EntoowlJ

74^

OF THE /
OLLEGE OF^ /

( Bulletin No. 140.

ISSUED BY

Gbe Department of agriculture,

SALISBURY, RHODESIA.

Insect Pests of Tobacco in
Southern Rhodesia.

By RUPERT W. JACK, F.E.S., Government Entomologist.

SALISBURY :
PRINTED BY THE ARGUS P. & P. Co., LTD.

er

ra. r

Insect Pests of Tobacco in Southern
Rhodesia.

By Rupert W. Jack, F.E.S., Government Entomologist.

Tobacco in Southern Rhodesia is not as yet attacked by
insect pests to an extent equal to what appears to be tHe case
in some other countries. Comparing our condition with parts
of the tobacco growing area of the United States of America,
we may congratulate ourselves that we have no "horn worm,"
no " true budworm," and no " flea beetle " to contend with.
At the same time, there are several pests in this country which
do not occur in the United States, whilst certain pests common
to the two countries are at least as destructive in this territory
as across the water. It is really astonishing to observe the
number of insects that will eat tobacco, and it is owing purely
to the tremendous vitality of the plant that the aggregate
damage is not greater. The most troublesome pests, from their
general prevalence, are the cutworms, especially in the seed-
beds. The stem borer (Phthorimaea Heliopa) and the so-called
" wireworms " sometimes cause serious and unexpected losses
in the field. The root gall worm (Heterodera radicicola) is a
serious tobacco pest occurring in the territory, but as yet only
once reported as affecting tobacco. To avoid the introduction
of this trouble into tobacco lands calls for watchfulness on the
part of the growers.

The writer owes it to himself to state that the following
notes on the pests of tobacco in Southern Rhodesia are very
incomplete, as comparatively little time has been available for

M219228

the study of these insects up to the present, whilst the number
of new forms not recorded as pests in other countries renders
the task of investigation a labour of some years.

CUTWORMS. — This name originated in the United States
of America, the term " worm " being erroneously applied to
•caterpillars generally, and the full name referring to the in-
sert's habit of severing the stems of plants close to the ground.
In England these insects are called " surface caterpillars," and
this name is more legitimate than the other, but crisp and
euphonious terms have a way of establishing themselves, and
it would be useless to attempt to dislodge the name " cut-
worm " from general use in this country. The Cape Dutch
call these insects " mest-wurmen," but the name is also ap-
plied to the whitish grub of certain beetles, many of these grubs
feeding in manure. The name " mest-wurmen," as applied
;to the insects under discussion, is, of course, absolutely incor-
rect, because, in the first place, they are not worms, and,
secondly, they do not in the usual way feed on manure. As
they are, however, likely to abound wherever a rank and succu-
lent vegetation exists, they are common enough on the borders
of manure heaps.

'Cutworms are the caterpillars of a number of different
species of night-flying moths of inconspicuous brown or grey
colouration. In Southern Khodesia there are several species
more or less injurious. Six species have already been separated
out at the Agricultural Laboratories, and no doubt there are
more that will €ome to light in time. One of the commonest
species., A gratis segetis, known in England as the ' turnip
moth," is figured on the plate. Another, A. ypsilon, the
" greasy cutworm," is also figured, and appears to be especi-
ally fond of tobacco seed beds.

In general, the habits of cutworms are simple. The gravid
female moth selects a situation amongst suitable vegetation,
and deposits her eggs on the stems of plants or on some con-
venient object near by. The eggs hatch in a few days. In
India the eggs of the ' ' greasy cutworm ' ' are reported to hatch
in as little as one and a half days, but the time taken by most
species is usually considerably longer. The young larvae enter
the soil, where they mostly lie concealed during the day, feed-

CUTWORM SAOTH (Ag'KOTtS

MOTH {A<S'1*OTtS

fO t u S S *

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Insect Pests of Tobacco in Southern Rhodesia.

( Pkt H

• — Thf Cigarette-beetle. <i, larva: A, pupa; c. adult; d,
side view of adult: <;, aatenuu— all ureail\' eiilai'L't d ; r, tlill
more enlarged., i Aft. r Cliittenden...^". S. l)r|»t. Airr. i

Insect Pests of Tobacco in Southern Rhodesia.

ing at night. The time taken by a larva to attain full growth
varies with the season of the year and the quantity of food avail-
able. A number of larvae of one species, bred from egg to pupa
in the laboratory with abundant food and moisture, began to
change to pupae on the thirty-eighth day, and had practically
all changed by the fortieth day. On the other hand, cutworms
•are quite capable of fasting altogether for several weeks, and
taking up the thread' of their development again after this
period, so that the duration of the larval stage is very variable
indeed.

The pupa or chrysalis stage is passed in the earth. Most
species construct cells of earth bound together by some gummy
substance which hardens on drying. These cells doubtless
serve to shield the pupa from sudden changes in temperature
and from contact with water. The duration of the pupal stage is
very variable. In India, where the " greasy cutworm " has
been studied in some detail, the pupal period is given at from
ten days to a month. In this country, one species has varied
from about twelve days to about six weeks, whilst another took
twenty days. A. segetis has been found to vary from a fort-
night to thirty-eight days in the pupal stage. The pupal stage
in general is longer in winter than in summer.

The female moth lays a large number of eggs. In the
case of A. segetis, as many as 1,700 have been counted from
a single female.

Preventive Measures. — Preventive measures must aim at
two things : (1) to see that the seedbeds are free from cutworms
when the seed is sown, and (2) to prevent them from becoming
infested after the plants are above ground. To ensure the
former, the beds should first of all be thoroughly burnt over
with wood or dry tobacco stalks. This is usually done in
Southern Rhodesia, but burning the beds alone is not sufficient
owing to the presence of cutworms in the surrounding ground.
To get rid of these, the use of poisoned bait is recommended.
This is an old and well-known method of destroying cutworms,
and several different formulae are used. A formula recom-
mended in the United States of America consists of :—

Molasses 2 quarts.

Paris green 1 Ib.

Wheat bran . 50 Ibs.

The bran should be made into a mash, of the consistency oi
porridge, with the molasses and sufficient water. The Paris
green should then be thoroughly stirred into the mash. Maize
may be substituted for bran and arsenate of lead for Paris
green.

The Mally formula recommended in the Cape Colony is as
follows :—

Arsenite of soda ... . 1 Ib.

Treacle or black sugar 8 Ibs.

Water 10 gallons.

The arsenite should be dissolved in about a pint of boiling,
water and added to the treacle or sugar solution. Arsenite of
soda is a cheaper and more rapidly effective poison than Paris
green. This solution can either be used to make up a mash
with bran or meal, or, if any greenstuff is available, it can be
chopped up finely, wetted with the poison, and distributed
broadcast but very thinly over the ground. The poisoned bran
or meal is usually distributed in spoonfuls about the ground,
and it remains moist and attractive longer if placed under a
piece of board or anything that will keep the sun off. It is
possible that maize meal is not quite such a good medium as
bran to carry the poison, but the meal is present on every
farm, whilst the bran, which is also a rather more expensive
material in this territory, would have to be purchased specially. -
Cutworms will eat sweetened meal quite readily when fresh,
and in cage experiments have shewn little preference for either
bran or meal. The chief drawback to meal is that it dries up
into a very hard and solid mass. The use of chopped green-
stuff, of course, lessens the expense considerably, but unfor-
tunately greenstuff is very scarce on most farms in September,
when the seed beds are being prepared. If irrigation is being
practised, or an early crop is being grown on naturally moist
ground, greenstuff will be the cheapest material to use. There
is, of course, no difficulty in growing a quantity of lettuce or
other hardy vegetable to furnish greenstuff for baiting purposes.

It must be borne in mind that tobacco seed beds in the
months of October and November constitute an attractive array
of succulent vegetation, when succulent vegetation is scarce
elsewhere , and that cutworms are likely to -be attracted thither
from some distance round. It is advisable, therefore, to clear

the ground for some distance round the beds, say 30 yards in
all directions, and to bait this ground thoroughly before sowing.
If the beds are in a rich vlei, as they usually are, the surround-
ing veld is liable to contain cutworms in September and
October. The clearance will leave a wide margin over which
the cutworms would have to travel to reach the seed beds.

Whatever form of bait is used, it should be distributed to-
wards evening to avoid the drying effect of the sun's heat. The
bait is most effective the first night after distribution, and if
the ground treated has been cleared for some little time, the
cutworms will be hungry, and the great bulk should find the
bait and poison themselves during the first night. The baiting
can be repeated with advantage a week later.

To protect the beds from becoming infested with cutworms
after the plants are above ground, the greatest care should be
given to the soundness of the covering material, to its proper
adjustment each night, and to the tightness of the bricks en-
closing the beds. The aim is to exclude the adult moths, which
are liable to be attracted by the array of green, to deposit their
eggs on or about the plants. The plants are above ground in
the seed beds for nearly seven weeks, whilst cutworm eggs
hatch in from a week to ten days, and it has been found in the
course of feeding experiments at Salisbury that the larvae of
one species attain the length of three-quarters of an inch in
about seventeen days. They are then entering upon a very
destructive period in their lives, and are capable of severing
plants of some size. In twenty-eight days their length had
reached one inch, and from this time forward for about eight
days, when the insects began to pupate, their appetite was very
voracious and their growth very rapid. It will be seen, there-
fore, that eggs laid on young plants produce cutworms that in-
crease in size with the plants, and are big enough to sever the
plants when nearing a condition of suitability for planting out.
When it is remembered that a single female moth may lay up-
wards of seventeen hundred eggs, the desirability of excluding
them from the seed beds is obvious. Cutworm moths are noc-
turnal in habit, so that the coverings of the beds need only be
moth proof at night. 'A tour of inspection round the seed beds
the last thiner in the evening would repay the trouble. This
method can hardly be relied upon to exclude all moths, as some
are likely to find their way in through any opening that is left.

The great preventive measure in other countries is given a&
clean cultivation, especially as applied to keeping down the
weeds during the time the crop is off the land. In this terri-
tory, however, the dryness of the winter usually ensures the
absence of succulent vegetation from most tobacco lands be-
tween the months of May and November, except it be volunteer
tobacco plants growing out from the ploughed-in stalks. These
should always be destroyed, on account of several pests. As
a matter of fact, cutworms are rarely very troublesome in th&
lands. Sometimes, however, naturally moist soil is used to
secure an early planting, and if such a course is intended, care
should be taken to keep the ground free from weeds during the
winter, or the loss from cutworms may be considerable. The
planter should always bear in mind that cutworm moths are on
the wing in September, looking for succulent plants amongst
which to deposit their eggs, and that if cutworms hatch and
enter the ground, subsequent ploughing will destroy the avail-
able food, but not the cutworms themselves to any great extent,,
and that the tobacco plants, when placed in the ground, come
as a welcome supply of nourishment to the hungry insects.

The land may, of course, be baited for cutworms, as already
described, before planting out, or a spoonful of the bran or meal:
may be placed by each plant as a safeguard.

Remedies. — When cutworms are abundant in a tobacco
seed bed full of plants, they are not by any means as easily
destroyed as they are before the plants come up.
There is an immense supply of succulent food everywhere, and,,
though the bait be distributed through the bed, its attractive-
ness does not extend probably beyond a few inches — hence the
value of preventive measures. To get the best effect, it will
probably be best to make up a bran or meal bait of arsenate oi
lead or Paris green, so as not to injure the plants, and distribute
it abundantly through the beds, so that as many cutworms
as possible will come into the sphere of its attractiveness.
Arsenite of soda, being a soluble form of arsenic, is injurious
to vegetation with which it comes into contact. This is about
all that can be done if the cutworms are very small and attack-
ing the young seedlings. Larger cutworms can easily be found
by digging in the surface of the soil near the newly-severed
plant. Natives usually nave something in the nature of a special
aptitude for this kind of work, and a few good " boys " are

Insect Pests of Tobacco in Southern Rhodesia.
Stem Borer Moth and Bored Plant.

Insect Pests of Tobacco in Southern Rhodesia.
Tobacco Miner Moth and Mined Leaf.

capable of ridding a considerable quantity of seed bed of cut-
worms in a short space of time, and of rendering the use of
insecticides unnecessary. Each half -grown cutworm destroyed
may be reckoned as a score or more of plants saved.

In the field, cutworms may be destroyed by hand as above,
but here the plants are very much wider apart than in the seed
beds, and the distribution of poisoned bait after the damage has
commenced is of considerable value, and should be practised if
necessary.

STEM BORER. (Phthorimcea heliopa. Lwr.}— This little-
insect is, without doubt, a native of South Africa, but it is also-
recorded as injurious to this crop in India. The moth is closely
related to the tobacco miner, and is similar in size. It is, how-
ever, readily distinguished by its redder coloration. The larv»
of the two species are very much more difficult to identify..
They are whitish caterpillars, often delicately tinted with pale
green and pink. They reach a length of half an inch. Th&
life history has not yet been followed in this country. Mr,
Maxwell Lefroy gives the following short account of the life
history in India :— ' The moth lays a single egg on the leaf
stalk, the emerging larva boring down through the leaf stalk to-
the stem in which it lives. Pupation takes place inside the-
stem, the full-grown larva preparing an exit hole through which,
the moth can escape." He adds, elsewrhere :— " Apparently
the pest is not injurious to healthy vigorous tobacco, but is
wrorst in a season of drought." Experience in Southern Kho-
desia points to the fact that serious damage usually occurs as
the result of infestation of the seed beds. The moth is evi-
dently on the wing very early in the season, for the seedlings
are frequently attacked when quite small. The presence of the
larva in the stem causes a swelling to form, and above this
swelling the plant will not grow. Suckers grow out from be-
neath the swollen portion on the stem, but if unaided, practi-
cally no leaf worth reaping is produced.

Preventive measures lie in keeping the moths from the
seedlings in the beds, by careful attention to the soundness and
adjustment of the covers, especially at night, and in discarding
seedlings shewing swellings when planting out. All volunteer
tobacco plants growing on the lands about the seed beds and
about the homestead should be destroyed during the winter, as
they provide breeding places for the moth.

Eemedial measures are not practicable in the general way,
but it is said that if the plant is severed below the swelling, and
all but the strongest suckers removed, a fair amount of leaf will
be produced, provided the plant is young enough.

THE TOBACCO MINER OR SPLITWORM (Phthorimcza opercu-
lella). — This insect is closely related to the preceding, and it is
a very difficult matter to distinguish between the larvae of the
two insects. The tobacco miner, however, chiefly attacks the
leaves, and, although also found in the stems, is not known to
produce any swellings. The insect is also a bad pest of pota-
toes, not only mining the leaves and stems of the plants, but
boring the tubers. It thus possesses an alias in the form of the
potato tuber moth."

The female moth lays her eggs singly on the plant. The
eggs hatch in from six to ten days, and the young larvae eat into
the tissues. They eat out the substance of the leaves in irre-
gular patches, leaving only the upper and lower skins. These
patches are semi-transparent when the leaf is held up to the
light, and the larvae may commonly be seen inside the leaf.
They have a habit of leaving old mines and starting new ones,
and this habit is of some importance in connection with control
measures. When full-fed the larva changes to a pupa inside
the plant, the moth under favourable conditions emerging in
about five weeks from the hatching of the egg. The time,
however, depends upon the temperature.

As tobacco is not at present grown for the purpose of mak-
ing cigar wrappers in Southern Ehodesia, the injury to the
leaves is not of the same importance as it is in some other
tobacco-growing countries. The lower leaves of the plant are
chiefly attacked, and where priming is carried out, many of the
infested leaves are removed. Much good leaf is, however,
liable to attack, and it is no uncommon sight in the barn to
see hundreds of these caterpillars hanging by threads from the
drying leaves, or crawling rapidly over the ground in endeavours
to escape the uncomfortable heat.

Preventive measures lie in covering the seed beds thor-
oughly at night, and in destroying the plants which might serve
as breeding places for the moth during the winter. This insect
also breeds in fhe common weed known as the thornapple or
;< stinkblaar " (Datura stramonium), and this should be des-
troyed as much as possible about tobacco lands.

9

Spraying the plants with arsenate of lead or Paris green
would be likely to destroy many of the insects when starting
new mines. In some parts of the United States it is the prac-
tice to send labourers through the fields to crush the larvae in-
side the leaf tissue, but this is probably only done where the
leaves are used as cigar wrappers.

' WIREWOEMS."-— The insects which go under this name
in Southern Khodesia are not true wireworms as the word is
usually applied. The destructive wireworms of Europe and
America are the grubs of " click " beetles or " skipjacks," be-
longing to the family Elateridce. The grubs injurious to
tobacco in this territory are the young of a family of soberly
coloured beetles of the family T ' enebrionidte , which includes the
" tok-tokje " beetles amongst others. These grubs have not
yet been bred out to the adult stage, but there are probably
several species involved. The grubs are of a slightly flattened
sub-cylindrical form, light yellowish brown in colour, and may
reach a length of two and three-quarter inches. They are
;armed with a formidable pair of jaws, with which they are able
to sever tobacco stems of some thickness, thus destroying the
plant. They are usually brought to light when the wilted
plant is noticed and dug up. They attack the plants as soon as
the field is planted, but are also reported to kill healthy plants
In full growth.

The probability is that the eggs are laid in the natural veld,
•and that the insects attack tobacco because it happens to be the
plant within their reach, and not because they have any natural
preference for it, but that they thrive upon the diet is shewn
by the fact that land is often found to be infested the second
year as well as the first. Probably the insect takes more than
one vear to mat u re-
in rare cases the injury to tobacco by this pest may be
severe, the crop being rendered altogether unprofitable. Usu-
ally, however, the insect is present in but small numbers, and
the percentage of plants destroyed is quite inconsiderable.

So little is known about these insects, that it is not possible
to recommend remedial measures. It is probable, however,
that when other crops come to be grown in rotation with
tobacco, injury by these insects may become a thing of the
past. With the present system of growing tobacco for two
years on one piece of land , and then allowing it to lie fallow for

10

several seasons, the tobacco will always be liable to attack. It
may be mentioned that when the grubs are present in great
numbers in the soil, they are very manifest during ploughing
operations, and much good would doubtless result from the use
of " boys " to collect and destroy them as they are brought to
the surface. If the numbers are seen to be very great, how-
ever, the wisest course, if practicable, would doubtless be not to
plant tobacco on that piece of land.

KOOT GALLWORM (Heterodera radicicola) . — This is an
important and dangerous pest which at the present time occurs
very rarely in tobacco lands in Southern Khodesia. It is, how-
ever, prevalent in several parts of the country in land that has
been used for potatoes, and is likely to be introduced into-
tobacco lands if growers are ignorant of its dangerous nature,
and the facility with which it may be transported, 'especially
through the medium of infested seed potatoes.

The pest, and the injuries caused by it, are illustrated in
the adjoining plate. The eggs are hatched within the swollen
body of the female, who gives up her life in the process of repro-
duction. The young worms, shewn in the plate very greatly
enlarged, are threadlike and provided at the anterior end with
a spear-like instrument, which can be thrust out of the mouth
opening and withdrawn. The newly-hatched worm is, of
course, exceedingly minute, and not to be distinguished by the
unaided eye. After wandering about on the plant tissues for
some time, it comes to rest, and finally changes to an adult.
The adult males remain slender,, and measure about a twenty-
fifth of an inch in length. The females swell up, and assume
the shape shewn in the illustration. They become distended:
with eggs that hatch within their bodies.

Migration from plant to plant in the field is effected
through the activity of the young worms, which may either
voluntarily leave their host plant to seek a new home, or may
be released into the soil by the decay and breaking away of the
infested tissues of the plant. The young worms make their way
into the rootlet of a new plant, by means of the piercing organ
with which they are provided. In travelling from plant ta
plant, they seem to be much assisted by a soil of a sandy charac-
ter, and it is usually such soils which become badly infested
with the pest. As they are fond of damp ground, it is likely
that many of the wet vleis of granite sand in different parts of

11

the territory may become infested, and that the pest will flour-
ish greatly under the conditions there provided. This is unfor-
tunate, because these useful vleis occur on many good tobacco
farms, and are very liable to be planted with potatoes for an
early crop. Seed potatoes are, without doubt, the chief agent
by which gallworm is transported, although nursery stock may
also play an important part. Once the pest has been intro-
duced to a farm, it is liable to be carried about by farm imple-
ments, the boots and feet of labourers and others, including
animals and birds, by flood wrater, by drains, by irrigation, and
perhaps even by the wind. Once a suitable soil has become
infested with gallworm, it is likely to remain so as long as suit-
able plants are provided for its use. The variety of plants
attacked is very great, and includes nearly all the crops that
can be grown profitably in Southern Khodesia, with the for-
tunate exception of cereals, including maize. The damage
done to the plants is due, in the main, to the irritation set up
in the tissues, which stimulates the formation of swellings or
galls. The thickening of the tissues of the root interferes
seriously with the functions of the plant, causing a feeble
growth, wilting and frequently death. Seeing that remedial
measures against this pest are hardly practicable on tobacco
lands in this territory, it is obvious that great care is necessary
to prevent the introduction of the pest. As already mentioned ,
seed potatoes constitute the most likely vehicle by which the
pest may be brought to the farm, and on this account a potato
tuber shewing galls caused by a gallworm is shewn in the
adjoining plate, in order to enable growers to recognise the
trouble, and to discard such infested tubers for seed purposes.
Every endeavour is made in South Africa to prevent the spread
of this trouble with nursery stock by means of the Government
inspection of nurseries. Burning the seed beds acts as a pre-
caution against infestation of the transplants, and should
always be carried out, in spite of the fact that some growers
express doubts as to whether the work and expense involved are
justified. Land that has become infested should be discarded
for tobacco and planted to maize or another cereal for several
seasons.

CATERPILLARS. — Two species of caterpillars have been
reported as injurious to tobacco in Southern Khodesia. One
is Laphygma (Caradrina] exigua, a cosmopolitan pest known

12

in the Transvaal as the " pigweed caterpillar," and in the
United States as the " beet army worm." The other species
has not yet been ascertained, but from descriptions furnished
It appears to be one of the " semi-looper " caterpillars. The
looper caterpillars do not progress by crawling in the ordinary
way, but by bringing the hinder part of the body up to the fore
part and arching the back, and then taking a grip with the
hinder pro-legs, extending the fore part to take a grip further
on. They are sometimes called " measuring worms." The
semi-loopers are more or less intermediate between ordinary
caterpillars and loopers.

The eggs of L. exigua are laid in clumps upon the plant
upon which the caterpillars feed, and are partially covered over
with hair from the body of the parent. They hatch in about
four to five days, and the caterpillars feed up rapidly, changing
to pupa; in as little as twenty days. Pupation takes place in
the ground, and in the warmer portion of the year the moths
may emerge in from nine days. The caterpillars feed on the
foliage of the plants, but may also eat the stems and parts of
the roots.

In ordinary years it has been found that these caterpillars
can be kept under sufficiently by making the " boys " collect
and destroy them during topping operations, but in certain
seasons they appear in too great numbers to be left so long,
and, in the absence of a supply of spray pumps, the whole
labour on the farm has to be devoted to collecting and destroy-
ing the caterpillars. It, therefore, should pay the grower to
keep a few pumps of the knapsack pattern on hand, in case of
a bad invasion of caterpillars. In the parts of the United
States where the " hornworms " constitute an annual tax on
the production of leaf, machines for distributing dry Paris
green and for spraying are a necessary part of the grower's out-
fit. Knapsack pumps may be purchased in Ehodesia for from
65s. upwards.

Probably the most suitable spray is : —

Paris green, 1 Ib.
Fresh slaked lime, 2 Ibs.
Water, to 160 gallons.

Tobacco Pests of Southern Rhodesia.
Root Gallworm.

f

1 - * *

'--"

Insect Pests of Tobacco in Southern Rhodesia.

13

This will not render the resulting tobacco poisonous or inferior
in any way, but it will probably be best not to spray within
a fortnight of reaping the leaf, thus leaving a wide margin for
safety.

THE BUDWOEM. Chloridea obsoleta (Heliothis armiger).

—This is a cosmopolitan insect that attacks a variety of crops,
including cotton, maize, tomato, etc. In America it does
damage to tobacco by eating into the opening buds, and later
by attacking and boring into the seed capsules. The insect
occurs in Southern Ehodesia, but injury to the buds has not
been observed, and injury to seed capsules, although common'
enough, is at present of no great moment, as seeds are not col-
lected in this -country. The reason for the immunity of the
buds is not apparent. It may be that the insect has not yet
contracted the habit, but may do so later, or that its enemies
are more effective here than overseas. It is noteworthy that
it has not yet been observed in the tassels of maize or in toma-
toes within our borders, although these are its favourite feed-
ing places in America and in Cape Colony. The remedy for

' budworms ' ' used in America is a mixture of a half teaspoon-
ful of Paris green with a quart of finely ground maize meal.
This is sprinkled on the buds from a can perforated like a
pepper canister, and renewed frequently, especially after heavy
rains.

BEETLES. — Several species of beetles eat the foliage and
gnaw the stalks of tobacco in this territory, especially when
newly planted. The beetles are very dissimilar in appearance,
but almost all belong to one family, the Tenebrionidce. The
beetles of this family are very lacking in popular names, the
" tok-tokje " being probably the most familiar to South Afri-
cans. Beetles belonging to the following genera have been
observed or reported to damage tobacco : — Zophosis, opatrum,
gonocephalum, psammodes (tok-tokje), dictha and anomalipus.
Of these, the most to be feared are zophosis and opatrum.
These beetles will apparently gnaw any part of the plant within
reach; they are not, however, provided with feet adapted to
clinging to aerial foliage. It is probable that the damage is
done almost entirely to newly-set-out plants, which are natur-
ally in a checked condition, or to plants suffering from drought.
Strong freely-growing plants appear to be almost exempt from
attack, or at least to noticeable injury. It has been noted

14

that deeply-set plants, of which the growing heart is well
underground, escape serious damage even where the beetles are
abundant and hungry for food. The beetles eat the exposed
part of the plant, which consists of the ends of a few leaves,
but do not burrow more than about half-an-inch underground.
The general opinion is that. the deeply-set plants grow quite
well once a good start has been obtained, and, although in go-
ing over a field shortly after planting, half the plants may ap-
pear to be missing, a few weeks later the grower may be able
to congratulate himself on an excellent stand. Plants of which
the heart is above ground are apt to be severed through the
stems, and are then of little use, for although a plant may grow
up from a sucker, the resulting leaf is likely to be disappointing.

The use of grass dipped in cutworm poison is efficacious in
destroying opatrum, and has been reported to be effective
against zophosis. All these beetles are fond of sweets, but the
larger species are probably best destroyed by hand if they prove
troublesome. Opatrum has a propensity for gathering under
heaps of rubbish, and by placing heaps of in-
flammable rubbish about the fields, many of the
beetles may be destroyed by burning in the earlier part of the
dry season. The genera of the beetles figured in the plate,
reading from left to right, are psammodes (tok-tokje), anomali-
pus, dictha, and zophosis (2 species).

LARGE CRICKET. — This insect is sometimes a troublesome
pest of tobacco. It is undoubtedly chiefly associated with this
crop because of its preference for light, sandy soils, and not be-
cause of any special preference for tobacco. The adult insect
is shewn in its natural size in one of the plates. The adult or
fully-winged form has been collected from December to March ,
but immature forms, in which the wings are not fully
developed, also do damage.

The insect's mode of attacking plants is to sever the leaf
and drag it to its burrow. In order to get the leaf into its bur-
row, it is rolled up in a way that stimulates speculation as to
how the operation is performed. The cricket seems to lurk
within the rolled leaf in the ground, and can be dug out easily
enough inside its self-made house.

The following poisoned bait is reported to be effective
against this pest in the Transvaal : — 3 Ibs. bran, green grass or
lucerne, J Ib. sugar or treacle, and one dessertspoonful arsenite

15

•of soda or Paris green. As a rule, however, they are dug out by
hand. The natives are fond of these crickets for eating pur-
poses, and take kindly to the work of capturing them.

GRASSHOPPERS. — Several species of grasshoppers attack
the tobacco in the seed beds and in the field, mostly in the
•earlier part of the season. When serious, they can be des-
troyed by spraying, as for caterpillars, with an arsenical pre-
paration. Transplants can be dipped in poison as far as the
roots as a protective measure.

THE CIGARETTE BEETLE (Lasioderma serricorne). — Stored
tobacco in Ehodesia is very much subject to attack by this cos-
mopolitan insect. The whole life of the beetle is passed in the
tobacco, and, under favourable conditions, the rate of increase
is very rapid. Bales of tobacco may be ruined if left to them-
selves for a season or two. Cigarettes and cigars are also
attacked. The different stages of the insect are shewn in the
plate very much enlarged. This pest, of course, concerns the
manufacturer rather than the grower, as the latter rarely
wishes to hold his stock longer than necessary. The beetle can
be destroyed by fumigation for 24 hours with carbon bi-
sulphide, at the rate of 1 Ib. to 1,000 cubic feet of space, but
bales need to be opened up to enable the gas to penetrate. This
gas is poisonous, and, when mixed in certain proportions with
air, highly explosive, so its use calls for caution.

TRIBOLEUM CONFUSUM. — This is usually a pest of grain,
meal and other stored products, and it occurs over the greater
part of the inhabited world. Ehodesia is apparently the only
country where this pest has been recorded as attacking tobacco.
It seems likely that the attack is generally dependent upon the
proximity of infested grain or meal to the tobacco. The insect
has not been found to breed in tobacco, but to attack it freely
enough in the adult or beetle stage. Eemedial measures that
apply to the cigarette beetle will be effective in the case of
triboleum.

TOBACCO AS AN INSECTICIDE. — Tobacco has a considerable
value as an insecticide. It is used as a fumigant for green-
houses, in the form of snuff for dusting on the plants and as an
infusion. It is effective against plant lice, thrip and other soft-

16

bodied insects. It is one of the earlier insecticides, and is in-
creasing in popularity to-day. Some years ago its use was not
much recommended on account of the difficulty of preparing a
wash, etc., containing a given quantity of the active insecti-
cidal constituent, namely nicotine. At the present time, how-
ever, there are a number of extracts on the market in which
the proportion of nicotine is fairly constant, and by diluting
these a reliable wash can be obtained. The home-made wash
is very unreliable. It is usually prepared by soaking tobacco
stalks and waste in water, at the rate of one pound of tobacco
to one gallon of water, for several days. The water should not
be boiled, as this drives off some of the volatile nicotine, and so
weakens the wash. The darker and stronger the tobacco, the
better the wash. In South Africa tobacco wa.sh is recom-
mended for use against the following important insect pests
amongst others : — Woolly aphis on apple trees, green aphis on
peach trees, black aphis on orange trees, cabbage aphis, black
peach aphis, bean and pea aphis and onion thrip.

MOSAIC DISEASE. — One of the most common diseases of
growing tobacco is called " calico," or " mosaic " disease, be-
cause of the mosaic-like appearance of the light and green por-
tions of the leaf. The disease causes the leaf to grow more
rapidly near the veins than elsewhere, and thus become
wrinkled and corrugated. A portion, or all of the plant, may
be affected. Slightly diseased leaves are worthless as wrappers,
and highly diseased leaves are of no value for any purpose. For
many years the nature of this disease has been a mystery, and
has been variously regarded as due to a fungus, as the result of
an excess or deficiency of minerals in the soil, as produced by
bacteria or induced by faulty drainage. Dr. Woods, of the
United States Department of Agriculture, who has carefully
investigated the disease, has arrived at the conclusion that it is
due to none of the generally supposed causes, but that it is
due to defective nutrition of the young dividing and rapidly
growing cells, due to a lack of elaborated nitrogenous reserve
food, accompanied by an abnormal increase in activity of
oxidising enzymes in the diseased cells." These are the same
enzymes that prove so beneficial in the fermentation process
later. The enzymes are liberated by the decaying plants or
roots, and, if in excess, may enter the roots of young plants set

17

in the same soil, and induce a diseased condition, from which
the plant will never completely recover. Plants with injured
roots are more than commonly susceptible to attack.

The sowing of seed on fresh or burned plant beds, the
avoidance of injury to roots in transplanting or in cultivation,
and the making of conditions favourable to a steady, even
growth , appear at present to be the only things within reach of
the planter for the prevention or moderation of this condition.

Seed from diseased plants should not be saved, for, while
the disease may not be carried in this manner, still an inherited
tendency to this condition may be transmitted.

"FROG EYE," OR LEAF SPOT. — This disease is also called
"' white speck," because of its appearance in the form of small
white specks in the tissue of the leaf. It appears to a certain
extent in nearly all tobaccos, and does not do any large amount
of damage. A few years ago cigar tobacco with this specking
was in demand, but the style changed as soon as it was found
possible to artificially produce this marking on any leaf. It is
supposed by some to be caused by too much water at the tap
root, and by others to be due to the presence of an excess of
potash in the soil. It does not appear, however, that it is due
to either of these causes, and is probably bacterial in its nature.
This specking must be differentiated from the small white
specks due to sun burning where there has been a particle of
sand upon the leaf. No successful treatment is yet known.

TOBACCO MILDEW. — The most prevalent and injurious
disease of tobacco in Southern Ehodesia is that which is
variously termed by the planters " mildew," " mould," or
white rust." This disease makes its appearance in the form
of a white, downy growth on the leaves, usually attacking the
lower leaves of the plant first of all. It flourishes especially
under conditions of dampness, crowding and insufficient air :
hence it is generally more prevalent on Turkish leaf than on
Virginian, but Virginian is also attacked to a serious extent.
When it has once put in an appearance it spreads rapidly under
favourable conditions, and if not checked is liable to ruin a con-
siderable quantity of leaf. Leaves attacked by this fungus are
quite useless for curing, and it is waste of time to reap them.
They are said to turn black in the curing barn.

18

The usual method of checking the spread of the trouble
is to remove and destroy the infested leaves as soon as noticed,
and a sharp watch should be kept for them. This tends to check
the dissemination of spores, which would otherwise be produced
in great numbers and be carried to fresh plants. This method
is stated to be effective as a rule, and is perhaps the most econo-
mic in a country where labour is cheap.

There is little doubt that spraying with one of the standard
fungicides would be effective in checking the fungus, but the
writer is not in possession of information concerning the use of
fungicides on tobacco plants, 'and'it is possible that copper salts
would have an injurious effect on the final product.

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