young potatoes which also become diseased.”

“The produce of a diseased tuber is always diseased.” “ Potatoes
from a crop known to be diseased should never be used for seed.”

These authors were committed to a most pessimistic outlook upon
the whole problem.

Now as a matter of fact, sections of healthy tubers invariably fail
to show the mycelium of Phytophthora in its accustomed place—the
air spaces—whiist microtome preparations through the junction of
diseased and healthy tissue, show that the mycelium present in the
diseased portion ceases at the boundary line between the two. The
question of dormant mycelium in the sense used by Marshall Ward, there-
fore, passes beyond the pale of argument or controversy. The conclusion
is reached that the disease is not carried by entirely healthy tubers unless
the mycelium reside saprophytically in the skin, and of this there exists
no positive evidence. Attention should therefore be concentrated upon
diseased tubers no matter how slightly diseased, as a means of causing
an epidemic. The first question that naturally arises is this, can
the mycelium present in diseased tubers maintain itself through the
winter until the planting season begins? Pethybridge states definitely
that it can and the writer can confirm his statement so that a positive
answer must be returned. Secondly, does this fact explain the infection
of crops each season ? Upon planting diseased tubers the fungus might
be returned in a living condition to the soil and remain there to infect
the young tubers, but no evidence has been obtained on this point.
On the other hand, the fungus might pass from the planted tubers to
the young shoot. The evidence available in this connection leaves
much to be desired.

Massee2 claims to have found Phytophthora present upon shoots
originating from diseased sets presumed to contain this fungus.

1G. Massee in Diseases of Cultivated Plants and Trees, p. 125.
2 G. Massee in Kew Bull., 4 (1906).

190 Potato Diseases

Pethybridge! found that one plant out of nine raised from diseased sets,
planted in a cool greenhouse “ produced a shoot only 2 or 3 inches high
which quickly became diseased from below upwards and soon died.
Doubtless the mycelium had entered the shoot from the parent set.”
The plant was removed but Phytophthora was subsequently detected
on several plants in this house. Pethybridge states “ although
absolute proof is lacking, it seems practically certain that the plants
whose foliage became diseased must have become infected by means of
‘spores’ from the single diseased sprout sent above ground by one
of the diseased sets.” It is not made evident from the description
that Phytophthora had been actually observed upon this single diseased
shoot and its upward course from the tuber traced, so that the experi-
ment as described does not demonstrate that the fungus developed with
the developing sprout. This important point still needs to be settled and
evidence obtained from experiments in greenhouses would need to be
supported by evidence from extensive field experiments.

That diseased tubers may produce healthy plants is a matter of
common knowledge. The crucial question in relation to the infection
of crops is whether and, if so, in what proportion, will diseased tubers
yield diseased plants. A single diseased plant as everyone knows
becomes a centre of infection and the possible source of an epidemic,
since the fungus possesses the power of rapid growth, rapid sporulation
and the spores are rapidly disseminated. It is important to realise
that a single diseased plant in, say, a twenty-acre field of potatoes
might start an epidemic. What then are the chances for, or against,
the occurrence of one bad plant in a twenty-acre field ? Results which
show complete failure to obtain Phytophthora in the aerial parts
produced by diseased potatoes must be received with some reserve,
owing to the small number of tubers planted and since information is
usually lacking as to whether the fungus was actually observed or
demonstrated to be living or even present in the tubers when planted.

There are of course other possible methods whereby an outbreak in
spring might be occasioned but these have either no positive evidence in
favour of them or they have not yet been investigated.

Payen? in 1853 records that he had observed Botrytis infestans on
the tomato and since Payen’s time the fungus has also been recorded
as occurring upon various wild Solanums. According to Howard §.

1 G. H. Pethybridge in Sci. Proc. Roy. Dub. Soc., x1 (N.S.), No. 2 (1911), p. 21.
2 Payen in Des maladies des pommes de terre. Paris (1853).

A. S. Horne 191

Reed?! (1912) the Phytophthora of tomato is identical with that of the
potato. The formation of conidia upon hosts other than the potato
may therefore prove to be a source of infection and the cause of an
epidemic.

A very attractive solution appeared to be in the possible discovery
of and wide occurrence of sexually-formed resting spores such as occur
in the related fungus Pythium. Oospores of Phytophthora are now
known, and chiefly owing to the work of Clinton? who obtained them,
in pure cultures of the fungus in artificial media. In spite of diligent
and persistent search by numerous investigators, oospores, however,
have not yet been discovered within or upon the potato plant so that
they do not appear to be formed upon this particular host. There seems
to be no reason, of course, why oospores should not be found upon
some other host and be discharged to the soil from the host, but no
extensive study in this connection has yet been made.

Another point that needs to be determined is whether the mycelium
of Phytophthora can maintain existence in the soil from the autumn
until the following potato-growing season, either parasitically in the
many small potatoes remaining in the soil or saprophytically in frag-
ments of tuber and pieces of skin.

Another phase of the Phytophthora problem must now be con-
sidered—the actual occurrence and mode of occurrence of the disease.

Infection of the foliage may be brought about in two ways. Firstly,
the mycelium present in a planted diseased tuber might extend into
the growing sprout and thence into the leaves and infect them. Secondly,
the leaves might be directly infected by means of conidia, wind borne
or brought by some other means. In this case the zoospores liberated
from the conidia germinate forming mycelium which enters the tissue
of the leaf and causes it to droop and die. Spraying when properly
performed has been found an efficient remedy against the premature
death of the foliage ; the disease is checked and the growth of the
plant is actually stimulated.

Tuber infection also may be brought about in two ways. Firstly,
in the case of plants with infected foliage the mycelium could extend
into and along the vascular bundles ultimately reaching the growing
tubers, but this method does not appear to be of frequent occurrence.
Secondly, the growing tubers might be attacked directly from the soil.
Irrefutable evidence of the frequent occurrence of this mode of infection

1 Howard 8. Reed in Phyt. 1. (1912), p. 250.
2G. P. Clinton in Science, N.S. xxxiv (1911), p. 744.

192 Potato Diseases

may be obtained by scanning diseased tubers in the field when they are
lifted. In such cases the following points furnish a guide : (1) the stalk-
end of the tuber when cut across may be entirely without discolouration,
(2) the brown marks in the flesh of the tuber caused by the fungus,
frequently do not extend from the skin as far inward as the principal
cylinder of vascular bundles, (3) the brown shallow areas of diseased
tissue near the skin are often quite isolated and sometimes limited to
the neighbourhood of an eye.
The subterranean attack might be occasioned by :

(1) Mycehum, if it exists.

(2) Oospores, if they exist.

(3) Zoospores.

‘ 2
Fig. 1. External view of tuber attacked by Phytophthora from the soil.
Fig. 2. Healthy tuber with clean skin for comparison with Fig. 1.

As already stated no evidence has yet been obtained relating to the
presence of mycelium or oospores in the soil. With regard to zoospores,
it may be fairly reasoned that if the foliage is attacked, the conidia
formed on the leaves can be carried by the wind and distributed not
only to neighbouring plants but on the surface of the soil. During
a period of heavy rain the conidia or zoospores would be carried into
the soil and eventually reach the surface of the tuber and penetrate it.
This matter still needs adequate experimental proof.

One of the chief puzzles afforded by the Phytophthora problem is
afforded by the case of field crops which are badly diseased when lifted

‘

A. S. HORNE 193

although no disease had been detected in the foliage. An instance
occurred in 1909, on a large field in Durham County. I observed no
Phytophthora on the foliage during the season, but at the lifting, there
were very few plants without one or more diseased tubers (Fig. 1). The
uniform infection of the field seemed extraordinary. It could be ac-
counted for in three possible ways :

(1) Phytophthora may have been present on the plant, but in-
conspicuous and escaped observation.

(2) The soil may have become infected with wind-blown conidia
from some potato field in a neighbouring farm.

(3) The soil may have been infected with mycelium or oospores,
if such do exist in the soil.

Fig. 3. Tuber cut cpen to show the brown rot caused hy Phytophthora.

The whole Phytophthora problem needs very careful study with a
view to determining whether there is or is not a definite soil-factor,
occasioned by the power of the fungus to rest or live in the soil. If it
can be shown that there is not, the prospect of eradicating the disease
is not hopeless since effort could be concentrated in the selection of seed
tubers and widespread and efficient treatment of the foliage.

A third line of enquiry which relates to the conditions that favour
the development of the blight fungus and involves two issues—(1)
blighted tubers, (2) blighted foliage—will be pursued in a later paper.

194 Potato Diseases

Sprain.

Sprain has caused considerable loss to potato-growers within the
last few years, affecting certain varieties in the field crop, often rendering
the yield practically unsaleable.

Sprain includes two forms of tuber-disease— blotch (internal disease)
and streak (sprain) which have not yet been proved identical. Blotch,
under the name internal disease, is reported to have been under investi-
gation by Marshall Ward nearly twenty years ago but I have been
informed by Prof. Seward that Marshall Ward left no records of such
investigation. ‘The word sprain, as used in the north, is applied to
tubers with internal, brown, streak-like markings. This word has been
adopted by the Board of Agriculture to include both blotch and streak.

Fig. 4. Section of a tuber showing internal disease or blotch.

Under the name of Buntwerden or Eisenfleckigkeit, sprain has long
been known on the continent of Hurope and recognised as a distinct
disease not caused by fungal organisms. In Britain blotch and streak
were supposed by some authors to be either directly or indirectly due
to the late blight fungus and by others to the dry rot organisms. These
suppositions, however, as the writer! has recently shown, cannot be
upheld.

The importance of ascertaining whether the disease is caused by an
organism from the practical point of view is evident since the question
of the infection of crops is involved. Disease might arise from planting
diseased tubers or owing to the presence or transference of infected
soil, Frank considered that Buntwerden was due to the prevailing
conditions of soil and climate but his point of view is founded upon the

! A. S. Horne in Jour. Agric. Science, m1, Pt. 3 (1910).

A. S. Horne 195

apparent absence of an organism and insufficient experimental evidence.
There are three experimental methods of attacking the problem: (1)
that of analysis by means of field experiments, (2) that of attempting
to isolate pathogenic bacteria from diseased tubers, (3) that of analysis
of the bacterial flora of soils from “ sprained” areas. At present only
the first of these methods has been seriously adopted by the writer
with the following chief results :

(1) In four consecutive years a certain proportion of diseased
tubers was obtained in the yield from diseased sets upon every occasion
when diseased sets were planted, in Northumberland (1909, 1910),
Devonshire (1909-1910), Ireland (planted by Dr Pethybridge, 1910),
Chelsea (1911), and Wisley (1912).

(2) In the fifth year at Wisley (1913) no diseased tubers were
obtained in the yield from diseased sets.

(3) In 1909 the writer selected disease-free tubers of the Sutton
Flourball variety from a sack containing a high percentage of diseased
potatoes given to him for experimental purposes by Messrs Sutton.
The issue from these selected tubers has proved healthy in each suc-
cessive year—1909, Northumberland and Devon ; 1910, Northumberland,
Devon and Ireland; 1911, Chelsea; 1912, Wisley and Walton-on-
Thames (in sprained soil); 1913, Wisley.

(4) Disease-free tubers of the susceptible variety, Duke of York
obtained from a locality where sprain is absent, yielded a diseased crop
when planted upon “sprained” land, at three different stations in
Scotland in 1911.

(5) Tubers selected disease-free from the produce raised in
~ Scotland in 1911, yielded only a few diseased tubers at Wisley and none
at Oxshott in 1912 and none at Wisley in 1913—but in this season
diseased sets produced healthy tubers.

It is clear that “ sprain” is influenced a great deal by conditions of
soil and weather, but it is by no means certain that it is entirely due to
these conditions as Frank supposed. Analyses of soils from different
centres where considerable harm had been done to the potato crop by
internal disease showed that they were exceptionally poor in phosphates,
potash and lime, being moorish, sandy soils, but sprain is by no means
confined to such soil, and moreover selected tubers of susceptible varie-
ties when planted experimentally on similar soils have not taken the
disease. It is exceedingly difficult to interpret all the evidence entirely
on a physiological basis. But the evidence is not at all incompatible
with the theory of the existence of an organism-factor—the organism

196 Potato Diseases

being of bacterial nature. The apparently conflicting evidence, such
as is production of a healthy crop from susceptible varieties upon
“sprained ” land and the occurrence of healthy issue from diseased
tubers, is paralleled among the organism-caused diseases. Thus the
potato crop including that obtained from the susceptible varieties may
not be appreciably affected by the canker organism although this parasite
is actually present in the soil, whilst the production of healthy plants
and potatoes from sets affected with Phytophthora is, as I have already
stated, of common occurrence. The failure to obtain sprain in the
vegetative generations proceeding from tubers originally selected as
disease-free from diseased stock of susceptible varieties when planted
in soils of several kinds in different localities seems opposed to a purely
physiological explanation.

5 6

Fig. 5. Section of a tuber showing sprain or streak.
Fig. 6. Another section of the same tuber.

Pending attempts to isolate pathogenic bacteria, additional evidence
might be gained by attempting to infect potatoes with sprain through
the agency of soil derived from lands liable to it.

In the meanwhile the best means of preventing loss through sprain
will be those which have certainly occurred to skilled potato-growers ;
firstly, to avoid as far as possible the use of “ sprained ” tubers for seed,
and secondly, to cultivate varieties which are the least susceptible to the
disease. The most thorough method of procedure would be to obtain an
accurate record of the distribution in Britain of the lands liable to sprain,
and to carry out potato trials in different localities where the disease is
most troublesome, with the object of discovering the most suitable and
relatively sprain-immune varieties for the district about each experi-
mental area.

A. S. HoRNE 197

Fusarium disease.

Two types of Fusarium disease are recognised by Orton’. The
first, Fusarium wilt, caused by Fusarium oaxysporium described by
Smith and Swingle in 1904, affects the field crop and is one of the most
serious diseases of the potato with which the United States has to deal.
According to Orton, there is no evidence that the Fusarium wilt occurs
in Kurope. Wollenweber? has been able to differentiate the Fusariwm
oxysporium of Smith and Swingle from other potato Fusaria and finds
it to be distinct from any Kuropean form. The second or dry rot
disease, according to Wollenweber’s investigations, appears. to be caused
by one or more species of Fusarium. The dry rot Fusaria do not, as
a rule, attack the tubers when in the soil, although they are certainly
present there as shown by Miss Dale*, who includes F. solani in the
fungus flora obtained by her from sandy soils. Miss 8. Longman4
records that Fusarium solani attacked the potato plant in experimental
plots at Reading in 1909, but cases appear to be of rare occurrence in
Britain.

Fusarium becomes evident in the potato pit or store especially
when potatoes are stored in a damp condition, a state of affairs often
difficult to avoid in some potato-growing districts. A crop that has
been attacked by Phytophthora or sprain is especially liable to suffer.

The question of the parasitism of Fusarium solani was fully discussed
by Pethybridge and Bowers? in 1908. These authors state it is quite
clear that the fungus is a true parasite capable of directly producing
the disease in absolutely healthy potato tubers. The disease can be
communicated therefore to healthy tubers in contact with diseased ones.
A similar conclusion was arrived at by Miss Longman.

Curl.

“This disease, so far as I can learn, first began to be alarming to
the growers of the potato, about thirty-five or forty years ago. Since
that time, it has continued to engage the attention of many eminent
agriculturists and gardeners ’’—Thomas Dickson, 6th March, 1810,
in Mem. Caled. Hort. Soc. 1 (1814).

W. A. Orton in U.S. Dept. Agric. Bur. Pl. Ind. Bull., No. 64 (1914).

H. W. Wollenweber in Phytopathology, v. 3, No. 1 (1918).

Elizabeth Dale in Ann. Myc. x, No. 5 (1912), p. 471.

Sibyl Longman in Jour. Linn. Soc. Bot., xxx1x (1909).

G. H. Pethybridge and E. H. Bowers in Econ. Proc. Roy. Dub. Soc., 1, Pt. 14 (1908).

ao ff. 6 NS =

198 Potato Diseases

“No plant disease in this generation has been the subject of such
general discussion as that known in Germany as the ‘ Blattrollkrank-
heit > herein named ‘ Leaf-roll.’. None has aroused greater difference
of opinion as to its nature and cause, and no other single malady of
plants is to-day receiving so much investigation by skilled pathologists

Fig. 7. Foliage froma plant of the President potato affected with curl showing the under
surface of the leaflet exposed owing to the curl, small brown blotches and dead
leaflet-ends.

as this. Possibly no disease which has appeared since the advent of
Phytophthora infestans in the forties presents a greater menace to potato
culture ’—W. A. Orton, Feb. 10, 1914 in U.S. Dept. Agric. Bur. Pl.
Ind. Bull., 64 (1914).

A. S. Horne 199

By far the most important case of curl recently recorded in Britain
has occurred in connection with the President potato, a variety imported
from Germany and Holland on several occasions during the last few
years. On land in the neighbourhood of Dunbar, the President yielded
an enormous crop—fifteen tons to the acre—-and produced only a small
percentage of bad plants. But in certain other localities, this variety
produced a high percentage of dwarfed plants with foliage of a lght
green colour or tinged with yellow or pink and leaves rolled upward
and frequently much blotched as already described by the writer!.
(Juanjer?, who has investigated curl in certain varieties in Holland, states
that the phloem strands in the stem of leaf-roll plants are shrunken and
henified so that the translocation of food material to the tubers is
interfered with. The bad plants produced by the President in Britain
produced an exceedingly small yield of very small tubers.

Curl has often been attributed to fungi and notably Fusarium,
Verticillium, and Macrosporium. Thus Appel originally believed that
it was due to Fusarium and this view obtained for quite a considerable
time and is held still by some authorities, notably Kéch and Kormanth.

But abundant cases of leaf-roll have been recorded, as already
pointed out by Sorauer, including the present case of the President,
where no fungi are present. Macrosporium was present in the blotched
fohage of the President, in the potato field in 1910, but since blotched
foliage of a similar nature was produced in localities where Macrosporium
was entirely absent from the plants, the disease could not be attributed
to this or any other fungus.

It was next necessary to establish to what extent, if any, the condi-
tion of the foliage in bad plants might be brought about by injurious
insects. Accordingly a joint enquiry into the subject was instituted
by Professor H. Maxwell Lefroy and the writer, and yielded results
which show that although the insect factor is of more importance in
relation to diseased foliage than has-been hitherto supposed, neverthe-
less this particular malady is not caused by insects.

But considerable light was thrown on the probable nature of the
disease during the study of the plants raised from seed of the President
for the purpose of insect infestations by Professor Lefroy and the writer
at the Royal Horticultural Society’s gardens, Wisley (1912—1913-1914),
the Chelsea Physic Garden (1911-1912), and at Messrs Sutton’s trial
grounds, Reading (1912), and evidence was obtained which points

1 A. 8. Horne in Jour. Roy. Hort. Soc. xxxvi, p. 618 (1911).
2 H. M. Quanjer in Med. van de Rijks Hoogere Land-, Tuinen Bosch., Deel vi (1913).

200 Potato Diseases

conclusively to the non-parasitic nature of the disease. Hence the
question of infection does not occur.

A similar conclusion has been reached by W. A. Orton from a study
of leaf-roll in seedling varieties in the United States.

Professor Lefroy and the writer found that the seedling plants used
for infestations exhibited considerable variability not only in the habit,
shape of leaf, and other external characters but in physiological charac-
ters as evidenced by selection by the White Fly (Aleurodes) and by the
uneven response exhibited by the plants when under similar experimental
conditions. These physiological characters are not in any way associated
with particular external plant features. The tubers themselves, as the
writer! has pointed out, also exhibit considerable variability in shape,
kind of eye, and other characters, whilst Doby” has recently shown that
tubers from plants affected with leaf-roll give a higher reaction with
respect to oxidase, peroxidase, and tyrosinase; also they had a slightly
higher ash content and less starch and protein.

Taking everything into consideration it is very evident, firstly, that
physiological variability plays an important role in the curl problem,
and secondly, conditions of culture. There appear to be certain optima
that favour the production of good plants, as at Dunbar in 1910, below
these optima the percentage of bad plants increases. Pathological
symptoms are the outward expression of the response made by particular
plants to conditions which do not suit them.

The value of selection under the circumstances must now be con-
sidered. In the course of recent experiments, at Wisley, small tubers,
whether from good or bad plants, produced bad plants as a rule—tubers
from bad plants being usually small, produced bad plants. Of greater
importance, however, was the result obtained from tubers that had been
specially selected as desirable for seed purposes, obtained from the Dunbar
ground which produced a heavy crop in 1910. These tubers produced
both good and bad plants and a high percentage of the latter. The
occurrence of bad plants, however, did not bear any relation to any
particular characters of the tubers which produced them. Selection
becomes, therefore, an exceedingly difficult matter, since there appear
to be no external tuber-characters that can be used as a guide in selecting
favourable physiological plant-characters. Selection on the basis of
favourable external characters (shallow eyes, etc.) leaves entirely to
chance the selection of favourable internal properties.

1 A. S. Horne in Jour. Roy. Hort, Soc., xxx1x (1914), p. 596.
2G. Doby in Zeit. fiir Pflanzenkrankheiten, Bd. xxt, xx (1911, 1912).

A. 8S. HoRNE 201

For this reason the percentage of bad plants obtained through a
particular stock of the President might be greater than that obtained
through the use of another stock and the total yield proportionally less—
other conditions being similar.

Canker.

Owing to the serious notice given to potato canker, in a recent
Bulletin issued by the United States Department of Agriculture,
investigators in Great Britain may be compelled to devote considerable
attention to this disease, although as already pointed out by the writer,
the worst cases in this country are to be found in ill-kept gardens, whilst
comparatively little damage is done to the potato harvest by canker.
The tubers in the field crops are sometimes scabby but the scab is often
less noticeable than the brown scab of unknown origin prevalent in
many parts of the country. I. EH. Melhus!, the author of the United
States Bulletin, devotes little attention to the comparatively trivial
damage caused by the canker organism in Britain whilst prominence
is given to the statements of serious damage to the potatoes in Ireland.

In Ireland canker is reported as causing considerable loss to the
potato crop. Johnson? states “ I have no doubt myself, that this Spongo-
spora scab has a good deal to do with the miserable average yield per
acre of potatoes in the west of Ireland. It is in some districts of Ireland
as injurious to potatoes as finger-and-toe in Turnips,” and Pethybridge®
writes of the attacks caused by Spongospora, “ they were particularly
disastrous on those portions of the land which for special purposes have
now been cropped for four successive seasons with potatoes, the can-
kerous form of the disease being extremely common.”

Giissow4 with regard to canker in Canada states “ the disease should
by no means be regarded lightly. Severe attacks occur when potatoes
are planted year after year in infected land.” ‘The disease was also
regarded seriously by Pole-Evans, in a circular issued by the Transvaal
Department of Agriculture in 1910.

Pethybridge and Giissow specially note the occurrence of canker in
land that has been cropped year after year for potatoes and it seems
clear, from the published accounts of its occurrence in Ireland, that the

1 |. E. Melhus in U.S. Dept. Agric. Bur. Pl. Ind. Bull., No. 82 (April 6, 1914).

2 'T. Johnson in Econ. Proc. Roy. Dub. Soc., 1 (1908), p. 453.

3G. H. Pethybridge in Jour. Dept. Africa. Tech. Instruc. Ireland, x1, No. 3 (1913),
p. 16.

4H. 'T. Giissow in Phytopathology, v, 3, No. 1.

202 Potato Diseases

disease in its worst form occurs in poor or badly cultivated land and
is favoured by the wetness of the season. These points should
be borne in mind in attempting to arrive at an estimate of the
relative importance of the canker disease from an economic stand-
point, and to avoid the danger of unduly exaggerating the danger of
canker. It is surely undesirable that the potato industry in Britain
should suffer more than absolutely necessary, and that other countries
should lose by rejecting British-grown potatoes for seed which still rank
amongst the finest in the world.

E

Fig. 8. Wart stage of potato canker.

Nevertheless the point of view and the attitude of investigators in
the United States must receive consideration. Melhus points out that
scabbiness is a more serious handicap in the American markets than in
those of European countries, and further states that “ If powdery scab
(canker) should prove no more troublesome in the United States than it

A. 8S. Horne 203

has been up to the present in Europe, it would be rated as a disease of
secondary importance as compared with late-blight or with Fusarium
wilt. But there are reasons for fearing that it may become more pre-
valent here. ...It quite often occurs that introduced parasites are more
destructive in a new habitat than in their native environment. Likewise
it is not impossible that Spongospora may find the American varieties
of potato more susceptible than the European sorts.”

The prevalence of canker in many European countries and the
Dominion of Canada has prompted the Department of Agriculture in
the United States to extend for a time the Quarantine on foreign potatoes.
The attitude-of the United States in this matter may render it advisable
to ascertain the distribution of canker in Britain as in the case of the
tumour parasite, but statistics would be difficult to obtain and the process
of recording would need to be spread over several years for numerous
and obvious reasons.

The symptoms of canker have already been fully described by the
writer’, The organism Spongospora solani Brunchorst, as in the case
of Chrysophlyctis, can rest in the soil and there seems little immediate
prospect of arriving at a soil remedy. Both organisms form resting
bodies which are said to be capable of remaining for many years in the
soil, but whether there is any other mode of subterranean existence is
as yet quite unknown. Neither is it known exactly how the process of
infection is carried out, whilst we are almost entirely ignorant of the
conditions that favour or inhibit infection.

Some varieties of potato, which are more susceptible than others
in a certain district, in other districts may be almost immune. There-
fore generalisations from experiments in one locality only should be
avoided and tests established at several experimental stations.

+ A. 8. Horne in Jour. Roy. Hort. Soc. xxxvm (1911).

Ann. Biol. t. 14

A NOTE ON CELERY LEAF-SPOT DISEASE.
By We. CHITTENDEN Eis:

Tue disease of celery known as leaf-spot, rust, or blight, due to the
attack of the fungus Septoria petroselini var. apw B. and C., has spread
with alarming rapidity over this country since it was first definitely
recognised here in 19061.

An account of the disease and its spread, with notes on the fungus
that causes it and its distribution in Europe and America, are given in
the Journal of the Royal Horticultural Society? and it is there shown
that much of the commercial “ seed ”’ offered for sale is infected with
the fungus. The small black fruits of the fungus appear on the walls
of the celery “ seeds’ and the pieces of stem to which they are attached
with considerable frequency and may be readily seen by the aid of a
lens. Experimental cultivation from fresh seed proved the contained
spores to be viable and Klebahn showed? that spraying healthy plants
with the washings from affected seeds led to the infection of the plants
with the disease.

The author was led to suspect the seed as the principal, if not the
only source of infection, by the curious distribution of the earlier
attacks, the incidence of the disease on certain strains of celery, the
absence of any records of attack upon wild plants, and the fact that so
far as enquiry showed, the seeds from which the diseased plants had been
raised had been purchased from one or two sources. Against it was the
fact that all the earlier attacks had been noticed late in the year, gener-
ally from September onwards, though one or two attacks had been
seen in July. At this season the disease had obtained such a hold upon
the plants that spraying methods proved almost entirely inadequate
to prevent its spread and total loss of crop frequently resulted. Later,
attacks of a slighter nature were noticed nearer the beginning of the
growing season and spraying with Bordeaux mixture at frequent intervals

1 Chittenden, F. J. Journal R.HWS., xxxu (1907), p. exii.
* Chittenden, ¥. J. Celery Leaf-Spot, Journal R.H.S., xxxvu (1911), p. 115.
3 Klebahn, H. Krankheiten des Selleries, Zetts. f. Pflanzenkr. (1910), p. 4.

F. J. CHITTENDEN « AOS

mitigated the severity of the attack!, and in some cases proved a perfect
cure.

When the paper on “ Celery Leaf-Spot ” appeared we were in pos-
session of the knowledge that the disease was due to the fungus Septoria
petroselini var. apii B. and C., that it was spreading rapidly and in a
fashion that could best be explained on the assumption that the seed
carried infection, that the “seed?” frequently showed the fruits of
the fungus, that these fruits contained spores capable of germinating,
and that plants sprayed with water containing these spores succumbed
to the disease, but the actual infection of the seedlings from infected
seeds had not been observed. We have recently been able to demon-
strate this infection and to place this on record is the object of this
note.

Seed showing the fungus fruits containing spores was sown in the
ordinary way and the germination kept under observation. It was
found that in many cases the pericarp remained attached to the coty-
ledons for a considerable time after they emerged from the soil and
became green, and that many of the cotyledons turned yellow owing
to the attack of the fungus which quickly produced fruit containing
the typical spores. Only those seedlings which had grown from seed
showing the fungus were ‘attacked at this time and the pieces of peri-
carp attached to the diseased cotyledons showed the fungus quite clearly.
Side by side with the diseased seedlings were others which were at this
stage perfectly free from attack and which were developed from healthy
seed. The chain of evidence that the seed carries the infection is there-
fore complete.

Whether there are any other modes by which the fungus maintains
its infective powers from season to season, as, e.g. on diseased portions
of plants thrown on the rubbish heap or dug into the ground, is not
clear, but it is clearly a point of economic importance that seed-growers
should take every care to save seed only from healthy plants. If this
were consistently done the author feels sure it would do much to mitigate
the severity of the attacks and it would probably result in stamping
out the disease entirely.

The disease appears to spread more slowly during the seedling stage
than later in the season and the attack is more localised on the plant.
Diseased plants in September usually show the fruits of the fungus

1 See for instance Salmon, E., in Gard. Chron. 1913.
2 Tt ought perhaps to be noted that the commercial celery “‘ seed” really consists of
fruits or half fruits and therefore carries parts of the parent plant readily open to attack.

206 A Note on Celery Leaf-Spot Disease

dotted very closely over the whole of the diseased leaves which become
dull blackish-green in consequence, but the seedlings show, both on
cotyledons and on foliage leaves, yellow spots extending to the leaf
margin bearing the small black fruits of the fungus, and contrasting
markedly with the bright green of the healthy parts of the foliage.

When the matter was first enquired into about 40 °% of the commer-
cial ‘seed’ samples examined showed the presence of the fungus,
now the percentage has risen to 90°. The attention of seed-growers
and seedsmen in this country has been called to the extent to which the
infection has reached, and the danger to the crop from sowing seed
containing even a small number of infected “ seeds,” and it is to be
hoped that they will endeavour to produce “ seed ” free from infection.
Experiments have been begun to see whether the fungus can be killed
by immersing the “ seed” in fungicides, as it no doubt can, and it has
been shown that consistent attention to spraying with Bordeaux
mixture (much more easily and safely carried out on plants grown for
seed than in the growing of celery for market) will control the disease.
It seems, therefore, probable that seed-growers have it within their
power to provide their customers with clean seed.

It may be added that Celeriac, too, has fallen victim to the disease
with increasing frequency during the past two years.

207

NOTES.

A MEETING of the Association was held in London on April 17th
and 18th. Some of the papers read at the meeting appear in this issue
and a complete list is attached. We regret that no complete account
of the meeting has appeared in any paper but the accident which befell
the Honorary Secretary three days before the meeting upset the arrange-
ments including those made for reporting the papers and discussions.
The chair was taken by the President, Professor Newstead, F.R.S., and
after the election of members the following papers were read :—

Dr H. T. Gissow. The Organism of Common Potato Scab. In the absence of
the author this was read by Mr A. G. L. Rogers.

Mr A. S. Horne. Potato Diseases.

Professor E. 8S. Satmon. Observations on the Perithecial Stage of the American
Gooseberry Mildew (Sphaerotheca mors-uvae).

Professor Percy Groom. Brown Oak.

Mr A. G. L. Rogers. The Phytopathological Conference.

Mr E. Harareaves. The Life-history and Habits of Alewrodes vaporariorum.

Professor R. 8S. MacDovuaeatu. Hylastes palliatus and its rank as a Forest Enemy.

Mr E. E. Green read a recently published bulletin of the United States Department
of Agriculture entitled *“* Economic Points in regard to the Migratory Habits of
the House Fly.”

Mr J. W. Munro. A Braconid Parasite of Hylobius abietis.

Mr F. J. Carrrenpen. A Note on Celery Leaf-Spot Disease.

Mr H. Wormatp. A Bacterial Rot of Celery.

Mr R. A. Warpte. Life-history Notes on two previously unrecorded Parasites
of the Large Larch Sawfly.

Mr A. W. Westrop. The Golf-green Maggot.

The PRESIDENT communicated a note by Mr A. D. WALKER on ‘“‘ The Migrations
of the Coccinellidae.”’

The Scope of the Annals.
The Annals of Applied Biology has been founded to publish the

scientific papers of the members of the Association and to represent
as far as may be their interests. Its scope is as wide as the membership
of the Association and we are not desirous of its falling into the narrow

208 Notes

rut of one limited subject. How wide its interests are to be, how exten-
sive its scope, depends upon its contributors. We will endeavour to
ensure the Annals reaching all who are interested in the subjects dealt
with and we are securing a wide circulation outside our actual members.

We have already stated that purely systematic work in any group
does not come within its scope; nor does the enumeration of the flora
or fauna of defined areas ; both are very amply provided for. We do
however invite contributions in all branches of Applied Biology and
efforts will be made to ensure that the Annals reach all centres of
research in the subjects these papers deal with.

There is no desire to encroach on the spheres of influence of other
journals and among our members are those who contribute to these
journals ; we hope that papers will be read at the meetings which will
perhaps be published in the Journal of Agricultural Science or elsewhere ;
the Association does not claim the right to publish in the Annals all
papers read at its meetings and we shall find a wide scope for the
Annals without encroaching on the scope of other publications. We
do hope that the range of subjects of our meetings and of our members
may be so wide as to include workers in every branch of Economic
Biology, whether they contribute to the Annals or not, and that the
distinction between the scope of the meetings and membership and
that of the Annals may be recognised.

The Association.

At the last meeting forty new members were elected; there are,
however, at least twice the total of our members in workers in Applied
Biology who might reasonably be expected to become members. We
hope that a large proportion of the potential members will become
actual members: if our membership really embraces a large majority
of workers and teachers in the Empire, the Association benefits, the
individual member benefits and when the need comes, we may reason-
ably hope to be able to represent the interests of the whole body or of
the individual in a satisfactory manner; we do not propose to invite
members to strike ; we are not a trade union; we do not even propose
to discuss the rewards given to scientists by the state, a subject that
has considerably exercised a few prominent scientific men lately ; but
a really representative Association is needed and can exert an influence
attainable in no other way.

We hope also that the Association may be a focus for ideas and

Notes 209

knowledge ; that members in distant parts of the Empire will send
us notes and papers; that the originality developed by dealing with
new problems may find expression in our Annals ; and that we in
England may be stimulated by the progressiveness of the Dominions
and stirred by their newer and more thorough ways of tackling problems,
born of the stress of circumstances of new lands. We are, in England,
too prosperous, too peaceful, too settled ; we are not at grips with
problems that count ; if one crop fails, another succeeds ; we have not
staked our all on a crop of apples nor does American Blight or Codlin
moth really matter, bad though they are; nor if it does matter, can
we apparently stir up any interest in getting anything done ; so we in
England take things easily, we have practically no legislation, every
man may disseminate disease from his neglected garden and, in a great
deal, we must look to the Colonies to give us a lead.

With this invitation we expect all who have interests common with
our members here to join, and we look for support from all who are
solving the big problems of applied biology and who can learn from the
experience of others and with their own experience help others who have
similar problems to work out.

Migration of Ladybirds.

The following note by Mr A. D. Walker, was read by Professor
Newstead at the last meeting of the Association :

The following fact in the bionomics of the common “ Ladybird ”
(Coccinella) may interest you.

Mrs Walker’s bedroom has three windows, two facing south and one
east. Since 8 a.m. to-day something like 100 Ladybirds have been
taken on the east window only—none on the two south windows, except
a few on the one next to the east end. The same thing happens every
year—always the east window! It is not because of east winds for
the winds here lately have been predominantly southerly and this
morning there was a “ moderate gale” from W.S.W.

There are roses trained both on south and east sides, so their presence
will not account for Coccinella’s preference for the latter.

The only way I can see to account for it is that there must be a
spring migration from the continent. Our house, standing on the
top of a fairly steep slope to the east, on which side there is a valley,
would be a conspicuous obstacle to the insects flying across it. But it
is curious that they should be so abundant this year when there has

210 Notes

been so little east wind and that with so much southerly wind, they
should not strike the long south side of the house. It looks as if they
could only cross the channel at the Strait of Dover which hes east from
us; also that they can fly “on a wind ’—+.e. with a side wind.
Another migration note. Last November countless flocks of Wood
Pigeons flew over the great Kings Wood here. Some, perhaps all,
stopped to have a feed of acorns but nearly all flew on to the west to
become such a plague in Wilts and Dorset, that they have had armies
of men with guns to shoot them. Here I can say with confidence that I
have not seen a dozen since Christmas, though constantly in Kings Wood!
Surely this is a blind migratory impulse like that of the Lemmings !

Westminster Hall Roof.

The fine timber roof of Westminster Hall has suffered great damage
from the attack of the larger timber-boring beetle, Xestobiwm tesselatum.

A committee has been meeting to advise the Office of Works and an
investigation into the beetle has been commenced by Mr J. W. Munro
at the Imperial College of Science and Technology. We refer to this
since the preservation of this roof is really a matter of national interest
and because members of the Association may be able to materially assist
if they can help Mr Munro to get infested timber. Naturally the timber
in the roof cannot be cut to provide material for experiment and a large
supply of beetles and timber is an essential for testing the many possible
lines of treatment that have been proposed. It is curious how little is
known of this beetle and one very essential fact is not apparently de-
finitely known, whether the beetles emerge from the wood or whether
they can continue reproducing inside the large timbers, only emerging
if they wish to. It might be easy to prevent the re-entry of beetles
if they had to emerge, but, as it is, no treatment to the outside of the
wood only can be adopted for fear it might keep them inside and intensify
the damage. It is probable that a satisfactory treatment will be found. -

Notes.

We shall be glad to receive notes on matters of current interest and
on investigations in progress for publication in these pages; it is an
accident that the notes in this issue are mainly of entomological interest ;
all members of the editorial Committee will be glad of short contributions
which may be sent to them or to the General Editor direct. For the
notes in this issue the General Editor alone is responsible except where
stated.

Hi aM, al

VoLuME | JANUARY,..1915 Nos. 3 and 4

SOME DIFFICULTIES IN THE IMPROVEMENT OF
INDIAN SUGARCANES.

By C. A, BARBER, Disc:
(Imperial Department of Agriculture for India.)

(Plates XIJII—XVI and 3 Text-figures.)

Tue need for improving the class of sugarcanes grown in India has
long been recognised, and fitful efforts in this direction have been made
during the last hundred years or more. These efforts have, almost
uniformly, resulted in failure, chiefly owing to a lack of appreciation
of the factors involved. The subject has, however, again forced itself
on the attention of Government because of the steadily increasing
imports into India of Java sugar. There is, in India, a much larger
acreage under sugarcane than in any other country and it has been
not unreasonably maintained that there must be something wrong if
it cannot supply its own demand for sugar. The produce of the fields
is, however, so low that it is quite insufficient to meet the demands of
the growing population. 3

In approaching the problem anew, it has been considered advisable
to make a closer study of the canes themselves and the conditions of
soil and climate under which they grow than appears to have been done
before, and certain intrinsic difficulties have been met with which may
very easily account for former failures. Before considering these it
will be well to indicate briefly the conditions referred to. For the sake
of conciseness, it is convenient to divide the Indian sugarcane area into
two parts, a northern and a southern, as indicated in the accompanying
sketch-map. The southern portion, consisting of parts of Madras,
Mysore and Bombay, is on the whole well suited for sugarcane growing.
It is wholly within the tropics, the temperature is uniformly high
throughout the year and, in many places, the soil is good. The rainfall
is, however, of such a nature that irrigation is needed to supplement it.
India is not blessed with the well-distributed rainfall of tropical islands

Ann. Biol. 1 15

212 Improvement in Indian Sugarcanes

and, almost everywhere, there are long periods of drought, often extend-
ing for four or five months at a time. Where temperature and soil are
suitable, moistness is found to be a limiting factor. In the north, the

apy
Yin

Fey MN nye Seen

--

CENTRAL

o-

His ele

c=)

main sugarcane tract extends from Assam to the Panjab, along the foot
of the Himalayas, a distance of over 1000 miles. On comparing the
acreage of these northern and southern regions, it is found that the

C. A. BARBER 213

cane is much more thickly planted in the former, so that vastly the
greater part of the crop is grown in this northern region, constituting
an aggregate of something like 4000 square miles. This is entirely
outside the tropics. Moisture is adequate, by rain near the hills and a
complete network of canals farther south where, however, paddy is
no longer a serious rival. The soil is easily permeable, deep and rich,
but the total amount of warmth and especially the length of the growing
period are insufficient. The continuance of suitable high temperature
is the limiting factor here.

This difference in climate between the northern or continental
portion and the southern or peninsular has a marked influence on the
character of canes grown in the two regions. While the field canes in
Southern India are often comparable with those of tropical islands in
thickness and vigour, those of North India are much thinner, more
fibrous and much less productive of sugar in the crop. The canefields
look very different in the two tracts, as may be gathered from the photo-
graphs, those in Bengal standing intermediate between the extremes of
Madras and the Panjab. And, when the canes are carefully examined,
they are generally so unlike in morphological characters and habit that
it is worth while considering whether they have been derived from the
same ancestral species of Saccharum. These differences in climate and
character of the canes have a pronounced effect upon the whole course
of cultivation in the field and, while the cultivation of sugarcane in the
south is intensive and costly, the crop in the Gangetic plain has little
attention paid to it.

Judging by the periodic returns issued by Government, the area
under sugarcane remains more or less stationary, but, on the other hand,
the population is rapidly increasing. It is still doubtful whether the
diminution in poppy-growing will bring much more land under sugar-
cane, and although there are indications of extension in some localities,
there is no immediate prospect of any great increase in the area under
this crop. Improvement in production must therefore take the line of
increasing the yield per acre. With this object in view, a small depart-
ment has recently been opened by the Indian Government for the
general study of the sugarcanes of the country. There are, of course,
various ways in which the problem may be approached. Leaving
aside the whole question of improvement in agricultural practice, which
is now receiving a good deal of attention, the canes are seen to be
obviously inferior in character in North India, and it is natural to
consider whether success may not be obtained most rapidly and

15—2

214 Improvement in Indian Sugarcanes

economically by replacing them with better kinds. There are four
ways in which this may be attempted :—

(1) The introduction of exotic canes which have proved of value
elsewhere. This method has been the main line followed for many
years all over India, from Madras to Peshawar. Thick, tropical canes,
the relics of successive importations, are everywhere met with. But it
is generally found that these thick canes have not time to mature in
the north during the short, hot, moist period. They sometimes grow
surprisingly well and are full of juice, but the ripening process by which
the glucose is changed to crystallisable sucrose is arrested and, although
extensively used as fruit and eaten raw, these thick exotic canes are
generally useless for the manufacture of sugar. It is possible that
certain early maturing varieties may still be met with, or that changes
in treatment may lead to improvement along this line, and this is not
being lost sight of, but we have the advantage of actual demonstration
of their behaviour all over the country and the prospect of success is
not encouraging.

(2) The transfer of canes from one part of India to another. This
method of improvement is well known to the cultivator. He is not
only accustomed to the trial of new varieties valued elsewhere, but is
acquainted with the advantage of occasional change of seed in the same
variety. Exchanges of varieties are being actively carried on by the
Agricultural departments of the various Provinces and _ occasional
advantage accrues from this. Collections of different varieties of sugar-
cane growing together are a constant feature on local farms. The fine
new canes introduced into Madras through the Samalkota farm are now
to be met with in every part of India, even extending to the North-West
Frontier Province. But success along this line is limited and, in the
main, the introduced kinds cannot hold their own against the best
local kinds, the latter themselves being the outcome of centuries of
selection by the cultivators.

(3) The improvement of local canes by selection and the observation
of sports. This method has perhaps hardly received the attention
during recent years that it undoubtedly deserves, but there are special
difficulties in the way with a crop that can only be finally judged after
it has passed through the mill and been chemically analysed. The
sugarcane has, from time immemorial, been propagated by cuttings,
and it is difficult to determine whether chance variations in growth are
or are not due to better local treatment or feeding.

(4) The production of seedlings, This has been tried many times

C. A. BARBER 215

in India, but in the past always unsuccessfully. The experiments have
not always been conducted very carefully, and on the founding of the
new department it was decided to examine the matter afresh and try
to determine the cause of failure in the face of the successful results
obtained in Java, the West Indies and elsewhere. The solution of the
problem turned out to be remarkably simple. Almost all the experi-
ments were made in North India and it transpires that the stamens do
not mature and pollen is not formed in the cane flowers there. A
cursory glance showed that this was not the case in South India, and in
the Government farm opened at Coimbatore in the Madras Presidency
some 40,000 seedlings have been raised during the past two years.

Problem 1. During the short time that the cane-breeding station
has been in existence, a very important step in advance has been
taken and the first problem, that of obtaining seedlings, has been
solved. But in considering the ultimate aim of the station more care-
fully, a number of difficulties have cropped up and it is the intention in
the present paper to detail some of these further problems, in the hope
that help may be available from the great body of readers interested
in plant-breeding.

Problem 2. Most, if not all, of the difficulties in procuring suitable
cane seedlings have arisen from the fact that the flowering is irregular—
in fact, comparatively rare. If a cane flowers and we obtain seedlings
from it, we cannot count on these seedlings flowering. We have no
means at present of inducing the canes we are most interested in to
flower. Control of the flowering is the second difficulty we have
encountered.

Arrowing of the cane, as the production of the inflorescence is
called, is comparatively rare in North India, but occasionally it occurs
over large areas. It is viewed with alarm in certain regions, and there
appears to be some reason for connecting it with the weather and
especially with a failure of the normal rains. Flowering of the sugar-
cane appears to be commoner in years of drought, but details on this
point are not yet available. In Mysore and Coimbatore, typically dry
tracts, flowering is common, and on the other Madras farms where sugar-
cane is grown, in Malabar, Godavari and South Arcot, the amount of
flowering seems to vary inversely with the moistness of the climate.
On the other hand, it is a common belief among Coimbatore cultivators
that arrowing is most frequent in water-logged conditions of the roots.
Experiments are now being conducted on the farm with different
soils and different amounts of moisture to see if any effect is produced,

216 Improvement in Indian Sugarcanes

for it is felt that, until some control of flowering is obtained, working
along Mendelian lines is more or less out of the question. If the sup-
position of the Coimbatore ryots is correct, it would seem to indicate
that flowering ensues whenever the flow of sap is interfered with, whether
by the paucity of water or the unhealthiness of the root system.

Problem 3. Another matter which has attracted our attention 1s
that there appears to be a very close relation between richness and
purity of juice and vigour of growth. The first requisite in a seedling
cane is a high percentage of sucrose and purity of juice, but the total
quantity of sugar is what is aimed at in the field, and this will obviously
depend upon vigour of growth and the number and size of millable canes
in the crop. The first year’s seedlings when analysed and weighed
showed a markedly converse relation between purity and vigour. The
smallest and most meagre plants had the richest juice and those seedlings
which were distinguished by the abnormal vigour of seedlings were
very poor indeed in sucrose content. Richness and purity, if dependent
on lack of vigour, may to all intents and purposes be regarded as a
diseased condition and, if so, must be very carefully distinguished from
purity and richness which are inherent and varietal. Among my
colleagues, Mr Parnell has drawn my attention to a similar relation in
indigo seedlings between meagre leaf production and richness in indigotin,
and Mr Anstead states that, in analyses made by him of individual
rubber trees in South Indian plantations, the latex richest in rubber was
obtained from poorly grown or stunted trees.

Problem 4. One important line of work in the cane-breeding station
is the selection of suitable parents and inducing them to flower together.
But, even if we are successful in this, we are confronted with another
serious difficulty. How shall we determine if seedlings obtained are
really crosses? We can approach this problem either directly or
indirectly. In the first place we may actually cross the two varieties
with scientific precautions against self-fertilisation. This has been
successfully carried out in Barbados for several years. In Coimbatore
there are special difficulties in the way. The bulk of the canes arrow
during the heart of the north-east monsoon, a period of violent winds
and torrential rains. As the long stalk of the inflorescence (arrow) is
very easily damaged and the slightest bend appears to cause it to wither,
we have to erect over each arrow a gallows-like support, with a hanging
iron cage covered with muslin—much after the plan adopted in Java.
The difficulties in crossing such inflorescences can be readily imagined.
There are an enormous number of flowers on each arrow and the male

C. A. BARBER 917

and female organs mature at practically the same time. For certain
crossing it will be necessary to emasculate all the flowers of one parent
arrow. ven if we succeed in cutting off the majority of the flowers
without injuring the rest, each experiment would mean the erection of
a lofty staging with practically a glasshouse at the top in which an
assistant could use a dissecting microscope. The state of the weather
would usually render futile any less cumbrous arrangement. This is
at present out of the question. Certain, direct crossing does not at
present appear to be feasible at Coimbatore and, added to this, the
outlook for such work is discouraging because the results obtained at
Barbados appear to have been unsatisfactory, one after another of the
carefully nurtured crosses having been abandoned on being tested
in the field.

There are two ways which suggest themselves of approaching the
problem of obtaining known crosses indirectly. It has been noted that
the different cultivated varieties of sugarcane vary a great deal in the
development of their essential organs. Some have never been observed
to flower: others have flowers which do not emerge from the en-
veloping sheaths: yet others have partial or total sterility in male
(or female?) organs, while a number produce healthy arrows with good
pollen and fertile ovules. The commonest case at Coimbatore is that
only a certain percentage of stamens open. If we could obtain a variety
in which no pollen is formed at all or no stamens open (and there seems
to be a close relation between the two, stamens which do not open not
containing fully formed pollen and the converse), crossing that variety
with one producing good pollen would be easy. One or two such cases
have already been observed and crosses obtained, but these happen to
be of little value from the economic point of view. The best local cane
at Coimbatore, the ‘Vellai,’ arrows freely every year but produces
comparatively little good pollen. Advantage has been taken of this
during the past year to pollinate this variety with about a dozen others,
in the hope of obtaining crosses between them. The withered flowers
of each arrow are kept and carefully analysed as to the percentage of
open anthers, and the probability of obtaining crosses or selfed seedlings
is calculated therefrom. But, unfortunately, some open anthers are
always noted (often about 2 °%) in Vellai, and we shall have to depend
on further study of the seedlings before we can definitely say whether
we have been successful.

A second way of approaching the problem indirectly is opened for
us by the fact, now observed for two years, that certain varieties produce

218 Improvement in Indian Sugarcanes

many seedlings, when selfed, which, however, die off at a very early
stage. In one case 13 survived out of 4000 in the first year, and a
hundred or two out of 10,000 in the second. This would appear to be
a varietal character, and two other kinds appear to share this peculiarity.
It is, therefore, proposed to pollinate these three, if possible, from other
good kinds during the next season on the chance of obtaining a more
vigorous lot of seedlings. If we succeed in raising thereby a large number
of vigorous seedlings, it may be safely assumed that the bulk of them will
be crosses.

Problem 5. It has been suggested that it may be possible to decide
the parentage of seedlings by observing their subsequent habit and
growth, but we shall require for this purpose a very complete knowledge
_ of the morphological differences of the parents. The problem of classi-
fying the canes thus acquires additional importance. Considerable
progress has been made in this direction during the past year and a
half. A remarkable number of minute distinguishing characters have
been recorded in examining the different canes collected, although this
work is still far from complete. A few of these characters may be
mentioned here and those interested in the subject are referred to a
paper on ‘‘ The Panjab Canes” about to be published as a Memoir of the
Indian Agricultural Department. In this paper a summary of the
chief characters studied up to date is given, in order to explain the
descriptions of the canes figured.

The habit of the cane as it strikes the eye appears to be extremely
important and characteristic. Its erectness, tillering power, shooting
of buds, rooting at aerial nodes, leaf angle and leaf endings, as well as
liability to be attacked by certain fungi, form useful determining
characters. The joint (made up of a node and the internode above it)
varies in thickness, length, shape, number, growth curve (the relative
length and thickness in different parts), ovalness, hardness of rind,
quantity of fibre, juiciness, richness and other properties of the juice,
colour, waxy bloom and relative development of leaf scar, circlet of
hairs, root zone, growth ring, bloom band, etc., in different varieties.
The bud presents important details as to shape, size, mode of bursting,
flanges (lateral expansions of basal scales), vestiture in bristles, basal
patches of hairs and minute black hairs. The lamina, leaf-sheath and
ligule all show similar acts of diagnostic characters, in which various
types of hairs play an important part, the leaf-sheath especially pre-
senting a surprising number of differences. As a result of this minute
morphological examination of the canes, there appears to be some

C. A. BARBER 219

prospect of arranging the Indian canes into a series of alliances, although
it is not always possible to determine whether similar canes from

= : Minute
z black hairs
Cushion-..... £< ZA y) =:-\------. Basal
= \ patches
\

Torn leaf scar |
Fig. 8.
different localities are permanently separable or merely local varieties

induced by their special surroundings. A natural system of classifica-
tion is being attempted in which the members of the different groups

Iie, Bh

resemble one another in as many as possible of the characters referred
to above. In such a system agricultural, botanical and chemical
characters will all have a place.

Problem 6. The question now naturally arises, are these characters

220 Improvement in Indian Sugarcanes

constant in different localities and under diverse conditions? What
stability is to be expected in such minute vegetative separating marks
and what are the limits of variability, especially in quantitative char-
acters? There is no doubt that the sugarcane responds very readily
to change of habitat. This fact will increase the scope of the detailed
study described in the last section, in that the same varieties must be
studied for several successive seasons both in North India and at
Coimbatore. We already know of characters which are unstable in
certain varieties under changed conditions, although they appear to
vary less in others. The ivory markings in the joint are usually a good
character, but in some kinds of cane they are readily affected by changes
in climate (moisture?). The colour of the cane has been observed to
change in some varieties in transfer. Canes which appear to be im-
mune to fungus attacks in one district are at once attacked and des-
troyed by the same species of fungus in another. There are a number of
other characters which have been noted as varying in this way, and it
is possible that, while firmly fixed in certain kinds of cane, they are
variable in others. These facts will naturally increase our difficulties
when we attempt to trace the characters of any parent in a seedling by
observing its morphological characters. But, in consideration of the
facts noted in the next paragraph, it will be seen that these difficulties
are greatly increased.

Problem 7. Of what value are the characters noted above in
separating seedling canes? Are any of the minute differences observed

in varieties propagated vegetatively handed down unaltered in seedlings -

derived from them? At present there is not sufficient material avail-
able to answer these questions. But one of the most obvious features
in any batch of seedling canes from a common parentage is the extra-
ordinary amount of variation among them. And this is especially
noticeable in those characters of habit which appear to be so stable
and valuable in varieties in the field. The seedlings appear to differ in
every direction—habit, joint, colour, leaf, juice, etc. We have already
collected a certain amount of material for the detailed study of this
question. Last year we obtained 70-80 seedlings from Strakarchynia
(a thin Behar cane) fertilised by Saccharum spontaneum; 13 from
Chin (a thin U.P. cane) also fertilised by Saccharum spontaneum, and
71 selfed seedlings of Saretha (a thicker cane of the U.P.). As far as
time has permitted, a detailed study has been made of these seedlings
and the descriptions of them recorded, and it is hoped that, when
these descriptions are analysed, some useful facts may be obtained.
One difficulty is encountered, however, in our inability to apply the

No

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NOS. 3 AND 4 PLATE XIII

Fig. 2. A canefield in Madras.

‘sie

Fig. 3. A canefield in Behar.

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NOS. 8 AND 4 PLATE XIV

sa es SS eS
Stee 2h np eat Re 2

< a sat cg Mak ME T= cas Be :
ia a A Ms ca tebe

Fig. 4. A canefield in the Panjab.

“%

.
-
tik
i
~
-
‘
cc an
>
¢ _ =
¢ \/ 7 vy
1 Ad

e P " ~~ ena
ia

THE ANNALS OF APPLIED BIOLOGY. VOL. |, NOS. 8 AND 4 PLATE XV

Fig. 6. Cane arrows, left Vellai, right Ashy Mauritius, middle Saccharum narenga.

Fig. 7, Arrows protected from casual pollination,

XVI

PLATE

| NOS. 3 AND 4

VOL

THE ANNALS OF APPLIED BIOLOGY

—————— eS

C. A. BARBER 221

stereotyped description of cultivated canes (Saccharum officinarum) to
the wild Saccharum spontaneum, for this species is regularly propagated
by seed all over India, and the seedlings appear to vary so much among
themselves in certain characters that individuals may be placed in
almost all the groups already marked out among the cultivated forms.
This, however, is a fact not without its significance in our efforts to trace
these cultivated forms from Saccharum spontaneum itself.

The attempt to determine the parentage of seedlings by their
morphological characters of their vegetative parts is thus beset with
difficulties, and these are not decreased by the possibility of many
characters being intermediate or recessive in the offspring.

Taking these uncertainties into consideration—and there are,
naturally, many chemical and agricultural ones not yet fully grasped—
the main line of work in the cane-breeding station for the present lies
in the direction of selecting suitable parents, preserving the healthy
ofispring of the best of these, analysing the juice after the first year’s
growth and observing the relative vigour of growth and choosing the
best for further observation—a narrowing circle in which ultimately
a few of the best all-round will remain to be sent to the chain of agri-
cultural stations in the north for a renewed series of tests there before
dissemination among the cultivators. In all cases it will be our aim to
cross good North Indian canes with good South Indian or Exotics, and
in the case of the former the importance is recognised of choosing one
parent which is largely grown and valued in the particular part of
India to which it is intended to send the resulting seedling for trial.

EXPLANATION OF FIGURES.

Fig. 1. Map of India indicating roughly the northern and southern tracts over which
sugarcane is grown. The acreage under cane is ten times as great in the northern
region as in the southern.

Fig. 2. A modern canefield in Madras.

Fig. 3. A good canefield in Behar.

Fig. 4: A good canefield in the Panjab.

Fig. 5. Cane seedlings at the Cane-breeding Station at Coimbatore.

Fig. 6. Cane arrows, in left of Vellai, in right of Ashy Mauritius. In the middle, the
arrow of Saccharum narenga.

Fig. 7. Arrows protected from casual pollination (at a village ten miles from the cane-
breeding station).

Fig. 8. A typical sugarcane bud.

Fig. 9. Various forms of sugarcane buds.

Fig. 10. Saretha cane in the field—a moderately thick North Indian variety—with
very characteristic, erect and ascending shoots.

Fig. 11. Selfed seedlings of Saretha cane. These vary from strict, erect to absolutely
prostrate seedlings. The latter are seen in the foreground (left) and the prostrate
habit is fixed in all descendants produced vegetatively from them.

THE PEA THRIPS (KAKOTHRIPS ROBUSTUS).

By CC. B. WILLIAMS. B.AL Eis:

(The John Innes Horticultural Institution, Merton, Surrey.)

(With 12 Text-figures.)

CONTENTS.
PAGE
Introduction and history : : : : c : : 222
Species and synonomy . : : : 224

Habits of adult. Appearance, sexes, pairing, parthenogenesis, flight,
food, oviposition

The Egg .

Larval stages .

Pupal stages : : :

Distribution. British Isles, abroad .

Nature of damage

Food plants. 5 : : :

Other thrips found on peas and beans

Www rye wv
rare ©

H
Co ow

5b bo bt b& bo bo bt bs bs bo
= ww
—) fr)

Natural enemies : : : : 41

Effect of rain, soil, varieties, time of planting 42

Control, sprays, rotation, soil fumigation ‘ : : : : 243

Methods of collecting and breeding ‘ ‘ ; : 3 : 244

Summary : ; C : : : : : f ; : 245

Bibliography . : : : - ° : < , : : 245
History.

ALTHOUGH no doubt damage has been caused to peas and beans for
many years by thrips, apparently the first record of such an occurrence
is found in 1871 when A. Miillert describes shortly, without however
mentioning any locality, an attack on peas, which was certainly due
to the species here discussed.

In 1880 Westwood gives a much fuller account of an attack at
Oxford, with figures of the damaged flowers and characteristically
curled pods. He gives the name Thrips pisivora to the black-tailed
yellow larvae, which were in numbers on the damaged plants, under
the impression that they were the adult females, and only just mentions

1 All references will be found under author and year in the Bibliography at the end.

CG. B. WILLIAMS 75

the real adult as a black winged form which he supposes to be the
male! As his name was given to the larval stage it has to be given up
in favour of Uzel’s name of fifteen years later.

In 1890 Kirchner shortly described damage to peas in Germany
as due to Thrips cerealium. This, name, however, was at that time
used to designate any Thysanoptera, and, as in 1897, he figures the
orange black-tailed larva, there is no doubt that he was dealing with
the present species.

In 1895 Uzel described Physopus robusta occurring in various flowers
in Bohemia.

In 1898 the Board of Agriculture of England published a leaflet
(revised in 1905) entitled Pea and Bean Thrips, Thrips pisivora, in
which an account is given of damage to field and garden peas and
beans and also to scarlet runner beans (Phaseolus vulgaris). A copy of
two of Westwood’s figures is given and an account of the life-history
which is either due to mistaken observations or else should apply to
some other species. It is stated that the eggs are loose in the flowers,
that the nymph or pupal stages are found in the flowers and that the
insect hibernates as an adult. This latter belief, which has become
very widely spread, has caused many entomologists to recommend the
burning of the pea sticks during the winter, a proceeding which, as will
be seen, is quite useless.

In 1899 Trybom gave a very full account of a bad attack by the larvae
of Physopus robusta on peas near Stockholm and in Ostergotland in
Sweden. The attack was worst at the end of July and became so bad
that the whole plot had to be dug up and burnt. The larvae were
found in the bunches of unopened leaves at the growing points and
caused these to shrivel up; they attacked the pods, causing them to
discolour and curl. Eggs were found embedded in the tissue of the
plant at the bases of the young leaves and stipules. No pupae were
seen nor were any obtained by keeping the larva in captivity.

In 1900 Theobald described an attack of Thrips in scarlet runners
(Phaseolus vulgaris) at Crawley, Sussex. This must have been due to
some other species, as he does not mention the dark tail to the larva
and found the pupal stages in the flowers and also that the adults
hibernated. From the figures it would appear to be a species of Frank-
liniella and may be F. intonsa which I have found commonly in scarlet
runners. In 1906 and 1907 the same author gives accounts of attacks
on peas which were undoubtedly due to K. robustus.

In 1908 Warburton published an account of this pest and described

224. The Pea Thrips (Kakothrips robustus)

the eggs which he found embedded in the tissue of the stamen
sheath. He also believed that the insect hibernated in the adult stage.
He suggests as a remedy ‘topping’ the plants as is done in beans for
‘black-fly,’ as he found that the topmost shoots were most badly
attacked.

In 1913 I myself gave a preliminary account of the life-history, show-
ing that it is single brooded and passes the winter as a full fed larva in
the soil beneath the infested plants.

In 1914 Vuillet (ii) described a Chalcid Thripoctenus brui n. sp.
which he found among larvae and adults of the pea thrips in France
and which he believes to be parasitic on it.

Recently [Williams, 1914] I have separated the species robustus
from the genus Frankliniella and have erected for it a new genus Kako-
thrips on characters which will be given later. There are several
shorter or less important references which will be discussed as occasion
arises.

SPECIES AND SYNONOMY.

Although several different species of thrips may at times be found
in peas and beans, there is one in particular which seems always to be
present in large numbers when any severe damage is recorded. This
is at present known to systematists as Kakothrips robusta. It belongs
to the family Thripidae of the sub-order Terebrantia of the Thysanoptera.

To the unaided eve it appears as a minute black insect about a
twelfth of an inch (2 mm.) long, linear, more or less pointed at each
end, with short slender antennae. There is a lighter band across the
thorax due to the bases of the wings being pale coloured. The lighter
rings on the abdomen described by several authors are merely the
soft and lighter coloured connecting membrane between the abdominal
segments which shows when the body is distended, usually by killing
in alcohol.

As the literature on the Thysanoptera is very scattered and often
difficult to obtain, the following notes on the characters of the family
and sub-order are given:—the sub-order Terebrantia is chiefly char-
acterised, and may be easily recognised, by having the terminal segments
of the abdomen more or less constricted to a point (in the Twubulifera
the tenth segment is tubular), by having a saw-like ovipositor in the
female and two longitudinal veins more or less distinct in the front
wing. The family’ Thripidae has the antennae six to eight segmented
and the ovipositor of the female curved downwards.

C. B. WILLIAMS 29

Genus Kakothrips Williams 1914.

Characterised as follows:—antennae eight segmented, maxillary palps three
segmented. Labial palps two segmented. Ocellar spines between the posterior
ocelli. Fore vein of the front wing set regularly throughout its whole length with
spines. Short lateral processes on each side of the eighth abdominal segment in the
male, curving backwards and upwards ; rudimentary but distinguishable in the female.
Larva with 9th and 10th abdominal segments dark coloured.

Type K. robustus (Uzel 1895).

The characters in italics distinguish it from the genus Frankliniella!
Karny, to which it is closely allied.

Kakothrips robustus.

— Miller 1871.

Thrips pisivora Westwood 1880. Board of Agriculture leaflet 1898 and 1905.
Theobald 1900, 1906, 1907. Collinge 1906. Warburton 1908.

Thrips cerealium Kirchner 1890, 1898.

Physopus robusta Uzel 1895. Trybom 1899. Buffa 1907.

Thrips physapus von Schilling 1898.

Euthrips robusta Bagnall 1908.

Frankliniella robusta Williams 1913. Vuillet 1914.

Kakothrips robustus Williams 1914.

Female (Fig. 1).

Measurements. Head, length 0-170 mm., width 0-190 mm.; prothorax, length
0-200 mm., width 0-250 mm.; pterothorax, length 0-380 mm., width 0-340 mm. ;
abdomen, length (not extended) about 1:10 mm., width 0-40 mm.; wing, length
(from tip of basal lobe) 1-15 mm., width (about half-way along) 0-09 mm.

Antennae ] 2, 3 4 5 6 Ui 8
length () 2A Oe Omen dO Sen Las
width (1) A030 2 Gee One 2 LO) 8

Total body length of living specimen 1-85 mm. (usually 2 mm. or over in speci-
mens killed in alcohol), antennae 0-4 mm.

Colour. Whole body, legs and antennae dark brown, except for the third and
base of fourth antennal segments, the tarsi and fore tibiae, which are paler. Fore
wings heavily tinged with brown, lighter at the base, hind wings almost trans-
parent.

Head broader than long, cheeks almost parallel. Hyes dark not protruding.
Ocelli present, forming an equilateral triangle; crescents distinct. Two small setae
in front of the anterior ocellus and one on each side near the margin of the eye.

1 Uzel’s Physopus (= KHuthrips Hinds) was split up by Karny (1907) into five genera,
one of which was Physapus. This name being already occupied it was changed (Karny
1910) to Frankliniella, The type of this latter genus is F. intonsa Trybom (=F. vulgatis-
simus Uzel).

226 The Pea Thrips (WKakothrips robustus)

The two long ocellar spines are between the posterior ocelli. A long spine behind
each eye and two pairs of short ones in a row between these. A few short forwardly
directed spines on the cheeks. Faint striations near the hind margin of the head.
Mouth cone short and rounded, reaching about three-fifths across the prosternum.
Maxillary palps three segmented, the second segment shorter and the third longer
than the first. Labial palps two segmented, the basal joint very short. Antennae
more than twice as long as the head; the Ist segment short and broad, barrel-
shaped; the 2nd broad and truncate at apex; 3rd the longest with short pedicel
and dorsal forked trichome; 4th spindle-shaped slightly broader at the apex than
at the base, with ventral forked trichome; 5th narrowing slightly in the distal third

Fig. 1. Kakothrips robustus. Female.

and then truncate; 6th spindle-shaped; 7th shorter and broader than 8th. Colour:
1 and 2 dark, 3 and basal half of 4 light yellowish-brown, apical half of 4 and 5, 6,
7 and 8 dark.

Prothorax wider than long and longer and wider than the head. Two long
spines at each hind angle and one at each front angle, also two not quite so long on
the front margin, and four or five pairs of short ones on the hind margin, the inner
pair being longer and stouter than the others. A few minute setae scattered over
the pronotum. Very faint striations near the hind margin. Plerothorax large,
front angles rounded. Legs normal, all tarsi yellow, fore tibiae paler than femora.
The small projection on the front tarsus noted by Uzel (1895, Fig. 55) is not always
distinct. ‘Two rows of stout spines on the hind tibiae. Wings reaching to the ninth
abdominal segment. Fore wings clouded with brown except at the base; 25-30

C. B. WILLIAMS 227

spines on the costa, 17-20 on the fore vein, and 13-16 on the hind vein. Hind wings
clear, the single vein indistinct but distinguishable to near the tip of the wing.

Abdomen. The ventral pleurites pectinate posteriorly. A very short pro-
jection on each side of the eighth abdominal segment (corresponding in position to
the much larger ones in the male). A row of short pointed tooth-like projections on
the hind margin of the eighth tergite. The tenth segment longer than the ninth
and split dorsally for about three-quarters of its length from behind.

Male (Fig. 2).

About one-sixth smaller than the female. All the antennal segments, especially
the first two, much paler than in the female. On each side of the eighth segment is
a short process curving backwards and upwards and ending in a blunt point. The

SPRINT

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Oo, OF eS

eteeniealen

Fig. 2. Kakothrips robustus. Male. a, outlines of two forms of clear areas on the
third to seventh abdominal sternites.

transparent areas on the 3rd—7th sternites are elongate, but vary slightly in outline
as shown in Fig. 2a. Otherwise similar to the female.

Uzel’s type specimen is in the Bohemian Landes Museums, Prep. No. 13, but as

there is no doubt as to the identity of the species the above description has been made
from British specimens.

Separation from Frankliniella intonsa.

The only other closely allied species which occurs in peas and beans
and with which the pea thrips might be confused is Frankliniella
intonsa. This can, however, be distinguished by the absence of the

Ann. Biol. 1 16

228 The Pea Thrips (Kakothrips robustus)

lateral processes on the abdomen in either sex and by the following
other characters:

K. robustus. | F. intonsa.

Size larger 1°85 mm. Size smaller 1°3 mm.

Colour very dark in both sexes. _ Colour slightly paler in female, male
| light.
|

3rd and base of 4th antennal segments 3rd, 4th and base of 5th light.
light. |

Long ocellar spines between the Long ocellar spines between the
posterior ocelli. posterior and anterior ocelli.

3rd and 10th abdominal segments | 10th abdominal segment longer than
equal in length. | 9th.

HABITS OF ADULT.

Time of appearance. In the south of England the adult insects
usually appear from the middle to the end of May. The earliest date
‘ observed in 1912 was the 28th May, in 1913 23rd May, and in 1914 the
16th May. Several correspondents speak of damage due to ‘Thrip’
earlier than this but have never been able to supply me with specimens.
In the north of England it is later; in Sweden (Trybom) adults were
first noticed on the Ist July, while, on the other hand, Gaumont and
Vuillet (1914) found it in France at the end of March.

The first specimens are found in the terminal clusters of unopened
leaves and in the just opening flowers. Specimens collected at this
time contain a large number, sometimes even a majority of males (e.g.
16. v.’14 Merton, 9 gd 499 in flowers of Viera faber). Later in the
year the proportion of males becomes smaller and they soon disappear.
With the exception of one dead specimen found at the beginning of
August (Kendal, Westmorland) I have found no males after the end
of June and, indeed, very few after the middle of this month. The
females, on the other hand, gradually increase in numbers to about the
middle of June (later in the north) and remain more or less common
till towards the end of July, and may be found on into August together
with full fed larvae on late sown peas. Bagnall (1908) found them in
Scabious flowers in Durham as late as “ August and September.”

The males are more active than the females and escape more rapidly
from the flowers when disturbed. The females are often very sluggish
and do not leave the shelter of the flower unless this is pulled to pieces.

A female was kept in captivity for over a month and then only died
by accident. It is probable that they live much longer than this.

C. B. WILLIAMS 229

Pairing takes place in the manner usually found in this group. It
has been described and figured by Buffa (1907, p. 48) for Aeolothrips
fasciata. The male climbs on the back of the female with its front legs
on the thorax of the latter and the end of its abdomen curled under-
neath that of the female.

Parthenogenesis. Although the males are quite common early in
the year and pairing has been observed to take place, yet the eggs are
quite capable of developing parthenogenetically ; eggs laid by a female
bred in captivity and known not to have paired developed in the normal
manner. In many other species of Thysanoptera parthenogenesis is
quite normal, in some the male being still unknown.

The adults do not readily take to flight and when they are forced to
do so it is usually only for a very short distance. I have no evidence
as to whether they are capable of long sustained flight and migration,
such as is the case with the corn thrips (Limothrips cerealium).

The food of the adults consists, like that of the larvae, of the juices
of the plant, which are taken in by a piercing and rasping action of the
three stylets in the mouth. They usually confine themselves to the
soft tissue inside the flower and also suck the pollen.

The actual act of oviposition has not been observed in this species,
but in a closely allied species Taeniothrips primulae, which lays more
openly in the leaves and flower-stalks of the primrose (Primula vulgaris),
it seems likely that the egg flows gradually into the slit made by the
ovipositor similar to the method recently described for a sawfly by
Chapman (Trans. Ent. Soc. Lond., 1914, p. 173). Although the egg
is very large compared with the size of the insect, it could not be seen
to pass in bulk into the prepared slit.

THE Eee (Figs. 3, 4 and 5).

The egg is, as is typical for this family, soft, opaque white and more
or less bean-shaped but varies slightly in contour, sometimes the head
end being more projecting (Fig. 3). It is 0-35 mm. long x 0-25 mm.
broad and is large compared with the size of the parent. It is
laid embedded in the tissue of the plant, in a slit made by the
ovipositor. The slit is at an angle to the surface and the posterior
end of the egg is at the bottom, while the anterior (head) end is at the
opening quite visible from the surface and often projecting slightly
above it.

By far the greater number of eggs are laid in the outer surface of
the sheath round the stigma or young pod formed, in leguminous

162

230 The Pea Thrips (WKakothrips robustus)

plants, by the united stamens. This ‘stamen-sheath’ is very soft and
succulent and forms a very suitable environment for the soft egg and
also food for the freshly emerged larva. As many as 70 eggs have
been counted in a single stamen sheath of Vicia faber.

Eggs are also laid, in smaller numbers, in the young developing pod,
chiefly at the apex, where it projects beyond the stamen-sheath, or at
the base where there is an entrance to the interior between. the two edges
of the sheath; in the petals (keel, aleae, and rarely standard); in the
calyx; and also in the young shoots and leaves in the terminal clusters.
This latter situation seems to be rare in this country; I have only

Fig. 3. Eggs. Much enlarged.

Fig. 4. Eggs in stamen-sheath of
Pea. Diagram.

found a very few eggs there, but Trybom (1899) mentions it as the
chief place of oviposition in the attack he observed in Sweden.

About five to seven days after being laid two red eye-spots appear
at the head end of the egg. These, as pointed out by Warburton
(1908), make the egg quite conspicuous in the pale yellowish-green of
the stamen-sheath. Two or three days later (total 7-10 days) the
young larva emerges.

LARVAL STAGES.
First stage larva (Fig. 6).

The young larva as it emerges from the egg has the antennae bent
down below the head, but either before or just after freeing itself from
the shell they take up the normal position. The larva is now about

C. B. WILLIAMS ei

0-5 mm. long, semi-transparent white; the abdomen being unexpanded
the legs appear very large in comparison, the hind legs reaching back
almost to the tip of the abdomen. The abdomen extends rapidly on

ae
S

S
IK
Vn! '~

4

Fig. 5. Micro-photograph of stamen-sheath of Fig. 6. First stage larva.
broad bean with eggs of pea thrips. x 6. Sp. = spiracle.

feeding and the last two abdominal segments begin to darken. After
two or three days the body colour changes gradually to orange but does
not become so bright as in the next stage.

The Pea Thrips (Kakothrips robustus)

Description of first stage larva.
Measurements. Total length varies from 0-5 mm. when just hatched to 1-1 mm.
when about to cast its skin.

b of second stage larva.

Fig. 7. Antennae. a of first stage larva.

a of first stage larva.

Ninth and tenth abdominal segments.
b of second stage larva.

Fig. 8.

Width of head across eyes 0-080 mm.
Length of ninth abdominal segment 0-040 mm.

Length of tenth abdominal segment 0-060 mm.

Antennae 1 2 3 4 5 6
length (y) 18 28 40 54 12 30
width (p) al” 625) 26" 2a 12 9

Total length of antennae 0-18—0-2 mm.
Antennae (Fig. 7a) six segmented, the third and fourth segments divided by
narrow non-transparent rings into sub-segments. There are five or six of these

C. B. WILLIAMS 233

rings on the third segment and six on the fourth. The fourth segment is slightly
wider than the third.

The darkly coloured ninth abdominal tergite is about one-third shorter than the
tenth segment. On the hind margin of the ninth segment are six long spines (two
dorsal, two dorso-lateral, and two ventro-lateral and two short ventral ones), on the
tenth, six long and two short spines. The hind margin of the ninth tergite is fur-
nished with a number of small sharp teeth (Fig. 8 a).

L_~
_
~

Se
i mr

So
- |

t

| \

~
J
r

Fig. 9. Second stage larva. Sp. = spiracle.

The earliest date that I have found this stage was the 29th May 1914,
the latest 29th July 1913.

Hight or nine days after hatching the larva casts its skin and enters
on its second stage.

Second stage larva (Fig. 9).

This is about 1-6-1-8 mm. long, bright orange with the last two
segments of the abdomen dark brown. The head and legs are now
small compared with the much distended abdomen.

234 The Pea Thrips (Kakothrips robustus)

Description of second stage larva.

Measurements. Total length 1-4-1-8 mm.

Width of head across eyes 0-09 mm.

Length of ninth abdominal segment 0-08 mm.

Length of tenth abdominal segment 0-08 mm.

Antennae 1 2 3 4 5 6
length (x) 23 40 50-60 64 17 32
width (u) 32 29 28 2 7 12

Total length of antennae 0:20-0:24 mm.

Antennae (Fig. 7 b) six segmented, the third segment divided into five rings and
the fourth into six. The fourth segment slightly narrower than the third.

The dark coloured ninth abdominal segment equal in length to the tenth segment.
Near the hind margin of the ninth segment, in the position of the two most dorsal
spines in the first larva, are two short transparent processes about 0-040 mm. long
and rounded at the tip. On the tenth segment in a corresponding position are two
stouter processes of about the same length, but gradually narrowing from the base
to the apex which is sharp (Fig. 8 D).

The two stages are easily distinguished by the relative and absolute
lengths of the ninth and tenth abdominal segments, and by the stout
processes on these segments in the second stage which are only
represented by hairs in the first.

Both stages of the larvae are found in the flowers and on the develop-
ing pods, less commonly in the terminal leaf cluster; as the pod grows
and the petals fade and fall off they retire for shelter into the calyx,
which forms a cup round the base of the pod. If the larvae have been
sufficiently numerous to cause the pod to curl, they will be found chiefly
on the concave surface. Should the pod crack or be pierced by other
insects they may enter and produce on the inner surface the same
characteristic ‘silvering’ of the surface.

In about six days the second stage larva is full fed. It then descends
to the ground and goes beneath the surface to a depth of from three to
twelve inches where in some suitable crack or crevice it remains for the
rest of the year. There appears to be no attempt at the formation
of a cocoon or pupal cavity.

The earliest date in which larvae in captivity have entered the
earth was the 28th June (from eggs found on the 8th June), but larvae
from eggs laid in May must descend before this. The total time from
the laying of the egg to the descent of larva is about 24 days.

The larva remains without moving, in the position it has first taken
up, throughout the rest of the summer, autumn and winter until the
following spring when, sometimes during March, April or early May,
it changes into the propupa or first nymph stage.

©. B. WILuIAMs 235

PuPAL STAGES.

The Propupa.

This stage—in which the first wing rudiments should appear and in
which the antennae are still free—I have not yet seen. It apparently
lasts a very short time. In 1913 the only specimen which survived
fungus disease during the previous winter was still a larva when exam-
ined towards the end of April and by the middle of May had already
reached the pupal or second nymph stage. In the spring of 1914,

Fig. 10. Second nymph stage or pupa.

owing to an unfortunate misunderstanding, all my infected pots were
thrown away by a gardener, but prolonged searching, both by hand and
by means of the Berlese funnel, in the soil of a kitchen garden where
peas had been attacked the year before yielded many larvae up till
the 6th April and a single pupa on the 2nd May.

Pupa or second nymph (Fig. 10).

This stage is assumed during April or May. Normally it does not
move from the original position, but when disturbed it walks sluggishly
with frequent side to side rocking movements.

236 The Pea Thrips (Kakothrips robustus)

Description.

Colour. Head, thorax and abdomen shining orange-yellow. Antennae, legs and
wing cases more transparent and almost colourless. The last two abdominal seg-
ments are also pale and semi-transparent, not dark as in the larva. The eyes are
dark red-brown.

The antennae are laid back along the top of the head and reach to about the
middle of the pronotum; between them the ocelli are visible. The wing rudiments
reach to the seventh abdominal segment. The hind margin of the ninth abdominal
segment is produced into several long tooth-like processes. Two long spines near
each front angle of the prothorax, two near each hind angle, one near the middle of
each lateral margin and one pair on the hind margin. Length 1-6 mm. (measured
from life), broad in proportion.

The pupa darkens slightly before the emergence of the adult, but
the latter is still pale and soft on escaping. It remains alongside the
old pupal skin gradually hardening and darkening in colour for about
two days, after which it works its way through the soil to the surface
and is ready to start a new cycle of life and destruction.

The life-history of K. robustus as described above is very similar to
that of Taeniothrips (Euthrips) pyri, the pear thrips. This latter is
also single brooded, has two larval stages and spends the greater part
of the year as a full fed larva in the earth beneath the infested trees.
Stenothrips graminum, a species found on cereals in this country and on
the continent, also hibernates as a larva deep in the ground (Kurd-
jumov, 1913).

DISTRIBUTION.
British Isles.

I have received records or specimens from twenty-nine counties in
England, Wales and Ireland as shown in the map (Fig. 11) and below,
but so far have not any record for Scotland. I have received bags of
peas from a few localities in that country which were all quite free, and
Professor Macdougall, of Edinburgh, tells me that he knows of no record
of damage. It is probable, however, that it occurs at least in the
south as I had but few correspondents, and, as has been mentioned above,
the species occurs on the continent as far north as Sweden. Some of
the records below are based on only a few specimens. The districts
where it is numerous enough to do damage are chiefly in the south and
east; | have, however, one record of damage as far north as Cheshire.
The absence of records from counties in many cases only means that
I had no correspondents in that district and must not be taken to
imply the absence of the thrips from that district.

C. B. WILLIAMS 937

England.
Berkshire. Reading 1912.
Cambridge. Grantchester 1912, Wicken 1912, Cambridge 1914.
Cheshire. Hale* 1906, Neston 1912.
Cornwall. Lostwithiel 1913.
Derbyshire. Ludlow 1913.
Devonshire. Kingsbridge 1913.

© Probable.
@ Reported.
@® Widespread. Causes damage.

Fig. 11. Present known distribution of pea thrips in the British Isles.

Durham. Hart and Blaydon-on-Tyne (Bagnall 1908).

Essex (Theobald 1907). Witham 1913.

Hampshire. Romsey 1912, Brockenhurst 1912.

Herts. Penshanger 1912, 1913, Amersham and Berkamstead 1908*.

Huntingdon. St Ives 1912.

Kent (Theobald 1906). Sittingbourne 1912, Shoreham, near Seven-
oaks 1912, 1913, Maidstone 1913.

Tincoln. Burgh le Marsh 1913.

238 The Pea Thrips (Kakothrips robustus)

Middlesex. Richmond 1912.

Norfolk. Bessingham 1913.

Ozford. Walton Manor (Westwood 1880).

Shropshire. Near Shrewsbury 1913.

Stafford. Weston 1910*, Stoke-on-Trent 1910*.

Surrey. Reigate (Theobald 1906), Merton 1912, 1913, 1914.

Sussex. %Crawley (Theobald 1900), Hailsham 1912*, Ditchling 1912.

Warwick. Warwick 1907*, Lupworth 1908*.

Westmorland. Kirkby Stephen 1912, Kendal 1912.

Worcester (Theobald 1906). Walford-on-Avon, Evesham and Wor-
cester 1905*, Stourport 1907*, Redditch 1909*, Kidderminster and
Studley 1910*.

Yorkshire. Malton 1913.

[The records with an asterisk * were kindly furnished by Mr W. E.
Collinge. |

Wales.

Carnarvon. Pwllheli 1913.

Denbigh. Colwyn Bay 1913.

Treland.

Carlow. Bagenalstown 1913.

Cork. Rochestown 1913.-

Dublin. Glasnevin. I am informed that in 1897 a black active
thrips injurious to peas appeared in the botanic garden; it is almost
certainly this species.

Distribution abroad.

Bohemia (Uzel 1895).

France. Loiret, Darcy, Seine, Marseilles (Gaumont and Vuillet
1914).

Germany (Kirchner, von Schilling).

Italy (Bufia 1907).

Sweden. Stockholm, Ostergotland (Trybom 1899).

NATURE AND EXTENT oF DAMAGE.

The parts of the plant which suffer most from the ravages of this
insect are the young leaves in the terminal shoots, the flowers and the
pods. There is no record of the older leaves being attacked (cf. the
American bean thrips below). In this country the terminal shoots
appear to be infested only when the other situations are not available,

C. B. WILLIAMS

iw)

39

as on a very early attack (May) before the flowers are out, or later in the
year on late sown varieties. It was this type of injury that Trybom
(1899) describes as being most prevalent in Sweden, when the injuries
caused whole terminal clusters to wither. Later when the flowers are

Fig. 12. Pods and flowers of peas damaged by thrips.

attacked these shrivel up and turn brown and in bad cases no pod at
all may be formed. Usually, however, it is when the pods are small
that the damage is most noticeable; they are sickly, undersized and
curled and covered with very characteristic silvery brown areas where
the larvae have been feeding. These areas are generally near the base

240 The Pea Thrips (Kakothrips robustus)

or the tip of the pod, but often, when the pod is much curled, the whole
of the concave side may be ‘silvered’ (Fig. 12). The silvering is
due to the presence of air in the outer cell layers of the plant let in by
the sucking of the larvae.

The damage can be very extensive and occasionally the whole crop
is spoiled. A correspondent at Sevenoaks, Kent, speaks of “several
rows hopelessly ruined,” while another at Reading had to give up growing
beans because of the injury they suffered, but he unfortunately tried
peas instead.

Foop PLANTs.

The species seems to confine itself chiefly to the edible pea (Pisum
sativum) and the broad bean (Vicia faber) and their varieties. Both
field and garden crops may be attacked, but the latter seem to suffer
more frequently. This may be due to the fact that in fields there is
usually a rotation of crops, while in gardens the same crop is often
grown on the same plot or quite close by year after year. I have not
yet found this species on either sweet peas (Lathyrus odoratus) or
scarlet runner beans (Phaseolus vulgaris), though Gaumont and
Vuillet (1914) mention these as host plants in France. Thrips are
often abundant on both plants, especially the latter, but, in my exper!-
ence, always other species (chiefly Frankliniella intonsa, Thrips tabaci,
Thrips valida, Physothrips atrata), and I am inclined to think that
when damage is recorded on runner beans that it is due to one or more
of these species and not to Frankliniella robusta.

I have also found this species on flowers of knapweed (Centaurea
nigra) and both Uzel (1895) and Bagnall (1908) have taken it in flowers
of Scabiosa arvense. Gaumont and Vuillet (1914) mention also Medi-
cago sativa, Cujuga reptans, Ecbalium elaterium and Coronilla vulgaris ;
the two last do not occur in Britain.

OTHER SPECIES FOUND ON PEAS AND BEANS.

Aeolothripidae (Antennae 9-segmented).

Aeolothrips fasciatus. Common; easily recognised by its large size
and banded black and white wings. Partly carnivorous, but also feeds
on pollen and plant juice.

Melanothrips fuscus. Occasional; recognised by its large size and
smoky black wings with very distinct veins.

C. B. WILLIAMS 241

Thriprdae.

Frankliniella intonsa. See above (p. 227) for separation. Not
infrequent, often common in scarlet runners.

Physothrips spp. (atrata, vulgatissimus (pallipennis)). This genus,
which lacks the spine at the anterior angle of the prothorax, contains
many species which are only identified with difficulty.

Thrips tabaci. Antennae 7-segmented; colour varying from greyish-
yellow to brown; male lighter; common. I have found larvae and pupa
of this species on peas.

Thrips physapus. Antennae 7-segmented; colour brown; not
uncommon.

Thrips flava. Bright yellow; antennae 7-segmented. This species,
which is sometimes common in the flowers, also lays its eggs in the
stamen-sheath and other parts of the flower. The larva, however, has
not the dark tail which is characteristic of F. robusta. It usually
appears to be more common when the latter is absent, but I have never
found it sufficiently numerous to do any great damage. It also occurs
in scarlet runners and many wild flowers.

In the United States beans are much injured by Heliothrips fas-
ciatus, which, however, unlike the present species, attacks chiefly the
leaves and also spends all its life, including the pupal stages, openly
on the food plant, there being several generations during the year.
It hibernates as an adult (Russell 1912). Damage has also been re-
ported caused by Heliothrips phaseoli (Hood 1912). We have three
species of the genus Helvothrips in England, but all are confined to green-
houses; there would therefore appear to be little danger of the American
_ species establishing itself in this country.

Kirchner (1890) mentions a species, Thrips pisi (Kubler), which
would appear from its name to be connected with peas. I have, how-
ever, been unable to find the original or any other reference to this
name.

NATURAL ENEMIES.

Fungus. There was very great mortality of hibernated larvae
owing to a fungus which attacked them even in very dry conditions.
The hyphae radiated out from the attacked larvae and any other larvae
close by became infected in a short time.

Coccinellidae. I was able to feed larvae of Coccinella bipunctata in
captivity on larvae of the pea thrips, but in the wild state I have never

242 The Pea Thrips (Wakothrips robustus)

found the ladybird larvae in the infested flowers, and believe that they
exert little, if any, controlling influence.

Chaleidae. Vuillet (1914. 11) has recently described a Chaleid Thrip-
octenus brui n.sp., belonging to the Tetrastichinae, which he found
among the larva of the pea thrips at Darcy, Aisne, France, in July 1913.
Although he has not actually bred this Chalcid from the larvae, yet
there is little doubt that it does parasitise them as it was always found
in conjunction with them, and further the only other known species
of this genus (7. russelli) is parasitic on Heliothrips fasciatus, a species
which, as mentioned above, is injurious to beans in the United States.

Thripoctenus russell, or a closely related species, has been taken in
England by Bagnall (1914), but I have found no species of this genus
as yet among the pea thrips in this country. I have, however, found
on several occasions in different localities Chalcids among larvae of the
pea thrips, but cannot be certain whether they have any connection
with these or not. M. Vuillet has kindly offered to let me have some
living specimens of his species if he finds it in sufficient numbers,
and an attempt will be made to establish it here.

OTHER CONTROLLING FACTORS.

Weather. Wet weather always causes great mortality among thrips
and also causes the plants to grow more rapidly. In this species, un-
fortunately, the rain has less effect than usual owing to the sheltered
position of the insect in the flowers. However, several correspondents
mention that the attack is greatest in dry weather and is lessened by
a heavy shower of rain.

Soil. The pea thrips is most prevalent on light soils. In the
majority of cases reported to me the soil has been light or gravelly, and
a correspondent at Shoreham, Kent, states that the damage is always
worse in the village where the soil is light than at Highfield near by where
the soil is heavier. It is probable that the conditions in a light soil
are more suitable for the hibernating larvae.

Varieties and time of planting. No variety of pea or bean is immune
to the attack, but the earlier sown plants usually escape severe damage.
As the females lay their eggs chiefly in the stamen-sheath of the flowers,
any plants which have passed the flowering stage before the adults
become common escape almost entirely. Actual varieties of pea
mentioned as having suffered less severely in infested districts are
‘Gradus’ (an early variety), ‘Primus,’ and ‘Autocrat, but a careful
examination of nearly forty varieties at a seed testing ground at Witham,

C. B. WILLIAMS 243

Essex, in July, 1913, gave no indication of resistance, except that due
to time of planting. In Report on Field Experiments, 1912, Kast
Anglian Institute of Agriculture, Chelmsford, it is stated that ‘Tele-
graph’ was destroyed by thrips, while ‘Gradus,’ ‘Essex Star,’ ‘ Alder-
man’ and ‘Blue Seedling’ gave good crops.

ARTIFICIAL CONTROL.

The habits and life history of this insect make the application of
remedial measures of great difficulty. Sprays will not reach the adults
or larvae in the flowers, and during the winter the great depth to which
the larva descends (they have been found in the wild state more than
ten inches below the surface) makes the application of gas lime or soil
fumigants of doubtful value. In March of this year numbers of larvae
were found deep down in a plot of soil which had been heavily limed
last autumn.

When plants are attacked late the larvae, however, are often found
in numbers feeding openly on quite large pods. At such a time spraying
with any contact spray (soft soap, rosin, etc.) should give good results.
On a small scale the following has been found successful

Stock solution
Water 1 qrt.
Soft soap 3 OZ.
Tobacco powder 3 oz.

The whole boiled for a short time and diluted for use about one part
to twenty of water.

When only a small area is attacked fumigation of the soil during
* the winter with carbon bisulphide, gas lime, creosote, or such trade
products as vaporite or creol should give good results, provided that it
is done to a sufficient depth. Experiments are now in progress to test
carbon bisulphide-oil emulsion recently described and which it is hoped
may prove satisfactory.

Whenever possible a rotation of crops should. be practised and peas
and beans grown as far as possible from the areas attacked in the
previous year.

Traps employing benzaldehyde, anisaldehyde and cinnamyl aldehyde
as attractive agents, as described by Howlett (1914), were tried and
found to be of no use. These aldehydes have no attraction for this
species of Thysanoptera,

Ann. Biol. 1. 17

244 The Pea Thrips (Kakothrips robustus)

The burning of the pea sticks during the winter, frequently re-
commended, is of no use. Many thrips may be beaten from the sticks,
but not this species (chiefly Limothrips cerealium and species of the
sub-family Tubulifera).

Notes oN METHODS OF COLLECTING AND BREEDING.

Thrips for identification purposes are of no use when dry. They
should be collected into 70 °% alcohol, or a mixture of 70 % alcohol and
glacial acetic acid in equal parts. In the latter case they must be
transferred after a few hours into 70 % alcohol. The latter method is
better for larvae as they are less distended than in the alcohol alone.
For critical examination they must be cleared and mounted in balsam
as a microscope preparation. I find Griibler’s ‘Turpineol’ the most
satisfactory clearing agent as it leaves the insects sufficiently pliable
to allow of the moving of the wings and legs into suitable positions.

Living specimens of pea thrips have been obtained from all over
the country in parchment bags closed with slide-on paper fasteners.
These bags are sent out in suitable boxes with instructions to fill with
flowers or pods placed in the bag straight after picking. In this way
material was obtained from friends and others who knew nothing of
entomology, many not even knowing by sight the thrips in question.
Many other thrips and insects were found in the bags in which the plants
would keep fresh for four or five days, and the method appears to be
worthy of wider application. Most of the bags I used were supplied
by Messrs Miller and Sons, Renfield Street, Glasgow, but the bags
sold for ‘paper bag cookery’ also answer quite well. They should,
however, be as transparent as possible as some idea of the contents can
then be got by holding up to the light before opening.

Eggs were obtained, and larvae bred in small glass tubes plugged
with cotton wool. Frequent changing was necessary or the moisture
which condensed on the sides of the tubes was a great danger, and the
sun should on no account be allowed to shine directly on to the tubes.
Larvae were hibernated in beakers filled with soil and in flower pots
sunk in the ground. They were also obtained in soil during the winter
with Berlese’s ‘Insect Funnel’ which, by means of warmth, extracts
all the small insects from the soil which is placed in a sieve at the top!.

1 T have given a short account of this in the Hntomologist, xvi, 1913, p. 273.

C. B. WILLIAMS 245

SUMMARY.

(1) Peas and beans in England and Western Kurope are damaged
by a thrips Kakothrips robustus (sub-order Terebrantia, family Thripidae).

(2) The adults appear from May to August; males only in the
earlier part. The eggs are laid chiefly in the tissue of the stamen
sheath. They hatch in about nine days. The larvae are orange-
yellow with the last two abdominal segments dark brown. ‘There is
one moult. The second stage when full fed (about 24 days from the
laying of the egg) descends into the ground to a depth of from three
to twelve inches.

(3) The full fed larva remains in this position till the following
spring when the two pupal stages are passed through and the adult
emerges. There is only one brood each year.

(4) The damage is greatest on light soils. No varieties are immune,
but early sown plants are less damaged. A chalcid parasite, T’hripoc-
tenus bruz, has been recorded from France, but has not been found in
England.

(5) Artificial control is difficult. Spraying is only of use when the
larvae are feeding openly on large pods. Soil fumigation during the
winter should give good results, but must be done to a sufficient depth.

BIBLIOGRAPHY.

BaGna, R. 8. (1908). Notes on Some Genera and Species of Thysanoptera new
to the British Fauna. Hnt. Mon. Mag. 2nd 8., x1x, p. 4.

(1914). A Chalcid Parasite of Thrips. Rept. Brit. Assn. Adv. Sct. 1913,
London 1914, p. 531.

BoarD OF AGRICULTURE OF ENGLAND (1898, revised 1905). Pea and Bean Thrips,
or Black Fly (Thrips pisivora). Leaflet 48.

Burra, P. (1907). Trentuna Specie di Tisanotteri italiani. Pisa, p. 60.

CotLincE, W. E. (1906). Report on Injurious Insects, 1905, p. 12.

Gaumont, L. et Vurrter, A. (1914). Sur un Thysanoptére nuisible aux Pois.
Bull. Soc. Nat. Agric. France, txxtv, pp. 168-173.

Hoop, J. D. (1912). A new Genus and three new Species of N. American Thysano-
ptera. Psyche, x1x, p. 113.

How tert, F. M. (1914). A Trap for Thrips. Journ. Econ. Biol. rx, p. 21.

Karyy, H. (1907). Die Orthopterenfauna des Kiistengebieles von Osterreich-
Ungarn. Berlin. Ent. Zeit, uit, p. 45, footnote.

—— (1910). Neue Thysanoptera der Wienergegend. Mitteil, Naturw. Ver. Univ.

Wien, vim, p. 45, footnote.

17—2

246 The Pea Thrips (Kakothrips robustus)

Karny, H. (1912). Revision der von Serville aufgestellten Thysanopteren genera.
Zoologische Annalen, tv, p. 334. (Key to 15 species of Frankliniella.)

Krrcuyer, O. (1890). Die Krankheiten und Beschidigungen unserer landwirt-
schaftlichen Kulturpflanzen. Stuttgart 1890, p. 71.

und BoutsHAvUsET, H. (1897). Atlas der Krankheiten und Beschadigungen
unserer landwirtschaftlichen Kulturpflanzen. Stuttgart. Series m1, pl. xvu.

Kurpsumov, N. V. (1913). The more important insects injurious to grain crops
in Middle and South Russia. Studies from Poltava Agric. Expt. St. No. 17.
Department of Entomology, No. vi. (in Russian). [Also Rev. App. Ent. ta,
p- 170.]

Mitier, A. (1871). Thrips destructive to Green Peas. Proc. Ent. Soc. London,
1871, ps xi

Russetx, H. M. (1912). The Bean Thrips. U.S. Dept. Agric. Bur. Ent. Bull. 118.

von ScuILiine (1898). Die Schidlinge des Gemiisebaues, p. 53.

Soraver, P. (1913). Die Pflanzenkrankheiten. Vol. 11, p. 231. (Suggests Thrips
flava as cause of injury.)

THEOBALD, F. V. (1900). Thrips attacking Leguminous Plants. First report on
insect pests. Journ. S.E. Agric. Coll., Wye, No. 9, pp. 27-365.

(1906). Report on Insect Pests for year 1905-6. Journ. S.E. Agric. Coll.,
Wye, pp. 84, 85.

— (1907). Report on Insect Pests for the year 1906-7. Journ. S.E. Agric.
Coll., Wye, p. 110.

TryBom, F. (1899). Blasfotingar (Physapoder) SAsom Skadedjur p& Sockerarter.
Ent. Tidskr. Xx, pp. 267-277.

Uzet, J. (1895). Monographie der Ordnung Thysanoptera. Ké6niggratz, p. 104.

Vourttet, A. (1914). i. Note Synonymique sur le Thrips de Pois. Bull. Soc. Ent.
France, 1914, No. 5, pp. 161-162.

—— (1914). ii. Sur un Chalcidien Parasite des Thrips des pois. C.R. des
Seances de la Soc. de Biologie, LXXv1, p. 552.

(1914). iii. La 'Thripsose de Pois. Revue Scientifique, Paris, 1914, pp. 626-627.

WarBuRTON, C. (1909). Annual Report for 1908 of the Zoologist. Thrips on garden
peas. Journ. Royal Agric. Soc. England, uxtx, 1908, pp. 321-327.

Westwoop, J. O. (1880). The Pea Thrips. Gardeners’ Chronicle, London, 1880,
vol. 11, p. 207, fig. 42.

WituraMs, ©. B. (1913). Records and Descriptions of British Thysanoptera. Journ.
Econ. Biol. London, vol. vu, p. 219.

(1914). Kakothrips n. gn. a division of Frankliniella Karny (Thysanoptera).

Entomologist, London, vol. xtvu, p. 247.

247

THE APPLE SUCKER, WITH NOTES ON THE
PEAR SUCKER.

By P. KR. AWATI

(Sir John Wolfe-Barry Student, Imperial College of Science
and Technology, South Kensington).

(With Plates XVII, XVIII and 21 Text-figures.)

CONTENTS.
PAGE
Introduction : : 5 . é : : : 247
I. Apple Sucker—Life-history. Egg to Larva . : 3 248
II. Summary of Instars 250
II. Description of the Instars . 252
IV. Habits of the Young Insects 256
V. Effects produced by the Larvae 257
Mit iethe Adult; : : : 258
VII. The Tracheal System . 260
VIII. The Reproductive System . 261
IX. Pear Sucker : 265
X. Insecticide Treatment. 267
XI. Natural Enemies 271
XII. Immunity . 271

INTRODUCTION.

Tue following pages contain an account of a study of the apple
sucker made by Mr Awati at Acton Lodge, Brentford, during the summer
of 1913. The fact that the life-history of apple suckers occupies one
year implies that in one season no stage repeats itself, and Mr Awati
could not repeat or check the observations he made.

The most notable point brought out is perhaps the nature of insecti-
cides; so much spraying is done against apple sucker with so little
result, simply because the fruit-grower knows no way of checking his
results, that the method here adopted should be of interest to fruit-
growers generally. It is quite simple and does give a real check on the
results one is getting.

248 Apple and Pear Sucker

Mr Awati left for India and had not time to fully revise the text,
so I have done so. I also express herewith our acknowledgments to
Sir John Wolfe-Barry, whose generous provision of the studentship
made possible Mr Awati’s paper on the Mechanism of Suction in Lygus
~ pabulinus (Proc. Zool. Soc. London, 1914, p. 685) and the present paper.
I hope that the work on apple sucker will be of value to fruit-growers
in England, and I think the method of checking it is a real advance on
anything hitherto used in this country.

H. M. LEFROY.

THe APPLE SucKER (Psylla mali).

I. gg to Larva.

(a) Diestribution of Eggs (Fig. 21). (Black dots on twigs represent
eggs of Psylla mali.) The eggs are laid singly on the twigs of the apple
trees. They are never found in clusters or groups, but on the contrary
they are irregularly distributed on the twigs, which are chosen according
to their age. It seems that new twigs (of the first year’s growth) are
chosen by the female on which to lay the eggs. In some cases I have
found that the eggs are deposited on one side while the other is tolerably
free from them. It is possible that light may have something to do
with this kind of deposition. The eggs are found along the scars (on
a twig) left on the leaf petioles.

(b) Description (Fig. 1). An egg of Psylla mali is oblong, tapering
to both ends. It is sculptured into fine little circles. It is pale white
when laid, but begins to change colour when it nears the hatching
season, then it becomes distinctly pale brown or reddish. At one end
there is a long stalk which hangs free in the air, while at the other there
is a sucker-like expansion which glues the egg to the twig. Its position
on a twig is such that its long axis lies parallel to that of the twig.

(c) Hatching. The eggs begin to hatch when spring sets in. If
the weather is warm before the spring they may hatch earlier, but
generally the larvae begin to come out in the last week of March. Ihave
seen an egg hatching on March 23rd; the hatching may go on for some
time, until the last week of April.

(d) Mechanism. The eggs are split up longitudinally (Fig. 2).
It seems that there is some mechanism, which is shared partly by the
egg and partly by the larva. The spot where the larva comes out is
provided with minute teeth which from either side form a dovetailing

P. R. Awat! 249

device (Fig. 3). At the same time the larva is provided with an egg-
breaker on the front part of its head. This egg-breaker consists of some
stout spines attached to the flat part of its head. The spines push
the dovetailing device apart, and the larva crawls out. There are a
number of spines both dorsally and ventrally which keep the sides of

ev

x
\
Fig. 3.

the egg apart, while the larva is creeping out. The following is a com-
plete diary of a larva hatching out:
21. 3. 13:
10.30 p.m. The larva began to come out.
11.30 p.m. It was completely extruded from the egg but was still
attached to it.
11.50 p.m. Sitting at the opening of the egg, moving its antennae
and thus taking rest after a great deal of trouble.
2.30 a.m. Quite free from the egg and walking about.

The larva is completely yellow when it comes out and the egg-shell
is opaque white. Thus it seems that the change in colour of the egg
is due to the larva which becomes brown or reddish as its time for
hatching out is nearing.

(e) Behaviour of the first larva. The larva, after resting a while,
begins to crawl up towards the apical bud of that twig. It has a pair
of well-developed antennae, the last segment of which is drawn out and

250 Apple and Pear Sucker

is provided with two bristles. The larva is moving its antennae and
is possibly attracted to the bud by a kind of chemotropism; otherwise
it is impossible to say why the larva should crawl up towards the bud,
which at this time is also sprouting. It sometimes happens that the
bud, on that twig, is not yet opened. In that case the larva is at a
standstill. It can live without food for two or three days, at the end
of which period it succumbs to death. But on the whole, the time
for the larva to hatch and the bud to blossom is so finely adjusted,
that the former has not to wait for the latter.

Il. Summary of the Infe-History.

There are in all five instars, the last of which is here called the
“Nymph,” from which the adult insect emerges. Larvae were bred
artificially in the experimental house. The method of breeding them
was as follows: tender short apple twigs were cut and embedded in

Fig. 6. Fig. 7.

wet silver sand in a museum jar, the top of which was covered with
a thin piece of muslin. The wet sand enabled the twigs implanted in
it to keep fresh for two or three days, at the end of which time they were
replaced by fresh twigs. The larvae were carefully picked from the
old twigs and placed gently on new ones. Thus it was possible to
study them very closely. The temperature of our room was equable
and was somewhat higher than that outside. Small apple trees were
used for checking the period of each stage, and it seems that this arti-
ficial method has no appreciable effect on the life-history of these
insects.

P. R. Awati 251

The following table shows the period taken by each stage for its
moult.

Ist instar (Fig. 4). On twigs in the sand. On plants outside.
]. 23.4.—30. 4. .. .. 8 days
2. 21. 4.—28.4. .. .. 8 days
3. 25. 4.—ql. 5. .. .. 7 days
2nd instar (Fig. 5). There was no time for checking the period
of these instars.
]. 18. 4.—25. 4. .. .. 8 days
2, 20. 4.—27.4. .. .. 8 days
3. 26.4.— 3.5 8 days
3rd instar (Fig. 6).
1. 29. 4.—6. 5. 8 days 1. 26. 4.—3. 5. . 8 days.
2. 28. 4.—4. 5. 7 days 2. 29. 4.—6. 5. 8 days.
3. 25. 4.—1. 5. 7 days 3. 26. 4.—3. 5. . 7 days.
4, 26. 4.—3. 5. 8 days 4, 29. 5.—65. 5. 7 days.
5. 30. 4.—7. 5. 8 days 5. 29. 4.—6. 5. 8 days.
6. 25. 4.—1. 5. 7 days Oh Me 76 Gn 8 days.
7. 24. 4.—1. 5. 8 days
8. 26. 4.—3. 5. 8 days
9, 27. 4.—3. 5. 7 days
10. 26. 4.—3. 5. 8 days
4th instar (Fig. 7).
ee oe I 5 5 .. 12 days 1 §3.5—12.5. . 10 days.
2. 30. 4.—10. 5. .. .. 11 days 2. 5. 5.—13. 5. . 9 days.
3. 1.5.—I11.5. .. .. 12 days 3. 29.4.— 9.5. . 1] days.
4, 3. 5.—12. 5. .. .. 10 days 4. 1.5.—10.5. . 10 days.
5. 29: 4.—13. 5. «. .. 15 days 5. 5. 5.—18. 5. 9 days.
6. 30.4.—10. 5. .. =.) Ll days
ey O00, 5a. .. 10 days
8 3.6.—I12.5. .. .. 10 days
9. 30.4.—10. 5. .. .. ll days
LOls * Gz 615. 5.2% .. 10 days
5th instar or “Nymph” (Fig. 8).
I. 9.5—21.5. .. .. 13 days 1, 9.5.—18. 5. .. .. 10 days.
2. I. 5.—23. 5. .. .. 13 days 25) 12. D:— 2259. 3. .. 10 days.
3. 10. 5.—23. 5. .. .. 14 days 3. 13. 5.—22. 5. .. .. 10 days.
4. 10. 5.—23. 5. .. .. 14 days 4, 13. 5.—22. 5. .. .. 10 days.
5. 12. 5.—24. 5. .. .. 13 days At this time the plants were trans-
6. 13. 5.—24. 5. .. .. 12 days ferred to the frames, where the heat
7. 8. 5.—20. 5. .. .. 13 days was greater than outside. The

variation in the time may be due
to this fact.

6th or adult stage (Fig. 9). June to November,

252 Apple and Pear Sucker

There were many larvae bred from beginning to end. But I had
to replace those that died in the course of breeding. There are pecu-
liarities of each instar by means of which the different instars can
be distinguished. These peculiarities will be described below.

Fig. 9.

III. Description of the Instars.

(a) General description. (i) Colour. A larva of each stage
passes through the same cycle, though it is growing bigger in size. It
is bright yellow when it hatches out or has moulted. The colour
gradually changes to yellow-brown, or in some cases distinctly reddish.
This change in colour may be due to exposure to atmosphere. But
there is a complete change of colour in the nymphal stage, when it
becomes entirely green. The larva of the fourth instar changes its
colour from brown to pale green as it matures for the fourth moult.

(ii) Secretion (Fig. 10). The larvae of these insects are unmistake-
ably recognised by their secretion. All the larvae, including the nymphs,
have opaque white secretion, a long thread of which is hanging out from
the hinder portion of the abdomen. This thread consists of a central core
of translucent liquid covered externally by the whitish material which
prevents its exuding and thus wetting the surface of a leaf. The larva
begins to secrete as soon as it hatches out or has moulted. The thread
in some cases reaches a great length; at the end there is a big knob-
like swelling. If the thread is pricked, the translucent liquid exudes
and wets the surface. This secretion is of a waxy nature and is soluble
in alcohol. Besides this big thread issuing from the anus, there are
small spine-like threads projecting from the extremity of the abdomen.
They are shining and seem to change colour, which is not their intrinsic

P. R. AWAT! 253

property as some investigators think, but it is due to the refraction of
light; this is clear since the colour seems to change as one sees it from
fresh points of view.

:

i} } \\
( / Dan \\\\
\ Ii |
/
int

'

Fig. 10.

/

(iii) Heart-Shaped Organ (Figs. 12, 13, 14). (a) External appearance.
Every larva has this characteristic organ, which is cordate in shape
(Fig. 12) and is bordered with several rows of big pores, besides
which there are also minute pores in many tiers inside the boundary.

ampulla

Fig. 11.

In the centre of this organ there is a peculiar-shaped structure which
is due to the invagination of chitin. Just above the notch of this
organ is an aperture presumably functioning as the anus or the opening
of the waxy glands. On either side of this opening there are two

254 Apple and Pear Sucker

strong spines which may direct or support the thread of secretion
alluded to above.

(b) Internal structure (Figs. 13, 14). Inside this heart-shaped organ
are situated two kinds of glands both of which are of a waxy nature.
The larger of the two finds its exit through the aperture mentioned
above. This is demonstrated by the longitudinal section (Fig. 19).
It is a big coiled structure occupying the whole of the abdomen of a
larva and secreting the big thread of wax mentioned above. The
other consists of small glandular cells opening out through those pores
referred to already. They secrete fine, shining, small spine-like threads

aperture to the
, outside
/

Fig. 12.

projecting from the extremity of the abdomen. This structure will
be clearly understood from a transverse section (Fig. 14). This organ
with the glandular structures is left behind when the nymph moults to
the adult insect. There is not a trace of these structures in the adult,
which does not secrete honey-dew.

(iv) Wing Lobes. These begin to appear in the third instar. In
the second instar their places on the meso- and meta-thorax are already
marked, but in the third there are small protuberances in these places.
They become well developed in the fourth instar, while in the nymphal
stage they are broad and elongate, lying at the sides. There are also small

a big hollow cup (ampulla).

buds.

P, R. Awat! 255
vestigial nervures on them, though the whole appearance is entirely
different from the wings of the adult insect.
(v) Claws (Fig. 11). It is not necessary to describe the legs of a
larva in detail, inasmuch as it does not differ from those of any ordinary

insect. But their extremities are very interesting. There are two strong
curved spines, in the midst of which there is a sucker-like organ which has

in gy
f mites

Non
e
\ i

as
Z=
ZB
Zs

| VA
Fig. 13.

Fig. 14.

These claws are adapted for the larval life
as the larva has to crawl on the waxy and slippery hairs of the apple-

The ampulla enables the larva to fix its leg very firmly on the

surface, while the spines may help the larva in locomotion.

(vi) Eyes. The larval eyes are red or reddish in hue, though in
the nymphal stage the colour changes to dark green, while in the adult

the eyes are distinctly black.

256 Apple and Pear Sucker

The larvae are distinguished from stage to stage; the distinction
being in the increase of the number of segments of the antennae. The
first and last segments seem to remain unchanged, and the rest are inter-
calated from instar to instar. The external appearance of the last
segment with its two bristles is very characteristic through the whole
life-history of Psylla mali.

The following table will give the characteristic differences of the
antennae of each instar :—

Instars No. of segments
lst instar (Fig. 4) 2
2nd. ,, (Fig. 5) 3
3rd os (Hug. 6) 4
athe st", Bigs '7) 5
5th Nymph (Fig. 8) 7
6th Adult imago (Fig. 9) 9

IV. Habits of the Young Insects.

A description of the habits of the larvae or the insects in general can
never be too important nor too detailed, since the basis of insecticides
is founded on that. The more we know of the habits of an insect,
the easier does it become to kill it.

(i) Chemotropism. The larvae are positively chemotropic, their
antennae are very well developed, especially the last segment with its
two bristles. The first larva, as soon as it is hatched, crawls towards
the apical bud of the twig. It is moving its antennae in the air. The
larva seems to be attracted by a smell emitted by the bud, to which
smell we seem to be insensible. The same phenomenon is repeated in
other instars, which are all attracted to the buds by means of some
chemical substances.

(u) Helhotropism. All the instars except the nymphs are negatively
heliotropic. They avoid light and are always found in the dark recesses
of the bud. As soon as they are brought to daylight, or an artificial
light (electric) is brought to bear upon them, they try to avoid it.
It is this habit which enables them to find the tender leaves of the buds
inside. The nymphs, on the other hand, are positively heliotropic.
As soon as the fourth instar moults for the nymph, the latter leaves
the darkness of the bud and comes to live on the open under surface
of the leaf. This change of habit may be beneficial to an imago emerging
from it, as the latter must have an open surface to fly.

(ii) TLhigmotropsm. This is peculiar to these larvae, except the
nymphs. They are positively thigmotropic, 7.e. they react positively

P. R. AWATI 257

to pressure. The leaves of the buds are pressed against each other and
the larvae like to be among those closely packed leaves. This habit
combined with (ii) is very advantageous to them, since both habits
enable the larvae to get at the most tender leaves of the buds. The
nymphs, on the contrary, are negatively thigmotropic. They avoid
being pressed together and come to live free, uncrowded on the open
surface of the leaves. ;

(iv) Gregariousness. All the instars, except the fifth, are gre-
garious in habit. They are found crowded together, and try to come
together however much they may be separated from one another. I
have tried many cases when the larvae were put separately on different
buds of the same twig. On the second or at most the third day they
were found to be together. This gregarious habit of the larvae is
extremely useful since one can kill all of them in one lot. The nymphs,
however, are never gregarious. They are always separated from each
other and try to avoid the neighbourhood of other larvae and nymphs
as well.

(v) Powers of endurance. The larvae can live. without food for
two or three days, after which they collapse and die. The fact that
they can thus exist temporarily is very beneficial to the first instar,
as it may not immediately find a fully-opened bud on its twig.

(vi) Situation. The larvae are always found in the recesses of the
_ buds. They are rarely found outside, except in the nymphal stage,

when they are found on the under surfaces of the leaves. The buds
infected by them can easily be recognised. They are all covered with
the waxy threads hanging down like icicles. The nature of the threads
has already been described above. The position of the larvae in the
bud seems to be fairly constant. The head is turned away from the
growing point of the apex of the bud and the abdomen is turned towards
the apex. In the case of nymphs, the position is very indefinite. The
larvae, when sucking, press themselves down against the surface of a
leaf and the whole body seems to be heaving up and down as the stylets
are withdrawn or thrust into the leaf. The length of the stylet is
enormous. In all stages they are twice or thrice as long as the whole

body.
V. Effects produced by the Larva.

Psylla mali is most dangerous to apple trees in its larval stages.
While in the adult, it does practically no damage. As described above,
the larvae are gregarious in habit and plenty of them are thus found in

258 Apple and Pear Sucker

a single bud. Hach larva thrusts its stylets deep into the tissues and
begins sucking the juices. The suction-pumps of the larvae are at
work night and day sucking the juices of the bud until it completely
dries up. The leaves become brown, as if they were frost-bitten, wither,
and drop down one by one. The buds, both floral and foliage, are thus
destroyed wholesale and the apple trees cannot, of course, bear any
fruit. If there is any remedy to be applied, it should be applied when
the insect is in the larval stages. It seems that the growth of the buds
(floral and fcliage) runs parallel with the development of the Psylla
mali. Soon after the flowers are set, Psylla mali is in the adult stage,
when it does no damage. There are other effects produced indirectly
by these larvae. They soil the bud-leaves by the secretion of waxy
substances when the threads of secretion are broken up. The trans-
lucent stuff of the core exudes and covers the surface of the leaf. Par-
ticles of dust get glued to the leaf. In fact the wax forms an impervious
layer over the surface. This may interrupt free transpiration of the
leaves, which may thus be smothered and suffer. It is, however, curious
that no fungus is seen growing on the leaves thus wetted by the larvae.
This effect is not universal and may only be found in some places.

VI. The Adult.

(a) The external sexual differences. (i) Both sexes seem to be alike
in general appearance, though there is an obvious difference in the shape .
of the genitalia. In the male they are curved and turned upwards,
while in the female they are straight and pointed and lie concealed in
the upper and lower anal segments. Their anatomical description in
the female only will be given below in the reproductive system.

(ii) Colour differences. The colour of the male seems to be brown
or at the most pale green; it is never green nor deep green; while the
females are nearly always deep green. The colour in both the sexes
changes with the age of the insects, but it never becomes uniform in
both the sexes.

(iii) Abdomen. The abdomen of the female seems to be broader
when it is fertilised, while that of the male is very narrow and
tapering.

(b) The proportion of the sexes. In the beginning of this investi-
gation it was suspected that there was parthenogenesis among these
insects. If so there would be a disproportion among the sexes—the
females outnumbering the males. To solve this question the adult
insects were caught at different times from the period they emerged from

P. R. Awatl 259

the nymphs to the time when they laid eggs. The results of those
different catches are given below :—

Time Female Male
May 27, 29 40 36
June 2 39 oi

16 34 32

19 and 24 97 99

July 2 44 38
9 36 46

Aug. 12 49 47
22 24 23

363 372

It seems clear that there is no great disproportion in the sexes and
no reason to anticipate parthenogenesis.

Habits of the Adults.

(a) Change of colour. The adults, both male and female, undergo
some change in colour as they grow older. The uniform brown, pale
green, or deep green gives place to a tinted pattern of the same. Some
females of reddish brown have been found.

(b) Feeding habits. The males and females sit on the leaves—either
on the upper or lower surface. They are very harmless in this stage,
though they produce certain characteristic symptoms of their presence.
They suck the juices of those leaves, which become marked with very
minute circular white spots. These spots seem to increase in size and
afterwards the spotted surface disintegrates and small holes are formed.
Thus the presence of Psylla mali in the adult stage can easily be recog-
nised. Another class of insects (Jassids) also produces white spots,
but these can be easily distinguished from those of Psylla mali by mere
observation.

(c) Flight. They are rarely seen on the wing unless disturbed.
Then they seem to jump forward with their hind legs and take a short
flight—trom leaf to leaf or twig to twig.

(2) Habitat. Psylla mali seem to choose the under surface of
leaves, though they are sometimes found on the upper. In the adult
stage they are not confined to apple trees alone, but seem to migrate to
different plants interspersed with the apples. They are found on
gooseberry bushes, pear trees, plums, etc., besides apple trees. This
migration may explain how the infestation is carried from one orchard
to another, because their powers of flight would not sustain them in
direct migrations from one apple-orchard to another.

Ann. Biol. 1. 18

260 Apple and Pear Sucker

VII. Tracheal System (Figs. 15, 16).

From the economic point of view none of the internal organs of an
insect 1s of more importance or deserving of more attention than the
tracheal organs. They constitute the chief medium through which a
contact-poison insecticide acts. Prof. Lefroy has proved this point
by his experiments on meal worms. The tracheal system differs in
different insects, as also in the larva and the imago of the same insect,
specially with regard to the way the respiratory organs open to the
exterior. In some insects the spiracles lead directly to the tracheae,
while in others there are various modifications for closing and opening
the mouths of the tracheae. This difference in the arrangement of the

Fig. 15.

spiracles and the tracheae may explain why a certain insect with simple
tracheae succumbs to an insecticide more easily than others with
modifications of the tracheal apparatus. In Psylla mali there are two
kinds of trachea, one in the imago and the other in the larvae,
including the nymphs.

(i) Tracheal system in the imago (Fig. 16). It is of the simplest.
The outer integument is invaginated to form a spiracle which leads
directly to a tracheal trunk. There is a structure in the spiracles which
may function as a strainer of the air which is sucked through the spiracles.
The structure of a spiracle of this kind may be easily understood from

the figure.

P. R. Awatt 261

(iu) Tracheal system in the larvae (Fig. 15). This system is extremely
complex. There are various devices between the external opening and
the tracheal trunk, which are:

(a) The spiracles (three on the abdomen and two on the thorax)
are situated in a pit which is covered over with long hairs.

(b) The external lid of the spiracle. This is formed by a thick
process which lies across the spiracle.

(c) The closing apparatus. It consists of thickened chitin stretching
from the one side of the tube to the other. It is acted upon by the
spiracular muscles which are attached to this apparatus. When these
muscles contract, this transverse bar of chitin is pulled apart and the
spiracle is opened.

(d) Atrium. Below the closing apparatus is a cavity which com-
municates with the main tracheal trunk.

The simple structure of the spiracle of the adult and the more
complex structure of that of the young lead one to infer the adult
will react more readily to an insecticide and this is actually the
case. In experiments with insecticides, I found that the adults
died as soon as the emulsion reached them, whereas the young
struggled for some hours before succumbing. The progress of the
insecticide into the adult is unchecked, whereas it is obstructed in the
larva; it has, in the latter case, to pass the hairs before it reaches
the spiracle, and it cannot then pass the closing apparatus till paralysis
is set up, opening the valve and giving it unrestricted entrance to the
tracheae.

VIII. Reproductive System (Figs. 17, 18, 19, 20).

(i) The reproductive system does not begin to develop until the
adult stage is reached, though the indication of this system is early seen
in the fourth and fifth instar, in which the external sexual differences
begin to be visible; the males (the larvae which are going to become
males) being short and the females longer.

(ii) Coupling. Coupling begins in the first week in June, but the
eggs are not laid until September. The coupling members lie side by
side dorso-ventrally, their heads being turned in the same direction.
This is a very characteristic position of these insects.

(iii) The reproductive organs of the female. Primary. These con-
sist of the following parts (Figs. 18, 19, 20):

(1) Ovaries (Fig. 19). They consist of small egg-tubules, from

18—2

Apple and Pear Sucker

NN

L
[Z,
/I4

-muscles

-- chitinous rods

Fig. 17.

18.

Fig.

P. R. Awatt 263

eight to nine on either side; each tubule is composed of three or more
cells. Hach tubule ends in a cell full of nuclei which may give rise to
the egg-nucleus. This kind of ovary has

(2) Oviducts (Fig. 18). There are two oviducts, one on each side.
The ovarian tubules open into them, and they in their turn open into
the vagina as a single duct. The oviducts are coiled and nearly bent
upon themselves on their way to the vagina, with which they com-
municate ventrally after they have formed a common duct.

(3) Vagina (Fig. 20). This is a single median muscular sac, com-
municating externally through the ovipositor. There are circular
muscles which seem to be very powerful.

accessory
a 3 gland

(4) Accessory glands (Fig. 20). They open into the distal part
of the vagina. They consist of two kinds, one larger than the other,
the smaller opening into the larger. At the entrance into the vagina
there are muscles which regulate the opening of these glands.

(5) Spermathecum (Fig. 18). There is a single median sperma-
thecum lying ventrally below the vagina, and the oviducts. It opens
into the distal part of the vagina by a duct which runs dorsalwards.
This spermathecum is used for storing the sperms. The vagina changes
in structure distally and opens into the tube formed by the ovipositors.

Secondary characters. The ovipositors (Fig. 17). This structure is

264 Apple and Pear Sucker

formed by the invagination of some of the posterior segments of the
abdomen. They consist of the following parts:

(1) Supra-anal segment.
(2) Infra-anal segment.
(3) Chitin rod on each side, ending distally in a pointed structure.
(4) Muscles attached to these chitinous rods.

Fig. 21. The Eggs on Twigs.

(iv) Oviposition.

The points of the chitinous rods, between the
vagina opening, are concealed by the supra- and infra-anal segments.
When the muscles, which are attached to the proximal ends, contract,
the chitinous rods are pushed forward and the points project further
than the anal segments which are applied to the surface of the twig.
The egg, which is pushed forward by the circular muscles of the vagina,

P. R. AWAtT! 265

enters the cavity formed by the ovipositors. Distally there are recurved
minute hairs which prevent the egg from going back. One egg is laid
at a time.

(v) The maximum number of eggs produced by a female in one
case was 30, in another 37.

(vi) The egg-laying season. This is very short and only extends
over a week. The females began egg-laying early in September. By
the middle of the month the season was over.

(vii) The males and females seem to outlive this egg-laying season
for some time. They are found as late as October and they appear to
die towards the end of that month. In November I could not find
any specimen of the Psylla mali.

IX. THe Pear Sucker (Psylla pyricola).

This insect is the most important pest of pear trees on the Con-
tinent and in America. Unfortunately, it has recently been found in
the United Kingdom, and was reported last year by Prof. Theobald,
of the Wye Agricultural College. This insect has the same life-history
as Psylla mali, but there are many important differences and features
which make this insect more formidable than Psylla mali.

(1) Higgs.

They are elliptical and narrow. Their colour varies from pale yellow
to brownish yellow. They are found in clusters or groups of 30 or more
on the upper surfaces of leaves but scarcely on twigs. They can easily
be distinguished from those of Psylla malt.

(2) The Larvae (Plates XVII, XVIII).

(i) There are five stages, the imago emerging from the fifth (or the
nymph). The first four stages correspond closely to those of Psylla
mali in the external structure, but the fifth instar or the nymph is very
characteristic of this insect. It is not uniform in colour but is spotted
on the abdomen. The other structures seem to be similar.

(ii) Secretion. These larvae exude a waxy secretion which wets
the surface of a leaf. There are no white threads as there are in Psylla
mali. The larvae of Psylla pyricola are always wallowing in the secre-
tion. On this honey-dew grows the injurious fungus which has been
identified by Massee (of the Royal Botanical Gardens, Kew) as Clado-
sporium herbarium. Thus it will be seen that the habits of these larvae
as to secretion are quite different from those of the larvae of Psylla mali.

266 Apple and Pear Sucker

(i) Satuation. These larvae are always found on the open surfaces
of the leaves of the pear trees. Their responses to surroundings have
not been observed.

(iv) Injurious effects produced by larvae. These effects are two-
fold:

(a) Effects due to Cladosporium herbarium, the Sooty Mould.

(6) Those due to the larvae. The larvae suck the juices of the
leaves and thus starve them. - The leaf becomes curled and withered
and afterwards dries up. When the leaves die the metabolism of the
whole plant is interfered with and thus the plant may ultimately be
killed.

(3) The Adult.

(i) The imago is green when it emerges from the nymph, but it
soon becomes dark in colour. The external structures with reference
to sex are identical with those of Psylla mall.

(i) Feeding habits. P. pyricola do not produce any, white spots
on the leaves, but on the other hand they produce rather injurious
effects. The adult insects secrete honey-dew and wet the surfaces of
the leaves, on which grows the same injurious fungus.

Thus P. pyricola is injurious in both its stages, 7.e. in the larval as well
as in the adult forms; while P. mali is harmful only in the larval form.

(iil) Reproduction. P. pyricola is tri-voltine; while P. mali is
uni-voltine, 7.e. the former has three generations while the latter has
only one.

The following are the probable dates of the three generations of
P. pyricola:

Ist generation .. .. April and May.
2nd 3 vr .. June, July.
ord 5 és .. August, September.

P. mali has only one generation from March to September. P.
pyricola hibernates in the imago stage. The adults of the third gener-
ation pass through the winter and lay eggs in the following spring
when the females are fertilised. P. mali hibernates in the egg-stage;
the eggs are laid in September and the larvae hatch out from them in
the following spring. In short, P. pyricola, when compared with P. mali,
seems to be as dangerous to pear trees. This pest is gradually spreading,
though at present it is only known locally. America and the Continent
suffer from this pest. It requires more working out. I have given its
description as a contrast to P. mali.

P. R. AWAtr 267

X. Insecticide Treatment.

In the course of the investigation of the life-history of Psylla mali
it was found that the larvae are covered with waxy secretion. As
they secrete the waxy stuff the under surfaces of the leaves get soiled by
the wax and become impervious to water. The buds besides having
a waxy covering have also got minute hairs and other structures of their
own which make it more difficult for water to reach them. My task was
to find a fluid which would thoroughly saturate the bud leaves and so
reach the larvae. I have used different percentages of the soap (soft)
solution and found one per cent. of the soap solution satisfactory.
One per cent. means ten pounds of soap in 100 gallons of water. But
the soap solution by itself was not effective enough the kill the larvae.
It was tried on some apple trees with the result that 72 per cent. were
killed and the rest were healthy enough. The soap solution not only
saturates the bud leaves but it engulfs the larvae also, though in some
cases without killing them. The reason why 28 per cent. were living
seems to be that the soap solution is very effective if it dries instan-
taneously. By doing so it blocks the respiratory pores (stigmata) of
the insects, which are thus suffocated and killed. This means that the
soap solution will be more effective on leaves exposed to the wind and
thesun. But in the case of buds the leaves are not so exposed and larvae
in these buds do not run such risks as those on the open leaves. The
soap solution is not poisonous by itself, and if it does not dry up im-
mediately it is utterly ineffective, for the larvae can be happy in it and
crawl out of it before it dries up and their stigmata closed up once for
all. This would explain why such a large percentage was living with
the soap solution. As the soap solution was deficient by itself, I had
to seek some poisonous stuff which would facilitate the action of the
soap solution. The stuff had to be one of the wax solvents, and for this
purpose I used many things:

(1) Petrol. (4) Acetone.
(2) Kerosene. (5) Creosote.
(3) Xylol.

All these are more or less wax solvents. The last reagent proved
to be the best on trial and I have made use of it. These reagents do
not increase the surface tension lowered by the soap solution and they
are miscible with it. It must be remembered, however, that though
they are poisonous to the insects and wax solvents, they do a great deal

)

266 Apple and Pear Sucker

of damage to plants if used in excess. Before I begin the description
of my experiments with regard to different insecticides, it would be
correct to state the particular times for spraying apple trees for apple
sucker. I was very late last year owing to many difficulties. The
proper time for spraying is before the floral buds have opened. The
eggs begin to hatch as soon as the foliage buds open and there is a great
interval before floral buds blossom. If put off too long the spraying
will shake the pollen from the flowers and the ovaries will remain
infertile. In no case should there be any spraying when the blossom has
opened. The setting season begins and the petals begin to drop off and
the fruit become set. Then there is another chance of spraying the
stragglers—the nymphs which may have been unfortunate enough in
the previous larval stages. This final spraying combined with the
previous one will completely exterminate the apple sucker from the
orchard.

It is a curious fact that spraying at different times in the day has
varying results. The same mixture was sprayed over the apple trees
at different times:

Spraying time Result
12 noon. It was light and All died instantaneously.
windy and hot.
25. 5. 13 {5.380 p.m. It was cool. All died eventually, but at the time of

examination 10 or 11 were still
struggling for existence.

These variations can be explained. On a bright, hot, windy day the
soap solution dries up immediately and the creosote acts very effectively ;
while, when it is cool, the insecticide does not dry immediately, and
creosote seems to be very slow in its action.

These experiments will at least show that the different times of
the same day have different effects, though the insecticide may be
the same.

Different washes used.
(1) Rosin Wash.

(a) Composition :

Rosin... € .. 2 Ibs.
Washing soda .. Ss eeDEOS.
Water .. a .. 20 gallons.

(b) Action. As the stuff gets dried, rosin is deposited on the
surfaces of the insects and blocks the air holes, the stigmata; the insects
are suffocated and thus killed.

P. R. AWATI 269

(c) Effects :
(1) It has not penetrated the buds at all.
(2) None of the larvae were touched by it.
(2) Paraffin Emulsion.

(a) Composition :

Paraffin .. uA .. 2 gallons.
Bar soap .. se 2 Ip:
Water of .. 1 gallon.

Diluted 1 gallon to 9 gallons water.

(b) Action. The fluid is sprayed into minute droplets spread over
the surfaces of the leaves—each droplet consisting of two parts—the
central core of paraffin surrounded by the outer crust of soapy water.
The water then evaporated, and the paraffin core being exposed spread
over the surface and the larvae touched by it are killed. The paraffin
acts as a contact poison. It has nothing to do with respiration. Thus
its action is quite different from that of rosin wash. This is shown by
the fact that the larvae do not die as long as there is water, but they do
so when the water evaporates and the paraffin spreads.

(c) Effects :

(1) If used in excess it burns the plants, especially on a bright
sunny day.
(2) More than 50 per cent. of the nymphs were killed.
(3) It did not wet evenly. Some drops were resting on the hairs
of the bud leaves.
(4) Nymphs were not wetted on the lower surfaces of the leaves.
(3) Soap-Creosote Emulsion.
(a) Composition :
100 gallons of water.
10 tbs. of (soft) soap.
Quart creosote oil (crude, commercial).

I found this emulsion the best of all. Not only is it simple and
effective, as it will be presently seen, but it is the cheapest thing on the
market. One hundred gallons of the wash only cost 2s. 6d., and this
price compares favourably with any insecticide available.

I started first of all with the soap solution only, but the results,
though not poor, were not very satisfactory. I have already explained
why the soap solution by itself is not effective. There is another
possibility that the larvae recover the next day. They can withstand
suffocation for many hours, and the soap, unlike rosin, does not

27() Apple and Pear Sucker

completely block the stigmata, rosin being a solid thing. The soap
solution has two defects:
(1) It is of use only in case of buds where the leaves are not

exposed to the wind and the sun.
(2) The larvae may and generally do recover from the effects

of a soap solution after some hours.
The results of the soap solution were (the solution being | %):

72%, dead. 28 % living.

In order to remove these two defects the creosote oil was emulsified
with it—the oil being poisonous to the insects. These several experi-
ments were tried with differing percentages of the oil, that of the soap
(solution) being constant.

(1) With 1-10 or -1% of creosote.
22500 cc. water
8 oz. soap Spraying 2.30 p.m., 24. 5. 13.
224 cc. creosote oil
The result being :
39 living

74 dead
~—— - Nearly 50 % dead.
106 dead |
54 living
(2) With -2 % of creosote.
4 0z. soap
11200 cc. water Sprayed at 12.30 p.m.
22 ce. creosote
110 dead |
8living J
(They were dead next day.)
(3) With -25 % of creosote.

-Nearly 93 % dead.

There were three trials. Every time

the result was that all the

larvae were killed by the time
| of the examination.

4 oz. soap
11200 ce. water
28 ce. creosote

(a) The method of the examination. The observers (Prof. Lefroy,
Mr Davidson, Mr Miles and myself) used to wheel the machine to the
apple trees. One of the heavily infected apple trees was selected and
was sprayed with the driving jet. Each of us then broke the twigs at
random and collected them together. Those twigs were brought home
and spread in an open space on papers. When they were fully dry
Prof. Lefroy picked out the dead and the living larvae, and thus the
different results and the percentages were obtained.

The creosote oil is very harmful to plants and especially to tender
leaves. It was tested in those percentages used in the experiments

P. R. AWATI Fa i

on different apple trees by Prof. Lefroy, who examined those trees
next day and found that no harm was done to them. It seems there-
fore that the creosote oil in the percentage used (-25 per cent.) is not all
harmful to the trees.

(6) Its action. The action of this emulsion is two-fold and there-
fore very effective. As it is shown above, the soap solution by itself
kills 72 per cent. of the larvae. Its action is also explained. The soap
solution, by being mixed with the creosote oil, becomes a deadly poison.
The soap solution enters the tracheae and blocks the stigmata and thus
introduces the creosote poison into the body. It acts both internally
and externally, and thus it becomes very effective. There is no chance
of recovery for the larvae, as is the case with the soap solution. The
percentage of the creosote, however, seems to be fixed—'25 per cent.
being the optimum. Below and above it the results are not very
satisfactory.

(c) Effects. They have been already dealt with. The death roll

by this emulsion is very great.

XI. Enemies of the Apple Sucker.

As far as I have observed there are no enemies. I have not been
able to see any parasite, internal or external, preying on it. The larvae
are healthy and normal, and I have not seen any malformation owing
to its being parasitised. So it is impossible to say whether there is any
parasite controlling the growth and spreading of this pest.

Occasionally I have seen mites attacking the nymphs and adults.
The mites are red and large—like those which generally attack aphides
(aphis). Besides these mites I have not seen any enemy to the apple
sucker.

XII. Immunity of the Apple Trees to the attack of the
Apple Sucker.

There seems to be no reason why there should be immunity to the
attack. Immunity may be acquired or inherent. The apple suckers in
the adult stages do not make any damage, and therefore there is no
pathological response. The inherent immunity may be due to the
fact that the juices of certain apple trees may be distasteful to the
apple suckers, while those of the others are sought after with avidity.
It must be remembered that the real damage is done by the larvae
and not by the adults. The larvae suck the juices of the buds and
not the fruits. It seems from what I have observed that there is no

272 Apple and Pear Sucker

difference in the quality of the juices of the different varieties of the
apple trees—they seem to be the same, whether sweet or sour, and
they are not disliked by any batch of the larvae.

No doubt there are different trees which are less heavily infected
than others, and there are some which are not infected at all. I doubt
whether the latter form the case of the immunity. The same variety
passes through all stages of infection—some with no larvae, while others
are heavily infected with them. It seems to be the case of the chance
distribution of the eggs of the apple sucker on different plants.

I have noted down the results of my experiment with regard to
the immunity :

Name of the variety Sweet or sour Infection
(1) Duchess favourite | very sweet | none
” ” | ” ” fair F
2 2 | ” 0 median
2° ” ” ” heavy
(2) Yellow injesting sweet fair
(3) Warner’s king | sour none
(4) Stirling Castle | es median
= 3 p fair
| 2

3?
= medium
' + re ” fair
(6) Worcester pearmain sweet none

(5) Early Julian”

INSECTICIDES FROM A CHEMICAL STANDPOINT.

By W. F. COOPER, B.A. (Canras.), F.CS.,
anp W. H. NUTTALL, F.1.C., F.C.S.

(From the Cooper Laboratory for Economic Research, Watford.)

As the title implies, this paper puts forward some ideas which, to
us, appear to lead to a wider range of choice in insecticidal substances,
and to possible improvements in their methods of application,

We are chemists and make no claim to a special knowledge of
entomology; yet we have been concerned for some time with the
practical control of various horticultural pests and animal parasites,
and we venture to hope that the experience thus acquired may be of
some little value to the economic entomologist.

On glancing down a list of the substances most generally used in the
preparation of insecticides, a chemist is at once struck by the surprisingly
small number of compounds which have been employed. It would
seem that until recently the changes have been rung on little more than
half-a-dozen materials: Bordeaux mixture—lime-and-sulphur—quassia
—arsenic—pyrethrum—paraffin, and so on. So-called improvements,
which are claimed from time to time, appear as a rule to be confined to
some slight modification of one or other of the existing formulae, the
number of which is already legion.

In the past the attempts to control entomological pests have been
of too empirical a nature. Substances have been tried with little, if
any, regard to their precise mode of action, and when a moderately
satisfactory material has been found the experimenter has rested
content, where he might with profit have continued his enquiries along
those lines which this result should suggest. Empiricism generally
tends to stifle true research, and genuine progress rarely follows in its
train, while patient research on well-organised and systematic lines
almost inevitably paves the way to final success.

It is not sufficient to discover that a certain compound is more or
less effective for the destruction of specific pests—the further step must

274 Insecticides from a Chemical Standpoint

be taken, of ascertaining what particular characteristic of that com-
pound is primarily responsible for the results obtained. For example,
in the absence of proof to the contrary, it is not wise to assume that,
because tar substances possess insecticidal properties, the latter are
wholly dependent upon the presence of phenolic compounds. In the
case of coal-tar disinfectants it was the practice until recent times to
determine the germicidal value by a chemical estimation of the phenolic
content alone, whilst no account was taken of the non-phenolic con-
stituents. It has since been shown, by actual tests on living cultures
of bacteria, that some of the non-phenolic constituents may possess
an even higher germicidal value than the phenols themselves, and,
in consequence, germicidal values of coal-tar disinfectants, based on
chemical determinations, have fallen into disrepute. This would have
been avoided had a careful examination of the factors which influence
the germicidal action of a coal-tar disinfectant been made.

It follows, therefore, that until many, if not all, of the factors which
determine the efficiency of an insecticide are known, the observer is
lable to draw similarly erroneous conclusions.

Hitherto the economic entomologist in his search for suitable
insecticides has confined himself to those compounds which to him
appeared to be cheap and easily obtained, but it seems to us that a
wide field still remains unexploited, in which, nevertheless, these
essential conditions obtain.

There are many organic compounds of probably high insecticidal
value, which are readily prepared in the laboratory, and which, if a
suitable demand arose, would be commercially possible. The choice
of these for experimental trials should not be made in a haphazard
manner, but should be preceded by a systematic investigation, so
arranged as to determine what particular characteristic conferred the
insecticidal property. Two illustrations will suffice to make our meaning
clear.

It has been found that xylene is the most effective of the tar hydro-
carbons in destroying wood-boring beetles. To what particular pro-
perty is this superiority due? Does some special grouping of the atoms
in the molecule play a part, or is it a purely physical question? If it is
a special grouping of the atoms which endows xylene with such a degree
of insecticidal efficiency, then it is reasonable to suppose that other
compounds with a similar molecular constitution would be equally
effective. If, on the other hand, the insecticidal characters of xylene
are dependent on its physical properties, then other fluids with identical

W. F. Cooper AnD W. H. Nvutrauh 275

physical constants should behave in a similar manner. Unfortunately
there is no reliable information at hand to decide the point, invaluable
as such knowledge would be as a basis for research on these lines.

Again, the efficiency of carbolic and cresylic acids as insecticides
is universally known, and it is reasonable to presume that these
compounds possess insecticidal properties by virtue of their phenolic
groups. Benzene compounds containing a nitro-group have germicidal
properties, and have been suggested as insecticides—as for example,
nitro-benzene. It is conceivable, therefore, that the nitro-group, like
the phenolic group, may confer insecticidal properties, if introduced into
a molecule. Would the insecticidal properties of carbolic or cresylic
acid, therefore, be increased by the introduction of one or more nitro-
groups? This was the question which the Bayer Farbenfabrik asked
themselves as early as 1892, and, as the result of systematic research,
they were able to answer it in the affirmative and produce a most
valuable insecticide, “Antinonnin.” This is ortho-cresol into which
two nitro-groups have been introduced, the potassium salt of the result-
ing compound, owing to its greater solubility, being employed in practice.
It is non-corrosive, and attacks neither metals nor textile fabrics.
Antinonnin has been extensively and successfully applied in the
destruction of the “Nonnen’’ (Monacha) larvae, infesting the forests
of Bavaria and Wiirtemberg; and has also been largely used as a
substitute for creosote in the preservation of timber. This affords an
excellent illustration of the value of systematic research as opposed to
empirical methods. ; |

The subject of insecticidal effect of the introduction of various
atomic groups into the molecule needs to be worked out systemati-
cally, much in the same manner as that in which Ehrlich carried out his
classic investigations on the effect of various organic arsenic compounds
on blood parasites. Ehrlich found that the position of the arsenic in
the molecule had an enormous influence on the toxic effect of the
compound, both on the host and the blood parasite; and, as a result
of a long and systematic research, he at length evolved his famous
“606,” efficacious doses of which, whilst highly toxic to blood parasites,
are practically innocuous to the host.

Speaking generally, metals in organic combinations, as distinct from
inorganic, are considerably less toxic towards the higher animals and
plants, whilst they retain their poisonous action on the lower organisms.
This fact suggests the possibility of the use of organo-metallic com-
pounds as insecticides. The insecticidal properties of the metal might

Ann. Biol. 1 19

276 Insecticides from a Chemical Standpoint

be thereby retained, whilst the injurious effect on the host might be
diminished. We are not aware that any organic arsenic compound
has been employed in this connection, the principal reason being,
possibly, that such compounds are usually too expensive for the purpose ;
but the use of an interesting organic compound of copper has been
suggested. This is cupric-di-methanal-di-sulphite (Cu(H,C.OH .SO.),),
which is easily prepared by passing sulphur di-oxide into a suspension of
copper hydroxide in 40 % formalin. A clear blue solution, containing
3 °%, of copper is thus obtained, which, it is claimed, combines in itself
a copper insecticide and a sulphuring agent.

The high insecticidal value of emulsions of paraffin or other oils
has long been recognised, whilst copper, in one form or another, is
in very general use as an insecticide and fungicide. Is it possible
to combine the advantages of both? Copper resinate is soluble in
mineral oils, so that by emulsifying such a solution of copper resinate,
a preparation would be obtained, which might possess the insecticidal
properties of both an oil emulsion and of copper.

According to Pickering, the action of Bordeaux Mixture is due to
the gradual liberation, by the atmospheric carbon-dioxide, of small
quantities of soluble copper sulphate. It is a well-known fact that
certain substances are much more reactive when freshly liberated from
their compounds.: In many cases this is due to their “nascent state’ ;
in others, the extremely fine state of division, in which they are
deposited, is doubtless responsible for their increased activity. Atmo-
spheric carbon dioxide might be employed with the greatest advantage
in the precipitation of insecticidal compounds in this super-active form,
but, with the exception of Bordeaux Mixture, and possibly potassium
sulphide, little, if any, use of it has been made up to the present. Let
us consider, for example, B-naphthol. This is a constituent of coal-
tar; it has high bactericidal properties, and, being a phenol, presumably
would act as an insecticide. It is a simple matter to prepare a solution
of 6-naphthol in caustic soda, so adjusted that a mere trace of carbon
dioxide would precipitate a minute quantity of the B-naphthol. Such
a solution used as a tree spray might prove to be of the greatest value,
because its active constituent would be liberated gradually, and so
could only act upon the foliage in extremely minute quantities.

To take another example: preparations containing potassium
sulphide (liver of sulphur) are largely used as insecticides. To what
particular property these owe their insecticidal action is apparently
doubtful, The gradual precipitation of sulphur from the admixed

W. F. Cooper anp W. H. NuttTau OTT,

poly-sulphides is probably largely responsible. But the necessary
quantity of carbon-dioxide to effect the precipitation of sulphur from
commercial potassium sulphide is very large; consequently the process
is Slow, and probably some weeks elapse before the beneficial effects of
precipitated sulphur come into play. It is, however, not a difficult
matter to prepare solutions from which sulphur can be precipitated in
an exceedingly finely divided state by a mere trace of carbon-dioxide,
and there is little doubt that these would be found more effective than
ordinary sulphide preparations.

The efficiency of many insecticides is entirely dependent on the
fact that they suffocate the insect by blocking up its breathing orifices.
Of this type, viscose suggests itself to the chemist as a most excellent
material. Viscose is a derivative of cellulose, which is extensively
employed in the manufacture of artificial silk. It is characterised by
the fact that even in dilute aqueous solution it forms an extremely
viscous liquid, which by exposure m thin layers gives a tenacious and
impermeable film. Obviously, viscose preparations could not be used
for spraying the entire foliage of trees, but as a winter wash or as a
local application, in the case of scale, such are certainly worthy of
trial.

So much then for the directions in which a search for new and
improved insecticides might be made. Many more could doubtless
be suggested, but the foregoing will suffice to indicate the wide field
awaiting inquiry.

Quite apart from the quest for new substances, there is another
point, which we take this opportunity of emphasizing, because it is one
which many economic biologists are apt to lose sight of, in the selection
of remedies for the eradication of insect and fungoid pests. This is
the extraordinary importance of the physical condition of the insecticide
in its influence on the efficiency. Attention has already been drawn to
the fact that a chemical assay of a carbolic disinfectant is really no
measure of its bactericidal power, because it is based on the false assump-
tion that only phenolic compounds have bactericidal properties. But
the chemical assay of a disinfectant fails for another reason, and that
is because it takes no account of the physical condition of the active
compounds. It has long been known that, of two preparations con-
taining equal percentages of the same tar acid, emulsified in the one
case, and in a state of sémple solution in the other, the emulsified
preparation possesses a much higher bactericidal power than that
containing the tar acid in solution, Chick and Martin (Jowrn. of Hygiene,

19—2

278 Insecticides from a Chemical Standpoint

vill, 5, pp. 698-703) have shown this to be due to the fact that the
bacteria are adsorbed on to the fine emulsified particles of the tar acid
and are thus brought into direct contact with the germicidal agent in
a highly concentrated form. Now, whatever may be the cause, there
is little doubt that, of liquid insecticides, an emulsified one is far more
efficient than a non-emulsified one. Whether Chick and Martin’s
explanation holds good in this case also, is questionable; possibly, with
very minute insects, adsorption may play some little part. Where,
however, an emulsified insecticide is undoubtedly vastly superior to a
non-emulsified one is in its wetting-power, and with insecticides this is
a point of paramount importance. It is needless, here, to point out the
extreme difficulty of wetting the chitinous integument of an insect, or
the protective woolly secretion of the aphis of American blight; nor is
it necessary to dwell upon the fact that an insecticide cannot do its
work unless it actually comes in contact with the insect: such are self-
evident to all who have to deal with entomological pests. Perhaps
what is not so generally recognised is the fact that different liquids have
very different wetting powers. A simple experiment serves to illustrate
this. The American cloth back of an exercise book may represent,
sufficiently well for the purpose, the chitinous integument of many
insects. When water is poured on to the back of such a book it runs
into droplets and flows off without wetting it, precisely as water would
run off the integument of the insect. If, however, an emulsion is
poured on to the book, the whole surface is completely wetted, and the
liquid forms a continuous film. If, now, the emulsion is washed off by
a stream of water, the unwettable character of the surface again becomes
evident, the water flowing into droplets and running off. A liquid
insecticide, in order to be efficient, must be capable of thoroughly
wetting the insect and its surroundings. It must “rwn’’ easily and be
able to penetrate the interstices of the buds, the folds and crinkles of
the leaves, waxy secretions, hairy or woolly surfaces, the minute orifices
of the insects themselves, etc.; and experience has shown that liquids
of low surface tension, e.g. emulsions, are best suited to this end.

There is an additional advantage in the use of an emulsion, which
was brought out in a pertinent manner in some work carried out by one
of us (W. F. C.) in South Africa four or five years ago. We were then
concerned with the eradication of the Bont Tick, which infests cattle
and transmits the fatal disease—heart-water. Sodium arsenite had
long been used as a means of destroying these ticks, but it was found
that, at the strength necessary to kill the ticks, the cattle themselves were

W. EF. Cooper anp W. H. Nourrau 279

frequently so badly scalded that death ensued. By employing an
emulsified oil in conjunction with the sodium arsenite and so ensuring
complete wetting of the hide, Cooper found that a much lower per-
centage of arsenite was sufficient to destroy the ticks and that the risk
of scalding was practically removed. The scorching of sprayed trees
is not an uncommon occurrence, and it is most probable that the means
adopted for the prevention of the scalding of animals would also prove
effective in preventing injury to foliage.

With solid insecticides or fungicides, such as copper carbonate, lead
chromate, lead arsenate, etc., which are usually applied, as aqueous
suspensions, in the form of a spray, the physical condition of the solid
plays a by no means unimportant part in the efficiency of the pre-
paration. According to the manner of precipitation, these compounds
may be obtained in either a coarse granular state, or as a fine light
flocculent precipitate. In the first case, the suspension settles rapidly
and requires constant attention in the matter of stirrmg; further, it
is liable to clog the nozzles of the spray-pump and, in addition, after
drying, is apt to fall from the sprayed leaves. On the other hand, a
fine, flocculent precipitate has none of these disadvantages.

These examples will serve to show how very greatly the efficiency
of an insecticide or fungicide is dependent upon conditions other than
chemical; they indicate that, as with disinfectants, a chemical assay
alone must give a wrong impression of the actual value; and these are
facts which must not be lost sight of in the consideration of the standard-
isation of insecticides.

As a matter of fact, we are only just entering upon the scientific
study of the preparation and application of insecticides. That our
methods have been too empirical in the past is largely due to the lack
of co-operation between the economic entomologist and the chemist;
neither can hope to achieve real success alone. It is for the entomo-
logist to investigate the various pests, their life history, habits and
vulnerability; it is for the chemist to devise and elaborate means of
attack, based upon the information supplied by the entomologist and
-upon the chemical and physical properties of the substances with
which he has to deal.

280

INSECTICIDES.

By H. M, LEFROY.

(Imperial College of Science, South Kensington.)

Ir would be interesting to collect information as to the insecticides
in general use in horticulture in different countries in any one season
and to determine as far as possible what were the circumstances leading
to their use. There is, I believe, a fashion in insecticides: at one time
Paris Green and London Purple ruled; then came Lead Arseniate in
America; this is apparently giving place to Zinc Arseniate and Barium
Arseniate, while there is reason to hope that Lead Arseniate, and
perhaps Lead Chromate, will be more familiar in this country.

So, too, for contact poisons. I remember the era in America of
paraffin emulsions and rosin washes; then came whale oil soap; lime
salt and sulphur followed, then the heavy oils and then “miscible
oils.” The vogue of the lysol and similar mixtures on the Continent
has to be noted, and we may note that miscible oils are being used
more freely in Australia and South Africa.

In estimating the causes of these successive fashions one would
need to distinguish the effect of the recommendations of State Depart-
ments of Entomology and the influence, increasing in recent years, of
the weight of pure advertising by firms interested in the sale of the
particular products they were able to handle. In this paper I omit
entirely the “ patent’? or “proprietary’’ insecticides in so large use,
since it is not always clear on what ingredients their action depends,
and I confine myself to insecticides of definite known constitution, or
those which depend upon the presence of some known chemical com-
pound.

It is not easy to ascertain exactly what insecticides are at present
used on a large scale in this country, but I have tried to do so from three
sources: the first is the published recommendations of horticultural
journals; the second is the recommendations in the leaflets of the
Board of Agriculture; the third is those that I gather from general

H. M. LEerroy 281

information, observation, reports, papers in actual use. For the
first I attach extracts from 16 consecutively weekly issues of the
Gardeners’ Chronicle in 1913, these occurring in the contributions of
head gardeners or in editorial advice. I think they reflect accurately
current ideas and practice.

Hardy Fruit Garden
For aphides

Abies diseased
Aphis. Editorial

Broad beans
Black fly
Cool orchard house

Market Fruit Garden
Insect pests

The tree syringed with a very mild insecticide. In
some cases it will be found necessary to use tobacco
powder, which should be left on for two or three days,
and then thoroughly syringed off with clear soft water.
p. 268, 26. 4. 13.

Spray three times at intervals of four days, with a
solution of soft soap and quassia chips, and repeat
the spraying in September. p. 279, 26. 4. 13.

Syringe the plants frequently with a fairly strong solution
of soft soap. p. 280, 26. 4. 13.

The eradication of insect pests can be done either by
fumigation with nicotine, or by spraying with some
good insecticide. p. 288, 3. 5. 13.

For some unknown reason, insect pests are troubling me
at present much less than usually. It is many years
since I found so few Apple suckers. Most varieties
of Apples in my orchards are almost free from this
enemy, and many are nearly exempt from the attacks
of aphides and caterpillars. It would be interesting
to learn whether this comparative immunity is general
or not. If it is not so, perhaps persistence in des-
troying the pests for years past is meeting with a fitting
reward. But it may be that suckers and aphides
hatched prematurely during the mild winter or in
March were killed by frost. Or, again, spraying with
a strong solution of lime-sulphur just before the buds
burst may have done something in coating over eggs
or destroying mother queen aphides. It is too early,
however, to assume that the comparative immunity
will continue. There can hardly be a bad attack of
the sucker after this; but the aphis and the caterpillar
have plenty of time during which to appear in strong
force. Already the hope that Plums would escape the
usual infestation of aphis has been disappointed. On
April 24 no attack could be observed on any but two
varieties; but on the 29th there were aphides on all.
As the leaves are curled over the pest, spraying would
be a mere waste of time and money.

The first summer spraying Owing to the partial immunity of Apples from insect

pests, the usual spraying before the expansion of

28? Tnsecticides

blossom was to a great extent dispensed with, only
varieties which were badly attacked by aphis, sucker,
or caterpillar, or all three pests being sprayed. This
was a great relief, and it is not by any means certain
that it might not have been extended to all varieties
without any bad results. For on every occasion rain
fell a few hours after the spraying was done, probably
washing most of the spray fluid off the trees, and off
the insects that had been wetted by it. There was
no question of waiting for settled fine weather,, as
the work had to be done before the expansion
of the blossom. Arsenate of lead was combined
with the soft-soap wash for aphis and sucker, in order
to poison the food of caterpillars. If pests should
attack the varieties not sprayed, they will be treated
after the fall of the blossom, and in any case varieties
subject to scab will be sprayed with lime-sulphur of
summer strength.

Results of spraying One of the most unsatisfactory features of spraying is
the difficulty of determining its results, and that diffi-
culty has proved particularly great this season. Even
in the cases of Apples most infested, such as those in
which five or six out of twenty trusses of blossom were
found to contain aphides, and three or four a few
suckers, I could not find more than one dead aphis or
sucker in fifty trusses examined a day or two days after
the spraying. I found more live ones, but very few
even of these. The question, then, is whether the pests,
killed or weakened by the wash, were washed out of
the trusses by heavy rain. It is commonly assumed
that aphides are washed off the trees by rain, and
particularly by a thunderstorm; but, so far as I know,
this is an assumption which has never been actually
proved. Some trusses found to be infested by aphides
could be labelled, some of them being sprayed and
others not sprayed, care being taken to avoid any more
thorough spraying than would be given on a large
seale. If the insects could be counted beforehand, so
much the better. Examination could be made 24
hours after the spraying, results being noted; and again
after the next fall of rain, if it occurred soon enough.
Rain might hold off too long, and the experiment would
then have to be repeated. In noting-the results after
rain, if any pests were found to have been washed off
the trees, it should be noticed whether more were
ousted from the sprayed trees than from the others.
As to a thunderstorm, there can hardly be any special

THE ANNALS OF APPLIED BIOLOGY. VOL. 1, NOS. 3 AND 4

Apple Sucker. 3rd Instar.

Apple Sucker. 4th Instar,

BEATE

XVII

THE ANNALS OF APPLIED BIOLOGY. VOL. |, NOS. 8 AND 4 PLATE XVIII

Apple Sucker. 5th Instar. Pear Sucker. 4th Instar.

Pear Sucker. 5th Instar

Roses
Aphis

Hardy Fruit Garden

Gooseberry caterpillar

Editorial
‘Vine weevils

Fruits under glass
Red spider

Hardy Fruit Garden
Apricot

Market Fruit Garden
Apple sucker

Editorial a
Apple blossom
Bud moth

H. M. Lerroy 283

effect from it, unless the rainfall happens to be more
violent than in an ordinary storm, as it is not at all
likely that a specially electrical condition of the atmo-
sphere affects the aphis. A busy fruitgrower can
hardly find time for such experiments as are suggested.
They should be carried out by the authorities paid out
of public funds to undertake research. As matters
stand, I do not know whether the expense incurred in
There is
too much reason to fear that the arsenate of lead has
been all, or nearly all, washed off the trees by rain, and
that the caterpillars will be able to go on feeding with
impunity. They, like the other pests, were in the
trusses of blossom buds and the surrounding leaves.
“*A Southern Grower.” p. 301, 10. 5. 13.
Should the pest appear on the leaves, syringe the trees
with a mixture of soft soap and sulphur.
will also check mildew.

spraying has been useful or almost useless.

The sulphur

Caterpillars are particularly
numerous this season and unless they are diligently
sought for they may do much damage. _p. 308, 10. 5. 13.

If the pest has already taken a hold on the bushes, they
should be syringed at once with a good insecticide.
Some mixture containing a certain proportion of
nicotine will answer the purpose best, it will kill the
grub in afew minutes. The trees should be afterwards
syringed with clean, soft water. p. 309, 10. 5. 13.

Place freshly tarred paper under the vines, then approach
the vines with a lantern in the hand, giving each rod
a slight shaking....[t is difficult to kill the larvae in
the soil for they seem proof against any but the
strongest and most dangerous applications. p. 320,
10. 5. 13.

The vines will need syringing occasionally with an
insecticide to destroy red spider. p. 326, 17. 5. 13.

A small yellow caterpillar is a great pest: this pest
should be hand-picked and destroyed. After a
thorough search syringe the trees with a weak solution
of nicotine. p. 327, 17. 5. 13.

Our trees were sprayed with Buxton lime. and in the
case of Warner’s King, which I have always found the
most susceptible to sucker, I used salt with the lime.
The spraying was done just before the flower buds
parted from the cluster ready for expansion. p. 332,
D8. ae

The trees should have been sprayed with arsenate of
lead. ..as soon as the petals have fallen, spray with 1 Ib.
of arsenate of lead paste to 25 gallons of water. As

284 Insecticides

there are some aphides in the trusses add 2 lb. of soft
soap to the 25 gallons of wash. _ p. 336, 17. 5. 13.

Editorial at .. Spray in winter with a wash of 3 lbs. soft soap, 5
Spruce fir gallons water, and 1 pint of paraffin thoroughly
‘Spruce gall’ mixed. p. 336, 17. 5. 13.

Hardy Fruit Garden .. Black and green aphides will soon make an appearance
Pear trees on walls on the ends of the shoots and should be destroyed by

syringing with insecticide. Leaves that are infested
with caterpillars or (? of) the Pear moth, should be
gathered and burned. p. 367, 31. 5. 13.

Editorial on .. To destroy aphis, it is best to fumigate with a nicotine
Aphis and red spider on _— preparation. For red spider, the leaves may be
vines sponged with a little soapy water—half an ounce of

soft soap to one gallon of water—mixed with half a
pound of flowers of sulphur and kept stirred. Or
flowers of sulphur may be applied dry with the Malbec
bellows. p. 375, 31. 5. 13.

Roses. «. a .. Syringe roses with an insecticide at least once a week to
The flower garden keep aphis in check. p. 383, 7. 6. 13.

Fruits under glass .. The trees should be syringed frequently with an in-
Red spider secticide. p. 383, 7. 6. 13.

Public parks and gardens The Goat moth (Cossus ligniperda) is far more common
Tree pests in London over the London area than is generally supposed, and

this may also be said of the Wood Leopard moth
(Zeuzera esculi), both of which attack the Elm, Poplar,
Ash and Oak. The larvae of both moths, which are
deposited on the bark of the tree in July or August,
tunnel into the wood and do much damage to the
timber as well as the health of the tree. Placing
cyanide of potassium in the hole and closing the aper-
ture is the best method of destroying the caterpillar,
though we have used gas tar in a similar way with good
results. Dislodging the caterpillar by means of a
bent wire has been successfully carried out. Lime
trees all over London are attacked by the caterpillar
of the Lime Looper moth (Hybhernia defolaria), while
the Thorn fly, an Aphis, attacks whole hedges of the
Hawthorn as well as specimens standing singly.
Sponging with tobacco water is to be recommended for
the latter, and for the Lime trees caterpillar bands of
any sticky substance painted around the stems will pre-
vent the insects ascending to the branches. Red spider
(Tetranychus telarius) is another formidable insect
pest that not infrequently attacks the leaves of several
species of hardwooded trees, and is often the cause of
death of the Ivy, particularly when grown as a ground
carpet. The leaves turn a rusty-brown colour, crumple

Apples and plums

An important
lesson

H. M. L&EFrroy 285

up, and finally fall off, the whole plant dying in con-
sequence. Large areas of the Ivy used for ground
work in various parks and gardens of London have been
killed outright of late years. Spraying with soft soap
will prevent the insect from spreading. Though the
Beech is by no means a common tree in London, yet
of the few specimens to be found, many are attacked
by Cryptococcus fagi, which is alarmingly on the
increase in this country. Paraffin or petroleum emul-
sion will destroy the insect, and scrubbing the bark
with a rough brush and soft soap is an excellent
remedy. Wholesale destruction to the leaves of the
Spindle tree and other species of Euonymus is yearly
occasioned in some of the London parks by the cater-
pillar of the small Ermine moth, myriads of the cater-
pillars appearing on the foliage during summer. So
rapidly does this insect increase, and so verocious is
its appetite, that a shrub will be completely stripped
of its foliage in two or three days. Spraying with
XL All Insecticide or petroleum emulsion is. the best
remedy. Where Oak trees are found in London, the
Oak-leaf Roller moth (Zortrix viridana) is usually
present about the beginning of June. It is a very
destructive insect, and attacks not only the leaves, but
buds and inflorescences, and usually works from the
top of the tree downwards. Where only a single or
few Oaks are attacked spraying may be resorted to,
but hardly any remedial measure can be adopted in
a clump or plantation of the tree. Starlings, rooks and
other birds destroy vast numbers of this pest, and
should be encouraged. By “Superintendent.” pp. 400,
401, 14. 6. 13.

Spraying lime-wash just before the buds approach the

bursting stage in dry weather.

object Very striking evidence as to the advantage of spraying

Apples and Plums with lime-wash, as thick as it can
be got through the spraying machines, was obtained in
Mr Hooper’s orchards. In one portion of the farm all
the Apple and Plum trees had been sprayed with this
wash, nothing being added to the lime, except water,
while they were left unsprayed in the rest of it. The
lime-sprayed Apples and Plums were free from the
aphis blight, while those not sprayed were very badly
infested. If memory serves, the contrast applies also
to Apple sucker infestation. At any rate, a mere
glance was sufficient to allow any one to see it in
relation to the aphis blight, and growers elsewhere to

286

Flower Garden. Aphides

on chrysanthemums
Hardy Fruit Garden
Wall trees

Editorial

Cabbage root maggot

The spruce aphis

Hardy Fruit Garden
Black aphis

Editorial
Jonifer coecus
Fruits under glass
Peaches

Editorial
Celery fly

Insecticides

whom this striking case was named said that they had
seen similar results from lime spraying. Mr Hooper’s
explanation is that the lime coats over the eggs of the
pests, and extracts moisture from them, thus destroying
their vitality. Lime-wash must be strained before
it is put into a spraying machine, and it is important
to do the work only in dry weather, and to cover
every twig. If rain occurs before the stuff has dried
thoroughly on the trees, the lime is easily washed off;
but it sticks on well after being dried. In the case under
notice the spraying was done as soon as there was any
sign of an attack by birds upon Plum buds. Apart
from this attack, however, just before the buds approach
the bursting stage is probably the best time to apply the
lime-wash. “Southern Grower.” p. 414, 21. 6. 13.

It is wise to spray with some insecticide of moderate
strength. p. 436, 28. 6. 13.

Red spider, syringe the foliage constantly with water,
to which has been added a little quassia extract.

If the cherries are infested with black fly, the affected
shoots should be cut away and the trees syringed with
an insecticide. After each application a syringing
of clean water should follow. This method will be
found to be a great improvement on the old plan of
applying tobacco powder. p. 437, 28. 6. 13.

Soft soap, one quart, in one gallon of boiling water. Add
one pint crude carbolic acid and dilute with 30 times
its bulk of water. Syringe the ground around the
attacked plants. p. 444, 28. 6. 13. :

Spraying with paraffin emulsion is recommended. Soft
soap and quassia extract may also be tried. p. 5,
God. US:

If there are bad infestations the growths most affected
should be cut off and burned and the tree syringed
afterwards, first with an insecticide, then with clean
water. ps9): 5.72.13.

Next winter drench the trees thoroughly with soft soap
and paraffin emulsion. p. 20, 5. 7. 13.

The foliage should be syringed thoroughly or washed by
means of the garden engine two or three times a week.
This will cleanse the leaves of insect pests. p. 29,
12. 7. 13.

Pinch the maggots in the leaves and remove the leaves.
... Afterwards you can make the plants distasteful
to the flies by syringing them with quassia extract,
or you may scatter soot, lime, ete. op. 60,
19, 7. 13.

H. M. Lerroy 287

Remove the plants and spray the exposed roots and soil
with carbon bi-sulphide, using a small glass spraying
apparatus. The process must be repeated. Another
plan is to have holes in the soil and pour one tea-
spoonful of the carbon bi-sulphide in each hole. _ p. 76,
26. 7. 13.

‘Extract of Quassia.’

Editorial
Ripersia on palm roots

Kditorial. Rose leaves py 16, -26..7.°138:

Board of Agriculture Leaflets.

Mangold fly paraffin 1 gallon |
soft soap 4 Ib. Formula 1.
water 10 gallons
Onion fly paraffin 3 pints 1
soft soap $ Ib. Formula 2
water 7 gallons I)
Surface caterpillars soot and lime
|Paris green 1 Ib.
|water 50 gallons
( paraffin 1 quart
Celery fly . . soft soap 3 lb. > Formula 3.
water 10 gallons }
fe acid 1 pint
soft soap 4 lb.
satee 10 gallons
Carrot fly paraffin 2 gallons
soft soap 4 lb. Formula 4,
water 60 gallons
Red spider sulphur
paraffin 7 gallons
soft soa 6 Ibs.
liver of aint * 24 Ibs. | Hormals,b-
water 100 gallons
sulphate of iron 8 ozs.
caustic lime 4 ozs. | TGRERT TAGs
paraffin (solar) 16 to 24 ozs, |
water 10 gallons
liver of sulphur mixed
with quassia wash
Paris green Pb:
Asparagus beetle a { an ee 200 gallons
| as of lead 3 OZS.
treacle 1 Ib.
Katee 10 to 12 gallons
(preheom 1 oz.
Thrips . .. + Soft soap 1 oz.
water 2 gallons
Hop aphis soft soap 4 to 10 lbs,
water 100 gallons

or with 6 lbs. quassia chips

288 Insecticides
: {soft soap 6 to 10 lbs.
oe lwater 100 gallons

or with quassia 6-8 lbs. added

paraffin 2 gallons On dormant
soft soap 14 lbs. trees
caustic soda 6 lbs. (Woburn
water 28 gallons formula).
Cabbage fly paraffin 1 cupfull
sand 1 pailfull
( lime 1 lb.
Black currant gall mite + sulphur 1 Ib.
| water 20 gallons
(sore soap 1 quart
Vine weevils - crude carbolic 1 pint

Winter moth ..

water
{ Paris green
| water

30 gallons
1 Ib.

200 to 250 gallons
{arsenate of lead paste 2 Ibs.

| water 50 gallons
hellebore 1 oz.
Gooseberry sawfly . + flour 2 ozs.
lets 3 gallons
{Paris green paste 4 OZ.
‘water 10 gallons
Apple sucker .. paraffin 2 gallons
soft soap 3 |b. Formula 7.
water 11 gallons
(oe acid 2 to 3 gallons
soft soap 6 lbs.
| water 100 gallons
caustic soda 10 lbs.
Woolly aphis ora of potash 10 lbs.
(Winter washes) | soft soap 2 or 3 lbs.
\water 100 gallons
14 lbs. 5

paraffin
caustic soda
\water

2 gallons | Woburn
6 lbs, | formula.

(ee soap
| 28 gallons

Speaking generally, the following are methods in fairly general use:

1. Lead arseniate or Paris green for caterpillars.

2. Soft soap and quassia for hop aphis; soft soap alone or with:
quassia extract for aphides generally.

3. Sulphur in some form for red spider.

4. Washes containing free caustic alkali for cleaning tree trunks
in winter.

5. Paraffin in very weak emulsion with soft soap or paraffin stirred
up in water for garden pests.

H, M. LeErroy 289

6. Lime, salt and sulphur in vague proportions for apple sucker, etc.

7. Lime washing for winter use.

8. Nicotine as a general panacea for all pests, as a stomach poison
for caterpillars, as a contact poison for apple sucker, aphis, etc.

It will be admitted probably that these insecticides have come into
use on purely empirical lines; the use of arseniates has probably come
from human toxicology, and a very exhaustive inquiry into the action
of some mineral compounds in India! has not produced anything more
poisonous; it is probably a question of the form of arsenic to be used.
But what has governed the choice of insecticides that do not act on
the internal organs, but those acting from without? I think none but
tradition and purely empirical practice, with experience in large scale
experiments as a deciding factor.

Is experience on a large scale experiment of much real use? It is
in some cases, such as mussel scale, where the insect is one-brooded ;
I doubt if it is much use in a many brooded or migrating insect, such as
an aphis. The factors that control the increase of aphis are many and
it would require very careful examination of the conditions to say that
the spraying had done the real work, or that the actual nature of the
insecticide had been the deciding factor. Suppose a grower of plums
sprays for the Leaf Curling Aphis in June; a week after he looks for
aphis and finds none; he thinks it is the spraying, whereas it is the
migration of the aphis from the plums that has produced the
absence.

It is worth while thinking for a moment how these insecticides act;
what actually happens when paraffin emulsion is applied; where does
the paraffin go to, what tissue does it affect, how does it work? A
Board of Agriculture Leaflet states “The presence of the soft soap causes
the wash to touch the aphis, and as it dries the thin layer of soft soap
clogs the breathing pores and kills the insect”? (Hop aphis). Did the
author of this statement really know this, or was it simply the generally
accepted statement? If so, why do most growers add quassia, and
why does quassia kill aphis? what does quassia actually do? I do
not think actually that anyone can tell us what the quassia extract does,
and I believe that we shall get much better insecticides when we know
how it is that these things kill. What is it that happens? If we know
that, can we not devise insecticides that make this happen, not that
happen to kill?

1 Lefroy and Finlow. Memoirs of the Agricultural Dept., India, Entomology,
vol. Iv. no, 5.

290 Tnsecticides

If we did, it is likely that some of them would be much the same as
before, since the sum total of human experience, however got, brings one
near the truth. Experience tells us that paraffin kills; it does not
tell us how; but knowing how is not going to tell us not to use it.
Paraffin will still kill; only ultimately out of knowing why, we shall
know whether paraffin itself is the best or whether there is something
better not yet tried.

In considering the question of insecticides there are a number of
points and I would like to suggest two:

1. Spreading over and wetting the plant. In many cases it 1s
necessary to spread over or wet the plant in order that the substance
contained in suspension or in solution should be spread over the leaf.

If a leaf is sprayed with mercury, the mercury would not spread
over or wet it; the mercury would draw into drops and run off.

If it is sprayed with water, the water might spread and it might
not ‘wet’; on a cabbage leaf it would not spread or wet, on others
it might.

If you sprayed it with pure paraffin it would spread over and wet
all the plant and the paraffin would ‘creep.’ Why this difference of
behaviour? It is partly due to two things: the surface tension of
the liquid, high in mercury, middling in water, low in paraffin; the
question of the inter-solubility of the liquid of some constituent of the
surface of the leaf, e.g. the wax on the cabbage leaf, being totally in-
soluble in the water and causing the water to roll off at once.

To spread, therefore, one must presumably have a low surface
tension, and to wet also have a wax solvent or a liquid that will be
absorbed by or dissolve the outer coat. Now leaving the question of
a leaf with its broad surface, take the case of a bud or a curled leaf:
here still more the surface tension question is apparent as the liquid
might need to penetrate the curled leaf and act by capillarity. I will
quote a case here I had need to go into carefully: we had a disease on
indigo in which the plant curls into a compact knot at the tip; in this
lives a Psylla. It was a question of finding an insecticide that would
wet and penetrate. We found by experiment that some insecticides
penetrated better than others. We found that they varied according
to the concentration, and we eventually found one that penetrated so
well as to go right in.

Dr Leather, the Imperial Agricultural Chemist, very kindly
measured surface tensions for me and this last had the lowest.

‘

It was an “oleic’’ acid soap at 1 lb. in 12 gallons of water. It was the

H. M. LEFRoy 291

best soap we got and it was better than rosin compound, oil emulsions,
soda solutions and other things. An oil emulsion in -8 per cent. soap
solution has a higher tension than the soap solution. We tested
‘penetration’ by dipping curled heads of the plants, then cutting them
open and seeing what had happened.

Now in this case it was purely one of getting a commercial product
of low enough surface tension to wet and penetrate the curled plant.
We had to think afterwards of what we could put in to kill the insect.
A similar case exactly will be described to you in the paper by Mr P. R.
Awati.

Apart from the mere surface tension, what of the different behaviour
of a liquid on an ordinary leaf or on a cabbage leaf: is there a reaction
between the liquid and the surface depending on the latter? I am not
a physicist and cannot say, but I believe there is and, so far as I under-
stand it, I explain it below. But you can get round this in some cases
by adding to the liquid a solvent of the wax (if any) in the plant. For
instance, a cabbage leaf behaves very differently to a liquid containing
a solvent of its wax than it does to the liquid without; for the solvent
dissolving the wax eliminates the wetting question since the wax is
there already, and it becomes therefore a question of ‘spreading.’
Spreading power, even more than wetting, depends on low surface
tension and we may, I think, distinguish “spreading of a liquid over a
surface it never wets’’ and wetting due to the liquid actually entering into
solution with a substance on the leaf surface. You may attain ‘spread-
ing’ of the liquid by either method but not wetting.

I am indebted to Dr Vaughan-Cornish for a reference to Clark-
Maxwell’s Theory of Heat, in which surface tension is discussed.
I have endeavoured to extract the gist of the physics of surface tension
so far as it refers to this problem.

The spreading power of a liquid on a solid depends in this way on
surface tension :

When a solid body (the leaf) is in contact with two fluids (air, wash)
then if the tension of the surface separating the solid from the second
fluid (wash) exceeds the sum of the tensions of the other two surfaces,
the second fluid will gather itself into a drop and the first fluid
spread over the surface, 7.e.

\_8.T. of Wash and Air

If _§.T. of Wash and Solid 7 +. Air and Solid,

then the Wash goes into a drop.

Ann. Biol. 20

29? Insecticides

If the reverse, the Wash spreads over the whole surface and will
wet the Solid.

Assuming then that the surface tension of the air and the solid
(the leaf) is always the same, and that the surface tensions of Wash-
Solid and Wash-Air vary proportionately according to the nature of
the wash, then clearly the measure of the surface tension of Wash-Air
is an indication to us of the wetting power, and the lower this is the
greater the chance of wetting.

The equation is
/ Wash-Air
\ + Air-Solid,

clearly the lower the two Wash surface tensions, the more likely are we
to get the one we want.

Wash-Solid

_Air-Wash per sg.cm.

LEAF Wash -Leat
per sg.cm.

The Air and Water surface tensions of these liquids are:

Air Water
Water fe ae Ge 205 —
Petroleum .. on Se aes 2-834
Mercury es af ¥.) 90-03 42-58

I have not the surface tensions of any of these with a leaf surface
so I cannot work out an equation, but the above figures show why, for
instance, mercury and petroleum and water behave differently as regards
leaf surfaces.

It will be noticed that it is not only the wash-air surface tension that
counts, but the wash-solid and the solid-air. The difference between
the wetting power of water on a cabbage and on an apple leaf is due to
the difference in surface tension to air and wash between the wax on
the cabbage leaf and the substance on the apple leaf. In the first case

N Wash-Air
Wash-Wax > Wax-Air

and no wetting occurs by the wash.

H. M. LeEerroy 293

In the second case
: Wash- Air
Wash-Apple leaf < hip leone Ate
and wetting occurs.

Therefore, the nature of the actual substance on the surface of the
leaf determines whether the wash will wet or not.

If then we knew the surface tensions of

plant-air,

plant-wash,

wash-air,
we could always tell if the wash would roll off or not. So for the insect:
if we knew the surface tension of

aphis-air,

aphis-wash,

wash-air,
we should know if our wash would wet the aphis or not. As we do not
know these, and as our plant-air, or aphis-air, remains a constant, we
strive to make the wash a practical success by getting one in which
wash-air (measurable) and therefore wash-plant is as low as possible.
One imagines that, had insecticides received attention from chemists
and physicists, the constants surface tension of plant-air, plant-wash,
wash-air could be looked up, as also the more complex surface tensions
of emulsions. When drops of oil float in an emulsion they affect the
surface tension of the emulsion in relation to air and plant.

2. The next point is this: how do these insecticides act; must the
liquid spread over the insect, must they ‘wet’ it, and, if so, then how
do they act?

There are, | think, three points:

(1) Mere spreading over mechanically.
(2) Wetting with spreading.
(3) Toxic action after wetting.

(1) In the first case I take such actions as lime wash, which spread
over mechanically and never wet; the action may be due to mechanical
causes solely, probably suffocation.

(2) Wetting, including spreading, means the insecticide is in
physical contact with the body. What does this really mean? Does
it mean that the head, the segments, the antennae and legs are wetted,
or that only parts are, or that there is a film of the liquid lying over the
whole insect but not actually in contact, say, with the under surface ?

20—2

294 Insecticides

I take it to mean that the insect is actually in contact with the insecti-
cide all over without any air-film between. It means, for instance,
that the liquid is in contact with the spiracles.

(3) Means that 2 also has a toxic action. Now assuming that we
have an insecticide that spreads, that wets and that penetrates to the
insect, what happens then we do not know.

With a view to getting some accurate ideas I made a large series
of experiments with meal-worms with these results:

1. No action is got by applying any liquid for a short time to the
skin, but many act at once if applied to a single spiracle.

2. Interference with the mechanical functions of at least five pairs
of spiracles is necessary to produce any symptoms due solely to mechan-
ical interference.

3. Closing all spiracles produces a condition we may call ‘rigour,’
in which a liquid will enter the spiracles.

4. It is impossible to get a liquid to enter one spiracle unless this
condition is produced.

5. Dipping a meal-worm in a liquid produces the condition in which
the liquid enters. We can therefore compare the effects of liquids by
this means.

6. Of liquids tested the following results were got:

Killed all Killed some Killed none
Clove oil Quinoline Picric acid in water
Xylol Carbolic acid Alcohol 70 %
Turpentine Formol 4 % Nicotine 1 % aq.
Nitro-benzene Pyridine Acetone
Chloroform Acetic acid Ether
Amyl acetate Eucalyptus oil Chloral hydrate aq.
Cymene Methyl] salicylate Water
Pseudocumine Aniline

Acetic ester

Now results with meal-worms are not of much direct use and we
must, for the moment, eliminate the peculiar ‘rigour’ results. But
they show us, I think, that a much greater range of liquids than are
generally used have a toxic action and that we must attach far more
weight to the details of the structure of the spiracles and tracheal
system.

It would look even as if only through the spiracles could one reach
most insects with an insecticide, and that the insecticide that did not
actually fill the spiracles was not acting. I suggest this is why contact
poisons fail against large insects as a general rule; the liquid may wet

H. M. Lerroy 295

but does not wet the whole insect and so the spiracles, or part of them,
are free.

The positions of the spiracles, for instance in a Scale Insect, a Psylla,
an Aleurodid, and an Aphid, are very different indeed. Their structure
is different, they have different arrangements for closing them. In
Psylla and Aleurodes the adult is very readily killed with insecticides,
partly probably because it has very inefficient spiracles and requires
much air, whereas the young form is harder to kill because it has a very
efficient closing and protecting apparatus and requires less air.

What I suggest is that the way to tackle the question is first to
investigate the tracheal system of the insect. Second, to investigate
the wetting action of the insecticide on the plant, unless the insect
is fully exposed. Thirdly, to investigate the wetting action on the
insect, or the dissolving of its waxes or coating; and fourthly the
actual toxic ingredient that would be added to the insecticide to act
on the insect when it reached it.

Are any of these factors really taken into account in the recom-
mending of insecticides? I think they should be, and there is here a
large field for research.

In preparing this paper I have not attempted in any way to sum-
marise the present practice of insecticides outside this country ; this
would be a very large subject, complicated by the now enormous use
of insecticides sold under fancy names by firms who may or may not have
any real knowledge of entomology. But I would like to include ab-
stracts of some papers published in America.

“How contact insecticides kill,” G. D. Shafer (Michigan Sta. Tech. Bul. Xt, pp. 65,
pls. 2, figs. 7). This bulletin consists of two parts, the first of which (pp. 8-53) deals
with the effects of certain gases and insecticides upon the activity and respiration of
insects, and the second (pp. 53-64) with some properties of lime-sulphur wash that
make it effective in killing scale insects, especially San Jose scale. Abstracts of these
have been previously noted (H.S.R., XXv, p. 665). The investigations conducted
and here reported in detail have been summarised by the author in the following
general conclusions:

“Usually contact insecticides do not depend upon one property or means alone
for their effectiveness, yet as a rule some one property is chiefly concerned. Alkaline
washes, corrosive sublimate solution, and other fluids, which are capable either of
dissolving or of precipitating certain constituents of insect tissues, are able to pene-
trate the chitin of insects into the tissues slowly. The weaker the surface tension of
the fluid, apparently, and the thinner the chitin with which it is in contact the
more rapid the penetration. Gases and vapors may penetrate the chitin of
insects, especially through the tracheae into the tissues far more rapidly than
liquids.

296 /nsecticides

“It is through absorption into the insect tissues of the volatile portions of kero-
sene, gasoline, creolin, pyrethrum and such contact insecticides that they mainly
become effective agents against insects. Vapors from these insecticides enter the
tissues and become effective long before the liquids as such have time to penetrate
the chitin. Kerosene, miscible oils, etc., are able to enter the spiracles and tracheae
of insects even when a ‘closing apparatus’ is present; but the comparatively rapid
influence which such insecticides exert does not come from the plugging of the
tracheae alone.

“The general effects of vapors from gasoline, kerosene, carbon disulphid, creolin,
and the rest upon insects are very similar to the effects of the vapor of ether. The
nervous system seems to be especially affected. Small amounts of such vapors
produce, at first, more or less excitement; then a period of uncertain movements ;
and finally in larger amounts anesthesia or narcosis. The respiratory activity is
usually increased until after the insects become deeply affected, and it is then
depressed.

“Certain gases and vapors (e.g., sulphur dioxid, ammonia and hydrocyanic acid
gas) when present in respired air continue to be absorbed by insects while they are
alive. For the most part, these gases are not given off when the insects are exposed
to fresh air, but become rather firmly fixed within the tissues.

“Insect tissues quickly become saturated with any certain percentage of the
vapor of carbon disulphid, carbon dioxid, kerosene, gasoline, or similar vapor and no
more (at that percentage) is taken up. Then when the insects are exposed to pure
air, practically all of such vapors or gases are given off from the tissues again—but
not quite as readily as they were absorbed.

“Starvation, serious mechanical injury, and ammonia gas were all found to reduce
the value of the respiratory quotient below the value given when healthy strong
insects are breathing pure air.

“The vapors of gasoline, carbon disulphid, kerosene and To-bak-ine (i.e. nicotin),
when present in sufficient amounts to bring the insects near death, cause the value of
the respiratory ratio to rise above the value given by healthy, strong insects breathing
pure air—i.e., these vapors depress the activity of oxygen absorption more than they
do the carbon dioxid excreting activity. The insects tried could continue to give
off small amounts of carbon dioxid when no oxygen was present to be taken up, as
when they were kept in tested nitrogen, hydrogen, or carbon dioxid.

“The evidence gathered seems to indicate that the vapors of gasoline, kerosene,
carbon disulphid and the like, after absorption into the insect body, become mainly
effective through some tendency their presence exerts to prevent oxygen absorption
by the tissues. ‘

“Lime-sulphur is a special rather than a general contact insecticide. Its strong,
persistent reducing power, and its ability to soften the wax about the margin of a
scale insect like the San Jose scale, are the important properties that make it efficient
as a scalecide.” Hapt. Stat. Record, 1912.

“A contribution to our knowledge of insecticides,’’ C. T. McClintock, E. M. Hough-
ton and H. C. Hamilton (Rpt. Mich. Acad. Sci. x (1908), pp. 197-208, pl. 1, reprint)... .
“The work reported in this paper has to do with contact insecticides only... .

‘The insecticidal, germicidal, and toxic values (for higher animals) have little or no
correlation. It is possible to determine the relative strength or value of insecticides

H. M. LErroy 297

by immersing test insects in definite strengths of the insecticide, and noting the time
required to produce death. The common bedbug (Cimex lectularis) appears to
be the most satisfactory test insect. As yet the mode of action, the way in which
the contact insecticides cause the death of the insects, has not been determined.
Apparently, the fewer the number of spiracles, the smaller their size, and the better
they are guarded by hairs or valves, the more resistant is the insect to the contact
insecticides,

“Chemical standardisation of this class of insecticides is with our present know-
ledge impossible. With two substances, having essentially the same composition,
the insecticidal values may vary enormously. Even the same substance, prepared
with what are apparently unimportant chemical variations, gives widely different
insecticidal values.”

Relative efficiency of contact insecticides.

Kohlentear .. aa a to P45
As,O3 soap sol... Bio ve B00
Terpentin siure .. 5c Go eed
Schwafel siure .. ofc an ob
Nikotin Ae ar as aa ytd
Leinol seife 5¢ oc oA 5
KCN a ae Se +5 5
Kresyl saiure, seifen losung 5e 2°5
Karbol siure, seifen losung 56 2-0
Morphin sulphat .. se ae 2-0
Karbol siure, H,O ars 50 1:0
HgCl, oe 3 ee ae 0-5
Hel 495 Sic 56 50 0-5
Formaldehyd ae 336 eve 0-4

Alkokol ‘i ae ee ate 0-05

«<A further contribution to our knowledge of insecticides,’ C. T. McClintock, H. C.
Hamilton and F. B. Lowe (Jour. Amer. Pub. Health Assoc., 1 (1911), No. 4, pp. 227-—
238, pl. 1): “It is possible to standardise substances which are subject to sophis-
tication or deterioration by comparing the efficient dilution of their vapours with
that of a product of known purity. This is particularly applicable to solutions of
nicotin and to powdered chrysanthemum flowers. As yet there is nothing from which
to conclude what action the vapours have on the insects. If it were merely irrative,
formaldehyde would be valuable and the vapours of the burning insect powder
without value. If the action were similar to anesthesia, chloroform should have
been of greater value. If the action were purely that of poisoning one would have
expected the highly poisonous hydrocyanic-acid gas to be of exceptional value for
all species of insects.”

These show that the way in which contact poisons act is not by
any means clear, and that a great deal of research in insect physiology
is required before we do know anything about it.

In conclusion, I wish to emphasise the practical bearing of this
subject. I may have shed no light on it, but I do think that we owe it

298 Insecticides

to horticulturists to investigate these problems. The wetting of leaves
and plant-buds is one point; the wetting or penetration of insects is
another; the toxic action on insects is a third, and the last is to combine
the three together in efficient insecticides that really do kill the insect
every time and that cause a direct mortality of 100 per cent. In seeking
an insecticide for woolly aphis, I would first seek a solvent of its wax.
This is easy, but it is far from easy for instance with beech Coccus. In
seeking an insecticide for apple sucker we first sought one that would
wet apple buds. For mussel scale I would seek either a solvent of the
secretionary part of the scale, or a liquid that would penetrate under
the scale. These are protected insects, but what about naked insects
such as bugs, aphides and the like; each has to be tackled individually.
So too for stomach poisons. We know that we want to wet the leaves
uniformily. Does lead arseniate and water wet well? I think not.
In using lead chromate we add 25 % soft soap and 1-5 % of gelatine,
simply to secure wetting; it is worth while as we use less liquid to get
good even wetting and no dripping. What will wet one plant’s leaf
may not wet another. We know that for cabbages, for instance, but
it is a factor seldom taken into account except with cabbages. -

I hope I have shown that there is a field for research in this question.
I wish we could get a satisfactory basis of reason on which to proceed,
and not have to rely on empirical methods which really are not always
successful. And I am inclined to think that in England too much
reliance is placed on the tar and water principle to the detriment of the
estimation in which applied Entomology is held by horticulturists and
fruit growers.

299

THE COMPOSITION OF THE COFFEE BERRY
AND ITS RELATION TO THE MANURING OF
A COFFEE ESTATE.

By RUDOLPH D. ANSTEAD, M.A.,

Planting Expert, Agricultural Department, Madras, and Scientific
Officer to the United Planters’ Association of Southern India.

DurtinG the past five years I have been studying in Southern India
the manurial problem as it affects coffee-from a chemical standpoint
with the object of trying to obtain some hint not only as to the best
proportions of plant food to give this crop, but also at what time of
year the plant food is best applied.

The first step was to investigate the composition of the mulch
obtained from the shade trees and the coffee itself and to determine its
manurial value. The result of our experiments was to show that under
well-established mixed shade some four tons air-dry weight of mulch
is accumulated per acre each year, and that this mulch contained
108 Ibs. of nitrogen, 223 lbs. of calcium oxide, 36 lbs. of phosphoric
anhydride, and 118 lbs. of potassic oxide per acre. From this it was
concluded that the amount and composition of the mulch obtained
annually from the shade trees was an important factor and should be
taken into account when drawing up a manurial programme over a
series of years, and also that it was quite possible that the coffee, where
a heavy mulch was established as happens on many estates, was apt
to receive an unbalanced ratio of plant food, the nitrogen being in excess
with the result that leaf growth was encouraged at the expense of
fruit.

Attention was next devoted to the chemical composition of the
coffee berry itself. When an analysis of parchment coffee, or coffee
berries, is examined it is at once noticed that potash is a dominant
factor among the mineral constituents. This being so it is only logical
to suppose that a fertiliser containing a preponderance of potash should
help the coffee tree to ripen up and hold its crop, and the question at
once presents itself as to when this potash should be applied. Do the
coffee berries need it from the very beginning of their development,

300 The Composition of the Coffee Berry

as soon as they have set and the blossom has fallen, or do they need it
only towards the end of their development? The same question also
applies to the nitrogen and phosphoric acid. It seemed to us that if
an answer could be found to these questions it would have a profound
practical bearing upon coffee manuring practice.

During 1912 analyses were made of coffee berries each month from
July to December throughout their period of development from the time
they were quite small to the time when they were ripe and ready to pick
and pulp. As it was found impossible owing to the press of other work
to make a large number of analyses of different samples for comparison,
and to get an average uniformity was attempted by taking a careful
sample from a large number of berries of similar development carefully
picked in the field.

The results of the analyses are shown in the following tables:

Analyses of Fresh Coffee Berries from July to January.

} |
=— July | Aug. | Sep. Oct. | Nov. Dec. Jan.

Moisture’ a... coche 87-13 | 84-45 80°75 71-54 66-06 65:77 66-62
*Organic matter ... | 11:96 | 14-67 18-18 26:93 | 32-05 32:48 31-58
ASU, soonodr 0:04 | 0-01 0-03 0-02 | 0-02 0-04 0-05
Phos. acid .., 0:08 | 0:07 0:09 0-16 | 0-15 | 0-12 0:12
Potashesnn i. - | 0:37 | 0-43 0:49 0:77 0:93 | 0-88 0-96
Ameen | 0-04 | 0-02 0:02 0:02 | 0:04 | 0-02 0-02

Other mineral | |
matter .... 0:38 0-35 0-44 0:56 | 0:75 | 0-69 0-65

| = APS | ; |
Motaleenr 100:00 | 100-00 100-00 100-00 | 100:00 | 100-00 100-00

| |
*Containing nitrogen | 0-30 0-38 | 0-24 050 061 | 0-67 | 0-66

Analyses of the Ash of Coffee Berries from July to January.

if
= | July Aug. Sep. Oct. Nov. Dec. Jan.
Silicavetanta: (Acca cine 4-48 1:48 2-84 1:23 1-11 2°47 3:03
Phoswacioteaeecccn 8-48 8-04 8-20 8-40 7:87 6-56 6:83
IPotashese eerie 40-31 48-38 45:78 50-30 49-40 50-10 53-19
ame Sidin. sae s 4:27 2-04 1:89 | Siliyfe | 1:89 1:23) | 1-14
Other mineral matter 42-46 40-06 41-29 38-90 39:73 39:64 | 35-81
Totaline. 100-00 100-00 | 100-00 | 100-00 100-00 | 100-00 | 100-00
|

Ruponten D. ANSTEAD 301

The first table shows the actual composition of the fresh berries as
regards the constituents named, while the second table shows the
composition of the ash, that is the mineral part in each sample, it being
chiefly this mineral matter with which we are concerned. In July the
berries were very small and it required 72 of them to weigh one ounce.
In December the berries were fully developed but still green or only
just yellowing. At this stage the beans are developed and if pulped
yield good coffee. In practice the berries are allowed to ripen and
develop sugar, turning red in the process, in order to facilitate pulping
and subsequent fermentation of the pulp adhering to the beans which
enables the latter to be washed clean, the fermentation process having
no effect upon the quality of the actual coffee bean. The last column
in the tables is the analysis of the ripe berries as picked for pulping.

These analyses show that there is a markedly steady increase of
potash content throughout the period of growth, and from this it is
concluded that potash in an available form is needed all the time.
The phosphoric acid content appears to be a constant quantity at first
with a maximum about October after which it declines, hence it seems
likely that this constituent is needed in an available form chiefly in
the beginning of the season. The nitrogen content increases steadily
throughout the period of growth and keeps pace with the increase of
organic matter.

On these results a series of manurial experiments have been based
and are now being carried out, but I should like here to especially call
attention to the moisture content of the berries during their growth
and development.

From July to December when the berries are fully developed in
size there is a rapid and regular decrease in the amount of moisture in
the berries. It falls from 87:13 % in July to 71-54 % in October
and 65:77 % im December.

This confirms Mr H. B. Guppy’s results. In his recent book Studies
in Seeds and Fruits, he states that immature fruits contain more
water than mature fruits, and that in the living plant or its part the
decrease in the percentage of water is due to the fact that during the
building up processes involved in growth the solids increase more
rapidly than the liquid constituents.

During the ripening process, however, the moisture content increases
by nearly one per cent., and this would appear to be a critical stage in
the history of the berry.

Much more work is needed upon this point, but it is significant that

302 The Composition of the Coffee Berry

every year a certain amount of crop falls off and that in certain cases,
on certain types of soil, the trees fail to hold their crop late in the
season. This last year, 1913, was a dry one with also a large crop, and
it was most noticeable that many of the berries failed to complete the
last stage and would not ripen, but had to be picked and pulped while
still hard and yellow instead of soft and red. The moisture factor has
undoubtedly some bearing upon phenomena such as these, and it is
possible that they can be controlled by methods of cultivation and the
application of fertilisers which tend to increase the root area or con-
serve the soil moisture. The results so far obtained suggest at any rate
interesting side lines of research, such as the above and the study of
the physical condition of different types of coffee soils and their moisture
content at different times of the year in the relation to the ability of
the coffee grown on them to hold and ripen up a big crop.

303

THE LIFE-HISTORY AND HABITS OF THE
GREENHOUSE WHITE FLY! (ALEYRODES
VAPORARIORUM WEstTD.).

By E. HARGREAVES, A.R.C.S8c., D.I.C.
(Imperial College of Science and Technology, South Kensington.)

(With 56 Text-figures.)

THIS insect is commonly known as the “Greenhouse White Fly,”
from its general occurrence on greenhouse plants. It is classified as
follows :

Family, Aleyrodidae (“Mealy wings”). Wings white, not trans-
parent; antennae with seven segments; both sexes winged; tarsus
with two segments.

Sub-order, Phytophthires. Antennae long and simple; tarsi with
one or two segments.

Homoptera. Fore wings not thickened at the base; head bent over
to touch the coxae.

Order, Rhynchota (Hemiptera). The mouth parts form a jointed
beak (rostrum), bent under the thorax; two pairs of wings.

Aleyrodes vaporariorum has a wide range of food plants, and prefers
potatoes, and such greenhouse plants as tomato, cucumber, melon,
heliotrope, lantana, salvia. Although the flies and larvae are very
small, they occur in such immense numbers that the plants become
impoverished, and the quantity and quality of such fruit as tomatoes
and cucumbers decreased. The whole of the under-side of the leaves
is often completely covered with the scale-like larvae and pupae. They
produce a large amount of excreta (honeydew), which falls on to the

1 A paper on insecticidal treatment for White Fly has been delayed, pending the
result of further work: Mr Hargreaves’ departure for the United States prevented the
second part of this paper, dealing with the treatment of White Fly, being completed.
It will appear in an early number.

304 Habits of the Greenhouse White Fly

leaves below, inviting the prolific growth of fungi which ruin plants
used for ornamental purposes. The adults prefer the young leaves
for oviposition, and gradually ascend as the plant grows. Hence there
will be green eggs on the newest leaves; a little lower, brown eggs;
lower still the first stage larvae will predominate; below these the
second stage larvae; and so on. Finally, on the oldest leaves, adults
will be emerging. Occasionally eggs are laid on the stalks, flowers, and
upper leaf surface; but theyare generally laid in circles on the under-side,
if the leaves are not very hairy and the insects undisturbed. The
circle of eggs is made in a very ingenious way. The insect inserts its
stylets into the leaf tissue and, using that point as centre and its body
as radius, revolves as each egg is deposited. Hairiness of the leaves
prevents this turning and the eggs are then scattered. The eggs are
stalked, the stalk being short and partly embedded in the tissue of the
leaf and arranged perpendicular to the leaf surface. They are green

Fig. 2. Circle of eggs.

when first deposited and covered with the wax (“meal”) produced by
the adult, as also is the portion of leaf in the vicinity of the eggs. The
circles of eggs are generally incomplete, with a diameter of about
1-5 mm., and I have not seen more than 15 eggs in one ring. (Length of
stalk, 0-02 mm., total length of egg, 0-24 mm., greatest breadth, 0-70 mm.)

After two to four days (according to temperature, as I kept the
humidity fairly constant) the eggs begin to darken in colour, turning
from the original yellowish green to brown and finally to black. When
nearing the time of hatching, which is about ten days after deposition,
the meal drops off, leaving the egg smooth and shiny. The larva is
visible inside, and its two eyes appear as bright red spots shining through
the egg case near its free end. When about to hatch, the egg moves
slightly from side to side, and two surfaces may now be distinguished :
a convex, corresponding to the dorsal, and a concave, corresponding
to the ventral surface of the larva. Hatching occurs ten to thirteen
days after deposition. A crack appears near the free end of the egg on

E. HARGREAVES 305

its concave side (Fig. 3), and the anterior end of the larva emerges.
The insect bends towards the leaf until it can get a hold, the legs, as they
emerge, being used to push the egg-case free of the larva. The process

Fig. 3. Fig. 4. Stalk of egg embedded in leaf.

is further assisted by flexure and alternate contraction and expansion
of the abdomen. The empty egg-case is left standing on the leaf,
collapsed.

TD) i
SFP f
Cy Ly :
(Qirees:

J

QD /

Fig. 5. First instar. Fig. 6. First instar, from stained mount.

In an instance I observed, the time which elapsed from the appear-
ance of the crack to the complete freedom of the larva was seventeen
minutes.

Instar I (Fig. 5). The newly-emerged larva is very pale greenish
yellow in colour, and the eyes, being bright red, are very obvious,

306 Habits of the Greenhouse White Fly

because of the contrast. Each eye is completely divided into two parts,
each of which appears to consist of a single ommatidium. The larva
is 0:29 mm. long, transparent, with a pair of dark yellow masses (present
in all stages) in the abdomen, generally in the three or four anterior
segments, but sometimes extending into the thorax. This pair of
yellow masses is the mycetoma, or pseudovitellus. The segmentation
of the abdomen is not distinct until a few minutes after emergence,
when the chitin has hardened. There are six abdominal segments, but
no differentiation in the thorax. The body margin has a series of spines
(Fig. 6), fifteen pairs of which would seem to be segmentally arranged,
since they are so arranged in the abdomen. Between the posterior
two pairs is a pair of much longer spines; and posterior to all of these
are the very long cerci (Fig. 7).

Fig. 7. Lateral view of hind end.

This larva is active for about three days, during which time it wanders
about the under-surface of the leaf. It thus differs from some other
species in which the larva simply gets clear of the egg before settling.
Previous to settling down, or at about this time, the spaces between
the marginal spines become filled in with wax formed by marginal
wax glands.

The larva prefers a position alongside one of the leaf veins, and
since the site it occupies is retained by the later instars, which are
sedentary, the choice of this first larva is important. The waxy fringe
is much wider in this stage than in the succeeding ones, and it gradually
narrows in the succession. Behind the sixth abdominal segment,
dorsally, is the vasiform orifice, the consideration of which I leave till
later. Legs and antennae are functional during active life, and are
well developed compared with those of the three later stages.

Mouth parts. There is a very short rostrum situated between the
anterior legs. Two pairs of stylets correspond to the maxillae and

E. HARGREAVES 307

mandibles of other insects. The mandibles are outside (lateral to) the
maxillae, which are fused along their length, forming by their union
two ducts—a small posterior one for the passage of the saliva from the
salivary pump to the leaf, and a larger anterior one for the passage of
the food from the leaf. In the dorsal (anterior) wall of the pharynx
is the cribriform organ, to which is assigned the function of tasting the
food (sap) as it enters the mouth. The arrangement of the mouth-parts
is similar in all the stages.

When the larva inserts its stylets into a leaf, in all the cases I have
observed (by means of sections of leaves with the larvae in situ), the
stylets go to the phloem cells of the vascular bundles, which contain

Fig. 8. Larval stylets in the leaf tissue.

proteids and albuminous materials—obviously the most suitable
destination (Fig. 8). The entire sucking apparatus (viz. stylets, sali-
vary pump, and chitinous structures in connection with them) is capable
of a slight backward-and-forward movement, and this is the case in
the next three instars also. As to the stylets themselves, they have
a regular cycle of movements (Fig. 9), which is as follows. The man-
dibles (outer stylets) are thrust forwards (outwards) simultaneously,
sliding on the maxillae (inner stylets). Their tips are incurved. They
are then withdrawn one at a time, their curved ends scraping against
the tips of the united maxillae, as if to bring food towards the latter
to be sucked up.
Ann. Biol. 1 21

308 Habits of the Greenhouse White Fly

Tracheal system (Fig. 10). This is very simple, there being inter-
connected dorsal and ventral systems, with very few small branches.
This suggests that there may be some respiration through the skin.
There are two pairs of thoracic spiracles situated, one pair between the
anterior legs, the other between the posterior legs. Also there are two
pairs of abdominal spiracles, one pair on the first abdominal segment,

Mow

Fig. 9. Cycle of movements of
stylets.

Fig. 10. Dorsal view of a mounted larva.

the other at the sides of the vasiform orifice. All the spiracles are
ventral and placed upon elevations.

In preparations to show the tracheal system, there is seen a large
vessel which ends suddenly in the fourth abdominal segment, without
small branches. It is in connection with the dorsal system (Fig. 10).
The larva is very small and the abdominal spiracles are in any case
very difficult to observe. It is my belief that this large trachea indicates
the presence of a spiracle which I have been unable to demonstrate
with certainty. There is certainly an indication of a pair of ventral
pores on the fourth abdominal segment.

E. HARGREAVES 309

Legs (Fig. 11). These consist of five segments, homologous, I should
say, with the coxa, trochanter, femur, tibia and tarsus, of the legs of
other insects. The coxa is small with a large spine on its inner side,
and the trochanter comparatively large. The tibia has a large spine
on its outer side at about the middle of its length. The tarsus is very
small and seems to consist of two segments, the first one bearing a long
curved spine externally, the second one terminating in a kind of pad, and
possibly being the homologue of the pulvillus or paronychium of the
adult, in which case it would not count as one of the actual tarsal
segments.

Higa

Antennae (Fig. 12). Each consists of three segments—the basal
one is broad and short; the second is much longer and thinner, with a
spine placed near the middle and another at the distal end. The
terminal segment is twice the length of the second and terminates in
a fine point; there is also a spine at about a quarter of the distance
from the distal end.

Vasiform orifice (Figs. 13 and 14). In one of my mounts I was
fortunate enough to obtain a side view, and was able to see the hind-
gut opening dorsal to the lingula. The lingula is a finger-shaped organ,
and just anterior to it, overlying the base, is a plate, the operculum.
The anus opens between these.

Spines. In addition to the marginal spines there are five pairs
situated as follows: a dorsal short pair over the anterior end of the
mouth-parts; a ventral long pair near the middle of the mouth-parts;
a ventral long pair beneath the corners of the vasiform orifice; a dorsal

21—2

310 Habits of the Greenhouse White Fly

short pair anterior to the vasiform orifice; a dorsal short pair in the
first abdominal segment.

4 oA FN)
Nene,

Fig. 12. Antenna. Fig. 13. Dorsal view of vasiform orifice.

Jp A
Lu

=e

Fig. 14. Lateral view of hind end.

Instar II (Fig. 15).

This (and all stages previous to the imago) emerges from the
anterior end of the old larval skin by pushing it off, partly with the
aid of its short stumpy legs, but mainly by the flexure and alternate
contraction and expansion of the abdomen. The eyes are bright
red, and divided. When newly moulted, the larva flattens itself
against the leaf, and, being transparent, is very difficult to see. It
is a pale greenish-yellow in colour, with a length of from 0:37 to

K. HARGREAVES 311

Fig. 16. Mouth-parts of
second instar.

Fig. 15. Second instar.

Fig. 17. Second instar.

312 Habits of the Greenhouse White Fly

0-39 mm. A very noticeable feature is the great increase in size (length
and breadth), which has taken place at the moult. (This also apples
to the two succeeding stages.) The rostrum is more pronounced than
in the previous stage (Fig. 16), but the general arrangement of the mouth-
parts is the same. This larva generally retains the same position as
the last, but I have observed one to move slightly immediately after

YY

GB
LY

Fig. 19. Leg of
second instar.

Fig. 18. Second instar.

emergence. The margin is at first entire except for the cerci and the
pair of more anterior spines, both being shorter than in the previous
stage. Later, however, a waxy fringe is developed. When this is
dissolved, the body margin is seen to have become crenulated (Fig 17).
There is a metathoracic and six abdominal segments differentiated.
Tracheal system (Fig. 18). There are dorsal and ventral systems
which are connected, and very few small branches are present. There

K. HARGREAVES 313

are two pairs of thoracic spiracles arranged as in the preceding stage,
and two pairs of abdominal situated in the first segment and at the
sides of the vasiform orifice respectively. A pair of thick tracheae are
given off from the dorsal system with evidence of a pair of spiracles,
as in the first imstar.

Legs (Fig. 19). The legs are much smaller than in the first instar,
and they are functionless as ambulatory appendages. Hach consists
of three segments the homology of which could not be determined with
certainty. But it seems probable that the trochanter and tarsus are
absent. No spines are present.

Antennae (Fig. 20). The antennae are exceedingly small, and
each is made up of two segments, the basal one having a short
spine near the middle, and the distal one being covered with very
short hairs.

Fig. 20. Antenna of second instar. Fig. 21. Vasiform orifice and ventral spines.

Spines (Fig. 16). In addition to marginal spines there are—a long
dorsal pair over the anterior end of the mouth-parts; a short dorsal
pair on the first abdominal segment; a long dorsal pair at the anterior
corners of the vasiform orifice; a very short pair at the posterior sides
of the vasiform orifice; a short ventral pair beneath the vasiform
orifice.

Vasiform Orifice (Fig. 21).

Dorsal pores (Fig. 17). On the dorsal surface are six pairs of pores,
which I take to be the openings of the wax glands, the secretion of which
covers the general surface of the body. They have a peculiar and
characteristic appearance. My preparations were stained with acid
fuchsin, and the pores appeared as small dark red rings, surrounded by
an area which was of a paler pink colour than the surrounding chitin
of the general surface. They are situated as follows: a pair in front of
the anterior dorsal spines; a pair each near the thoracic and first
abdominal spiracles; a pair in the fourth abdominal segment; a pair
at the sides of the vasiform orifice.

314 Habits of the Greenhouse White Fly

Instar III (Fig. 22).

General appearance and habits as in the preceding stage, but
larger, with the wax fringe narrower and the marginal spines shorter.
It is 0°52 mm. in length, with six abdominal segments, and the
metathorax differentiated. Mouth-parts of the same general structure
as in the first and second instars.

Fig. 23. Leg.
Fig. 22. Third instar.
, =
Bowsal plate
: re)
oO
, Op
v
Fig. 24. Antenna. ig. 25. Vasiform orifice.

Tracheal system. As in the previous stage.

Legs (Fig. 23). The legs are very small, functionless for locomotion,
and the structure as in the preceding stage.

Antennae (Fig. 24). Each consists of two segments. The basal
one is broad and carries a spine distally; the second is hairy and
characteristically hooked.

Vasiform orifice (Fig. 25).

E. HARGREAVES 315

Spines. In addition to marginal, are four pairs arranged—a long
dorsal pair over the anterior end of the mouth-parts; a dorsal short
pair on the first abdominal segment; a dorsal long pair at the anterior
angles of the vasiform orifice; a ventral pair beneath the vasiform
orifice.

Dorsal pores. ‘Twelve pairs situated—a pair over the sides of the
mouth-parts near the middle line; a pair anterior to the bases of the
antennae, and a pair just anterior to them; a pair near each pair of
thoracic spiracles; a pair towards the middle of the first abdominal
segment; a pair each in the third, fourth, fifth and sixth abdominal

Fig. 26. Fourth instar,

segments; a pair immediately posterior to the sixth abdominal seg-
ment; a pair at the sides of the vasiform orifice.

Breathing folds. There is a pair of these folds opening opposite the
anterior pair of spiracles, and the lumen of each extends alongside the
thorax to the first abdominal segment. I could not find a posterior

fold. (See below.)
Instar IV (Fig. 26).
This stage, which may be taken to be the equivalent of the

pupal stage of other insects, differs very much in appearance from
those preceding. When newly emerged there are eleven pairs of

316 Habits of the Greenhouse White Fly

large round spine-bosses to be seen, situated: seven pairs near the
margin, a pair towards the middle line anteriorly, a pair in the
thorax, and a pair in each of the third and fourth abdominal
segments. Later, the glands at these points give rise to long waxy
processes (Figs. 26, 27), the arrangement of which is made use of in
systematic work. Like the preceding stages, this instar is at first
transparent and a pale greenish-yellow in colour and has small red eyes.
The length varies from 0-7 mm. to 0:82 mm. It differs from the others
in that much growth in length, breadth and thickness takes place.
There are six abdominal and two thoracic segments differentiated.
The body margin is at first entire, except for the cerci and posterior
spines, which are shorter than those in the preceding stage. Later,
waxy processes are developed along the margin generally to the number

Fig. 27. Fourth instar. Fig. 28. Fourth instar.

of 38 pairs (Fig. 28). The mouth-parts are similar in structure to those
in previous stages.

Tracheal system (Fig. 29). This is much more complicated than in
any previous stage, as numerous fine tracheal ramifications are present.
There are dorsal and ventral systems, which are in connection.

Spiracles (Fig. 29). There are four pairs of spiracles situated as
follows: a pair in the metathorax; a pair of more anterior thoracic ;
a pair in the first abdominal segment; and a pair at the sides of the
vasiform orifice.

Legs (Fig. 30). They are not functional for walking, and consist
of three segments, the basal one being very broad. No spines are
present.

Antennae (Fig. 31). Each consists of two segments, the distal one
terminating in a rather fine point.

EK. HARGREAVES our

Spines. In addition to the marginal and the eleven pairs of long
dorsal spines mentioned above, there are: a pair ventral to the vasiform

Fig. 30. Leg.

Fig. 29. Fourth instar, tracheal system.

orifice; a dorsal pair at the anterior corners of the vasiform orifice;
a dorsal pair in the first abdominal segment; an anterior dorsal short
pair over the sides of the mouth-parts.

Fig. 31. Antenna. Fig. 32. Vasiform orifice.

Dorsal pores. There are twelve pairs arranged as in the previous
stage.
Vasiform orifice (Fig. 32).

318 Habits of the Greenhouse White Fly

Breathing folds (Figs. 26, 33). There is a pair of anterior folds
opening ventro-laterally opposite the anterior pair of thoracic spiracles.
They are continued alongside the thorax to the first one or two abdom-
inal segments. In the living insect, the passage leading to the exterior

aie

Fig. 33. Ventral view of fourth instar.

appears to be a tube (Fig. 33), the floor of which is formed of wax, so
that in specimens which have been treated with a wax solvent, the
tubes have become simply grooves (Fig. 26). There is also a posterior
fold extending from the middle of the posterior margin to the vasiform

Fig. 34. Opening of posterior fold. Fig. 35. Opening of thoracic fold.

orifice, which communicates with the posterior spiracles. The character
of the margin at the external openings of these folds is peculiar (Figs.
34,35). Later, the body shrinks away from the cuticle, and the develop-
ment of the adult organs (eyes, wings, legs, etc.) begins. In sections

E. HArGREAVES 319

at this stage two layers of chitin are to be distinguished, one being that
which originally enclosed the fourth instar, the other, inside this, which
is destined to be the adult skeleton (Fig. 36). This may be called an

Fig. 36. Section through head of fourth instar.

internal moult. The eyes, from being mere spots in the young pupa,
grow enormously to form the compound eyes of the imago. The body
grows very much in thickness, becoming box-like in the older pupa
(Fig. 27). Also, the antennae, legs and wings may be seen curled up
inside the outer case, but outside the body of the insect. As is the
case in the preceding stages, the new legs and antennae are formed
inside the old ones, and since those of the imago are much longer than
those of the pupa, they become folded as they grow. The claws and
second tarsal segment easily fill one of the pupal legs (Fig. 37). The

Fig. 37. Adult leg developing in pupa.

wings are outgrowths of the inner layer of chitin, the growth being
continuous and gradual and thus differing from that which takes place
at successive moults, in steps as it were, in some other insects. So far
as I can make out, the wings arise as evaginations, and not as invagi-
nations, which are later evaginated as in insects like the Lepidoptera.

320 Habits of the Greenhouse White Fly

Instar V (Fig. 38).

This is the final stage, or imago. It emerges from a T-shaped
crack, the crossbar dividing the pupal abdomen from the thorax,

Fig. 38. Adult.

Fig. 39. Empty pupa-case.

the vertical bar being median, and extending from the crossbar to the
anterior margin (Fig. 39). The thorax is the first part to emerge;
then the head, with the rostrum and antennae, which gradually

E. HARGREAVES 321

straighten out and harden. The legs are then successively drawn
out and straightened, and simultaneously with this the rest of the
thorax, bearing the wings which are curled up on each side. When
the legs have hardened, the insect uses them to push at the pupa case
for the extraction of the abdomen. It takes an hour or so for the wings
to become straight. The newly emerged imago is quite devoid of any
waxy covering, but after some time, its body and wings become covered

Fig. 40. Adult’s abdomen, lateral. Fig. 41. Adult’s abdomen, ventral.

with the white substance (meal, or wax), from which the names “ white-
fly” and “mealywing” are derived. It varies in length from 0-95 mm.
to 1-4 mm. I placed a newly emerged female insect on a slide beneath
a coverslip in order, if possible, to observe where the wax was formed.
After some time, I found that two pairs of plates were covered with it.
These are situated ventro-laterally on the second and third abdominal

Distal end.

Fig. 42. Part of hind tibia.

segments (Figs. 40, 41). The rest of the body was quite clean. On
careful observation of one of the flies while on a leaf, by means of a
binocular, I saw that it scraped its abdomen with the tibiae of its hind
legs, and then stroked them on its wings, and the remainder of the
abdomen. Similarly, it uses its fore-legs for the head and thorax.
On the hind tibia is a row of stiff setae, which act as a comb for the
_ transference of the wax (Fig. 42). There are four pairs of wax plates

322 Habits of the Greenhouse White Fly

in the male, situate in the second, third, fourth and fifth abdominal
segments. The meal has a peculiar structure, being in the form of
spirals or parts of spirals, as if it had been forced through small
openings (Fig. 43). In thin sections (Fig. 44), taken through the
region of these wax glands, there is seen a single layer of secreting cells
with large nuclei, and containing vacuoles from which the wax has
been dissolved during preparation. There are also numerous granules
which are more numerous towards the exterior. The overlying chitin
at first appears to consist of a series of imbricated plates, which effect,
however, is due to the presence of small pores, thus giving the chitin
that striated appearance.

9 *S
¥

Fig. 43. Wax threads. Fig. 44. Section through wax glands.

[In order to determine with certainty the structure of the chitin,
special precautions as to lighting, to prevent error from reflection or
aberration, were found to be necessary, because of the high magni-
fication required. |

Antennae (Fig. 45). Each antenna consists of two broad segments
at the base and five longer and more slender ones. They are placed
just in front of the eyes, and show pseudo-segmentation. On each
of the third, fifth and seventh segments, situated on their distal ends
and on the dorsal (anterior) side, is a circular pit fringed by setae.
These are probably olfactory organs. The seventh segment terminates
in a fine point. The length of the antenna is 0-36 mm. in the male,
and 0-32 mm. in the female.

EK. HARGREAVES 323

Rostrum (Figs. 38 and 47). The rostrum is a prominent structure
equivalent to the labium of other insects, and consists of three segments,
with an imperfect joint again dividing the middle one. On its anterior

\

Trvoqunat von

—~

/ —
Imbevteel yount —

Fig. 46. Rostrum.

Fig. 45. Antenna.

Fig. 47. Rostrum.

surface is a deep groove, extending along its whole length, for the
reception of the stylets. The tip is sharply serrated, presumably to
enable the insect to get a grip on the leaf surface during insertion of

Ann. Biol. 1 22

324 Habits of the Greenhouse White Fly

the stylets. The rostrum may be drawn into the head to such a great
extent that the dorsal end of the groove nearly reaches the dorsal
wall. It may also be invaginated upon itself like a glove finger (Fig. 46).
These arrangements are for the insertion of the stylets, insomuch as the
rostrum is longer than the stylets. The portion of stylets outside the
plant is completely enclosed in the groove. Hence the rostrum function-
ally shortens as the stylets are inserted. There is no arrangement in
the head for the retraction or expulsion of the stylets themselves. When
the insect is not feeding, the stylets are completely enclosed in the
rostral groove.

Eyes (Fig. 48). The eyes of the adult are compound, and each
is divided externally by an area covered with short hairs, into lower and

Fig. 49. Side view of head.

upper portions, the upper having smaller facets than the lower. They
are very large, and just above each is an ocellus (Fig. 49). The two
parts of each eye unite inside the head.

Mouth-parts. The mouth-parts have the same general structure
as in the preceding stages, but there is one great difference. In the
larvae the stylets may be withdrawn inside the body (Fig. 50), probably
into a pouch as in Monophlebus (Coccidae). The mandibles are not
fused, either with themselves or with the maxillae, and they may slide
upon the latter. They are very slender structures without teeth or
serrations.

Segmentation (Figs. 38 and 40). The attachment of the abdomen
to the thorax is very narrow. From the dorsal surface smal] protho-
racic and large meso- and meta-thoracic segments are visible. Behind

E. HARGREAVES 325

the six abdominal segments which are to be distinguished dorsally, is
a portion in which the vasiform orifice is situated, and which terminates
as ovipositors in the female and claspers in the male. There are seven

Fig. 50. Stylets of first instar.

abdominal segments visible ventrally. Along each side of the abdomen
is a narrow band of thin chitin consisting of the pleura of the segments

(Fig. 40).

Fig. 51. Tarsus.

Legs. The third pair of legs are the longest and the first the shortest.
Kach consists of a coxa, trochanter, femur, tibia and a tarsus of two
segments. Articulating with the second tarsal segment is a small piece
supporting two long curved claws and a median hairy and pointed
pulvillus (paronychium) (Fig. 51). There is also a long curved spine

22—2

326 Halits of the Greenhouse White Fly

attached independently to the distal end of the second tarsal seg-
ment.

Wings (Figs. 52, 53). There are two pairs of wings in both male
and female, and the venation of both fore and hind wings is exceed-
ingly simple. There is a series of knob-like structures running round
the wing margin, each knob supporting two or three hairs (Fig. 54).

ae he lh wp eR Eee
ea ne Poster vor
Fig. 52. Fore wing. Fig. 53. Hind wing. Fig. 54. Wing margin.

Tracheal system. The tracheal system is very complicated, as in the
pupa, and there are four pairs of spiracles situated as follows: a pair
each in the pro- and meta-thorax; a pair on the first abdominal seg-
ment placed a little antero-dorsal to the anterior pair of wax plates;
a pair on the sides of the vasiform orifice, ventro-laterally.

[Quaintance® in his Classification of the Aleyrodidae, states that
there are three pairs of thoracic spiracles in the Aleyrodidae. Wood-
worth’, in A. citri, had also described three pairs. ]

Vasiform orifice (Fig. 55). The function of this peculiar apparatus

K. HARGREAVES 327

appears to be to get rid of the excreta (honeydew). The lingula moves
in a vertical plane, while the operculum moves slightly backwards and
forwards. The anus opens on the dorsal surface of the lingula (anterior
to it) (Fig. 55). Ventral to the base of the lingula is a cleft, which is
presumably to allow the lingula greater freedom of movement. Leading
from the base of the lingula near the anus to its tip is a row of rather
long setae, and at the tip there is a depression surrounded by them.
It would appear that the honeydew is conducted from the anus via the
row of setae, to the tip of the lingula, in the depression of which it can
accumulate and form a globule. It is got rid of by the flicking of the
lingula. This flicking is easily seen in the case of the pupa. The
honeydew on exposure becomes gradually more and more viscous,
and if it were not for the above arrangement the anus would become
occluded, and the insect killed. The position of the anus corresponds

Btheeece

Oe eH oe tae Posheyses

Fig. 56. Vasiform orifice with solidified honeydew.

with the general up-side-down habit of the insect on the under leaf-
surface. In some of my preparations there is a mass of clear structure-
less material filling in the space between the lingula and operculum.
This is honeydew which had become so viscous that the insect could
not get rid of it (Fig. 56). It may be that the fly had remained in an
upright position for some time.

Peal, 1903, considered that the lingula secreted the honeydew.

Miss Bernis® (Proc. U.S. Nat. Mus., vol. xxvu, p. 475) supports
Peal.

Quaintance® could not find a definite opening at the tip of the linguia,
and states that whether the anus opens at the base or tip, the lingula
functions as the supra-anal plate. He homologises the lingula with
the supra-anal plate of the Psyllidae, where the anus opens at the tip.

The small numerals refer to the bibliography. 3, 5, 6, 7, 8, and 9 are quoted from
Quaintance 1913.

328 Habits of the Greenhouse White Fly
Duration of the various stages.
Egg. Green when laid. Turn brown in two to four days. Hatch

in Il to 14 days from deposition. Mean of 13 cases, 11 days.

Instar 1, Active for two to four days, wandering about the leaf.

Duration 10 to 12 days. Mean of 13 cases, 11 days.
POS LOS LOS TO tT alas ie scl alent eealee

Instar 2. Inactive. Duration 14 to 22 days. Mean of ten cases,

17-8 days.
14, 14, 14, 14, 16, 19, 21, 22, 22, 22.

Instar 3. Inactive. Duration five to 36 days. Mean of 20 cases,
18 days.

D, 9, 0, 7, 7, 8, 10, 10, 14, 18, 21, 22; 23, 26,.°21,-21, 7211, 33, 00;-00:

Instar 4. Inactive. Pupa. Duration 21 to 59 days. Mean of
17 cases, 37 days. The pupa turns slightly yellow before emergence

of the imago.
21, 24, 24, 24, 25, 26, 31, 40, 41, 42, 47, 47, 51,
Instar 5. Imago. Duration.
was during cold weather.
The weather regulates the duration of all stages, except the egg,

which is not eed Cold weather increases the time, making them
live more slowly.

53, 53, 59, 40.

The longest was 38 days, which

Summary of Duration of the various Instars.

Stage Cases taken Mean
Egg 13 13 days
Instar | 13 1 aa
2 10 18 (17:8)
; 3 20 Sa
pee 17 Ol. is
Life Histories.
Egg laid Hatch Moult 1 Moult 2 Moult 3 Imago
16 Oct. 29 Oct. 6 Noy. 23 Nov. 19 Dee. 23 Jan.
Shas. 30 i) 27 2Ae aes PLE og
NS 28 a 25. , 22 PBI
Ges 30 10 1 Dec 24 23° 35
Gis 27 10 27 Nov 30 23
VON 30 10 208, LO eee Diss

E. HARGREAVES 329

Parthenogenesis. 1 placed three females, isolated before complete
emergence so as to be absolutely certain that they had not been fertilised,
each on a clean plant. From these I obtained ten, thirteen and twenty
imagos respectively, all females. From these I got females again, and
out of the hundreds of flies which I examined I did not encounter a
single male.

Morrill® on parthenogenesis in the Aleyrodidae, states that un-
fertilised eggs hatch giving larvae which result in male flies, and suggests
that the fertilised eggs will all give rise to females, as in bees. Morrill
and Back further established parthenogenesis in Aleyrodes citrt.

Some General Notes.

Spiracles. There is evidence for the presence of three pairs of
abdominal spiracles in the first three instars. In the other two, however,
there is not. It might be suggested that this reduction during develop-
ment is some indication that an ancestor of the Aleyrodidae had a pair
of spiracles in each abdominal segment. These may possibly be
developed in the embryo, all except the remaining three being absorbed
before hatching.

Breathing folds. In the case of the instars which are fixed in one
place during their existence, viz. the second, third and fourth, they are
fixed to the leaf by the waxy fringe. Since the spiracles are ventral,
there must be some arrangement for the access of air. This requirement
is met by the “breathing folds.’ On each side of the thorax, opposite
the first pair of thoracic spiracles, the ventral body-wall is transversely
folded, the fold being continued along the sides of the thorax and part
of the abdomen. This allows for the access of air to the thoracic and
first abdominal spiracles. The animal forms a floor of wax to these folds,
thus converting them into tubes (Fig. 33). The margin at the openings
of these differs from the rest (Figs. 34, 35). There is a similar median
longitudinal one posteriorly for the access of air to the spiracles on the
sides of the vasiform orifice. In the first larva, either the folds are absent,
or are too small for observation. But there may be other arrange-
ments in this case, if such are required. In the first place, I have seen
a few of the larvae walking about after the formation of the waxy
fringe, which suggests that the fringe is not in contact with the leaf.
This would obviate the necessity of breathing folds. Also, there is a
long spine on the inside of the basal joint of each leg, and a pair of long
ones beneath the vasiform orifice. These may function as resting

330 Habits of the Greenhouse White Fly

spines. These long leg-spines are absent in the other stages, and those
beneath the vasiform orifice, if present, are short.

When larvae are nearing the moult, they become fat and lose
their close contact with the leaves, so that they are then easy to see.
The first three instars do not grow in length during their existence,
this taking place entirely at the moult; but they grow in thickness
(dorso-ventrally). Thus, the length for each of these three instars is
constant, and it may, therefore, be used as a criterion of the stage. It
varies within 2. only. The fourth instar (pupa), however, grows con-
siderably (12,2) in length, and also very much in thickness (Fig. 27).

The honeydew on exposure becomes very viscous, so that any stage
which feeds for any considerable time with its dorsal surface upwards,
is quite likely to have its anus clogged, as is the case in some of my whole
mounts of adults. In these cases the plug of honeydew is situated
on the dorsal side of the lingula, thus confirming the dorsal position of
the anus with relation to the lingula, which I demonstrated both in a
whole mount and by means of sections.

Dorsal pores. On the dorsal surface of the second, third and fourth
instars are small pores, those in the abdomen and thorax being seg-
mentally arranged. They are probably pores for the passage to the
exterior of wax formed by the underlying cells, the body being covered
with it. But it is not a white powder or meal as in the adult.

It may be asked: Why are all the stages generally on the under-
side of the leaves?) The following points require consideration :

(1) The character of the cuticle of the leaf.

(2) Presence of stomata.
)
)

oo

( Protection from wet.
(4) Phototropism.
(5) Position of the anus and character of excreta.

(1) The cuticle is certainly thinner, and the vascular bundles are
nearer the surface, on the underside of the leaf.

(2) In all the sections of larvae in situ that I have examined, in no
case do the stylets penetrate a stoma.

(3) All the stages have a waxy covering, so that the position as
a protection from wet would appear to be a subsidiary matter.

(4) Ifa leaf with flies on the under-surface is turned over, after a
time all the flies migrate to the other side and may lay eggs there.
This fact excludes points (1) and (2). If a leaf hangs with its surface
in a vertical plane, the females do not show any preference of leaf-surface
for oviposition. To catch the flies, I turn a leaf over, and, holding a

EK. HARGREAVES 331

specimen tube over a fly, touch it with the edge of the tube. It may
behave in two ways: either it flies immediately upwards into the tube,
or it simply falls over on its side feigning death. If a fly is touched while
the leaf is in the normal position, it does not generally immediately
take to flight, but drops for three or four inches, and then flies quickly
away from the plant. If a number of the flies are placed in a tube,
they all congregate at the upper end. This seems to be an attempt to
get into the position with the dorsal surface downwards, and not a result
of phototropism. I placed some flies in a tube, and, as usual, they
congregated at the upper end. So I covered all the tube except the
lower part to exclude the light, and placed a Nernst lamp beneath, so
that the light was shining upwards into the darkened tube. It did not,
however, cause the flies to come to the bottom of the tube, which
indicates that they are not positively phototropic. And their general
behaviour points to their not being negatively phototropic.

(5) I consider that the situation of all the stages on the under leaf-
surface is correlated with the dorsal position of the anus. The following
considerations lead me to this conclusion:

If the insect were dorsal surface upwards

(a) it would be unable to get rid of its excreta, which would clog
the anus, or, accumulating on the leaf and becoming viscous, would
occlude the spiracles,

(b) any accumulation of honeydew (excreta) is a very suitable
medium for the growth of Fungi,

(c) the newly-hatched first larva would become entangled in the
viscous excreta which fouled the leaf and would be unable to settle
down,

(d) the various larvae when moulting would have difficulty in
casting off their old skins.

Enemies. Now as to the enemies of the insect. I have not en-
countered any animal parasites as yet, either of the nymphs or the adult.
On one occasion I caught a mite which was holding and devouring
a living fly. Spiders also prey on them. On one leaf a spider was
discovered surrounded by the remains of half-a-dozen of the flies.
Fungi occasionally kill both adults and nymphs.

Methods of eluding predaceous enemies. (1) Escape by dropping,
and flight.

(2) Transparency of the larvae is probably a factor in this, as it
renders them practically invisible.

332 Habits of the Greenhouse White Fly

cuR oh

oF

BIBLIOGRAPHY.

Westwoop. 1856. Gardeners’ Chronicle.

SigNorET. 1868. Hssai monographique sur les Aleurodides.

Riutey. 1880. Aleyrodes on Oxalis. Am. Hnt. vol. 11.

WoopwortH. Resp. system of Al. citri. Zool. Jahres. 1902.

Peau. 1903. The function of the vasiform orifice of the Aleurodidae. Jour.
Asiatic Society of Bengal, vol. LXxu, part 2.

Miss Bernis. 1904. Proc. U.S. Nat. Mus. vol. xuvit. p. 475.

TuLLGREN. 1907. Arkiv. fiir Zool. Bd. 3, No. 26.

Morritt and Back. 1911. White flies injurious to litrus in Florida.
Bull. 92, Bur. Ent. U.S. Dept. Agr.

QUAINTANCE. 1913. Classification of Aleyrodidae.

EXPLANATION OF FIGURES.

All figures are drawn at stage level with tube length of 150 mm. Leitz oculars and

obje
Figs
Figs
Figs
Figs

ctives throughout.

- 10, 15, 17, 18, 22, 46, 49; Oc. 1, Ob. 4.

lo 29) oS. Oca. Olbms:

£5, 65.75 165 2025. 30: 32.345 36. au. 42nd. 414 46. 0s DosoOs Oca. Oba

. 4, 8, 11, 12, 13, 14, 19; 20, 23, 24, 31, 43, 44, 50, 54; Oc. 3, Ob. =; (oil imm:)-

The following are reduced :

Figs
Figs
Fig.
Fig.
Fig.
Fig.

Fig.

. 12, 15, 17, 25, 31, 32, 35, 37, 38, 42, 44, 46, 48, 50 to §.
. 4, 5, 6, 8, 22, 45, 47, 49 to 4.

We UB fees.

2. Circle of eggs. Note surrounding meal.

3. Egg showing crack for emergence of larva.
4. Section of egg in situ on the leaf.
5. Ventral view of living first instar. Note the broad fringe of wax, cerci, legs,
antennae, eyes, stylets, mycetoma, segmentation.

. 6. Ventral view of stained preparation to show spiracles, mouth-parts, eyes, marginal

and other spines.

. 7. Lateral view of posterior end of abdomen to show the length of the cerci.

ig. 8. Larval stylets in the leaf tissues.

ig. 9. Cycle of movements of stylets.

. 10. Dorsal view showing tracheal system. Note dorsal and ventral parts.

. ll. Leg of first instar from the outer side. Note the basal spine on the inner side.
. 12. Antenna.

13. Dorsal view of vasiform orifice.

. 14. Lateral view of posterior end of abdomen of first instar showing vasiform

orifice. Note the anus opening between the lingula and operculum, and marginal
spines.

ig. 15. Dorsal view living second instar. Note wax fringe, cerci, and pair of posterior

marginal spines. -

. 16. Mouth-parts of second instar. Note peculiar folded rostrum, short length of

protruding stylets, dilated pharynx with the dilator muscles and their direction of
action (indicated by arrows).

EK. HARGREAVES 333

Fig. 17. Dorsal view second instar, showing spiracles, dorsal pores, crenulated margin, etc.

Fig. 18. Ventral view showing tracheal system, mycetoma, eyes.

Fig. 19. Leg. Note spine on basal segment and hairy terminal one.

Fig. 20. Antenna.

Fig. 21. Ventral view vasiform orifice and adjacent spines,

Fig. 22. Dorsal view living third instar, to show the narrow wax fringe, cerci, eyes,
mycetoma, marginal spines.

Fig. 23. Leg.

Fig. 24. Antenna. Note spine on basal segment and the hairs on the hooked terminal
segment.

Fig. 25. Dorsal view vasiform orifice, with adjacent spines, spiracles, dorsal pores.

Fig. 26. Ventral view mounted pupa showing breathing folds, legs, spine bases, seg-
mentation, short cerci and marginal spines.

Fig. 27. Dorso-lateral view of late pupa to show box-like form, dorsal and marginal
wax processes. The eye of the imago inside is seen through the wall.

Fig. 28. Dorsal view living pupa to show the marginal wax processes and cerci.

Fig. 29. Dorsal view showing tracheal system and spiracles. Note the small rami-
fications.

Fig. 30. Leg. Z

Fig. 31. Antenna. Note the pointed end.

Fig. 32. Dorsal view vasiform orifice and adjacent spines.

Fig. 33. Ventral view living pupa showing tubular entrances to breathing folds.

Fig. 34. Opening of posterior breathing fold. Note cerci and character of margin.

Fig. 35. Opening of thoracic fold. Note position of spiracle, and margin.

Fig. 36. Section through region of head of late pupa showing the two layers of chitin.

Fig. 37. Portion of partially emerged adult showing relation of adult leg to that of pupa.

Fig. 38. General outline of adult female. Only coxae of legs and bases of wings

indicated. Note position of spiracles, antennae, eye, ocellus, wax plates, rostrum,
ovipositors, position of vasiform orifice with hind gut; small prothoracic segment.

. 39. Dorsal view of empty pupa case. Note T-shaped crack through which adult

has emerged and the 11 pairs of long dorsal wax processes.

. 40. Lateral view abdomen of female showing position of wax plates and the pleura

of the segments.

. 41. Ventral view of same.

. 42, Proximal two-thirds of hind tibia. Note comb of spines on inner posterior side.
. 43. Some of the meal. Note spiral form.

. 44. Section through wax glands. Note character of gland cells and overlying

chitin. (Section passes through the juncture of two segments.)

. 45. Antenna. Note pseudosegmentation, sense organs, terminal point.
ig. 46. Rostrum, showing invagination at end of first segment, and the imperfect

joint in the second.

. 47. Side view part of rostrum. Note groove and the toothed tip.
. 48. Adult eye. Upper facets are smaller than the lower, with intervening short

hairs.

g. 49. Side view of head. Note position of salivary pump and stylets, and the portion

of rostral groove in the head.

. 50. Side view of mouth-parts of first instar, to show loop of stylets inside body,

and the rostrum.

g. 51. Claws and second tarsal segment. Note the small piece with which the claws

and pulvillus articulate, and the long curved spine attached to the tarsal segment.

334 Habits of the Greenhouse White Fly

Fig. 52. Ventral view forewing. Note simple venation.

Fig. 53. Hind wing.

Fig. 54. Portion of wing margin.

Fig. 55. Lateral and slightly dorsal view of vasiform orifice.

Note anus opening dorsal

to the lingula, the row of hairs on the lingula and the depression at its tip.
Fig. 56. Vasiform orifice, with solidified honeydew between the lingula and operculum.

Anus

Abdomen

Antenna

Cercus

Claws

Coxa

Dorsal spine

Dorsal wax pore
Dorsal surface ..
Dorsal tracheal system

Dorsal wax processes ..

Eye

Femur ste
Future adult chitin
Granules

Hardened honeydew
Leg Be

Lower facets
Lingula ..

Leaf tissue

Meal

Mandible

Maxilla ..
Mesothorax
Metathorax :
Marginal wax processes
Marginal spines
Mycetoma

Ocellus ..
Operculum
Ovipositor

Pleura

A,
Ab.
Ant.
Cr

Abbreviations used in figures.

Pupal chitin .. us
Posterior breathing fol
Phloem .. : ye
Posterior marginal spine
Prothorax

Probable spiracle
Pulvillus

Pores for wax ..
Rostrum

Rostral groove

Stylets ..

Salivary pump

Base of spine

Spiracle

Sensory pit

Thorax ..

Tarsus .. oi EM
Thoracic breathing fold
Tibia

Trochanter

Upper facets

Ventral spine ..
Vacuole 5.6
Vascular bundle
Vasiform orifice
Ventral surface

Ventral tracheal system
Wax plates

Wax fringe

Wax secreting cells
Xylem ..

**
—~
°°
—_
ae
ww €

INFECTION AND IMMUNITY STUDIES ON THE
APPLE AND PEAR SCAB FUNGI (VENTURIA
INAHQUALIS AND JV. PIRINA).

By 8: P. WILTSHIRE, B:se:
(With Plates XIX—XXIT.)

THE diseases of apple and pear caused by Venturia inaequalis (Cke.)
and V. pirina (Aderh.) exhibit many interesting phenomena with regard
to the resistance and susceptibility of varieties of the hosts. The
investigations described in this paper were commenced with the object
of discovering the method by which these fungi attack their hosts, in
order finally to investigate the features concerning the question of
relative immunity. Notwithstanding the rather considerable amount
of work which has been done on these diseases—especially the extensive
reports of the Agricultural Stations of the United States—little definite
knowledge is available, either as to the minute details of infection or
the power of resistance of attacked varieties. The recent paper of
Wallace! contains an exhaustive review of previous work on these
diseases: here therefore it is unnecessary to do more than make a brief
reference to those points which concern the subjects dealt with in this
paper.

The previous work which has been done with regard to the infection
of Venturia is limited to comparatively few papers. Aderhold’s work?
on these fungi is by far the most important that has ever been published,
and to him we are indebted for most of our knowledge of them. In
his description of the germ tube he states that it broadens slightly at
the point of entrance, which is usually directly over the junction of
two or more epidermal cells, and bores directly through it. He mentions
that the appressoria are frequently surrounded by a zone of mucilaginous
material, but his figures show no signs of the collar which is described
below, neither do they indicate the characteristic sub-cuticular mycelium.

1 Wallace, Scab Disease of Apples. Cornell Univ. Agric. Exp. Station, Bull. 335.
2 Aderhold, R.. Pie Fusicladien unserer Obsthaume Land. Jahrb. xxv, 875-914.

336 Apple and Pear Scab Fungi

Fischer! states that Venturia cannot attack a completely uninjured
fruit without previous injury to the epidermis. The attack is dependent
on the weather, cold nights followed by warm days cause injury to
the epidermis. Small cracks arise which can be seen with the aid of
a lens, and he explains the conditions favouring infection, as due to
the injuries of the cuticle brought about by them.

Voges? notes the presence of a “gelatinous envelope” round the
appressoria which he suggests are functionary in attachment of the
fungus.

Wallace (loc. cit.), by boiling up the leaf with caustic potash and
thus releasing the cuticle, gathered that the germ tube of an ascospore
bores its way directly through the cuticle and continues to grow
between it and the epidermis. His figure, which, as far as the writer
is aware, is the only one published of the entrance of the germ tube
into the host, shows the hypha growing through a crack without the
formation of an appressorium and without showing any difference
between superficial and sub-cuticular mycelium.

For investigation of the problems of disease resistance connected
with any pathological fungus, it is important first of all to determine
the actual details of infection by the fungus. Having ascertained the
facts of infection, knowledge as to the fate of the fungus after penetra-
tion into the tissues of the host is required. The work described in
this paper deals primarily with those two subjects. In the case of the
disease under investigation, a detailed study of the germination of the
spores of V. inaequalis and V. purina, the method of penetration into
the hosts and the fate of the infecting hyphae was made. The methods
of investigation adopted, the results and their bearing upon the above
questions are described in turn below.

Methods. The germination of the conidia was examined by the
method of drop cultures, conidia being obtained both from pure
cultures of the fungi on artificial media and from affected leaves and
fruits of apple and pear. The same sources served for a supply of
conidia for the inoculation experiments. The inoculations were carried
out on cut shoots and fruits under bell jars or on shoots which were
enclosed in lamp chimneys held in position by clamps on the trees.
The atmosphere was kept saturated with water vapour, and the inocula-
tions were kept moist by means of addition of sterilised water from time
to time.

! Fischer, Pflanzenkrankheiten, x1x, 432-434.
* Voges, Zeitschr. Pflanzenkrankheiten XxX, 385-398.

S. P. WILTSHIRE 337

These very artificial conditions were rendered necessary by the
peculiar and special conditions under which the fungus infects the
host and even under these, apparently the most favourable, infection
is by no means always successful. There must remain, therefore, some
slight possibility that the results obtained are simply pathological, but
since the growth of the mature mycelium in nature is in many ways
similar to that of the germ tube in infection, it is thought that this
possibility 1s not very great.

Methods. Examination of inoculations was carried out by the
ordinary method of serial sections, the fixatives mostly employed being
chromacetic and acetic alcohol, with fuchsin and Licht Griin, and iron
haematoxylin as stains. The course of infection was also watched from
surface view from permanent preparations made as follows: inoculated
portions were fixed in acetic alcohol for about half an hour, then washed
and decolorised by absolute alcohol and finally mounted in Gilson’s
mounting medium, which is not so refractive as Canada balsam.

Germination. The conidia of V. inaequalis and V. pirina germinate
readily in water, most of them showing a germ tube of considerable
size after 24 hours, although some take a much longer time. The
conidia are easily wetted, and their specific gravity is so heavy (or
immediately becomes so on moistening) that on immersion in a drop
of water they almost immediately sink to the bottom of it, where
some change takes place, so that the conidium becomes attached to
the surface on which it is resting. The comparative difficulty with
which conidia about to germinate are washed from the slide on which
they have rested suggests a definite attacking envelope, but although
indications of an outer gelatinous layer have been seen under the
microscope they are in all probability optical illusions, for similar
indications are found with conidia of other fungi. In nature the
germinating spore must after a short time experience desiccation and
other changes due to the weather, but it is an extremely important
point with regard to the beginnings of infection, that notwithstanding
subsequent drying up germination can only be initiated after complete
immersion in water for some time—a fact originally discovered by
Aderhold, but perhaps hardly fully appreciated by the few more recent
workers. It seems indeed rather curious that in an atmosphere
saturated with aqueous vapour a spore will not germinate; and, as
will be seen later, the correct appreciation of this fact, which has been
repeatedly confirmed by the author, is of importance in understanding
some of the characteristics exhibited by these fungi. Immersion in

338 Apple and Pear Scab Fungi

water for a sufficiently long time having once initiated the first stages
of germination, subsequent periods of desiccation seem to help rather
than hinder the growth of the fungus. The appearance of the germ
tube in the two species is characteristic, for in V. inaequalis it is rather
a continuation of the spore, being formed by the more pointed end
growing out as the germ tube; whilst in the case of the V. pirina it
is sharply defined, arising as a lateral growth near to one end of the
spore.

In a hanging drop, the germ tube continues to grow out as a long
thin colourless hypha, but on the leaf desiccation soon brings the germ
tube in contact with the cuticle and this immediately brings about the
formation of an appressorium, the stimulus of contact, shown by
Aderhold, causing the germ tube to swell up and at the same time to
be closely applied to the cuticle. Some substance is excreted round
it so that a flange-like structure is formed round the end of the germ
tube, fixing it firmly to the cuticle (see Fig. 1). The changes in shape
of the fungal hypha and the exact method by which the flange was
formed could not be definitely followed, but the latter seemed to arise
as an excretion from the fungal hyphae, no part of the cuticle being
involved. At first the flat portion of the flange, which is usually very
thin, especially at the edges is colourless; but it soon becomes brown
and can readily be seen under the microscope. These “collars” or
flanges are much more prominent in some cases than in others, apparently
depending upon the state of health of the spore and the conditions of
growth of the fungus. The nucleus can usually be seen to be very
evident in the appressoria denoting probably great metabolic activity
in this region. The formation of the appressorium is not limited to
the germ tube, as the tip of any growing hypha may respond to the
stimulus, although there is no evidence that the mature mycelium is
capable of doing so. If after the formation of the appressorium, the
spore is still kept immersed in water, the appressorium begins to put
out a hypha from its upper surface, and later its appearance may
suggest that it was a lateral outgrowth from the mature hypha. The
germ tube generally forms only one appressorium, normally at a short
distance from the spore, but sometimes it branches and even develops
a short superficial mycelium producing five or six appressoria.

Aderhold and many other workers have noted that the germ tubes
frequently swell up into the appressoria over the junctions of the
epidermal cells, especially where three or more cells meet. Very
careful examination of moculations in superficial view has been made

S. P. WILTSHIRE 339

and there is apparently a tendency for appressoria to be formed
at the place recorded. Further details on this point are referred to
later.

Penetration. A point of great importance in infection is that only
young leaves or fruits are capable of being infected. This fact has
been firmly established both by observations in the field and by direct
experiments. In July the ordinary summer pruning was carried out
in the nursery at Long Ashton, and at the end of September a good
number of young shoots had developed from the dormant buds which
had thus been roused into activity. On the susceptible varieties this
young foliage was heavily infected while the mature foliage showed no
recent infection. Aderhold has noted the lability of the young organs
to be attacked, but recently Wallace cited instances where V. inaequalis
spread rapidly amongst apples in storage. Whilst under certain
conditions therefore mature organs may be successfully infected, it
appeared certain in the case of the trees under inspection at Long
Ashton that little late infection took place.

To avoid possible misunderstanding it should be explained that the
use of the term “infection” in the previous paragraph includes not
merely the penetration of the fungus into the tissues of the host, but
also its development afterwards to such a degree that the infected area
carrying a crop of conidia can be seen with the naked eye. It is
possible that penetration may occur on older foliage and fruit: but if
so, the fungus appears unable to grow to any appreciable extent in the
tissues of the host.

In view of the above it is clear that normal penetration of the cuticle
and further growth of the fungus must be followed on very young
leaves. When the appressorium is firmly established a growth of the
hypha into the cuticle takes place, beginning as a small bulge from the
centre of the attached disc (Fig. 5 and compare Figs. 11, 12). The
hypha usually grows directly into the cuticle at right angles to the
surface of the leaf, but occasionally it is inclined obliquely (Figs. 6 and
7). As it penetrates inwards it very often becomes enlarged, possibly
in order to secure the further attachment of infecting hypha. The
cuticle being extremely thin in the case of young leaves, the wall of
the epidermal cells is reached almost at once by the hypha which then
begins to grow between the epidermal wall and this cuticle, forming a
plate-like mycelium of very characteristic appearance (Figs. 2 and 3).
The cells at first are very thin and the plate is on y one cell in thickness,
but soon the fungus gets food from its host and the hyphae begin to

Ann. Biol. 1 23

340 Apple and Pear Scab Fungi

increase in size and divide so as to form a pad of cells, sometimes
pushing the cuticle outwards, sometimes crushing the epidermal wall
inwards. This subcuticular mycelium continues to grow out in all
directions, sometimes long arms of the mycelium projecting from the
original point of infection. It may at first consist of one long hypha
which will divide to form the mycelium afterwards, but usually the
mycelium spreads in a plate-like manner. The cells always remain
hyaline and do not become brown as in the ordinary superficial mycelium.
The growth of the mycelium seems to be hindered to some extent at
the junctures of the epidermal cells, for it is not uncommon to find one
epidermal cell covered with mycelium and most of the neighbouring
ones quite free (Fig. 4).

The exterior walls of the epidermal cells are usually convex, and
projecting portions of the cuticle fit in between adjacent cells. In
passing from above one epidermal cell to the next the fungus almost
always keeps between the cuticle and the epidermal walls without
dissolving away the former to any great extent. Therefore it seems
probable that for mechanical reasons it might be difficult for the fungus
to pass over these junctures, and especially would this difficulty “be
felt by the older mycelium growing out laterally from the original
invading strand rather than by the young hyphae meeting the juncture
at nght angles. The attack of one of these scab fungi at first has no
apparent influence on the epidermal cells, the nuclei remaining in their
normal position which is near the lower walls; but later various changes
may take place, the cell contents being frequently conglomerated into
a granular gumming substance, especially with artificial infections made
in bell jars. A substance which gives the red colour characteristic of
wound gum, with phloroglucin and hydrochloric acid, has also been
found excreted into the intercellular spaces of the leaf of the pear when
its lower surface is attacked. The final effect usually produced on the
affected leaf is the extension of the palisade layers into a kind of
phellogen round the scabbed area, this development frequently causing
the leaf to be somewhat curled.

Sometimes in the thickened region of the cuticle above the vertical
walls of the epidermal cells there appears a structure resembling a
hypha cut in transverse section and a similar structure can occasionally
be seen strictly following the junctions of the cells, if an inoculation be
examined in superficial view (Fig. 25). It does not seem that the
infecting hypha always behaves in this manner before it enters upon
its true subcuticular position: but when it is remembered that the

S. P. WILTSHIRE 341

appressoria appear to be formed over the same points, it seems to afford
some significance, the importance of which is discussed below.

The subcuticular mycelium having been formed in the leaf, the
uppermost cells of the stroma begin to enlarge, and push out the cuticle
until they burst it open and form the conidiophores from which conidia
begin at once to be cut off.

The method by which the conidiophore passes through the thick
cuticle on the fruit may be of interest as affording a comparison with
the method of entrance. There are two ways in which it does this:
(a) by eating away the cuticle in exactly similar manner to which it
infects, (b) by growth of the subcuticular stroma at right angles to the
surface so that the cuticle is burst off. The fungus lives typically
between the cuticle and the outer wal] of the epidermal cells, but on
the fruit it does not simply force its way between the layers. It also
partially eats away the cuticle as it is invariably seen that this layer is
thinner where it covers the mycelium. Sometimes at the edge of the
scabbed patch the actual hypha can be seen completely embedded in
the cuticle. Hence there is absolutely no doubt that there is some
cuticle dissolving excretion exuded by the fungus in its passage through
this layer.

It is not purposed to continue a description of the life-history further,
since in a resistant variety the fungus never reaches a stage beyond
that already described. In the following account of the resistance and
susceptibility of the hosts, reference will be made again to various
stages in inoculation of other portions of the plant; but the above
account is typical of what happens in the normal infection of a young
leaf.

The Question of Immunity.

Perhaps no other important disease exhibits such irregular behaviour
as these fungi as regards their immunity. For example, it is well
known that one variety may be heavily attacked one year and remain
almost immune the next, although the organism may be quite near.
Wallace says “it is found that certain varieties may be resistant in one
year and susceptible in another year under conditions which for average
varieties are as favourable to the disease in the one case as in the other.”
Salmon reports that at the Wye College Cox’s orange pippin had almost
every shoot attacked by V. inaequalis but at this station extremely
little of this fungus was found on the variety at all during 1914. It is
considered that the suggestion which at once occurs, viz. that this

23—2

342 Apple and Pear Scab Fungi

characteristic behaviour of the disease may be due to variations in the
climatic conditions at the time when the hosts are in most susceptible
condition, is not a sufficient explanation, and Wallace thinks that the
fungus itself is adapting itself to hfe on the “resistant” hosts. Again,
too, there is great variation in the parts of the host attacked. Some-
times it is especially the stem, sometimes the leaves, sometimes the
fruit. Again, the part of the host especially attacked, whether leaf,
stem, or fruit, varies considerably under conditions of which we know
little. The absence of adequately definite facts makes it at present
unprofitable to formulate hypotheses to account for these phenomena,
but on fuller knowledge it seems probable that much of the accessory
factors connected with the immunity of these fungi might be explained.
In the following instance some such explanation is attempted. It is
well known that the pear fungus appears on the fruit first and on the
foliage afterwards, whilst in the case of the apple the conditions are
reversed. Now it seems likely that the very thick woolly coating of
hairs on the young fruit of the apple very efficiently protect it from
becoming wetted and consequently infected. Later when this covering
disappears infection very readily takes place. There are many fungi
in common with Venturia which attack their hosts in a more or less
localized portion, and it is usually the young organs which are most
susceptible. There seems to be a definite correlation between the age
of the leaf and its powers of resistance. We might point to a parallel
amongst animals in the everyday fact that the young are more sus-
ceptible to certain diseases than adults. In the case of plants it is not
known whether this increased resistance accompanying age is due to
the better protection of the host against attacks of fungi, such as might
be afforded by the thickening of the cuticle, or whether the limiting
factor is intimately associated with the life of the living cell, and the
fungus is killed after penetrating the cuticle. Definite experiments
were therefore made to find out what happens when spores attack the
mature leaves of various varieties of some of which the young organs
are susceptible. For this purpose the mycelium from a pure culture
was used for inoculations, in order that the fungus might have a larger
reserve of food material to sustain itself in the attack than that
contained in the spore. In the case of the pear William’s Bon Chretien,
a susceptible variety, the fungus developed normally up to the stage
of the formation of the appressorium and the issuing of the hypha
from its underside into the cuticle. Instead, however, of the infection
hypha penetrating completely through the cuticle, and developing

S. P. WILTSHIRE 343

immediately a subcuticular mycelium, it showed a great tendency to
grow out horizontally into the cuticle (Fig. 21), which on the older
leaves is of sufficient thickness to allow this. There seems some pre-
ference of the fungus for the outer portion of the cuticle, rather than
that adjacent to the epidermis, but finger-like processes, especially from
the underside, are given off as branches from the main hyphae. Some-
times these processes reach the epidermal cell-wall and the formation
of a subcuticular mycelium takes place: but it was never observed to
reach any advanced stage in development, always remaining very
simple (Fig. 22). After a varying interval of time the cells of the fungus
die off, their contents becoming converted into dark brownish spherical
granules. From very many inoculations on mature leaves, both in
bell jars and on the trees in plantations, no conidia have ever been
produced. Even when the mature leaves of a resistant variety are
inoculated, the same course of events is followed. Fig. 20 shows the
dead hyphae of V. pirina in the cuticle of the Catillac pear, a resistant
variety which was very heavily inoculated with pure mycelium. It
will be noticed also that the epidermal cells show the beginnings of the
formation of a phellogen, which in the normal progress of the disease
is developed after the attack has developed for some time, and which
has been reported by Voges.

In the inoculation of the mature fruit much the same thing happens,
although the cuticle here being much thicker it is much easier to
follow what takes place. The infection hypha from the appressorium
grows directly into the cuticle (Figs. 11, 12 and 15) and then at its
innermost end swells slightly until it becomes almost spherical (Fig. 14).
Growth can now proceed in all directions, but much more easily in
a plane parallel with the surface of the fruit (Fig. 15). Occasionally,
however, it penetrates slowly, following its original course (Figs. 16
and 17). The cuticle is apparently laid down in layers, for with all
kinds of stains the innermost layers almost invariably take on a deeper
colour than the outer ones, and distinct striations can nearly always
be seen, especially where it covers the juncture of neighbouring cells
of the epidermis. The direction of growth of the hyphae now seems
to follow these striations sometimes to an astonishing length, suggesting
perhaps that the physical character of the cuticle is an important
factor (Figs. 18 and 19). It has been found extremely difficult to
infect successfully the mature fruit (using the term “infect” as explained
above); and although this is reported to occur under certain conditions
the ordinary course of events seems to be for the fungus to die off in

344 Apple and Pear Seab Fungi

exactly similar manner as when attacking mature leaves as above
described.

Although great differences occur between the attacks on certain
varieties in successive seasons, yet there are some varieties which
always remain highly resistant, if not completely immune, to this
disease. It was therefore interesting to determine the fate of the
fungus on the young leaves of resistant varieties. For this, Bramley’s
Seedling and Newton Wonder apples were selected as resistant varieties
for V. inaequalis, with Cap of Liberty, a well-known cider apple, as the
susceptible variety for comparison; also the pear William’s Bon
Chretien, a variety susceptible to V. pirtna, was infected, being regarded
as resistant to V. inaequalis. All were inoculated with conidia of
V. inaequalis obtained from the leaves of the “Cap of Liberty,” and
the results were very similar. Appressoria were formed as usual,
infection hyphae sent out into the cuticle, but in resistant varieties the
adverse effect of the host was quickly felt (Figs. 23, 24, 25) although
sometimes the fungus succeeded in penetrating completely through the
cuticle and forming a subcuticular pad. This usually appeared quite
unhealthy, the cells being smaller and narrower. The cuticle being so
thin no horizontal development of the mycelium in it could be detected
except in a few cases. Inoculations of V. pirina also were made on
the fruit of the apple, King of the Pippins, which is susceptible to
V. inaequalis, but in no case was the infecting hyphae seen not to have
penetrated into the cuticle. The apple fungus easily penetrated into
the cuticle of the pear and the pear fungus that of the apple. On
Bramley’s Seedling the fungus exhibited a preference for that portion
of the cuticle above the junctures of the epidermal cells already referred
to (Fig. 25). Eventually in the resistant types the mycelium ceased
to grow and practically died off. With the susceptible types on the
other hand a healthy subcuticular mycelium was quickly formed and
developed in the normal way described above until the production of
conidia resulted.

General Considerations,

The problems of immunity are particularly difficult because in
dealing with them we have to deal with fundamental life processes
which do not lend themselves to experimental conditions. All the
work which has been done towards the elucidation of the limiting
factors of immunity has been done with obligate parasites such as the
Mildews and the Rusts, but unfortunately none of these fungi will

S. P. WILTSHIRE 345

grow apart from the host. The facultative parasite affords a line of
attack of this difficult problem, for after a determination has been made
of what can be seen to happen to the fungus within the host of both
susceptible and immune varieties it might be possible to submit the
fungus to culture apart from the host and in media which may have
been directly derived from the host. If we are to attempt to enquire
whether the non-infection of an immune form is due to a toxin, or
anything of a similar nature, we must follow some such line as this.
Venturia is quite a unique fungus in its normal habitat between the
cuticle and the host: and although the process of infection and subse-
quent manner of growth in the host may be peculiar to itself, yet it
may be well to discuss it in relation to what is known of other fungi.
It is not proposed to review the literature on this question in any
detail, since these results would not warrant such an exposition, but
a brief outline of the principal work has been done, especially that
associated with Venturia may be given.

Biisgen! found with Venturia that the appressoria are formed _
frequently over the epidermal walls perpendicular to the surface, and
endeavoured to show that diffusion of some substance takes place at
this place and which acts chemotropically on the germ tube.

Aderhold (loc. cit.) holds that no particular chemotactic stimulus is
necessary, but that there is simply a strong diffusion of the ingredients
of the cell contents; this, however, he was not able to ascertain in
demonstrable quantities in living tissues. He held that at the junctures
of the epidermal cells the external cell-wall must have other properties
than those of the flat surfaces of the remainder of the external walls.
He records experiments which are not very conclusive but from which
he gathers that the pectates (especially potassium pectate) act
chemotropically on the fungus and suggests that the middle lamella
may so act in nature.

In addition there is the work of Myoshi, Nordhausen, Fulton and
others on general questions of chemotropism, but, so far as we know,
no other paper discusses the question in relation to Venturia.

The question of how the infecting hyphae pass through the cuticle
must take into consideration the nature of the cuticle itself. The
work which has already been done does not give much information,
being chiefly concerned with the distinction of cuticle from cork,
whether cuticle contains any cellulose and similar chemical problems.

1 Biisgen, M., Ueber einige Eigenschaften der keimlinge parasitische Pilze. Bot. Zeit.
1893, p 53.

346 Apple and Pear Scab Fungi

The cuticle is a protective covering layer to all young parts of plants
and hence must be capable of very rapid extension. It is not known
how such growth takes place, whether the outer walls of the epidermal
cells become gradually converted into cutin or whether the cutin itself
is a secretion of the cell. The cuticle, however, must not be regarded
as being a simple homogeneous body. Von Héhnel?! in 1878 stated that
the external layers of the cuticle are free from cellulose, whereas those
layers bordering on the external walls of the epidermal cells represent
cellulose saturated with cutin. More recently Géneau de Lamartiere
in 1906 has seen fit to distinguish the former as the epicuticle. With
all the common stains it is found that the portion of the cuticle next
the epidermal cells is coloured more deeply than the rest of the cuticle,
particularly in the projections which fit between the adjacent epidermal
cells; and moreover, the general staining of the cuticle suggests that
it has been formed in layers. The outer layers, being continually
exposed to complete desiccation, must be under greatly different
conditions from those next to the epidermis. Hence it appears probable
that the cuticle has a structure of its own: and this may be an
important factor in the penetration of the infection hyphae through it.

The permeability of the cuticle is of interest, as regards the
chemotropic attraction which certain substances have on fungal hyphae.
That substances can diffuse through the cuticle in some cases cannot
be doubted, since the copper of Bordeaux mixture slowly passes into
leaves of certain plants, such as potatoes, which have been sprayed
with it (Barker and Gimingham®*). Whether any substance which may
render the copper in such cases soluble diffuses out through the cuticle
is not known, and the position is similar with regard to the diffusion
of substances possibly chemotropic to fungal hyphae. Nevertheless it
must always be remembered that such a thing may happen in nature.

The observation that the appressoria are formed frequently over the
juncture of epidermal cells, seems to be justified from a careful
examination of inoculations in surface view. But it is by no means
the case that they are formed only in these positions. On examining
300 appressoria, 26% were found to be over the centre of the cells
and between 14-19 % did not touch the junctures although they were
perhaps near them. If we take into account the relative sizes of the
appressoria and the cells, this result may not appear to be particularly
unexpected. The area within which an appressorium if it fell would

* See Czapek, Biochemie der Pflanzen, p. 702, 1912 Ed.
> Barker and Gimingham, Ann. Applied Biology, Vol. 1. p. 19.

S. P. WILTSHIRE 347

touch the juncture of the epidermal cells would be bounded by a line,

the breadth of the appressorium within the edge of the cell; and taking

the relative sizes of the diameters of the cells and appressoria roughly

as 6:1, we should find this area would be { that remaining. Hence

we might expect the appressoria to touch the junctures of the epidermal

cells more often than not. On the other hand, however, other fungi

as well as bacteria are said to show a similar liking for that part of the’
cuticle above the junctions of the walls. The elaborate paper of Fulton,

in which he calls in question the whole of the work done on chemotropic

attraction of fungal hyphae, makes us suspicious of accepting altogether

the works of earlier investigators and it becomes more and more evident
that a further study of chemotropism is necessary for the progress of
enquiry into the question of the attack of parasitic fungi. It is not yet
established whether chemotropism does exist at all; and not until we
know, not only whether it exists but also whether it plays any part in
infection, can we hope to attempt to solve the question why the fungal

hypha enters the host.

If some chemotropic substance does influence the direction of growth
of the germ tube, it must either be the exterior layers of the cuticle or
something formed interior to them and then excreted. There is no
reason to suppose that the exterior of that portion of the cuticle covering
the perpendicular epidermal walls has peculiar properties. Nordhausen
has suggested that the mechanical checking which the germ tube
undergoes on crossing a groove or the collection of water in it may
account for the predilection of the appressoria for this position, yet the
behaviour of appressoria is quite similar on varieties like Port and
William’s Bon Chretien which have no grooves (see Figs. 26, 27 and
compare Fig. 28). That the cuticle which covers the junctures of the
epidermal cells is, however, different from the remaining is shown by
the different staining properties it possesses; this fact, taken in con-
junction with the occasional occurrence of hyphae embedded there,
suggests rather pointedly that this may be a substance chemotropically
attractive to the germ tube. At the best, however, this chemotropism
can be only an accessory factor in infection since hyphae can penetrate
the cuticle quite well in the middle of the epidermal cell-walls.

The growth of the infection hyphae from the appressoria through
the cuticle itself is interesting in connection with the part played by
chemotropism. If the hypha entered solely because attracted by the
substances in the epidermal cells or cell-walls of the host, we should
suspect that it would bore directly through the cuticle to reach the

348 Apple and Pear Scab Fungi

subeuticular position. But although the cuticle of organs susceptible
to attack is very often so thin as to prevent the horizontal growth of
the infection hyphae in it, yet occasionally one finds stages as represented
in the Figs. 6 and 7. These figures suggest that there is no guiding
influence towards the epidermis, but that the fungus simply eats its
way slowly through the cuticle until it arrives between the cuticle and
epidermal cell-wall. With mature organs of both susceptible and
resistant varieties where the cuticle is thicker, we have still more
interesting cases. How can the long horizontal growth of the infection
hyphae in the cuticle (a very frequent occurrence) be explained? Does
it not rather suggest in place of an attracting substance the presence
of something which is repulsive to the invading hypha? The physical
layering of the cuticle may have something to do with the direction of
growth, but this horizontal habit is not confined to fruits but is also
exhibited in mature leaves, where the layering of the cuticle is not nearly
so evident on staining. Of course, the tendency is most clearly
developed in resistant organs because the young susceptible parts of
plants have very thin cuticles, but that it should occur at all strongly
negatives the view of the germ tube being attracted by the cell sap of
the host. The conclusion seems unavoidable that the fungus infects
in spite of the host, and that chemotropism if it acts at all must play
a very insignificant part in the process.

It has been shown that immunity does not depend on freedom
from the initial attack, any more than in the case of the rusts; immunity
there depends upon the non-entry of the infection tube into the host.
What the limiting factor in immunity is, we can only speculate—it
may be simple starvation of the fungus, as suggested by the gradual
reduction of growth, or it may possibly be the formation of some toxic
substance. With such possibilities existing it might be well to mention
here some experiments which were made on the growth of the conidia
of V. inaequalis in the expressed sap of the young leaves of certain
varieties of apples. Young leaves of King of the Pippins (susceptible)
and Bramley’s Seedling (resistant) were pounded in a mortar and the
sap then squeezed out of them. Conidia were then sown in the
sap and hanging drop preparations made which, although by no means
free from bacteria and yeasts, remained sufficiently pure for the one
or two days necessary for the experiment. Control drops were set up
with water instead of the sap medium. In all cases the growth of the
conidia in the sap was very much slower than in water and a much
larger percentage did not germinate. On diluting the sap, the conditions

S. P. WILTSHIRE 349

of germination were gradually improved until in media of which the
ratio of sap to water was 1 : 10 no difference from the water controls
could be observed. A few further experiments were made with Newton
Wonder (resistant) and Cap of Liberty (susceptible) which as far as
they went coincided with the results given above. In these sets of
preparations the conidia appeared to grow better in the sap of the
susceptible varieties than in that of the resistant kinds: but the
approach of winter rendered it impossible to carry this work any
further for the time being. The little which has already been done
seems to support the view obtained from the study of microscopical
preparations that the host is antagonistic to rather than attractive
towards the parasite.

The facts which are recorded in this paper are therefore considered
to suggest that the appressorium, being formed as the result of mechanical
stimulus as shown by Aderhold, penetrates into the cuticle, feeding on
it as it goes and finally reaching its normal habitat between the cuticle
and epidermis where it flourishes, if the attacked variety is susceptible.

Immunity is shown not to depend on the protection of the cuticle
and indications are recorded which suggest the probability of the cell
sap of the host being in all cases antagonistic to the fungus.

In conclusion I should like to express my deepest thanks to Professor
B. T. P. Barker, M.A., at whose suggestion the work was begun, and
who throughout has rendered invaluable aid by helpful criticism and
advice. I.am also indebted to him for facilities for working at the
Agricultural and Horticultural Research Station of the University of
Bristol.

LIST OF FIGURES.

Fig. 1. Spore of Venturia inaequalis germinating on the fruit of apple Stirling Castle.
x 1600.

Fig. 2. Spore of Venturia pirina germinating on leaf of pear Louise Bonne de Jersey.
x 1600.

Fig. 3. Same showing later stage. x 1600.

Fig. 4. Mycelium of Venturia inaequalis in leaf of apple Cap of Liberty, surface view
showing delimitation of mycelium juncture of the epidermal walls. = 1600.

Fig. 5. Appressorium of Venturia inaequalis on the leaf. x 1600.

Fig. 6. Entrance of infection hypha into the cuticle on leaf of apple Cap of Liberty.
x 1600.

Fig. 7. Same. x 1600.

Fig. 8. Same, later stage. x 1600.

Fig. 9. Same. x 1600.

Fig. 10. Penetration of mycelium of Venturia pirina from cuticular to subcuticular
position in young leaf of pear William’s Bon Chretien. x 1600.

350 Apple and Pear Scab Fungi

Figs. 11,12, 13. Entrance of infection hyphae of Venturia inaequalis into the cuticle of
the fruit of apple Stirling Castle. x 1600.

Fig. 14. Same ata later stage. x 1600.

Fig. 15. Same showing horizontal intracuticular development of the mycelium. x 1600.

Figs. 16 and 17. Same growth of infection hypha directly into the cuticle. x 1600.

Figs. 18 and 19. Growth of mycelium of Venturia inaequalis in the cuticle of apple
King of the Pippins, showing how it roughly follows the layering of the cuticle.
x 1600.

Fig. 20. Venturia pirina on mature leaves of pear Catillac (resistant). x 1600.

Fig. 21. Venturia pirina on mature leaves of pear William’s Bon Chretien (susceptible in
young leaves). x 1600.

Fig. 22. Same as Fig. 21. x 2050.

Figs. 23, 24, 25. Venturia inaequalis on the young leaves of apple Bramley’s Seedling
(resistant). x 2050.

Fig. 26. Cuticle of pear William’s Bon Chretien.

Fig. 27. Cuticle of pear Port.

Fig. 28. Cuticle of pear Catillac.

THE ANNALS OF APPLIED BIOLOGY. VOL. I. NOP 3 &4. PLATE XIX.

Cambridge University Press.

THE ANNALS OF APPLIED BIOLOGY. VOL. I. NOS 3 & 4. PLATE XX.

Cambridge University Press.

THE ANNALS OF APPLIED BIOLOGY, VOL. I. NOS 3 & 4. PLATE XXI.

Cambridge University Press.

THE ANNALS OF APPLIED BIOLOGY. VOL. I. NOS 3 &4. PLATE XXIl.

Cambridge University Press.

i
i
oa

WINTER COVER WASHES.

By A. H. LEES, M.A.,

Plant Pathologist, University of Bristol, Agricultural and
Horticultural Research Station.

WINTER cover washes or more properly late spring cover washes
were first tried on the large scale by Mr Howard Chapman of Kent.
He found by experience that a lime wash applied as late as possible
before the buds burst in spring produced a very decided lessening of
Psylla attack and consequent increase of crop. Cover washes have
also certain other subsidiary but very real advantages:

(1) They can be applied when labour is easily obtainable. A
summer wash has to be put on at the end of April, nearly two months
later, when labour is urgently needed for other operations.

(2) They tend to keep the bark clean.

(3) They add a small amount of lime or chalk to the soil.

Since its introduction lime wash has been tried by many growers,
some of whom have become enthusiastic advocates of it, while in the
hands of others it has produced no apparent good. It seemed there-
fore desirable to make some investigation into its action. Two
hypotheses were current to account for its good action, since undoubtedly
it has had good action in some places and under some conditions.
The first suggested that its action was due to the causticity of the hot
lime, which had some effect on the protoplasm inside the egg or at
any rate so influenced the egg shell as to render the ovum fatally sus-
ceptible to outside conditions. The second supposed that the lime
covering had no direct action but only an indirect mechanical one,
effectually sealing in the eggs and preventing the hatching of the
enclosed larva. It was obvious from the outset that the first explana-
tion was unlikely. When one considers that the chitin of insect eggs
can resist being boiled in strong caustic soda, it is not likely that the
feebly caustic lime would affect it. The second thus appeared a more

352 Winter Cover Washes

likely hypothesis. Working on this it is at once apparent that to make
such a wash most efficient certain conditions must be fulfilled. These
are:

(1) It must give a thick covering.

(2) It must resist all external conditions causing lessening of
the coat when once on the tree, 7.e. it should not flake when dry or
wash away when wetted by rain.

(3) It should be applied as late in the spring as possible.

(4) The materials should be reasonably cheap and easy to get.

(5) It should be easily made.

All the experiments hereafter described had to be done in the dead
season, beginning in the autumn of the year and ending in the late
spring of the following year when the buds had begun to burst. They
may be grouped more or less in a chronological order in order to retain
the sequence of ideas.

SEASON 1912-13.

Laboratory experiments.

Experiments were begun to find some mixture that was more
resistant to erosion than lime alone. In the first trials twigs were
dipped into the various mixtures and allowed to dry in the laboratory.

It was found, however, that this method gave unsatisfactory results,
as the twigs themselves soon dried and contracted away from the
coating of material applied to them, so that the best wash under these
conditions soon began to flake. On the living twig this is not so. In
all subsequent laboratory experiments the washes were poured upon
ordinary 3x1 microscope slides and allowed to drain as they dried.
The smooth surface of the slide was an additional guarantee of good
sticking qualities. In practice, in the field, twigs are always slightly
rough so that any wash adhering well to glass slides should do so quite
as well when applied to a tree. Plain lime wash at the rate of 2 lbs.
to the gallon of water was used as control. It having been frequently
stated that the addition of waterglass or sodium silicate improved
the adhesiveness, this was first tried. All quantities are calculated
in pounds of material to pounds of water or in grains per ¢.c¢.

The following (with the salt left out) recommended by Theobald

Lime Waterglass Water
20 1 100

A. H.:- Lens 3538

produced no improvement; if anything it was inferior to plain lime
wash. This is not surprising as calcium silicate, which is formed
by the action of lime on sodium silicate, is a hard brittle body and not
likely to give adhesiveness in the quantity used above. Greater
strengths would prove too expensive. The addition of salt, according
to the following formula:
Lime Salt Water
20 2 100
gave the same negative result.
It having been brought to the author’s notice that tallow was used
by many firms who did outside lime washing, the following was tried,
the tallow being added as the lime was slaking:

Lime Tallow Water
50 2 250

This formula proved of doubtful value.

Field expervments.

The lime and tallow wash was tried at five different centres in
counties within the advisory area of the Bristol University Research
Station, the lime and salt at eight and the whiting and size at three.
Control experiments were also done at Long Ashton.

The whiting and size formula gave very good results but as a practical
wash it is far too expensive.

Lime and tallow showed no superiority over lime and salt. Some-
times one gave a better result and sometimes the other, and it was
clear that good sticking power depended more on the freshness of the
lime than on any other factor.

Season 1913-14.

Laboratory experiments.

The whiting and size wash, though giving a good coat, proved
far too expensive. Less quantities of size than that used above gave
too thin a coating.

Accordingly an attempt was made to obtain a cheaper form of glue.
After some trial one was obtained at about 4d. a lb. in hundredweight
quantities. This brought down the cost to about 5d. a gallon which
was still prohibitive. It was found that smaller quantities of glue

354 Winter Cover Washes

gave ‘sufficient adhesive power but not sufficient covering power.
Starch paste was therefore tried to remedy this according to the formula:
Whiting Glue Starch Water
8 $ t 10
This gave a thick and fairly firm coat. Less starch gave too thin
and loose a coat while more glue became too expensive. In order
to get a cheap form of starch, ordinary flour was used after being
converted by hot water into paste.
Three formulas were made up with varying amounts of flour and
glue. The results and costs are included in the table below:

No. Whiting Glue Flour Water Result when dry Cost per gallon
(1) 8 4 4 10 Fair coat ag 2% 275d.

(2) 8 i 4 10 Better than No. (1) .. Qed.

(3) 8 4t i 10 Still better coat ve Quon,

The price of all these is rather high and they have besides other
disadvantages. ;

When such a coating is exposed to the action of water it quickly.
gets washed away owing to the solubility of the glue, but if a small
quantity of potassium dichromate is added the glue is rendered insoluble
on exposure to light. This action depends on the gelatine of the glue
which, mixed with dichromate and exposed to light, becomes insoluble.

The following formulae were then tried:

Whiting Glue Flour Pot. dichromate Water
8 3 cs z 10
8 3 + 3 10
8 4 , _ 10
8 4 } 4 10

In all cases the addition of the dichromate caused a great thinning
in the consistency of the liquid and a poor coat resulted. On trying
starch again according to the formulae:

Whiting Glue Starch Dichromate Water
8 4 t 3 10
8 $ t oY 10

good covering power and adhesiveness were obtained in both cases.
It was necessary therefore to obtain a cheap form of starch and this
was found in “Farina,” a potato flour which cost about 2d. a pound
when bought by the hundredweight. Accordingly the following two
mixtures were tried:

No. Whiting Glue Farina Water

8 1 1 10
(2) 8 } i 10

A. H. LEEs 355

Both gave good coverings and were more satisfactory than those
made with ordinary starch.

With the idea of incorporating a fungicide Bordeaux mixture was
added, but it caused great thinning of the liquid.

The same result was obtained when copper sulphate was added.
The addition of flowers of sulphur, with the same end in view, though
it caused no thinning was unsatisfactory as the dried coat showed
great tendency to flake.

The cost of No. (2) of the above table is 2d. a gallon of which the
whiting costs 1}d., the glue 3d. and the farina jd.

Owing to the expense of the whiting, due chiefly to the large quanti-
ties necessary to produce a thick coat, lime was again tried as the
covering material. The following mixtures were tried with the results
included in the table:

Lime Glue Farina Water Result
2 ~- — 10 Poor covering
2 3 — 10 Poor covering
2 1 4 10 Very good but flocculent and inclined to flake
2 ~- 4 10 Too thick but not firm enough
2 — i 10 As thick but not coherent and flaking when dry

In order to stop this flaking a mixture of lime and whiting was
tried with the idea that the different sized particles thus introduced
might interlock and so prevent the flaking:

Lime Whiting Glue Farina Water
14 7 1 1 80

This mixture, though it appeared not to flake at first after a few days
did so. It was suggested that the addition of cressyllic acid which is
supposedly used in some distempers might give good adherence.
1, 2 and 5 per cent. added to the ordinary lime wash, however, gave
mixtures which flaked as badly as the control.

Effect of aluminium salts.

The extremely gelatinous nature of aluminium hydroxide is well
known and it was thought that by incorporating it with ordinary
lime wash adhesiveness might be obtained. Accordingly aluminium
sulphate was added. Its reaction with calcium hydroxide gives
aluminium hydroxide which thus becomes thoroughly well mixed.

Ann. Biol. 1 24

356 Winter Cover Washes

The following mixtures were tried with the results included in the
table below:

Aluminium Copper

No. Lime sulphate Glue sulphate Water Result

(1) 2 3 — — 10 Thick coating when wet, very
hard and firm when dry

(2) 2 3 4 = 10 Thick coating when wet, but not
quite so good when dry as (1)

(3) 2 3 — ay 10 Decidedly thinner when wet and
powdery when dry

(4) 2 3 t ay 10 Thin when wet and loose when
dry

The addition of glue did not improve the mixture, and copper sulphate
again caused thinning and loss of adhesiveness.

Substitution of alum for aluminium sulphate.

It being possible to obtain alum at 14d. a pound while the cheapest
quotation for aluminium sulphate is 23d., the former was tried in its
place. At the same time iron sulphate was introduced as a fungicide
with the results given in the following table:

No. Lime Alum Tron sulphate Water Result

(1) 2 ty to 10 Too thick

(2) 2 20 ro 10 Too thin

(3) 2 oy wh 10 Right thickness

Unlike the copper sulphate, iron sulphate does not cause a thinning
of the mixture.

In order to test the rain resisting power of the various mixtures
that had been made up, slides covered with them were soaked in water
for 24 hrs. The mixtures and results are given in the following table:

Whit- Dichro- Iron Cressyllic Result after
No. Lime ing Alum Farina Glue mate sulphate acid Water 24 hrs. soaking
(1) 2 —- 1 — as -- 5 10 Very good. Still hard
(2d a a ay t £5 ta) ee ee
(3) — 8 _- } t dr — — 10; Resisted fairly well
(4) 14 7 — 1 1 t — — 80
(5) 20 — — — — — — 5 100 Poor
6 — 8 — t + = -= =
(7) ae 3 Pu I i = ‘a rat 7 Very poor

The mixtures in this table were subsequently tested in the field
(see Field experiments, 1913-14) when it was found that No. (2) gave
by far the best results. As, however, the whiting therein cost as much
as lid. in the total of 2d. per gallon of wash, it was necessary to try
whether lime could be substituted instead. At the time the fact

A. H. Ls 357

that gelatine, the essential body in glue, is insoluble in alkaline solutions
was not realized. Lime also appears to decompose glue, as a mixture
of the two becomes frothy and the glue loses its properties. The
following mixtures were tried with the results included in the following
table:

Y | Pot:
Aluminium dichro-
Lime Glue sulphate mate Water Method of mixing Result
2 i — a 10 Glue added after slaking Poor coating
2 4 —- — 10 Glue added to water
before slaking. Poured Poor coating
when hot
2 4 — — 10 Ditto but poured when Fair coating
cold
2 4 i — 10 Glue added first Very thin and poor
2 4 i — — The sulphate added first Fairly good coating
2 $ 4 eT 10 — Fairly good
None of these mixtures could be considered satisfactory.

Various other substances were added to the ordinary lime wash
with the idea of obtaining a firmer coat. These were miscellaneous
in nature and may be included for convenience in one table as follows:

No. Mixture Result
(1) Calcium chloride About as hard as lime alone
(2) Solar distillate paraffin in emulsion in Decidedly soft coat probably due to
the lime the oil
(3) Solar distillate and aluminium sulphate Also gave a soft coat due to the oil
(4) Various proportions of skim milk A soft coating due to the fat contained
in the milk
(5) Calcium chloride then waterglass Very soft and powdery coat
(6) Cement in the proportions of 1: 1, 1: 4, All gave flaky and soft coatings, the
EB oe Us softness increasing with the pro-
portion of cement
(7) Plaster of Paris in the proportions of Less flaky than the cement mixtures,

The failure of the cement was
proper setting could take place.
is mixed with a quantity of water

-1 - 1 -1
1:4, 1:4, 1:¢

but the flakiness increased with
increased proportion of plaster

probably due to its drying before
Under ordinary conditions cement
so that it has a chance of absorbing

some chemically before the mass dries.

the lime.
that gave the best result.

Methods of slaking lime.

During the course of these experiments it was obvious that the
firmness of the resulting coat depended largely on the manner of slaking

An experiment was therefore started to find the method
The usual way of slaking lime is to add

just sufficient water to allow chemical action to proceed, that 18, -it

24—2

358 Winter Cover Washes

is allowed to “dry slake.”” From previous trials, wet slaking, namely
covering the lime completely with water, promised the best results.
Taking always lime two parts to water ten parts by weight the
following ways were tried:

No. Method Result

(1) Excess of hot water added (in this case 4rd total Good coat
required) applied hot

(2) Ditto but applied cold Not quite so good
(3) Excess of cold water added Decidedly inferior
(4) Slaked dry with cold water. Then full quantity added Poor
(5) Slaked dry with hot water. Then full quantity added Poor

In these trials hot water gave decidedly the best result. This is probably
owing to the completeness of slaking thus obtained. Accordingly,
further trials were made with the object of getting conditions which
should give complete slaking.

The following methods were tried with the results as given in the
table below:

No. Method Result

(1) Made up with hot water and not allowed Thick but very brittle coat
to stand

(2) Made up with cold water and not allowed Not so thick or brittle
to stand

(3) Slaked with 4 full quantity cold water. Rather harder than (2) and slightly
Left for 12 hrs., remaining water added brittle
and applied

(4) Made with full quantity cold water. Left Fairly thick and not brittle
for 12 hrs. and applied

(5) Dry slaked and left for 12 hrs. Then Thin but firm coat
made up to full amount of water and

applied
(6) Made up to full dilution and allowed to The mixture became very flocculent
stand for 12 days and the surface covered with a

layer of carbonate. When dried on
the slide it gave a very soft and
powdery coat

(7) Ordinary lime coating dried slowly in It produced a hard marbly coat with

a moist chamber softer material underneath

(8) Lime mixture left in small quantities in This produced an exceedingly hard
a large evaporating dish so as to dry and firm coat
slowly

The results from Nos. (1) to (5) clearly show that in cases where
the lime was slaked slowly, as when a dry slake was given or the mixture
allowed to stand for 12 hours, a firmer, less brittle coat was obtained
though not necessarily a thicker one. This result was afterwards
confirmed by trials in the field. A dry slake gives a very thin and
therefore unsuitable coat for an egg cover in practice. No. (8) gave
an excellent coat, no doubt due to its slow drying in an indoor atmo-
sphere containing more than the usual percentage of carbon dioxide.

A. H. LEEs 359
These conditions formed a solid coat of calcium carbonate not only
on the surface but in the lower layers as well, thus making an exceedingly
hard and smooth coating. Unfortunately these conditions are im-
possible to obtain out of doors as drying takes place quickly and only
small quantities of carbon dioxide are present.

None of the additions made to the lime improved the coat, while
most of them made it distinctly worse.

To test whether carbonating before application improved the mixture,

carbon dioxide was passed into a beakerful.

When poured on a glass

slide and dried a brittle coating was obtained which is quite useless.

were subsequently found unreliable.
When sprayed on twigs of a tree the coating is subject to violent
movings of bending caused by the wind, which are absent in the case

of an upright post.

Field expervments.

These were first arranged on upright flat-sided posts.

The results

It was found that such bendings of the dried

coat was largely instrumental in causing flaking. The trial lasted
which much rain was experienced.

ten days in December during

ra) = q 5
o
es eae 5 3&
© 2 ee Epes 5: 5 fe =>
oe SESE Lae gs EL ge
Pee Oo Oo ey een eae nD m
(1) 90 2 — — — — =| — 100 Moderate coating Largely washed
“ away
(2) — — 8 } — — — 10 Moderate coating Showed slight signs
of thinning
(3) — — 8 } 4} + — — 10 Moderate coating Showed very little
signs of thinning
(4) 144— 7 1 #1 } — — 80 Moderate coating Very good and thick
coating
(5) eee ee Pe) 10 (thinned down: be- Very poor
fore applying as
too thick to go
through nozzle
(6) 2 — — — — — &§ ww 10 Do. Do. Thinned in places
(7) 2 eS ee 10) Unstramed? (andy Thimmned'’ in) ) places
thrown on and flaked
(8) 2—- — — — — 3% ww 10 Do. Do. Thinned rather more
than (6)
(9) 2— — — — — * ww 10 Do. Do. Too thin when ap-
plied
(10) wk-—- — — — — ww 10 Strained, sprayed, Showed very little
etc. signs of wear
(11) ee a eS ee 10) Dittoibut.too thin) Far’ too thin
(12) 14— — — — — 7 wo 10 Appeared most Thinned rather
suitable badly

360 Winter Cover Washes

Practically both (5) and (6) were too thick to put through a spraying
machine. As alum gave disappointing results, aluminium sulphate
was substituted to avoid the presence of the soluble potassium sulphate.
The following mixtures were tried:

No. Lime Al. sulphate lron sulphate Water
(1) 3 io (=1%5 alum) 10 10
(2) 14 + ( = ys alum ) io 10

No. (2) gave too thin a coat while No. (1) appeared satisfactory.
The better mixtures of those tried on the upright posts were then
sprayed on to trees with the results included in the table below:

£ ; z
o : Bw
op Kagel c= ics Be
A= ai tO. Dk 2 F Et
She yee ise es nie gee a oe oH 5 3
PA FS) Ase WOral Tob ay ey a des = Zs
(1) — 8 4 +} — — — — 10 Washed off badly Surface soft 2
(2) -— 6°} 2°35 — — About the same conditionaswhen 2
applied. Surface gritty
(3) 14 — — — i: — ,;, 10 Washed off badly. Surface very 3
flaky
(4) 1} ey =_ re Cis, 3 a? aa 10 Ditto 2
(5 14 7:1 1 ¢ — — — _ 80 Washed off rather badly. Sur- 2
face flaky
(6) 14°-— — — — — 3 we 10 Washed off badly. Surface very 2
flaky, possibly a little worse
than (3) and (4)
(lag ee oe ro a a DUS | 3

The weather in the three weeks of trial included rain, snow, frost
and wind. -

Of these mixtures by far the best was (2). The amount of whiting
was decreased from eight to six as the larger amount was difficult to
incorporate with the water required by the formula. The aluminium
sulphate and the alum mixture were disappointing as they had given
good results in the laboratory.

To test the effect of keeping lime mixtures for some time before

applying them the following formulae were tried with the results
included in the table below:

No. Lime Water Method Result after two months
(1) 2 10 Applied after keeping for 2 days Stuck better than (2)
(2) 2 10 Applied hot Not so good as (1)
(3) 2 10 Applied after being froze for 4 Came off very quickly
days
(4) 3 10 Applied hot Somewhat better but not good

From results from (1) and (2) it is clear that it is best when possible
to keep the lime mixture at least some hours before applying. This

A. H.* LrEs 361

result was confirmed in some experimental spraying done in Hereford-
shire. The explanation is probably this. When lime is slaked, at
first there is a violent action which soon subsides. In ordinary parlance
the lime is now “slaked’’ but chemical action goes on more slowly
for some hours. A 40 gallon barrel of lime wash made in the evening
was still warm the next morning, showing that chemical action had
been continuing. If applied directly after the first violent action
has ceased, in the words of the grower put on “hot,’’ further slow
slaking proceeds when on the tree, resulting in expansions of particles
in the coating. The expansion of small particles act like levers on
the rest of the coat, pushing and levering off particles that are completely
slaked and dry. The net result is that slaking sets in. This, however,
is certainly not the only cause of flaking. Wind causes much damage
on the smaller boughs. Owing to the bending to and fro of the twig,
at first the coat is too small, when the twig is convex, and then too
large, when concave. Another cause is frost after wet. Beating rain
causes washing off but not flaking. Insufficient slaking explains the
fact that good coatings often show completely bare patches sooner
than poor coatings. The poor coatings are generally made from
partially slaked lime or from a mixture too poor in lime. In each case
a more perfectly slaked mixture is obtained but a mixture which is,
of course, much inferior in egg covering powers.

A thick mixture like the 2 Ibs. to 1 gallon formula, allowing some
hours for complete slaking, not only gives a firmer coat but also a thicker
one, as one gets more of the very fine particles which are the most
important in forming a thick coat. These particles seem so small
that they aggregate when wet ijn an almost gelatinous manner so that
the mixture has quite a distinct viscosity. When dry this gelatinous
form disappears and does not reappear on wetting.

Of all the washes so far tried the whiting, glue, farina, dichromate
formula gave by far the best results and it was therefore tried more
extensively at Long Ashton.

It was also tried at centres in the three counties of Gloucestershire,
Worcestershire and Herefordshire on trees wel] infested with Psylla
eggs. One trial was spoiled by a subsequent frost cutting all the blossom
and another by the fact that the grower sprayed the treated trees
with a spring wash. The third, however, was left untouched and though
the application of the whiting wash was followed by heavy rain almost
before it was completely dry the resulting crop was good and equal
to trees sprayed with a summer wash only.

362 Winter Cover Washes

The whiting wash, though it gave good results as regards sticking,
presented difficulties owing to the large amounts of hot water required.
In order to get the starch and glue into solution about half the total
quantity of water had to be hot. This was a serious drawback and
a way was sought to overcome it. The fact that starch could be jellied
by caustic soda seemed to suggest a possible solution. It was found
that starch jellied by caustic soda gave the required thickness to a
whiting mixture but that at the same time it had no coherence and
gave a very thin coat. With lime, however, not only was the mixture
well thickened by this process but it also retained its coherence.

The following mixtures were therefore tried. They avoid the use
of hot water:

Dichro-

No. Lime Glue Farina Soda mate Water How made

(1) 2 4 4 ds ae 10 The soda added before straining the
mixture. This resulted in too thick
a mixture to strain but it was worked
through and applied to trees

(2) 2 t 4 4 wa 10 Lime mixed with half full quantity of
water mixture, strained and then the
soda added

(3) 2 q 4 ti tk 10. Lime mixed with full quantity of water
and strained. Soda then added

(4) 2 Bh q oe wa 10 Starch jellied by the heat of the freshly

strained milk of lime
Of the first three (2) was distinctly the best but (4) proved better
than all, having a good thick smooth coat. It showed however some
tendency to flake. It is hoped to extend these experiments this season.

Action of lime wash on insect eggs.

It seemed desirable if possible to ascertain the nature of the action
of a lime coating on Psylla eggs since it certainly does have some
checking action.

To do this, apple twigs abundantly covered with Psylla eggs were
cut off the trees in March. These were covered with various washes

and placed in a beaker of water till the eggs of the controls hatched.
The mixtures tried were

No. Whiting Lime Glue Water

(1) 6 —— 1 10

(2) — 2 — 10 applied hot
(3) — 2 — 10 applied cold

(4) == 1 ae 10

On the contro] twig the Psylla hatched in abundance by April 18.
(1) showed only two larvae hatched. On dissolving off the whiting

A. H. Less 363

coat with dilute hydrochloric acid many were found in a dried up
state in the egg which had not hatched. Others remained fresh and
juicy within the unhatched egg. They appeared normal but failed
to hold later on. Only a few eggs had hatched and of these only two
had succeeded in reaching the open bud.

(2) None were found in the buds. On dissolving the lime coat
by dilute hydrochloric acid many larvae were found to be unhatched
but dried up. Others had hatched but had failed to get more than
a little way out of the egg shell. Others had succeeded in escaping
from the egg but had been killed while traversing the lime coat. Newly
hatched larvae placed on a lime-coated slide become completely covered
with lime and usually die in about two hours, during which time they
only crawl a very short distance.

In a second twig coated with (2) larvae were found fairly abundantly
in the buds. In both twigs no fresh apparently normal eggs were
found as was the case in the whiting coated twig, and in both cases,
on solution of the lime coat, dried up larvae were found in the resultant
solution showing that they were actually present, held immovably
under it.

(3) Some were found in the buds. Lime flakings treated with
dilute acid showed presence of Jarvae. On treatment with acid the
shoot showed large numbers of hatched eggs, also of larvae dried in
the egg shell.

(4) Practically none in the buds. After solution of the lime
by acid many hatched eggs were found and a few larvae dried in the
egg shell. As in all the limed twigs living larvae were found crawling
on the lime.

From these experiments it appears that:

(1) A thick covering largely prevented the appearance of larvae
in the buds.

(2) The lime coatings largely prevented rupture of the egg shell
and where rupture had taken place many had not succeeded in getting
out of the shell.

(3) Of those that had, many did not succeed in getting to the
surface.

(4) Of those that had succeeded in getting to the surface a good
proportion were killed by the powdery lime adhering to their bodies.

(5) The whiting coat almost entirely prevented hatching but did
not have such a desiccating action.

(6) Under laboratory conditions a thin wash as lime one to water

364 Winter Cover Washes

ten produced as good a result as a thick, but under outside conditions a
thick coat is necessary in order to allow for the eroding power of weather
conditions.

In conclusion I have to thank Prof. Barker for much valuable
assistance and many suggestions.

ABSTRACT.

A. These experiments were started to find a cover spray which:
(1) Is thicker than ordinary lime wash;
(2) Resists weather conditions;
(3) Is cheap;
(4) Is easily made.

Of these a formula containing whiting, glue, starch, potassium
dichromate and water fulfils the first two conditions. It fails in
numbers (3) and (4) as its cost works out to 2d. a gallon and it is not
sufficiently easy to make as so much hot water is required.

B. If lime alone is used:

(1) It must be used when fresh.

(2) It should be allowed, if possible, to stand for 12 hrs. before
application. To do this on a large scale, one-third of the total quantity
of water may be added first. When it 3s to be applied, the other two-
thirds can be added. This does away with the necessity of having
a large number of tubs.

C. The beneficial action of lime wash on Psylla eggs is due to the
mechanical, sealing action rather than to any chemical one.

365

A PRELIMINARY INVESTIGATION AS TO THE
CAUSE OF ROTTING OF ORANGES FROM
BRAZIL.

By W. RUSHTON, A.R.CS., D.LC.,

Demonstrator in Biology, St Mary’s Hospital Medical School, Assistant
Lecturer in Botany, South-Western Polytechnic Institute, Chelsea, S.W.

(With 1 Text-figure.)

Hiruerto, so far as can be ascertained from literature and men
of long connection with Brazilian exports, oranges have not been
successfully brought over to this country on a large scale in a saleable
condition. The flavour and size of these oranges would make them
a valuable asset to our table as they would arrive in this country at
a time (July and August) when supplies from other sources are low.

The great problem which confronts us however is to get the oranges
over in a sound condition, as hitherto every consignment to this country
has been more or less rotten. The port of shipment from Brazil is
Rio de Janeiro which is about 18 days sea-passage from London,
and, allowing several days for packing, etc., an interval of at least
three weeks would elapse before their arrival on the London market.

In beginning investigations it was arranged that a box of 50 oranges
should be sent through a large firm of Brazilian fruit-importers to be
packed in the following ways:

4 oranges wrapped in tinfoil;

4 covered with thin tissue paper and buried in dry sawdust;

4 in dried banana leaves;

4 in tissue paper and not buried in sawdust;

4 subjected to steam for a few seconds, the excess of water drained

off and then wrapped in tissue paper;

The rest unwrapped.

The various lots were placed in separate boxes and these were then
put into one large perfectly closed box. This box during shipment
was conveyed as ordinary freight and not in the ship’s cooling chambers.

366 Investigation of Rotting of Oranges

When the oranges reached England their condition was as follows:

Number with traces

No. of Number of rottenness or
How packed oranges wholesome wholly bad
Packed in sawdust and thin paper 4 4 0
Packed in tinfoil .. 4 3 1
Ordinary tissue paper ee 4 2 2
Steamed and wrapped in caer wate a 4 0 4 very bad
In dried banana leaves .. + 3 1
Packed without wrapping of any ua: 30 About 20 10

From the above table it would indicate that the best series were
those isolated by thin paper and dry sawdust and the worst those
subjected to heat and moisture.

One noticeable feature about the unwrapped oranges was that
wherever a diseased orange occurred a large excess of moisture occurred
in the same area. This suggested a line of enquiry as to whether
moisture might not help in the spread of the disease.

The sound oranges were used for inoculation experiments and the
preparation of culture media.

Two fungi were found on the bad oranges; one was the common
fungus Penicillium italicum, while the other had short colourless hyphae
with small black zygospores and appeared to be one of the Mucorineae.
It was found impossible to isolate the latter but the former was easily
isolated and cultivated on a 3 per cent. gelatine medium mixed with
orange juice. This orange juice gelatine was used throughout, sterilised
in the autoclave. The pure cultures obtained were used for infecting
sound oranges, in some cases spores only being used, in others mycelium,
and in others mycelium together with a little culture medium. During
the time that cultures were being obtained the skin of the orange
was investigated and the various tissues met with tested as regards
their chemical composition. Externally a fairly thick cuticle occurs,
below which is a single layer of cells with cellulose walls forming a very
shallow epidermis, and beneath this a many-layered tissue with cellulose
walls and variable size of cells forming a many-layered parenchyma,
often filled with small granular cell contents and yellow in colour.
Embedded in this yellowish tissue are many oil glands which extend
in many instances quite up to the epidermis and buried deep in the
tissue at the other, the glands being more or less oval in shape and
lined with a single layer of epithelium.

Below this glandular layer another many-layered parenchyma
occurs with irregular shaped cells with large intercellular spaces and

W. RusHtTon 367

somewhat fibrous strands intermingled with them, the walls of this
open tissue being of cellulose, similar to that of closed tissue.
Dusting spores on the uninjured skin, laying on mycelium or
putting on mycelium together with gelatine medium, it was found
impossible to induce the fungus to attack the orange so long as the
cuticle of the skin was undamaged, but if the cuticle was pierced with
a sterilised needle or small pieces of it were removed with a razor,
then the fungus soon attacked the underlying parts of the skin sur-
rounding the oil glands or between the oil glands and the cuticle.

\
\ Yellow
/ tissue

mG White

2 hissue

rm

x

ere Irreqular

strand
Diagram of section of orange skin.

The first symptom of attack is a brown coloration in the region
of infection, which soon spreads in all directions under the cuticle.

Later on the white mycelium of the Penicillium appears and
follows in the wake of the coloured tissue, and as the discoloration of
the tissues continues so the Penicilliwm spreads at the same rate.

On examining this brown tissue no fungal hyphae could be found
and it appears that when the fungus gains an entrance into a host
it pours out an enzyme which acts on the tissues in the neighbourhood
causing them to change colour. This change occurs first in the cell
contents and later the cell walls break down.

368 Investigation of Rotting of Oranges

This brown area preceding the Penicillium on the orange also occurs
on orange gelatine cultures.

Another change that is undergone by the skin during attack is,
that in a sound unaffected orange it is impossible to strip off the cuticle,
which can only be removed by cutting the underlying tissues, but
when the fungus gets in the cuticle can easily be removed from any
of the coloured areas with forceps without any cutting whatsoever.
When the attack has become very bad the whole of the cuticle of the
orange can be stripped off.

No trace of the fungus piercing the cuticle could be found, although
hanging drop cultures of cuticle and fungus were taken.

When the attack is very bad the part of the skin below the cuticle
becomes a soft sticky mass, which sooner or later pours out a yellow
oily liquid on to the soft surface of the skin together with a large amount
of water.

When the orange became soft and pulpy it was noticed that large
numbers of small flies appeared on the orange and remained so long
as the orange kept its normal shape, but when it completely collapsed
the numbers decreased.

It was found impossible to infect a sound orange by leaving it in
a vessel with a badly diseased one even in contact with it, but the
pouring out of moisture by the diseased one caused the sound one
to become covered with moisture and in this way many more spores
would adhere to it than would otherwise have taken place and in this
way would have a greater chance of finding any slight puncture in
the cuticle.

Leaving a sound orange standing in a shallow dish of water the
wet portion becomes soft and discoloured and then the cuticle can
easily be removed and the tissues attacked with Penicilliwm when
removed from the water, but the dry portions out of the water were
never attacked unless a previous puncture of the cuticle had taken place.

From these few simple experiments it would appear that the most
promising way of sending oranges is that they be kept as dry as possible
and in picking and packing care being taken to prevent the cuticle
becoming damaged in any way.

Experiments were tried with various chemicals. Solutions of
2 per cent. copper sulphate and 5 per cent. formalin were used on
the cut surface of the orange skin and were found to be more or less
effective, for if spores were sown on the cut areas the fungicide appeared
to check their growth.

W. RusHTon 369

The question arises, “Can the oranges be safeguarded from fungal
attacks by immersion in some fungicide, or if the spores have already
settled in some slight wound can their action be stopped?” Further
trials are necessary to solve the problem but the first trials on an exten-
sive scale seem to indicate that Penicillium italicum can be checked,
but in its stead rottenness due to some other cause sets in; for the
first box of oranges sent to me treated with formalin before packing
and then packed in dry sawdust, of the three hundred it contained
not more than six were sound the rest all being bad, with not the
slightest trace of Penicillium on them: the cause of rotting appears
so far as can be made out on preliminary inspection to cause the fruit
to become perfectly brown and somewhat wrinkled, losing their orange
shape, the cuticle remains tough and does not come off easily, while
the parts of the skin below it are perfectly brown, and suggest a new
line of inquiry which I hope to conduct in the near future as further
boxes are sent over treated in various ways.

In conclusion I should like to acknowledge my indebtedness to
W. Austin, Esq., of London for the trouble he has taken to get the
oranges over and to see that instructions were as far as possible carried
out to ensure correct information being obtained.

370

EFFECTS PRODUCED BY SUCKING INSECTS AND
RED SPIDER UPON POTATO FOLIAGE.

By A. 8. HORNE anp H. M. LEFROY.
(Royal Horticultural Society's Gardens, Wisley.)

(Plates XXIII—-XXVIL.)

A sERIES of experiments is here described which was designed to
ascertain accurately what effects are produced in potato foliage by the
action of sucking insects.

The potato plants used were seedlings of the President variety, a
variety particularly subject to the curl disease. The first seedlings
were raised at Chelsea in 1911 and subsequent series of plants at
Chelsea, Wisley and at Messrs Sutton’s trial grounds. The greater
number were raised at Wisley, 1912-1914, nearly a thousand plants
in all.

The raising of these plants from seed, their variability and behaviour
under different conditions of growth, and experiments with them
not directly concerned with this present work will be described else-
where.

The objects we hoped to attain and succeeded in attaming were
firstly, to be in a position to assign definite symptoms to certain insects
and so to be able to eliminate them at once if one is seeking effects
produced by fungi or bacteria, as, for example, in the curl disease where
pathological symptoms such as dwarfing, yellowness, blotching and
dead leaf ends occur; and, secondly, the application of this knowledge
in seeking the distribution of pathological conditions due to insects in
the field.

A result of this work was the investigation of the mechanism of
sucking in two of the species concerned, in Lygus by P. R. Awati (Proc.
Zool. Soc. September 1914) and in Alewrodes by EK, Hargreaves (Ann,
App. Biol, 1. Nos, 3 and 4).

A. S. Horne AND H. M. LeErFrRoy 371

INFESTATIONS.

The following species were used in making infestations:
1. Alewrodes vaporariorum Westd.
2. Red Spider, Tetranychus telarius Linn.
3. Aphis, Rhopalosiphum solani Theob.
4. Jassid, Eupteryx atropunctata Goeze.
Chlorita viridula Fall (? C. solani Koll.).
Capsid, Calocoris bipunctatus Fabr.
Lygus pabulinus Linn.

The first three of these, being obtainable early in the year, were used
for the first series of infestations, commenced at Wisley on March 22,
1912. Jassids and Capsids were not obtainable until June, hence
infestations with these insects were not commenced until after the
earlier experiments were completed. Parallel infestations, using the
above-mentioned insects, were carried out at Chelsea upon the plants
raised at Chelsea.

The conditions under which the experiments with Aleurodes, Red
Spider, and Aphis were carried out were as follows: The floor of the
greenhouse adjoining the laboratory at Wisley was covered with a layer
of garden soil and a number of cloches arranged in rows upon it. Some
of the cloches rested directly on the surface of the soil. Under these
conditions, if the soil were regularly watered, the atmosphere within
the cloches would remain saturated. The remaining cloches were raised
above the level of the soil supported on inverted pots so that the air
inside the cloche was in communication with the air outside but would
be on the whole damper than that of the greenhouse and sometimes
saturated.

Four pots were placed under each cloche. Groups of four plants
not covered by a cloche were also stationed on the soil.

The experiments arranged at Wisley were as follows:

No. 2. Red Spider. Cloche on inverted pots. Plants watered
seldom.

No. 1. Aleurodes. Cloche on inverted pots. Muslin edging to
prevent escape of insects. Plants watered regularly.

No. 9. Aleurodes. Cloche on soil. Plants watered regularly.

No. 4. Aphis. Cloche on inverted pots. Plants watered regularly.

No. 3. Aphis. Cloche on soil. Plants watered regularly.

No. 5. Aphis. Plants not under a cloche. Watered regularly.

Ann. Biol. 1: 25

ON

312 Insects and Potato Foliage

No. 6. Control. To plants placed under cloches resting on inverted

No. 7. Control. To plants placed under cloches resting on the
soil.
No. 8. Control. To plants not under cloches.

No. 10. Control. Pots placed in a vessel containing water, and a
cloche inverted over the whole so that the atmosphere remained con-
stantly saturated.

The plants used for the infestations had been uniformly treated, and
we selected as far as possible plants of a similar character and equal
amount of growth.

Effect on the plants of the conditions under which they were placed.

The plants grown under the cloches soon differed from those not
covered at all and the difference was most marked in the case of the
plants grown in an enclosed atmosphere. In a constantly saturated
atmosphere the plants became larger but procumbent, and developed
larger but thinner leaves than the uncovered control (Fig. 1). The
plants under cloches resting on inverted pots were less changed.

Several of the plants responded to the experimental conditions by
the development of intumescences on the leaves. This feature was
more marked in the case of the plants grown under cloches placed
directly on the soil.

Red Spider.

No. 2. Four pots, on soil, under a bell-jar raised on inverted pots.
22. 3. 12. Put in leaves of Rhynchosia with many red spider on; the leaves
laid between the pots so as not to touch the plants or shade them.
5. 4. 12. Abundant red spider on the plants. The symptoms produced were:
cessation of growth;
yellowing of the leaves;
many minute discoloured spots, giving the leaf a speckled, brownish
appearance ;
eventual drying and browning of the plants, which die.
No curling was produced at any time.

One of the plants was photographed on three occasions—April 5, 13
and 17—to show the progress of the infestation. (See Figs. 2, 3, 4.)
The experiment was repeated, using leaves from the plants already killed
by red spider, with similar results.

It was observed that the plants did not all succumb to the attack

at the same time although the chances of being infested were equal.

A. S. Horne AND H. M. LEFRoy 373

Aleurodes. Fig. 5.

No.1. 22. 3. 12. Four pots were placed on soil under a bell-jar raised on inverted
pots; 20 flies from Salvia and 24 from potato were liberated under the jar, some
escaping.

5. 4. 12. Eggs seen on the leaves; the plants were clean, healthy and similar
in appearance.

17. 4. 12. Seale first observed.

24. 4.12. Young flies observed.

5. 5. 12. Many scales on the leaves, a few empty, the first flies having emerged.
There are no symptoms to record; the leaves are not spotted nor noticeably yellow.
The control plants, grown under similar conditions but without insects, do not differ
from the infested plants.

No. 9. 23. 3.12. Four pots on soil, under bell-jar raised on inverted pots, with a
double muslin curtain containing soil round the lower part of the jar and resting on
the soil. Sixty-seven flies from Salvia were liberated.

5. 4. 12. Many eggs on the leaves, some dark, some yellow. Two dead flies
seen with a cloud of white threads (? hyphae of a mould). Photographed 9 o’clock.

5. 5. 12. Good infestation of scales. The leaves are slightly yellow as compared
with the control kept under similar conditions. There are no other observable
symptoms and the leaves are clean, not curled, and well grown.

All the plants infested with Aleurodes were kept free from Red
Spider and Aphides.

Experiments set up out of doors were unsuccessful because the
plants were killed by frost.

Aleurodes. Gross infestation.

During the course of the experiments described above, the whole
of the plants raised at Wisley from the January sowing, and not used
for the infestations with individuals, had been kept in a cool frame
arranged in series according to the method of potting, kind of soil and
origin of the seed. Aleurodes soon appeared amongst them and was
allowed to increase unchecked. All the plants were examined critically,
one by one, on May 8, and there was noted by one observer the amount
of Aleurodes and Aphis, and by the other the characters of the plants
themselves, for example, height, whether upright or procumbent, size
and shape of juvenile and adult leaves, and the presence or absence
of blemishes, such as blotches, pinkness, discoloured veins, yellow-
ness, etc.

The first three series, potted in coarse soil, in large pots, will be
considered together since no attempt is here made to draw deductions

25—2

374 Insects and Potato Foliage

between them, but only between the individuals composing a particular

series. The series comprise:
Series I. Plants raised from seed obtained from both good and

bad plants, Edinburgh.
Series II. Plants raised from seed obtained from good plants,

Dunbar.
Series III. Plants raised from seed obtained from bad _ plants,

Dunbar.
The distribution of Aleurodes is shown below.
Distribution of Aleurodes. Series I—III.

No. of plants in series

I Il Ill Total

With eggs, scale and imago 1 1 2 4
5 » and imago 3 2 4 9
oP 5 ;, scale 1 1 4 6
53 » only 4 2 1 7
», scale ,, 5 4 5 14
Mago. 0 3 1 4
Without eggs, scale and imago 8 4 6 18
Total 22 17 23 62

There is not any very marked difference between the three series
and we may look at the whole 62 plants together:
There are 18 with no Aleurodes in any stage,
Nine in which eggs and flies are abundant, scale few,
Fourteen in which scale is abundant only,
Six in which both scale and eggs are both noticeable.
Without unduly straining the figures we may say that the plants
have been unequally selected by the flies of each brood and that there
is a very high percentage (29) of plants that have been avoided: is
this selection correlated with any plant character that can be noted?
We have been unable to find any character of the plants which we
can correlate with the presence or absence of either the scale form or
the eggs: clearly there is a connection between the presence of Aphis
and the discoloration of the veins: there is no connection between the
blotching and the presence of either Aphis or Aleurodes; and there is
not any character that we could note which is correlated with a marked
presence or absence of either the scale form of Aleurodes or its eggs. It
has been possible to note only certain physical characters: it is possible
that there is a character connected with the condition of the leaf surface,
or the texture of the leaf, or the composition of the cell substance or sap

A. S. Horng AND H. M. Lerroy 375

which does determine whether the fly lays eggs on a plant or not: we
believe that there must be some such character which is not revealed by
the physical characters that we can note. Had there been a marked
difference between the character of the foliage in Series I—III we could
perhaps have found some such character as is discussed in Series ITI,
but there is not sufficient difference in this respect to make it discernible.

Series IV.

Plants from seed from Edinburgh and Dunbar, still in small pots.
These are markedly less infested and it was possible only to note them
as having either no scale at all, scale numbering from one to ten or scale
clearly exceeding ten on the whole plant.

Edinburgh :
Clean 20
Under ten 18
Over ten 16.
Dunbar, seed from healthy plants:
Clean 17
Under ten 8

Over ten 5.
Dunbar, seed from diseased plants:
Clean 10
Under ten 11
_ Over ten 2.
Total:
Clean 47
Under ten 37
Over ten 23.

In this series also there is uneven distribution of Aleurodes and,
seeing that these plants had been kept side by side with the series in
larger pots which are more infested, it was suggested that the fly selected
for egg-laying those plants with more foliage or with healthy foliage not
likely to fall off. The plants as classed above for amount of Aleurodes
were then grouped according to the amount and condition of their
foliage, the resulting figures being:

Clean plants Bad foliage 23 Good foliage 21
Under ten plants __,, ws 12 ¥5 3 24
Over ten plants Ff es 4 i by 19

376 Insects and Potato Foliage

These figures point, not very decisively, to the fly selecting for
egg-laying those plants with more leaves and more perfect ones; this
may mean (1) the fly prefers itself to repose on such foliage, (2) it prefers
to feed on such foliage, or (3) it definitely selects such foliage for egg-
laying on. On this point we can only say that there is a fair concurrence
of plants on which flies were found as well as eggs: that is that the plants
on which the flies sit and feed are also those on which they lay eggs (see
Series I-III). It is noteworthy that there is very much less scale on the
far smaller plants of Series IV than of Series I—III, though they were
throughout kept together; there is no plant in Series IV which in
Series I—III would have been marked as more than “scale moderate.”
This may be due to the Series I—III plants being in higher pots and so
nearer the light or to their greater amount of foliage.

It seems to be quite clear that there is a definite selection of plants
by the Aleurodes which may be connected partly with foliage but must
also depend upon some other character that we cannot determine.

Apinss Wigs'6, 7.

No. 3. Four pots on soil under bell-jar placed on the soil.

22. 3.12. Placed twelve Aphides on each plant. These were of varied size,
including in each case two winged forms, and were taken from potato plants growing
in pots.

26. 3. 12. Intumescences observed in the plants.

1. 4. 12. Some leaves with discoloured veins.

2.4. 12. The Aphides were counted, being 43, 14, 6. 16 respectively on the four
plants.

5. 5. 12. One Aphis found on each plant.

No. 4. Four pots under a bell-jar which is raised on inverted pots leaving a space
between the jar and the soil. Put in Aphides from the potato plant on 22. 3. 12.
1. 4. 12. The Aphides total 97, 40, 19, 54 on the respective plants.
Some leaves with discoloured veins.
5. 5. 12. A heavy infestation, the most Aphides on the lower surface of the lowest
leaves. The symptoms noted are:
yellowing of the leaf generally;
the veins on the lower surface become dark coloured ;
the leaf tips and margins become brown, dry and brittle;
the leaf eventually falls off.

No. 5. 22. 3. 12. Four pots uncovered, each infested with 12 Aphides from a
potato plant.

1. 4. 12. Several leaves with discoloured veins in all the plants.

2.4. 12. Aphides on plants number 46, 89, 108, 103 respectively.

A. S. Horne anp H. M. LeErroy rel

5. 5. 12. Three plants very heavily infested, one not. Of the infested ones, one
is withering, the leaves limp, yellow, curling and browning at the tips, the veirs
dark; two have the leaves yellow, the veins dark, the tips brown. The plant now
free had the veins heavily dark, the leaves browning off from the tip.

Since the plants of No. 5 were not confined, they became infested with
Aleurodes which was present in the greenhouse. ‘The flies were con-
tinually removed to the extent that scale was present on only one plant
on April 19.

A comparison with the controls shows that these symptoms were
undoubtedly due to Aphis. The plant under Cloche 7, control to
Aphis 3 (plant enclosed), did not develop discoloured veins (Fig. 8),
either on the leaves present at the time of the infestation or on the
leaves newly formed whilst under the cloche. The plants under Cloche 6,
control to Aphis 4, were with difficulty kept free. On April 2, 106
were removed, 48, 8, 40 and 12 respectively on the four plants, and the
veins of some leaves on the third and fourth plants were slightly dis-
coloured. The plants under Cloche 8, control to Cloche 5, were not
enclosed and hence exposed to repeated infestation. The Aphides were
frequently removed, 53 were removed on April 2 and the veins were
not discoloured, but soon a relative difference only could be observed
between the infested and control plants and the two sets soon became
equally and heavily infested.

From the above results it will be seen that the earliest symptoms due
to Aphis show themselves on the leaves, the midrib and veins of which
become brown, and that these symptoms appear, irrespective of the
conditions under which the infested plants were placed, within ten days
from the date of infestation.

The further progress of the infestation and the development of
later symptoms were, however, influenced by the conditions under
which the plants and Aphides were kept. On April 1, the distribution
of Aphides was as follows: Cloche 3,79; Cloche 4, 210; Cloche 5, 346;
a result showing that the Aphides multiplied most on the plants not
confined, least on the plants entirely enclosed. In fact they gradually
decreased in number on the enclosed plants until on May 5th only four
remained.

The symptoms rapidly increased on the plants not enclosed, the
leaves becoming yellow, the veins dark brown, and the leaf tip curled,
brown and dead.

378 Insects and Potato Foliage

° Gross Infestation by Aphis. Chelsea.

The Chelsea plants were examined by one observer on May 17
and their characters noted. They were very different in appearance
from those raised at Wisley, being on the whole taller with more slender
stems and the leaves much smaller. No less than nine plants had
developed two or more slender stems instead of one, thus greatly
modifying the general appearance. The characters yellowness, pinkness,
and blotch, characteristic of the Wisley series, were entirely absent, but
five plants possessed hooded or curled leaves—the margin bent down-
wards—a character absent from the Wisley plants. No insects were
observed upon the plants on May 17th.

The plants were examined critically by the other observer for insect
characters on June 11. These had been free of all insects except Aphis,
which had been allowed to increase on the plants for three weeks
unchecked, the plants then being evenly and lightly infested. The
plants were examined individually and the points noted for each (as
these proved to be the same throughout it is not necessary to reproduce
them in full). The following points should be noted:

All the plants had colonies of Aphis on the large old leaves. Leaves
lightly infested showed no definite symptoms: darkening of the veins
occurred in all cases of more than light infestation and the oldest leaves
also showed marked yellowness, not necessarily due to Aphis.

In cases of severe infestation the tip and edges were brown. Old
broad leaves were not quite flat but curved: curling was not seen.
Small leaves were in many cases sharply curled, but this symptom was
not coincident with the presence of Aphis nor with the occurrence of
dark veins. Aphis was present in many cases on the small leaves, but
on picking out all plants with curled leaves these were not markedly
infested with Aphis on the small leaves.

There is no evidence of Aphis selecting plants; all had Aphis on now
or had signs of previous occurrence of Aphis.

Gross infestation by Aphis. Wisley.

A series of seedlings raised later than Series I—IV was examined for
Aphis on July 24. On this occasion there were three plants with curled
leaves and Aphis was absent from two of them.

A series of 80 plants raised from the original stock of seed, in
1914, and exposed to infestation yielded a somewhat different result.
Thirteen plants exhibited hooded or curled leaves and all were infested

A. S. Hornet anp H. M. Lerroy 379

with Aphis. The youngest leaves were chiefly affected and infested,
but in this case they were often considerably distorted and their veins
discoloured.

Jassid series. (A) Wisley.

1. June 5. Three plants were infested with 10, 9 and 9 Jassids respectively,
Eupteryx species and a green species.

June 8. Small white spots were present in the infested plants but absent on
the controls (Fig. 9).

The spots are about 1 mm. in diameter and possess an irregular outline. When
a number occur close together, whitish blotches or patches are formed, more usually
on the upper surface of the leaf. The spots are not confined to the young leaves
and do not occur in sufficient number to cause the death of the leaf directly. The
tissue of the leaf is not lacerated as in the case of injuries caused by Capsids. The
epidermis is punctured and the proboscis of the insect injures and destroys the
chlorenchyma. The white appearance of the spot or blotch is due to the loss of
chlorophyll and perhaps an optical effect, in part, due to included air.

2. June 11, 3 p.m. Single plants infested with one Eupteryx collected at
Wisley.

June 12, 10.30 a.m. White spots present on one leaf. Eupteryx still alive.
The spots have been produced within 20 hours. .

Jassid serves. (B) Chelsea.

June 9. Put three clean plants under a bell-jar with two winged Hupteryx
atropunctata. Controls all clean plants unspotted.

June 11. Removed the bell-jar and the two bugs; observed small light spots
on several leaves; controls not spotted.

June 13. The spots are slightly brown.

June 20. The spots are larger and in some cases have become holes.

Capsid series. (A) Wisley (Fig. 10).
1. June 12. Put one clean plant under cloche with four wingless green Capsids
collected at Wisley.
June 13. Small brown spots observed on youngest leaves.
2. June 12. Put one clean plant under cloche with two green winged Capsids
collected at Wisley.
June 13. The following symptoms had developed:
black stripe along petiole;
dark blotch on leaf lamina;
young leaves with dark brown irregular blotches on the upper
surface. }
3. June 12. Put one clean plant under cloche with two brown winged Capsids
collected at Wisley.
June 13. No visible result.
4. June 12. Put one clean plant under cloche with three small green and brown
grass Capsids.
June 13. No visible result.

380 Insects and Potato Foliage

5. June 12. Put one clean plant under cloche with one striped nymph off grass.

June 13. No visible result.

6. June 14. Put one clean plant under cloche with three Capsids collected
at Wisley.

June 15. No visible result.

June 17. Youngest leaves with brown blotches.

7. June 14. Put one clean plant under cloche with nine Capsids collected at
Oxshott.

June 15. Small brown spots appeared on the youngest leaves.

June 17. Attack severe. All the youngest leaves spotted and blotched and
nearly dead. Six Capsids were observed.

8. June 14. Put one clean plant under cloche with one Capsid collected at
Oxshott.

June 17. No visible result.

Capsid series. (B) Chelsea.

1. June Il. Put three clean plants under a bell-jar with one green winged
Capsid and one green nymph in the last stage, both collected at Wisley that day.

June 13. No visible result. Added two green nymphs from Walton.

June 20. One plant has the small foliage with holes edged with brown. Another
plant has two leaves the same. The third plant shows nothing.

2. June 11. Put two clean plants under a bell-jar with ten unwinged green
Capsid nymphs, collected that day on potato plants at Wisley.

June 13. No visible results. One winged form, the rest nymphs.

June 20. The small leading shoots are brown and dead. The smaller leaves
have holes edged with brown.

No control shows these symptoms at all; apparently the Capsids feed on the
shoots and youngest leaves and give rise to holes in the leaves and to the death and
browning of the apical shoots. This effect has not occurred on any plant at Chelsea
except those infested with Capsids. (The action of Eupteryx on the leaves is exactly
the same as that at Wisley.)

Capsid symptoms.

In these experiments the insects attacked the youngest leaves and
small irregular spots or blotches were formed which were either scattered
or so numerous as to give the leaf or leaflet a brownish appearance.
Each spot when first formed possesses a clear centre with a brownish
boundary. The spots are due to the laceration and destruction of the
tissue at the places where the insects feed—either on the upper or lower
surface (usually the latter) of the leaf. Small pits are formed which often
extend to the opposite epidermis and the leaf may be perforated or if
not, perforation soon takes place. The dark boundary to the spot is
evidently due to the discoloration of the broken cells which form the
wall of the pit. Veins near the pit are lacerated, discoloured and some-
times severed. When the attack is severe, the chief veins of the young

A. S. Horne anp H. M. LEFrRoy 381

leaves are partly severed, so that the leaf or leaflet soon withers and
dies. In severe cases the young shoot dies.

The discoloration of the veins caused by Capsids occurs rapidly
after the infestation and discoloured veins are associated with the
presence of lacerated pits or areas. Discoloured veins due to Aphis
develop after several days have elapsed since the infestation and they
are not associated with lacerated tissue.

The difference in symptoms produced by the Capsid and Jassid is
accounted for by different structure of the stylets of the mouthparts.
P. R. Awati (Proc. Zool. Soc. 1914, p. 685) figures the mouthparts of
Lygus and shows that the outer pair of stylets (the mandibles) are
barbed; when they are withdrawn the plant tissue is lacerated. In
the case of Hwpteryx, the outer stylets are smooth and they can be with-
drawn without further injury than that caused by the sucking.

The mechanism in Alewrodes is described in another paper above by
Hargreaves, but further work is required to compare the action on the
plant-tissue of the sucking mechanisms of Lygus, Eupteryx, Rhopa
losiphum and Aleurodes respectively. The actual structure of the
mechanism is not sufficient; we are ignorant of the action inside the
plant.

FIELD OBSERVATIONS.

We are enabled to report upon insect injuries to potato foliage at
the following places :

1. Barley (Herts). Potato breeding experiments by Dr Red-
cliffe N. Salaman.

2. Brentford. Private garden.

3. Chelsea. Experimental plots at the Physic Garden.

4. Dunbar. Field crop.

5. EHdinburgh. Field crop.

6. Hast Lothian. Field crop.

7. Midhurst (Kent). From specimen.

8. Oxshott. Private garden.

9. Reading. Messrs Sutton’s trial grounds.

10. Strawberry Hill. Private garden.

11. Walton-on-Thames. Market garden.

12. Wisley. Trial and experimental plots.

13. Woking. From specimens.

14. Wye (Kent). Experimental plots.

382 Insects and Potato Foliage

Field observations on Aphides.

Aphides were very closely under observation at Wisley in 1912.
On July 5 it was found that some varieties were badly infested and
others not at all. These Aphides were not observed on the Duke of
York; afew were found on Arduthie Early and Ringleader, associated
with discoloured veins, whilst there occurred among a single row of
Sharpe’s Express, twelve plants with dead foliage, eight with foliage
undoubtedly killed by Aphides and six with foliage still green. In
several cases the original injuries caused by Aphides had received
secondary extension owing to a period of wet weather—the portion of
the leaf-blade next the discoloured mid-rib first decayed, the decay
spread and ultimately involved the whole leaflet. In spite of the
presence of numerous Coccinellids, the Aphides appear to have got the
upper hand.

Certain varieties grown in another part of the Wisley Garden and
including the Duke of York, the Sutton Flourball, Up-to-Date, Lang-
worthy, Northern Star and President were scarcely affected by Aphides,
although these were present throughout the season. Coccinella was
abundant here also but appears to have held the Green fly in check.

Diseased plants received at the Wisley Gardens from Woking on
July 2, 1912, were stated by the sender to have stopped growing at
quite an early stage, and bore only six tubers of very small size. The
plants showed similar symptoms to those which appeared on the Sharpe’s
Express variety at Wisley—discoloured veins and a secondary extension
owing to bad weather. Living Aphides were present on the specimens
and the disease was certainly caused by them.

Similar specimens with remains of Aphides upon them were received
from Midhurst on July 6. The sender had been advised that owing to
disease in the haulms, potatoes should not be grown on the same ground
for two years. The haulms were not diseased, the condition of the
plants being again due to Aphides.

Owing to the kindness of Dr Redcliffe N. Salaman we were enabled
to study the experimental races of potatoes raised by him at Barley in
1911 and 1912. It was observed in 1911 that the foliage of certain
races was badly diseased, whilst the foliage of other races remained
almost entirely healthy. The chief symptoms of disease took the form
of brown blotches, dead leaflet-ends, and perforations, but no attempt
was made to ascertain the cause of these symptoms then.

A. S. Horne anv H. M. LEFROY 383

In the following year there was a recurrence of the phenomena
already mentioned, whilst again certain races remained quite healthy ;
nevertheless, the foliage of almost every plant of other races was badly
diseased. The whole question of the disease in the foliage at Barley
cannot be discussed here, since it must be considered in relation to all
the conditions under which the races in question were raised and grown.
Three types of injury could be distinguished :

1. Blotched foliage not associated with discoloured veins, neither
insects nor their remains present.

2. Badly blotched foliage associated with discoloured veins and
Aphides.
_ 3. Blotched foliage associated with the presence of Capsids.

A great deal of the damage was certainly due to a secondary extension
of the injuries primarily caused by insects, owing to a period of bad
weather following the infestation. Coccinella was not present in
abundance.

By kind permission of Messrs Sutton, the firm’s potato trials at
Reading were visited in 1912. The plants were remarkably free from
blemishes of any kind and on several varieties, notably Garden Favourite
and Maincrop, no injuries due to insects could be detected at all.
Amongst plants of Windsor Castle only one was infested with Aphis.
Several plants of the Up-to-Date had been attacked and showed the
characteristic brown veins. Curiously enough the Up-to-Dates were
adjacent to other varieties from which insect injuries were absent.
Coccinella was abundant.

Field observations on Capsids.

The President plants grown at Wye in 1911 were practically free
from insect injuries, but they were also free from blotches or discoloured
veins. On July 30, 1912, Professor Theobald informed us that he had
observed nothing but a few Aptera and some Capsids on potato plants
at Wye in that year.

The plants raised at the Chelsea Physic Garden in 1911 were badly
blotched and it is now quite clear that the condition of the foliage was
due to Capsids. On June 28, 1912, the plants grown from tubers in
the open at Chelsea were more carefully examined for insects. Several
plants had been injured by Capsids and many Capsids were observed.

The first Capsids used for experimental purposes were captured at
Wisley on June 11, 1912. This was almost their earliest appearance
at Wisley. On June 17 Capsids were active at Oxshott, especially on

384. Insects and Potato Foliage

the Duke of York variety. They blotched and killed many of the young
leaflets and young shoots.

Soon after the appearance of Capsids at Wisley a large market-
garden at Walton-on-Thames was visited. Here the foliage of a great
number of plants exhibited blotching in some form or another, but
the marks could not be attributed to the agency of insects nor fungi.
Capsids were observed only on the Eclipse and at this early date had
caused but little damage.

Capsids were in abundance at Reading on July 3 among plants of
the Up-to-Date, and the foliage of several plants was badly blotched.
Varieties adjacent to the Up-to-Dates appeared to be quite free from
these insects.

Capsids were occasionally abundant during June and July 1912 at
Wisley. Brown spots due to Capsids were especially noted on Arduthie
Early and a few plants of the Duke of York.

Brown spots due to Capsids were observed on potatoes near Cobham
on July 15.

Capsids were responsible for some of the damage observed at Barley
in July 1912. Many blotches had been recently caused by these insects,
other markings were secondary extensions from blotches formed prior
to the wet weather. Many young Capsids were found amongst the
plants in question.

At Brentford the action of Capsids generally on potato and other
plants was followed during 1913 and 1914. In both years the same
sequence occurred: red currant (Fig. 11) was first heavily attacked and
the foliage very much destroyed during April—May; then the Capsids
went to mallow, cherry (Fig. 12), some other weeds and potato (Fig. 13);
the potatoes developed quite normal signs of attack; the bugs then went
to Jerusalem artichoke (Helianthemum). The life-history has not been
worked out in detail, but the sequence of young and adults suggests
three broods a year.

The symptoms described above as produced by Lygus and Calocoris
under control are easily discernible in the field and a little searching
reveals the nymph or imago of one of the common species.

Field observations have been directed only to determining how far
these bugs are definitely associated with symptoms on potato foliage.
We think that the bugs deserve far more attention as general garden
pests and that far more damage is being done than is generally supposed.
- This is, of course, no new observation. Theobald (Lnt. Mo. Mag. 1896,
p. 60; Journ, Bd, Agric. London, 1909, p. 568) has drawn attention to

A. S. Horne anp H. M. LeErroy 385

Calocoris fulvo-maculatus de G. Carpenter (Report for 1896) refers to
C. bipunctatus F. and to Lygus pabulinus L. (Report for 1911). Theobald
also refers to L. pratensis L. (Report for 1904, p. 63) and there are a
number of references to these species by continental authors. So far
as we are aware, these describe attacks observed in the field, not
symptoms definitely produced experimentally.

Field observations on Jassids.

Potato fohage was marked with white spots caused by Jassids in
many localities in 1912, and these insects were in every case observed
in the leaves. The spots were usually scattered and infrequently
united to form moderately large areas, and did not involve the whole
leaf surface, giving it a whitish appearance, as may frequently happen
in the case of the rose and various fruit trees.

The very characteristic white spots can be seen in the field on potato
at once and Hupteryx is in all cases found there. Similar spotting can
be seen on rose, plum, cherry (Fig. 14) and apple in the early stages of
Jassid attack, but in 1913, 1914 the attacks became so severe that the
whole leaf became yellow.

Such attacks are well known in England and have been described
by Theobald and by Curtis.

SUMMARY.

1. Definite and similar symptoms apart from any other cause were
obtained as the result of infesting young plants raised from seed of the
President variety of potato with Red Spider, Aleurodes, Aphis, Jassid,
and Capsid under various experimental conditions at Wisley and
Chelsea as follows:

(a) Red Spider.—Leaves became mottled, plant turns brown and
dies.

(6) Aleurodes.—Effect gradual, plants weakened but did not die.

(c) Aphis.—Leaves with discoloured veins, brown and dead leaf-
ends, yellowing and death of the plant.

(d) Jassid.—White spots, plants did not die.

(e) Capsid.—Dark brown blotches on leaves and young growth,
veins darken, young leaves and shoots killed rapidly.

These symptoms did not develop in the controls except in the cases
where the control plant became infested by the particular insect
experimented with.

386 Insects and Potato Foliage

2. The effect on the foliage tissue in each case is as follows:

(a) Red Spider.—Epidermal and sub-epidermal cells injured.

(6) Aleurodes.—Conducting tissue tapped, not followed by vein
discoloration.

(c) Aphis.—Conducting tissue tapped followed by vein discolor-
ation after nine or ten days.

(dq) Jassid.—Kpidermis punctured, assimilatory tissue destroyed.

(e) Capsid.—Tissue lacerated causing severance of the veins and
leaving ragged, irregular pits which become rapidly discoloured as do
the veins also within two days.

3. The markings caused by Jassids and Capsids proved distinctive
and could be recognised as such for some time after the injury, but for
the safe recognition of Aphis injuries the association of typical markings
with Aphides or their remains is necessary.

4. Evidence has been obtained that Aleurodes select inne

5. Definite symptoms due to Aphis, Jassid and Capsid, correlated
with the presence or remains of these insects, have been found in the
field crops in several districts in three consecutive seasons. During
and after periods of wet weather the original injuries, especially those
caused by Aphis and Capsid, frequently obtain secondary extension,
and the foliage is prematurely destroyed.

6. From field observations Aphides appear to exhibit a preference
for certain varieties or races of potato, but the question of selection has
not been experimentally studied by us.

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NOS. 3 AND 4 PLATE XXIII

Fic. 1. Plant in saturated atmosphere (left) and in the open (right).

Fie. 3. More advanced Red Spider attack.

ree

THE ANNALS OF APPLIED BIOLOGY. VOL. I, NOS. 3 AND 4 PLATE XXIV

Fig. 6. Aphis on underside of leaves. Fig. 7. Result of Aphis attack. Note

black veins on lowest leaf.

THE ANNALS OF APPLIED BIOLOGY. VOL. |, NOS. 3 AND 4 PLATE XXV

Fig. 8. Control plants to Figs. 6 and 7.

Fig. 9. Results of Jassid attack.

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THE ANNALS OF APPLIED BIOLOGY. VOL. |, NOS. 3 AND 4 PLATE XXVI

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11. Red Currant shoots injured by Capsids.

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THE ANNALS OF APPLIED BIOLOGY. VOL. I, NOS. 3 AND 4 PLATE XXVII

Fig. 12. Cherry leaf injured by Capsids. Fig. 13. Potato foliage injured by Capsids.

Fig. 14. Cherry leaf injured by Jassids.

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387

NOTES.
The Association.

A merrine of the Association has not been held since July and
the number of members who attended that meeting was not large.
A circular was sent to all members in the United Kingdom asking if
they would attend a meeting in September: replies were received
from about a quarter and only one member was prepared to attend.
The meeting was postponed for other reasons.

With this issue we complete the first volume of the Annals, the
material for the third and fourth numbers being issued as a single
part. This has been rendered necessary by events over which we
have no control and it is hoped that the first part of the second volume
will be issued by the end of March.

Two features of this issue are of special interest. We welcome
the papers by Dr Barber and Mr Anstead dealing with problems of
tropical agriculture, and we hope to receive many more contributions
from members in the tropics. The second feature is the number of
shorter articles and notes, dealing with a wide range of topics. Members
will assist the Annals specially by contributing such short articles
and notes.

We include in this issue a review; the publication of critical reviews
of important new books should become a feature of the Annals.
Volumes for review should be sent to the editor, who will send them
on to the member of the Editorial Committee concerned.

The Annals are sent in exchange to a number of biological publica-
tions. Members of the Association can consult the journals received
in exchange at the Association’s Library in the Royal College of Science,
South Kensington. The following are received :

Annales du Service des Epiphyties, Paris: Bollettino del Laboratorio di Zoologia,
Portici: Journal of Agricultural Science, Cambridge: Quarterly Journal of Forestry,
Oxford: Redia, Firenze: Journal of the Royal Horticultural Society, Westminster :

Ann. Biol. 1 26

388 Notes

Transactions of the Royal Scottish Arboricultural Society: Bulletin of Entomological
Research, S. Kensington: Review of Applied Entomology, S. Kensington: Tijdschrift
voor Pflanzenziekten, Wageningen: Monthly Bulletin and Bulletin Bibliographique,
International Institute of Agriculture, Rome: Publications of the United States
Dept. of Agriculture: West Indian Bulletin, Barbados: Agricultural News, Barbados:
Agricultural Journal of India, Pusa: Memoirs of the Agricultural Dept., Pusa:
Bulletin of the Agricultural Dept., Trinidad: Bulletins of the Indian Tea Association,
Calcutta: Gardens Bulletin, Straits Settlement.

We shall be glad to consider other exchanges and members will
find it useful to know that they can consult current numbers of these
publications in London.

The library has been added to by the gift of many separates and
other publications by members; there is room for much more and
members attention is again directed to this. We are laying the founda-
tion of the future library of Applied Biology and if members will
co-operate the library will presently be of real value to all workers.

H. -Miy i

AMERICAN GOOSEBERRY MILDEW.

At the last meeting of the Economic Biologists Association,
Mr Salmon read a paper on some observations on the “Life History of
the American Gooseberry Mildew” in which the theory was advanced
that the over wintered perithecia of the fungus that remain on the bushes
were sterile and could not reproduce the disease in the following season.

Shortly after the paper was read, viz. 24th April 1914, shoots
badly affected with the mildew were collected in Kent by one of the
Board’s sub-inspectors. They were submitted to Kew with a request
that they should be examined and the ascospores germinated if possible.
Shortly afterwards (6th May) the following report was received: “A
considerable number of the perithecia or winter fruits present on the
material sent to Kew were sterile. Others, however, contained normal
spores, some of which have germinated. The mycelium shows no
sign of life, and judging from the absence of oil globules and stored
food material must be dead.” A further sample was submitted on
the 7th of May, and on the 18th the following report was received:
“The majority of the perithecia present on the shoots are much smaller
in size than the normal ones and represent the morbid and imperfectly

Notes 389

developed examples that are apt to occur in every crop. Such remain
permanently attached to the mycelium. A few normal perithecia
containing spores that have germinated were also present. The
mycelium has shown no sign of life.”

In both of these cases the bushes from which the shoots were taken
developed disease in April. A very large number of other bushes
in different gardens in Kent developed disease in April also, but in
practically every case the diseased shoots had not been entirely removed,
and in no case did the mildew appear in that month on any bushes
from which the diseased shoots had been removed early in the preceding
summer.

Furthermore about the middle of May specimens were sent to the
Board by a private grower in Sussex with a request for information
as to the nature of the disease. American Gooseberry Mildew was
suspected since the berries showed the characteristic white oidium.
The writer, however, asserted disease had not been present the year
before. On examination, however, old dead mycelium was found
on the old wood about an inch or less from the affected berry. This
mycelium contained a number of perithecia which presented the appear-
ance of having dehisced in situ and the presumption that the infection
on the berry is due to the ascospores from these perithecia is at least
strong enough to merit consideration.

The two reports received from Kew together with the strong empiric
evidence collected by the Board’s Inspectors as to the conditions
under which early infection occurs appears to me to outweigh the
evidence collected by Mr Salmon and published in his papers, and I
submit that until much fuller evidence is obtained it would be a great
pity to allow growers to suppose that they can ignore the over wintered
perithecia on their bushes. All the officers of the Board who have
had any experience of this disease are agreed that early tipping is
essential for complete success against the disease, but they are I believe
all agreed that a partial success may be obtained by late tipping, and
that much good may be done by going over the bushes even as late
as February or March and removing the affected snags which were
overlooked when the bushes were tipped before the leaves fell. The
removal of every scrap of disease in the summer or early autumn
while the leaves are still on the bushes is a matter of great difficulty.
No one suggests that the first tipping should be delayed so long.

Mr Salmon states in the last paragraph of his paper that if tipping
is not carried out till the end of October or the beginning of November,

26—2

390 Notes

a considerable mass of perithecia must have dropped from the perithecial
patches. Many of these perithecia would doubtless lodge in the
crevices of the bark or between the bud scales, etc., and assuming
that these perithecia were mature ones capable of remaining dormant
through the winter, these would on liberating their ascospores infect
the adjacent berries. This is a theory to which he says on the whole
he inclines. It is of course a very old theory and was, I believe, advanced
by the Board in one of their earlier reports, but as I have never heard
of any case in which the spores were found in the crevices or scales
and as it has been shown that if the visibly affected wood is removed
and the bushes transplanted to uninfected soil no disease appears,
the theory appears to lack support and it seems to be at least as likely
that the reinfection each season is due to the winter fruit in the soil
or embedded in the mycelium and due to perithecia dehiscing i situ.

A. G. L. ROGERS.

EXOMIAS PELLUCIDUS AS A PLANT PEST.

On May 14th, 1914, an enquiry was received from Charles Townsend,
Nurseryman, Fordham, concerning the damage done to a number
of plants by the weevil Hxomias (Barypeithes) pellucidus. A visit
was paid to the Nursery on May 16th and the weevils were found
there in enormous numbers.

The plan of the nursery is on the opposite page:

The Thousand heads, Kohl Rabis, Poppies and Nemophylas were all
eaten off so that the ground was bare.

The Collinsia bicolor and Candytuft were badly damaged and were
only saved by a heavy application of lime and soot. The plot con-
tainng Gypsophila elegans escaped although situated in the middle
of the area attacked, so presumably this is not a suitable food for the
insect.

Some of the trees were examined and a few of the weevils were
found feeding on the leaves of Acer marginata aurea and A. negundo
variegata alba. The potatoes, peas and spruces were free from attack.

Near the attacked area under the spruces large numbers of the
insects were found.

There were some rabbit burrows on the nursery and from these
it was quite easy to take out a handful of the insects. They had

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392 Notes

apparently gone here and also under the spruces in order to shelter
from the sun. Some of the insects were feeding on a thistle under
the spruces.

Leaves of cabbage and rhubarb were put down and on lifting them
a few hours afterwards they were found to be entirely covered with
the insects on the lower surface, as also were the leaves of the Abele
Poplar which had blown from the tree.

The insects usually feed on the lower surface of the leaves at least
in the sunlight. A few were found on the upper surface and on the
edges. Many young plants were eaten off just above the ground
level, 7.e. through the portion of the stem below the seed leaves. On
others (which were not eaten through) were obvious marks caused
by the feeding of the beetles. Some of the leaves were damaged by
having large holes eaten out of them and in others large pieces were
eaten out of the sides of the leaves. They had eaten large holes through
some of the cabbage and rhubarb leaves put down to trap them.

The damage was first noticed on May 13th and on May 14th 75
bushels of soot was spread over the attacked area measuring about
two acres. This was followed by the application of 30 bushels of hme
on May 15th. On May 16th a large number of the beetles were found
dead. On June 17th large numbers of dead beetles were present
over the attacked area whereas only an occasional live one was found.
Cabbage leaves were put down on June 17th and on examining these
only three beetles were found. The lime and soot seems to have
been very successful in keeping down further attacks of this beetle.

In Fowler’s British Coleoptera the following is given as the habitat
of this beetle: “Sandy places; in moss, etc.; very local and, as a
rule, rare, but occasionally in profusion.”

It was thought from this that possibly the beetle was introduced
by means of peat-moss manure, but on inquiry it was found that no
straw manure was used.

I can give no explanation as regards the introduction of this beetle
into the nursery which is otherwise comparatively free from insects.

F. R. PETHERBRIDGE,
Cambridge University.

Notes 393

SOME FEEDING HABITS OF SLUGS.

THE connection of slugs and tapeworms has often been discussed.
Some slugs serve as intermediate hosts for certain bird Cestodes (Grassi
and Rovelli, 1892) and it has been suggested that they do the same
for the Anoplocephaline Cestodes of ruminants and, rodents although
no convincing evidence has as yet been brought forward (Riehm 1881,
Stiles 1893).

An examination into the habits and food of certain slugs made
in connection with a research upon lamb tapeworm disease has brought
out some interesting facts. The work was done at the Department
for Agricultural Research in the University of Birmingham during
the summer of 1914.

By the kind permission of their owners, fields were examined on
which lambs infected with tapeworm were grazing (the worm commonly
found in the Midlands is Moniezia expansa, the broad tapeworm of
lambs). The fields were in the following localities: Bradley Green
and Shurnock near Feckenham, Worcestershire; Oaklands, Allesley
near Coventry; Wigmore Grange, Leintwardine, near Ludlow. The
golf course at King’s Norton near Birmingham was also examined.
From the end of April until the end of June the ripe proglottides of
this worm were to be found lying about on the fields. At Feckenham
and Allesley rabbits were numerous in the same fields and were also
infected by a tapeworm (Cittotaenia pectinata) and, although I never
found the proglottides lying about, the eggs were on the field and could
be seen by taking some grass, soaking it in water, and filtering it through
cambric. On examining the filtrate the eggs were discovered.

Although Moniezia and Cittotaenia differ widely they belong to
the same group of Taeniids, the Anoplocephalinae, and in all proba-
bility their life-histories are somewhat similar.

In these fields were always found two species of slug and only
two—Agriolimax agrestis and Arion circumscriptus, the former very
much more common than the latter. In the daytime they are both
to be found at the roots of long grass, in holes with dead leaves or even
buried in the ground if the season be dry. The habit of burying itself
in the ground is very usual with Arion circumscriptus and not
infrequently it is to be found lying amongst the lambs’ faeces.

In the evening the slugs all come out and eat. They also emerge
in the daytime after warm rain. It is evident that they are exceedingly

394 Notes —

fond of the proglottides of Moniezia. I have shut both slugs up in
boxes with the lambs’ faeces contaiming proglottides and have always
found that they devour the latter with avidity selecting them in
preference to the other food. They also eat Cvttotaenia in the same
way.

On June 5th, 1914, twelve Agriolimax agrestis were collected and
put in a small tin at night with several Moniezia proglottides. In
the morning all had been eaten. On examining the faeces of the
slugs they were found to contain numerous Moniezia eggs having
apparently passed out with no alteration, some of the hexacanth
embryos being still alive. Examination was made of the slugs at
various intervals from two days to a month, by teasing up the tissues
and by sections. In no case could any trace of a larval Cestode be
discovered. Inside the alimentary canal were eggs, but only one
was found with the pyriform apparatus free from its outer shell and
the embryo itself was unaltered.

It is not only when there is nothing else to eat that the slugs eat
the proglottides, for in a specimen of Agriolimax agrestis found on the
fields at Leintwardine the stomach was full of Moniezia eggs.

It is the same with Arion circumscriptus. A specimen from Leint-
wardine also had its stomach full of eggs. One Arion hortensis was
put in a box with grass and a piece of Moniezia consisting of ten pro-
glottides. In half an hour at mid-day it had eaten the whole of this
piece. Examination of its faeces showed the eggs unchanged and
the embryos alive. The slug was sectionised and examined but no
trace of development of the embryo was found. Other specimens
gave similar results.

A large mass of Moniezia was found in a field at Lower Shuckburgh,
Northants, and in it was a small Arion circumscriptus. It is evident
that the slugs seek out Moniexia to eat it.

These slugs also eat Cittotaenia and are very fond of eating rabbits’
faeces. Both of these species are to be found in the fields devouring
the pellets, and their intestines are often full of the brown decaying
vegetation from these. Two Arion circumscriptus took half an hour
to eat one Cuvttotaenia-proglottis each, and four Agriolimax agrestis
the same length of time.

Eggs of both species of slug were hatched in earthenware pots
and the young fed with proglottides of Moniezia and Cittotaenia. These
were examined at intervals but in no case could any development
of the embryos be seen.

Notes 395

From these observations there is no evidence to show that Agriolimax
agrestis and Arion circumscriptus act as intermediate hosts for Moniezia
expansa and Cittotaenia pectinata. It was thought that possibly the
eggs might undergo some alteration in the intestine which though
not apparent might influence their development in other slugs. The
slugs’ faeces which were full of eggs were offered to other specimens
of these slugs but in no case would they eat them.

It is clear that both slugs eat tapeworms on the field. May they
not act much more as scavengers than we are in the habit of thinking
and do far more good in these fields than we imagine? What is the
reason of the abundance of such slugs in these fields? It is quite
conceivable that they are there because of the abundance of this Cestode
food of which they are so fond.

REFERENCES.

Rimum, G. (1881). “Studien an Cestoden.” Zeit. f. d. ges. Naturwiss. Halle, 54 Bd.

Grasst and Rovettt (1892). ‘‘Ricerche Embriologiche sui Cestodi.” Atti Acc. Cjoenia
di Sc. Nat. in Catania, vol. Iv, ser. 4.

Srines, C. W. and Hassan, A. “Revision of the Adult Cestodes of Sheep and Allied
Animals.” U.S. Dep. of Agric. Bureau of Animal Investig. Bull. No. 4, Washington.

MARIE V. LEBOUR, M.Sc. (University of Leeds), F.Z.S.,

Research Department in Agricultural Zoology,
Birmingham University.

NOTE ON THE REMARKABLE RETENTION OF VITALITY
BY PROTOZOA FROM OLD STORED SOILS.

Introduction.

In the sample house at the Rothamsted Experimental Station,
Harpenden, there is a remarkable collection of soils taken from the
experimental plots at various times since the commencement of the
famous work by Lawes and Gilbert in 1843. These samples have
been stored in bottles the corks of which have been covered with leaden
capsules and have thus been insured against the possibility of infection
from dust. Many bottles have remained unopened since the day
on which they were put up. The exact treatment to which the soils
were submitted before being bottled is rather uncertain, but it seems

26—5

396 Notes

that they were spread out and allowed to become slightly air-dried
so that they could be more easily sieved.

Large bottles capable of holding 200 ozs. were then filled with the
soil which had been passed through a sieve having } inch meshes. The
degree of dryness of the soils varies considerably, some having about
3 per cent. or 5 per cent., others having from 10 to 15 per cent. of water
by weight; the samples for any particular year however appear to be
of about the same degree of dryness. In most cases the soil was taken
from different depths at intervals of nine inches, sampling proceeding
in some cases into the deep layers of the sub-soil.

Experiments.

It was my privilege whilst working at the Rothamsted laboratory
to examine culturally soil from a few of these bottles for the presence
of protozoa and only samples from the top nine inches of a plot were
tested. In some preliminary experiments in 1912 it was found that
Broadbalk soil bottled in 1846 revealed no protozoa in culture, but
that Barnfield soil bottled in 1870 yielded amoebae and flagellates,
and Agdell soil bottled in 1874 yielded amoebae and flagellates, and
the ciliates Colpoda steiniti and Colpoda cucullus, in hay-infusion cultures.

These results were very interesting as showing that the protozoa
had retained their vitality probably in the encysted condition for
a period of 42 years in the case of the Barnfield soil and 38 years in
the Agdell soil.

As there were other bottles containing soil put up between 1846
and 1870, I decided to make cultures of some of these with a view
to finding out the oldest soil from which protozoa could be obtained
and the different species of protozoa which had survived.

Dr Russell, director of the laboratory, very kindly granted me
permission to take small quantities of the soil from those bottles which
I desired to test and I take this opportunity of thanking him for
allowing me to make use of these valuable soils.

The following soils were tested for the presence of protozoa; Broad-
balk 1856, Broadbalk 1865, Geescroft 1865, Agdell 1867, Hoosfield
1868, and Barnfield 1870. From all the cultures except those of
Broadbalk 1856 protozoa were obtained. The cultures were made
in small glass dishes under the usual bacteriological precautions of
sterile media and vessels, etc., so that there can be no doubt that
the organisms encountered really came from the soil and not from
air-borne dust particles by chance infection.

Notes 397

As a culture medium, saline egg-albumen consisting of 5 per cent.
NaCl solution 100 c.c., white of new-laid egg 15 c.c. was used.

Film preparations were made by floating cover-slips on the surface
or by placing them at the bottom of the cultures. The films thus
obtained were usually fixed in Maier’s solution and stained with iron-
haematoxylin.

It is not the purpose of this paper to go into details concerning
the different species of protozoa found, but especially to put on record
the remarkable fact of the survival of protozoa for practically 50 years
under conditions precluding the possibility of trophic existence.

The following protozoa have been identified. The list does not
include all the forms encountered, for there are a few which I have
not been able to classify satisfactorily yet.

Amoebae belonging to the limax group were obtained from all the
soils which yielded protozoa. I have made observations on the mode
of nuclear division in three of these with the result that all three appear
to be new species. One of them seems to be very closely related to
Amoeba glebae! Dobell. Flagellates : Monas termo, Cercomonas crasst-
cauda, Cercomonas longicauda, Bodo (Prowazekia) saltans, Bodo ovatus?
and Tetramitus spiralis, nov. spec.

In addition to the above I have obtained a rather remarkable
organism which undoubtedly belongs to the genus Sprronema Klebs?.
Klebs obtained his examples from ditch-water on only two or three
occasions and considered that they showed affinities with ciliates
and flagellates, forming perhaps a sort of connecting link between
these two groups. He did not, however, find out anything about
the nucleus.

I have succeeded in making out the nucleus which, though peculiar,
exhibits flagellate rather than ciliate affinities.

Historical.

It may be of interest, in view of the great length of time which
the resting cysts of these protozoa have retained their vitality, to state
briefly the previous records of similar phenomena.

According to Butschli®, Meunier (1865) saw Colpoda emerge from
cysts dried for fourteen months. Balbiani (1881) kept a slide with

1 “Qytological Studies on three species of Amoeba, ete.” Archiv f. Protisten. Bd. 34
(1914), p. 139.

2 Flagellatenstudien I. Zeitschr. f. wiss. Zool. tv (1892), p. 350.

3 Bronn’s Thierreichs 1, Abth. m1, p. 1663.

398 Notes

Colpoda cysts on it for seven years and resuscitated the organism
each year by moistening the slide; they afterwards encysted. I
think that this can scarcely be considered as a case of retained vitality
for seven years, for the Colpoda obtained a new lease of life each year
when the slide was moistened. Nussbaum found cysts of Gastrostyla
vorax capable of living after two years and Maupas saw Gastrostyla
stent cyst after twenty-two months drying in a watch-glass.

These records refer to ciliates only and the longest period of retained
vitality, excluding Balbiani’s results with Colpoda for reasons given
above, is two years. I have shown above that two species of Colpoda
have retained their vitality for 38 years.

I cannot find any reference to early work on these lines in the
case of flagellates and amoebae. Quite recently however Noc? has
published a short paper dealing with latent life in protozoa. Some
tubes containing a little water and various protozoa were hermetically
sealed in 1908 and recently opened. There was no trace of anything
but encysted amoebae, some of which revived after ten days or more.
This proves survival for six years. A minute flagellate Ovkomonas
termo was -obtained from some rough Tonkin paper after desiccation
for five years.

The retention of vitality for a period of forty-nine years which I
have recorded above shows that protozoa can survive in an encysted
condition for a much longer time than was known from previous
records.

I deal with the significance of these results in relation to the hypo-
thesis of protozoa acting as a limiting factor on soil bacteria in another
paper which I hope to publish very soon. A further paper embodying
the cytological work on the organisms obtained from these old soils
with descriptions of new species is also being prepared.

In conclusion I desire to express my thanks to Prof. F. W. Gamble,
director of this laboratory, who suggested, about three years ago,
the desirability of examining samples of old stored soils for the presence
of protozoa.

POSTSCRIPT.

Immediately after submitting the foregoing for publication I
obtained access to Noc’s paper?, only the abstract of which I had been

1 Noe, F., C. R. Soc. Biol. Paris, txxvi (1914), pp. 166-8. Abst. Jour. Roy. Mic.
Soc. 1914, pt. 3, p. 267.

2 “Sur la durée de conservation de Protozoaires 4 état humide ou desséché” (C. R.
Soc. Biol. Paris, uxxvt (1914), p. 166).

Notes 399

able to see earlier. In it he speaks of the results obtained by Certes
who found that various infusoria, flagellates, and. amoebae could be
revived after five or six years only from the sediments on which he
worked, whilst only Colpoda remained capable of revival after thirteen
years of storage.

A reference is also given to a paper by Fauré-Frémiet! on a ciliate
Mycterothriz. On looking this up I find that it records that Balbiani
working with desiccated material containing cysts of Mycterothrox
was able to revive the organisms by moistening after keeping the material
dry for four years.

T. GOODEY, M.Sc., Protozoologist, Research Laboratory for
Agricultural Zoology, Birmingham Uniwwersity.

NOTES ON A SCALE INSECT ATTACKING CACAO
IN UGANDA.

Ix 1909 a scale insect attacking cacao appeared in the Botanic
Gardens. Specimens of this new pest were submitted for identification
to Prof. Newstead, who described it as a new species, Stictococcus
dimorphus Newst.?.

The other food plants on which it has been collected by the writer
are mulberry, Markhamia platycalyx, ornamental Hibiscus, Anona
muricata, Croton tiglium, guava and Cajanus indicus. With the excep-
tion of M. platycalyx, all of these plants have been introduced, which,
together with the fact that this Coccid has been found in the depths
of a forest of something like 180 square miles on M. platycalyx, is
conclusive evidence that it is indigenous and that it spread from that
plant to the others.

From my observations cacao appears to be the favourite food
plant. When the varieties of cacao, foresteiro and creolle, are grown
side by side, the infestation on the former is invariably the most serious.
The infestation on cacao is always restricted to the pods and stems
of the pods, never having been found on the foliage or branches. (Fig. 1.)

1 “Te Mycterothrix tuamotuensis (Trichorhynchus twamotuensis) Balbiani.” (Arch.
f. Protist. xx, p. 223, 1910.)

2 Newstead, Bulletin Entomological Research, vol. 1, p. 63, f. 2 (1910); Green, l.c.,
p. 201 (1910).

Experiment

waraInmake & WY = number

400 Notes

Treatment. This is not readily killed by insecticides at the usual
strengths; but, fortunately, on account of its always being located
on the pods, insecticides can be used at greater strengths than they
could be applied to the foliage in this country, where the trees are
never dormant and where for some reason, probably altitude, oils
applied at the usual strengths are most apt to “burn” the foliage.

I have experimented with a large number of contact poisons with
the result that I favour the use of whale oil soap and soft soap-kerosene
emulsion. The results of some of the experiments are tabulated below.

Spraying Experiments against the Cacao Scale, St. dimorphus Newst.

First examination Second examination Third examination

SSE SSS —————

te oH oH

oi o we
Bey 8S) So oe Oey ee Ly ee
Treatment ae g28 3 £5 Bee gO £5 Boo Bd £§
QP Oe Bin Bo Sac Oo a Bo Oise ee ee
Se gfk go o¢ S22 os 828 cw
SS ovo ore Gees oe Se eee. ols i arc aaa
A7ASaAS6S ZS Ase Ass Zo Bsa Bos Ze As
Whale oil soap 8 300 288 96:0 300 281 93:6 300 285 95-0
Kerosene emulsion 8 300 226 75:3 300 214 71:3 300 210 70-0
Carbolic acid emulsion 10 500 242 44-4 500. 251 50-2 500 .-205 41-0
Resin-soda wash 8 300 83) 27 300 99 33:0 300 78 26-0
Lime-sulphur wash .. 112 500 491 98:2 500 436 87:2 500 401 80-2
Kerosene-lysol emulsion 12 500 268 53:6 500 261 525 500 274 54:8
Soft soap-kerosene wash 12 500 482 964 500 469 93-8 500 456 91-2
Check .. Es Sve . oo 300 23 7-7 300 17 5:7 300 28 9-3

Experiment 1 was sprayed with whale oil soap, 1 lb. to 4 gallons
of water.

Experiment 2. The formula of the stock solution of kerosene
emulsion was:

Kerosene .. 2 gals.
Soap, hard 3 Lg a 4 |b.
Water, hot se ae ss A: 1 gal.

The stock solution was diluted to a 20 per cent. spray, 7.e. 1 gallon
of the stock solution was diluted with 24 gallons of water.

Experiment 3. The stock solution of carbolic acid emulsion was
made according to the formula:

Soap, hard os a ets a lb:
Water... as i oe = 1 gal.
Carbolic acid, crude... oo ate 1 pt.

One part of this solution was diluted with 30 parts of water.

Notes 401

Photo by T. D. Maitland

Fig. 1. A typical infestation of a pod of Cacao theobromae var. forestiero,

with Stictococcus dimorphus Newst.

402 Notes

Experiment 4. The formula of the resin-soda wash was:

Soda, caustic... “ He aff 3 lbs.
Resin aa sh? e oe Me x lbs.
Fish oil & ey 2 Ri, 2 |b.
Water "=. - : He 26 gals.

Experiment 5. The stock polnaen of lime-sulphur wash was made
according to the formula:

Lime, unslaked .. ie Be ae 20 lbs.
Sulphur, flowers of ee aN Je 15 lbs.
Wiater, 1) 2: ore 5G 50 gals.

and this was diluted to 85 alton
Experiment 6. Kerosene-lysol emulsion was made by emulsifying:

Lysol y: Ps ae Be i 3 OZS.
Kerosene .. a oie fe oe 9 ozs.
Water... : a a 4 gals.

Experiment 7. The soft soap- ee wash was made by boiling
together 8 lbs. of soft soap and 5 gallons of kerosene. On cooling
this becomes a jelly, 10 lbs. of which was added to 30 gallons of water
for use.

Experiment 8. For the purpose of comparison eight untreated pods
were examined.

Natural enemies. I have frequently bred the Noctuid, Hublemma
costumacula Saalm., of the subfamily Hrastriinae, from this scale
insect. During the examination of the pods treated with the above-
mentioned sprays for dead insects several larvae of this moth parasite
were found.

At a distance I have observed the bird, Melanopteryx nigerrima,
picking at a cacao pod infested with this scale insect, but I could not
be certain whether it was feeding on the scale insect or on the ants
which accompany the scale insect.

The other local representatives of the genus Stictococcus are the
species recently discovered by the writer, St. formicarius Newst.,
and St. gowdeyi Newst.1 The former attacks a species of Ficus, and
the latter Harrogania madagascarensis and coflee.

C. C. GOWDEY, B.Sc., F.E.S., F.Z.8.,

Government Entomologist, Uganda.

' Newstead, Bulletin of Entomological Research, vol. tv, p. 70, f. 4 (1918).

405

REVIEW.

STEBBING, E. P. Indian Forest Insects of Economic Importance.
Coleoptera. London, Eyre and Spottiswoode, Ltd., 1914, pp. xvi 648,
Plates I-LXIII and 401 text-figures.

THE author of this work was formerly a divisional forest officer
in India who all through his career has devoted much of his energies
to entomology. It redounds to his credit that he urged the importance
of forest entomology in the eyes of the government of India, and in
this way did much towards securing the creation of an official post
to deal with the subject. In the year 1900 the office of Forest Knto-
mologist was established for a period of two years, and Mr Stebbing
appointed the first incumbent thereof. In 1904 the post was resanc-
tioned, while in 1906 it was merged into the new appointment of Forest
Zoologist. Mr Stebbing was also the first official Forest Zoologist to
the government of India. During his tenure of these appointments
he has produced a large amount of matter dealing with forest insects.
Published for the most part in sources not easily available to ento-
mologists, many of Mr Stebbing’s writings are little known outside
India, and have seldom had the advantage of scientific criticism.
Observers in India are so few and far between that little has yet been
done towards confirming or extending Mr Stebbing’s work. On his
departure from India he took upon himself the no light task of compiling
the book before us. Without hesitation it may be said that it is the
best piece of work Mr Stebbing has yet produced. Being free from
almost all the errors and faults which marred his previous text-book
of Indian Forest Zoology, we congratulate him on having written a
very readable and excellently arranged book. Notwithstanding the
title on its outside cover, the volume is limited to forest Coleoptera,
and in confining his remarks to this single order of insects Mr Stebbing
has exercised a wise decision. To have included the remaining orders
would have savoured of indiscretion in view of the scanty state of
our knowledge of Indian forest insects.

404 Review

In his Preface Mr Stebbing has been generous to all who have
helped him in any way. From Inspectors-General of Forests and the
Lieut.-Governor of a Province down to the toiling camp clerk, acknow-
ledgments are freely made. We do not ever remember having seen
quite such an array of names in any book before.

Chapters I-1v are devoted to general remarks on the distribution
of insects in the Indian forests, on injurious and beneficial species,
remedial and preventive measures and other problems.

Chapter v consists of a brief introduction to the Coleoptera. We
think, however, that the all-important section dealing with Coleopterous
larvae might have been greatly extended to advantage. References
to the works of Schiodte, Chapuis and Candeze, Perris, Rupertsberger
and others would have acquainted the reader with the sources to which
he must eventually turn for information concerning life-histories.
The greater part of the book is occupied with an account of the forest
Coleoptera arranged in systematic order and extending to over 560
pages. All the principal species known to the author are figured,
and a brief description of each is given. Wherever information is
available remarks on the injury they commit are made, which are
usually supplemented by really excellent photographic plates. Here
and there short descriptions of the larvae and pupae of various species
are to be found. These descriptions, however, in most cases are too
brief and vague to enable one to determine a particular larva with
any degree of certainty. To merely describe, for instance, the pupa
of Cyrtotrachelus longipes as being white and of the ordinary weevil
shape, really does not help very much. Neither can we recognise
the larva of Sphenoptera cupriventris when it is simply stated to be
yellowish white with stout black mandibles, and the prothoracic segment
broader than any of the segments behind it. In fact most Buprestid
larvae may be said to agree with that description. One of the best
hfe-histories in the whole book is that of the Longicorn Hoplocerambyx
spinicornis, concerning which a good deal of useful information is brought
to light by Mr Stebbing. It is not, however, absent from the Sal
forests of the United Provinces as he believes. Perhaps the most
interesting of the insects found by Mr Stebbing are the predaceous
beetles of the genus Niponius. Although usually placed in the family
Histeridae, there is something to be said for elevating them into a
family of their own. So far, we know nothing of the larva of
Niponius beyond what Mr Stebbing can tell us. If he can be
constrained to publish an illustrated account thereof, it will not

Review 405

fail to be of great interest to the Coleopterist as well as being of
economic value.

The Scolytidae (Ipidae) are treated the fullest of any of the families,
some 150 pages being devoted to them. The author has brought
to light many species, some of them very obscure and easily overlooked.
It is, however, hard to recognise some of Mr Stebbing’s species from
his descriptions. ‘The writer of this review has devoted many hours
over Tomicus (Ips.) longifoha and T. ribbentropi without being able
to separate the one from the other. The same may be said with regard
to certain of his Polygraphus and other species. In view of their great
economic importance, the Indian Scolytidae are badly in need of revision.
The government of India would do well to issue a monograph of all known
Indian species with detailed figures, exhibiting beyond any possibility
of doubt the diagnostic characters in each case. The monographs
of Dr Hopkins in America would serve as an admirable model to emulate.
In the Scolytidae closely allied species often exhibit dissimilar habits,
and it becomes a matter of the greatest importance to name any par-
ticular species with certainty. In no other group of forest insects,
that we are acquainted with, does the work of forest protection depend
so much upon accurate specific determinations as in the Scolytidae.

We would impress upon the author that it is neither necessary
nor desirable to describe new species in a general text-book of this
description. We find that Mr Stebbing appears to have done so in
more than a dozen instances. Furthermore to designate already
described species as “sp. nov.” is contrary to all recognised procedure.
The expression “sp. nov.” in such cases is highly misleading; for
instance on p. 621 the reader would at first sight conclude that “ Platypus
suffodiens Sampson, sp. nov.” is a new species described immediately
below by Sampson. On the contrary the reference is given to the
Ann. Mag. Nat. Hist. for 1913 where the original description is to
be found.

Notwithstanding the points over which we disagree with the author,
we think that the book will prove a distinct stimulus to Indian forest
entomology. Most of the divisional forest officers, scattered through
the length and breadth of the Indian Empire, are familiar with one
or other form of destructive insect life in the lands under their charge.
With the aid of this book perhaps some of them may be tempted to
make a more serious study of the subject, or by collecting specimens
and information help others to extend the boundaries of our knowledge
of a wide and little explored field.

406 Review

In conclusion we may add that the general “get up” of the book
is admirable, and reflects the greatest credit on all concerned with its
production. The majority of the plates are of a high standard of
excellence and the same may be said of many of the text-figures.
Exception, however, must be taken to figures 30d, 65, 96, 107, 125,
138, 150, 154, 157, 159, 200, 291, 305, 324, and 385—also to Plate XV,
figs. a and a’, and Plate XXXVI, fig. 2, all of which bear but little
resemblance to the objects they are intended to represent. The
paper and type utilised leave nothing to be desired, and we have
noticed an almost complete absence of misprints.

CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THI UNIVERSITY PRESS

Vol. I, No. 1 May, 1914

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F. J. CHITTENDEN, Royal Horticultural Society’s Gardens, Wisley

Proressor F, W. GAMBLE, The University, Birmingham

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CONTENTS
f 3 PAGE
1. Editorial . ; : 1
2. Impending Develsomenth in ‘Aopoalhuel ys
By Prof. F. W. GAMBLE . 5

3. The Action of Bordeaux Mixture on Plants. By
Prof. B, T. P. Barker and C. T. GIMINGHAM.
(With 6 Text-figures) 9
4. Notes on the Green Spruce Aphis (eke abianinel
Walker). By F. V. THEOBALD. (With 10 Text-
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Pollination in Orchards ‘iby F. J. CHITTENDEN . 37
6. Life-History of Pegomyia hyoscyami. By A. E.
CAMERON. (Plates I and II and 4 Text-figures) 43
Caterpillars attacking Oaks in Richmond Park. By

or

~I

R. H. Deakry. (Plates I-VI) . 77
8. A Bacterial Disease of Fruit Blossom. By B. T. P.
BARKER and OTTO GROVE ; 85

9, On the Preparation of Coccidae for Micuasahicn
Study. By E. E. GREEN . ; 98

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CAMBRIDGE: PRINTED BY JOHN CLAY, M.A. AT THE UNIVERSITY PRESS.

"Mol. U No. 2 July, 1914

THE ANNALS OF
APPLIED BIOLOGY

THE OFFICIAL ORGAN OF THE ASSOCIATION
OF ECONOMIC BIOLOGISTS

EDITED BY

Prorrssorn MAXWELL LEFROY, Imperial College of Science and Technology, London,
, AND
-Prorgssor B. T. P. BARKER, National Fruit and Cider Institute, Bristol
Dr $. E. CHANDLER, Imperial Institute, London
. F. J. CHITTENDEN, Royal Horticultural Society’s Gardens, Wisley
Proressor F. W. GAMBLE, The University, Birmingham
_ Prorgssor PERCY GROOM, Imperial College of Science and Technology, London
~ Dr A. D. IMMS, The University, Manchester
_ Prorgssor R. NEWSTEAD, The University, Liverpool
_ Prorgssor J. H. PRIESTLEY, The University, Leeds

CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, Manacer
LONDON: FETTER LANE, E.C.
EDINBURGH: 100, PRINCES STREET
also
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WILLIAM WESLEY & SON, 28, ESSEX STREET, LONDON, W.C.
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The Association of Economic Biologists

Sat So diel

President
ProFesson NEWSTEAD, F.RS.

_ Vice-Presidents

ProFressor CARPENTER, M.R.I.A.
Proressor HICKSON, F-.R.S.

R. STEWART MacDOUGALL, D.Sc.

Sir PATRICK MANSON, K.C.M.G., F.RS.
A. E. SHIPLEY, D.Sc., F.R.S.

Council

. BAGNALL Pror. P. GROOM, D.Sc.

. CHANDLER, D.Sc. A. D. IMMS, D.Sc.

R. S
S. E
F, J. CHITTENDEN
E. E. GREEN A. G. L. ROGERS
Hon. Treasurer
J. C. F. FRYER, Esq.,
Craven House,

Northumberland Avenue

Hon. Secretary

Proressor H. M. LEFROY,
Acton Lodge,
Brentford

CONTENTS OF Vot. I, No. 2

Preliminary Notes on Damage to Apples by Capsid ne By
J. C. F. Fryer. (Plates IX and X) :

The International Phytopathological Conference, 1914. By
A. G. L, RocErs

The Host Plants and Habits of ahh rumicis tae ee some
Observations on the Migration of,and Infestation of, Plants by
Aphides. By J. DAvIDSON

Some Observations on the Life-history and Picriowash af te
Knapweed Gall-fly Urophora solstitiaks Linn. By J. T.
WapswortH. (Plates XI and XII and 1 Text-figure)

A Braconid Parasite on the Pine Weevil, Hylobius abietis. By
J. W. Munro. (With 4 Text-figures) .

Observations on the Life-history of the American Gulesbarky:
Mildew (Sphaerotheca mors-uvae (Schwein.) Berk.). By
E. S, Salmon. ; ; ; ; : ; ; ;

Potato Diseases. By A. S. Horne. (With 8 Text-figures)

A Note on Be as ae Disease. By F. J. CHITTENDEN.

Notes . ; ‘ ;

Pror. J. H. PRIESTLEY

PAGE

107

113

118

142

170

177
183
204
207

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A LONDON: Cambridge University Press, Fetter Lane, C. F. CLAY, Manager
: ee : CHICAGO: The University of Chicago Press

THE ANNALS OF APPLIED BIOLOGY

The Association of Economic Biologists commences under the above title a
publication devoted mainly to the scientific papers read by members at the
meetings and devoted to those branches of Biology in which the Association has

been interested. During the ten years of the Association’s life, its meetings have — Pea >

discussed mainly horticultural, agricultural and forest biology; the specialised
parts of agricultural science, of genetics and of medical zoology are dealt with in
other journals and the Annals will appeal more to those interested in the diseases
and pests of plants, scientific problems of horticulture and forestry, tropical —
economic botany and agricultural zoology in the stricter sense.

The Annals will be edited by an Editorial Committee, including a General
Editor and Editors for each branch of Applied Biology in which members are
interested. The scope of the Annals is as wide as that of the membership of the
Association, and all members are invited to send in papers and notes to the
Secretary of the Association.

Contributors are asked to send type-written articles if possible and as far as
possible to make illustrations in a form suitable for reproduction as text-figures. —
Contributors will receive free fifty copies of their papers.

The second number will be published as soon after the Easter meeting as _
possible and will contain papers read at that meeting: if possible four numbers
will be published this year and thereafter it will be published quarterly.

Terms of subscription.

Members of the Association will receive the Annals free. To others the
annual subscription price, including postage to any part of the world, for a single
copy of each of the four parts making up the annual volume, is 25s. net; single
copies 7s. 6d net each. Subscriptions for the Annals are payable in advance and
should be sent to Mr C. F. Ciay, Cambridge University Press, Fetter Lane,
London, E.C., either direct or through any bookseller.

The publishers have appointed the University of Chicago Press agents for the
sale of the Annals of Applied Biology in the United States of America and have
authorised them to charge the following prices: annual subscription, post free, $6,
single copies, $2.

Members of the Association should send their annual subscription 5 the — meee

Society, One Guinea (£1. 1s.), which includes the supply of one copy of each of
the four issues of the Journal, to the Treasurer, J. C. F. Fryer, Esq., Craven
House, Northumberland Avenue, London. Editorial communications to Professor |
Lefroy, Acton Lodge, Brentford.

Claims for missing numbers should be made within the month following that
of regular publication.

CAMBRIDGE: PRINTED BY JOHN OLAY, M.A. AT THE UNIVERSITY PRESS.

ee cy). ¢

Pave A
ae

Vol. I, Nos. 3 & 4 January, 1915

THE ANNALS OF
- APPLIED BIOLOGY

THE OFFICIAL ORGAN OF THE ASSOCIATION
| OF ECONOMIC BIOLOGISTS

EDITED BY

Proressorn MAXWELL LEFROY, Imperial College of Science and Technology, London,
AND
Prorgessor B, T. P. BARKER, National Fruit and Cider Institute, Bristol
Dr S. E. CHANDLER, Imperial Institute, London ~~
F, J. CHITTENDEN, Royal Horticultural Society’s Gardens, Wisley
Prorgssor F. W. GAMBLE, The University, Birmingham
Proresson PERCY GROOM, Imperial College of Science and Technology, London
Dr A. D. IMMS, The University, Manchester
ProressoR R. NEWSTEAD, The University, Liverpool
Proressor J, H. PRIESTLEY, The University, Leeds

CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, Manacer
LONDON: FETTER LANE, E.C.

- EDINBURGH: IO00, PRINCES STREET
also
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PARIS: LIBRAIRIE HACHETTE & CIE,
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TORONTO: J. M. DENT & SONS, LTD.
TOKYO : THE MARUZEN-KABUSHIKI-KAISHA

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The Association of Economic Biologists _

12.
13.

President
ProFEssoR NEWSTEAD, F.RBS.

Vice-Presidents

ProFressorn CARPENTER, M.R.LA.
Proressor HICKSON, F.R.S.

R. STEWART MacDOUGALL, D.Sc,

Sm PATRICK MANSON, K.C.M.G., F.R.S.
A. E. SHIPLEY, D.Sc, F.R.S.>-*

Council
R. S. BAGNALL Pror. P. GROOM, D.Sc.

S. E. CHANDLER, D.Sc. A. D. IMMS, D.Sc. ~
F, J. CHITTENDEN Pror. J. H. PRIESTLEY
E, E. GREEN A. G L. ROGERS

Hon. Treasurer

J. C. F. FRYER, Esq.,
Craven House,
Northumberland Avenue

Hon. Secretary
Proressor H. M. LEFROY,
Acton Lodge,
~ Brentford

CONTENTS OF Votu. I, Nos. 3 & 4

Some Difficulties in the Improvement of Indian Sugarcanes. By |

C. A. Barper. (Plates XIII—XVI and 3 Text-figures) . .
The Pea Thrips (Kakothrops Stic By C. B. Wittiams. (With
12 Text-figures) . : ; ; ;
The Apple Sucker, with N otes on the Pear Sucker: By P. R. AWATI.
(Plates XVII and XVIII and 21 Text-figures)

Insecticides from a Chemical Standpoint. By W. F. Coorzr aus
W. H. Nourrati ‘ ; ;

Insecticides. By H. M. Lisrnoy: (With 1 Text- sinive

The Composition of the Coffee Berry and its Relation to the Man ciras
of a Coffee Estate. By Rupotpn D. ANsTEaD

The Life-History and Habits of the Greenhouse White Fly ( Aeyrailes
vaporariorum Westd.). By E. Harereraves. (With 56 Text-
figures) .

Infection and Tminanity Senaies on the Rule aad Pa Scab Futgi
(Venturia inaequalis and V. pirina). By S. P. Wi.tsHire.
(Plates XIX—XXII)_ . x A Bias

Winter Cover Washes. By A. H. Lams

A Preliminary Investigation as to the Cause of Rotting bf Oringes
from Brazil. By W. Rusuron. (With 1 Text-figure) ;

Effects produced by Sucking Insects and Red Spider upon Potato
Foliage. By A. 8S. Horne and H. M. Lerroy. (Plates XXITI—
XXVIT) 4 : Sak edceT tee, SLA ‘ ’

Notes. (With 1 Text- igure)

Review

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The Journal of Agricultural Science. Edited by R. H. Brrren, F.R.S., A. D. Hatt,
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The Journal is mainly intended to circulate among agricultural teachers and experts, farmers and
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It is issued in quarterly parts. The subscription price, payable in advance, is 15s net per volume
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The Journal of Hygiene. Edited by G. H. F. Norra, M.D., Ph.D., Sc.D., F.R.S.,
in conjunction with J. S. Hatpans, M.D., F.R.S., A. Newsuoitme, C.B., M.D., C. J. Marri,
D.8Sc., F.R.S., J. G»G. Leprnenam, M.B., D.Sc., and G. S. Granam-Smira, M.D.

The Journal is issued as material accumulates. A volume containing about 500 pages, with plates
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Parasitology. Edited by G. H. F. Nurratt, F.R.S., and A. E. Surety, F.RBS.,
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The Biochemical Journal. Edited for the Biochemical Society by W. M. Bayuiss,
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The Journal is published every two months. The annual subscription-price to non-members of the
Society is £1 1s net per volume (post-free).

Cambridge University Press, Fetter Lane, London
C. F. Cray, Manager

THE ANNALS OF APPLIED BIOLOGY

The Association of Economic Biologists begins under the above title a
publication devoted mainly to the scientific papers read by members at the
meetings and devoted to those branches of Biology in which the Association has
been interested. During the ten years of the Association’s life, its meetings have
discussed mainly horticultural, agricultural and forest biology; the specialised
parts of agricultural science, of genetics and of medical zoology are dealt with in
other journals, and Zhe Annals will appeal more to those interested in the diseases

and pests of plants, scientific problems of horticulture and forestry, tropical -

economic botany and agricultural zoology in the stricter sense.

The Annals will be edited by an Editorial Committee, including a General

Editor and Editors for each branch of Applied Biology in which members are ©

interested. The scope of The Annals is as wide as that of the membership of the
Association, and all members are invited to send in papers and notes to the
Secretary of the Association.

Contributors are asked to send type-written articles if possible, and as far as
possible to make illustrations in a form suitable for reproduction as text-figures.
Contributors will receive free fifty copies of their papers. -

If possible, four numbers will be published each year.

Terms of subscription.

Members of the Association will receive The Annals free. To others, the
annual subscription price, including postage to any part of the world, for a single
copy of each of the four parts making up the annual volume, is 25s. net; single
copies 7s. 6d. net each. Subscriptions for Zhe Annals are payable in advance and
should be sent to Mr ©. F. Cray, Cambridge University Press, Fetter Lane,
London, E.C., either direct or through any bookseller.

The publishers have appointed the University of Chicago Press agents for the
sale of The Annals of Applied Biology in the United States of America and have
authorised them to charge the following prices: annual subscription, post free, $6,
single copies, $2.

Members of the Association should send their annual subscription to the
Society, One Guinea (£1. 1s.), which includes the supply of one copy of each of
the four issues of The Annals, to the Treasurer, J. ©. F. Fryer, Esq., Craven
House, Northumberland Avenue, London. Editorial communications to Professor
Lefroy, Acton Lodge, Brentford.

Claims for missing numbers should be made within the month following that
of regular publication.

SAE TRU Teena NY Co MeN NHS oP A donde Od TE SO RM AEA, oe
CAMBRIDGE; PRINTED BY JOHN CLAY, M.A, AT THE UNIVERSITY PRESS.

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