461
M99 ENTOMOLOGIOAL SERIES—BULLETIN No. 6
ENT
if: DEPARTMENT OF AGRICULTURE
MYSORE STATE
; ee
PULSE BEETLES
(STORE FORMS)
BY
K. KUNHI KANNAN, m.a., F.ES.,
Senior Assistant Entomologist
ies

( seP 16 1958
SLIBRAB

BANGALORE:
PRINTED AT THE GOVERNMENT PRESS
1919

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FRONTISPIECE

Fra, 2.—T'wo bamboo bins used for storing cereals. The hut of the owner is seen
to the right.

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ENTOMOLOGICAL SERIES—BULLETIN No. 6

DEPARTMENT OF AGRICULTURE

MYSORE STATE

PULSE BEETLES

(STORE FORMS)

BY

K. KUNHI KANNAN, Mua. F.E.s.,

Senior Assistant Entomologist

BANGALORE:
PRINTED AT THE GOVERNMENT PRESS
1919

FOREWORD.

THE study of Pulse Beetles was commenced by Dr. Coleman
and myself more than eight years ago and was undertaken
-mainly with the idea of finding a simpler remedy than fumi-
gation. Whatever success has been achieved in this attempt
is chiefly due to the investigation of the local methods of
storing pulses some of which were found to be highly in-
genious and suggestive.

Before the investigation proceeded far, Dr. Coleman was
drawn off to more responsible duties, But I have always
had his sympathy and encouragement for which | am deeply
grateful. A good part of the experiments described were
carried out under my direction by Mr. B. C. Shantappa,
Junior Assistant Entomologist.

K. KUNHI KANNAN,
Senior Assistant Entomologist.

SMITHSONIA
INSTITUTION AUG 11 1958

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PULSE BEETLES.

———_q——_-

THe Store Forms.

Atmost all pulses such as gram, lablab, peas and beans
are liable to attack by species of tiny beetles which develop
inside the seeds and gradually render them unfit for human
consumption. A number of these confine their depreda-
tions to the field and cease to attack when the crop is har-
vested and stored. Other species, however, do the greater

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4

Fia. 1.—Damaged seeds showing beetles, their eggs, and the holes through which
they came out. At the corners above are shown enlarged the two
species concerned. .
part of the injury while the seed is in the store although
they may get their start while the crop is in the field. The
seeds in either case are damaged by the excavations of the
larve which -complete their development inside them.
Those that are so injured, show usually one or more round
holes through which the adult beetles have emerged and
small shining ivory specks which are eggs or egg shells from
which the larve have hatched out (Fig. 1). The infested seeds
will rapidly accumulate among them a mass of dead beetles
2 B

)

tet

nnd discs cut by them out of the seed coats as they emerged.
In cases of severe damage, the presence of these decaying

Fias. 2 & 3.—Outlines of a palse bsetle. Above, side view. Below, top view.

3 =
insects and riddled emptied seeds imparts an unpleasant
odour which renders it unsuitable for human food. Where
pulses are stored for seed, the damage may have more serious
consequences ; for, so much of the food material necessary for
development is destroyed that the seeds may not sprout, or,
if they do, the seedlings may not thrive.

Although, as stated, there are a number of different
species of these pulse beetles, they all resemble one another
greatly in appearance, (Figs. 2&3). They are usually about an
eighth of an inch long, but some may measure as much as a
quarter of an inch. The body is short and stout and con-
siderably swollen below. The prothorax is curved down so
that. the small head is scarcely visible from above. The
antenne are more or less toothed in the male. ‘The elytra
or wing-covers have parallel grooves in them. They usually
stop short of the abdomen of which the hinder portion is
therefore more or less conspicuous. The third pair of legs
is much enlarged somewhat as in a flea. The abdomen
below and wing-covers above are more or less hairy. ‘There
are various markings on the wing-covers, which, however,
vary both with species and individuals.

PACHYMERUS (BRUCHUS) CHINENSIS.

Of the species found in Mysore attacking stored pulses,
P. chinensis is among the commonest. Fig. 4 shows an in-
dividual of this species. The markings seen are not, however,

Fra. 4.—Pachymerus chinensis.

characteristic of all the forms, which by rearing have been
proved to belong to this species. Chittenden in deseribing
the species writes as follows :-—

“The ground colour is dull red, and sometimes more
or less variegated with yellow or white pubescence. ‘The

4

pattern of the elytra varies, that shown in the illustration
being the prevailing form of specimens reared in the Dis-
trict of Columbia. The darkest spots at the sides are not
round and conspicuous as in the four-spotted bean weevil
and the special spots are wanting while often black is the
prevailing colour of the dorgal surface’.”

The description shows quite clearly the variability of the
markings but not either the range or extent it has in Mysore.
The progeny reared from common parents show so wide a
range that, without the knowledge of their parentage, the
individuals are likely to be regarded as not belonging to the
same species. The extremes are represented on the one side
by the entire absence of markings and hairs on the elytra-and
on the other by a blackening which involves more than half
their length. Chittenden’s description is therefore that of
an intermediate form. The variation is not confined to the
markings alone. The male antenne are not always pecti-
nate but may also be serrate and the serrations may not be
conspicuous.

What these variations are due to, it is impossible to say
in the present state of our investigation. They are not,
however, the result of a difference in seed as cow-pea (Vigna
catiang) ; black-gram, green-gram (Phaseolus mungo), etc.,
made no difference in progeny. A large moisture content
appears to produce a darker coloration but not sufficient
to alter or obscure the markings. From the results
obtamed, it does not appear likely that forms now re-
garded as distinct species can successfully cross, but it is
too early to say whether this possibility can be altogether .
excluded. It is certain, however, that the limits of the
species are much wider than have been hitherto indicated
in the description by Fabricius and others.

Lire History.

7

The life history of all the forms attacking stored pulses
is more or less identical, the differences being confined to«
details. There are, however, interesting points which have
to be gone into at some considerable length to enable the
reader to understand the remedies tried and recommended
and to follow the discussion which has to be raised here-
after of the habits of some of the species.

The egg is oval-shaped, but unlike most eggs is drawn

“1, The Year Book of the Department of Agriculture of the United States for
1898. Page 243, Footnote No. 1.

3)

almost to a point at the narrow end. It is about °3 mm. in
length and about half of that in breadth (Fig.5). Imme-
diately before extrusion, the contents lie a little loose in
the shell. When laid, the egg, therefore, is able to adjust
itself to the surface of the seed so that it loses its
convexity on one side and becomes flat. With this flatten-
ing, the egg also becomes fuller. The egg comes out of the
body bathed in a gummy secretion which, besides fixing
firmly the flattened side of the egg to the seed, forms a broad
rim around the edge which further strengthens the attach-
ment. When the egg is first laid, it is clear and almost
. transparent; but later on, the protoplasm becomes granular
and opaque except at the broad end which remains clear for

Fie. 5.—Seed of Cajanus indicus showing eggs, disc cut by a iarva, and hole through
which a beetle emerged. To the left an egg is figured much enlarged
to show the rim around.

some time longer. In this latter region the black head of
the larva appears later. The larva takes from four to seven
days to hatch, the time varying with the season. When

_ hatched, it lies on its back and the brown mandibles are
seen at the most convex region, standing out conspicuously
against the shining black head.

} The larva is a thick-set grub about $ mm. long (Fig. 6). It
is pale and opaque and shows clearly thirteen divisions besides
the head. There are three pairs of legs which are all reduced
to conical stumps except the first pair which shows signs of
division and appears under the high power of a microscope
to be. terminated by a number of very small spines. The
mouth parts are adapted for boring. The mandibles are
capacious and prominent with a very broad hinge above
and narrowing down to a point at the tip below. The labrum
is drawn out in the shape of a tongue and lies close above
the mandibles. The maxille are reduced to bristly stumps
which are situated just behind the mandibles. The labium
is absent as is to be expected, for its presence would interfere
with the working back of the excavated powder or zeae:

: B2

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6

The chitinous plate from which it springs 1s prolonged into
a triangular process so that the meal will be worked along its
sloping sides.

The most remarkable feature of the larva is the presence
of a curved H-shaped chitinous plate (Fig. 6) which is situat-
ed far forward dorsally on the first thoracic segment. The

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Fia. 6.—Above, larva of Pachymerus chinensis, showing the chitinous process.
Below, the chitinous process as it stands on the prothorax. (Front view.)

upper limbs of the H have seven teeth gradually diminishing
in size towards the outer extremity and bent on themselves
so that they are all blunt. At the place of the cross piece in
the H there are four teeth similarly curved and blunt. The
whole structure is curved backwards so as to follow the cur-
vature of the segment, but it can be erected at an angle to
the body which may be very obtuse.

How tHE Larva BoRrgEs.

We are now in a position to follow the procedure of the
larva in effecting entry into the seed. The larva which is
on its back when hatched turns over so that the ventral

7

side is below. The head, as already stated, is at the broader
end of the egg where the hole is made. Before making
the excavation, the H-shaped chitinous plate is brought at a
convenient angle and fixed against the egg shell in which
process the re-curved teeth of the upper limbs are of consider-
able help (Fig. 7). Once the teeth of the plate are fixed, the
larva begins operation by working the mandibles alternately
or together according as the work is for excavation or for

Fie. 7.—Larva showing how the chitinous process is fixed against the egg shell.
Left side, top view. Right side, side view. Note the radiating grooves
made in the egg shell.

collecting the powder excavated. The chitinous process

apparently serves a two-fold object. It stands on a small

movable fold of skin which can be rapidly moved back-
wards and forwards so that the head may be nearly covered
or completely free. When the teeth are fixed against the
egg shell far behind, 7.e., near its greatest convexity in the
thoracic region, the head is freer and the mandibles are
engaged in the anterior half of the hole ; when, on the other
hand, the posterior half of the hole has to be made, the
chitinous structure is adjusted further forwards. In either
case, the angle at which the chitinous process is fixed against
the egg shell, appears to determine the inclination of the head
and consequently the part of the hole that the larva works
on at a particular moment.

To understand clearly why the larva does not actually
bend its head downwards as one might expect it a do in

B

8

these circumstances, it has to be remembered that its body
is very short and thick. It seems certain, therefore, that any
active bending of the body would have to take place i in the
middle so as to form a semi-circular shape which, in fact, the
larva does take in later stages of the growth. In these
earliest stages, while the larva is still practically restricted to
the narrow confines of the egg shell, there is no room for such
a bending process. Moreover, as the legs are atrophied, they
cannot function in gripping the surface of the seed. The
posterior end of the egg is also narrow and 1s fully occupied
by the abdomen of the larva.

The procedure which the larva follows in boring into the
seed is therefore very different from what one might expect.
The forces exerted in the process of boring into the seed
seem to be of two kinds. Firstly, the chitinous process being
fixed against the egg shell in the region of its greatest con-
vexity, forms a firm base for the action of the mandibular
muscles. Secondly, there is a thrust forward from the abdo-
minal end which, as already stated, is closely applied to the
egg shell. This forward movement is, by reason of the
attachment of the H-shaped process to the egg shell, con-
verted into a vertical force thrusting the mandibles against
the surface of the seed.

As the larva is working, the chitinous process sways for-
ward and backward with the teeth as fulcra, and the lower
limbs of the H expand and contract as the head is pushed
downward out of the hood or withdrawn. When the sides
of the hole have to be excavated, the larva turns a little to
the right or to the left. In the process of turning from one
side to the other, the larva may turn completely over. The
meal excavated is worked back to the pointed end of the egg
by a peristaltic movement of the ventral surface. A little
is also worked on the sides of the egg shell. When the hole
is sufficiently large, the head with the chitinous process
closely pressed against the first segment 1s first mserted. For
obvious reasons the operations inside cannot be followed, but
larvee which have penetrated thus far, when exposed, show a
much attenuated neck and a swollen abdomen into which
apparently the viscera have been pushed back. The ad-
vantages of a narrow neck in enabling the head to work all
round the hole with ease, are obvious. There are reasons to
believe from observations made on penetration by the
larvee of free living forms that the chitinous process is fixed
along the side of the hole during further excavations
deeper into the seed. From the above description it will

9

be seen that the chitinous process is not used as an exca-
vating organ. _

Occasionally, larvee may be found turning over to he on
their backs and nibbling the egg shell with the mandibles so
as to produce a transverse marking on it. What the object
of this operation is, is not clear. It is possible, however, that
it roughens that part of the interior of the egg shell and is
intended to get for the teeth of the chitinous process a better

ip.

at The tension on the egg shell exerted by the larva soon
reveals itself in minute folds radiating from the anterior and
posterior extremities of the egg shell (Fig. 7). There are also
shallow grooves produced by the teeth of the chitinous
process as they are moved forward or backward during the
course of larval adjustments. The force so exerted by the
chitinous process may be so great as to rupture the egg
shell. This break is usually observed in the region of the
greatest convexity of the egg and through it mea] from the
excavation may also be seen to come out.

There has been some obscurity in the past in regard to
the function of the chitinous process. Riley* was the first to
draw attention to this structure in the post-embryonic larva
of B. fabe. After describing the larva at length he pro-
Geeds:

‘We are not aware that similar structural peculiari-
ties in the first larval stages of Bruchus have been pointed
out before. They seem to indicate, perhaps, affinities with
Chrysomelidee and are evidently of advantage in aiding the
young creature in the work it has to do. This stage is very
evanescent. Immediately after finding the proper spot for
entering the bean, the larva gnaws its way in and
moults. ””

The description, while it does not disclose the function of
the chitinous process, attributes the actual excavation to the

aws.

Chittenden’ is even less clear in regard to the allocation of
functions. Apparently following Riley, in describing the
same larva, he states “that both plates and legs are evanescent
but they assist the larva in obtaining the entrance into the
seed.”’ Chittenden figures the chitinous plates for each of
the other species he describes but has not made any state-
ment in regard to it in these either. There is, however, little

. Riley. Insect Life, Vol. IV, Page 300.
. Chittenden. Year Book of the Department of Agriculture, 1898, Page 236,
Footnote No. 2. :

10

reason to believe that he looked upon them as having funic-
tions different from those attributed to itin B. pisorum. In
any case Lefroy’, apparently on Chitterfden’s authority, has
stated in regard to Bruchid larvee generally that “the larva
is provided with three pairs of incomplete but functional legs
as well as a series of thoracic plates which enable the larva to
bore into the seed and establish itself.” Fletche.* also
appears to attribute a share in the excavation to the chiti-
nous process of a free living form P. chinensis as he calls it.
He states “‘that the young newly hatched grub is slender,
darkish-coloured and hairy with long slender thoracic legs
and a well-developed prothoracic plate which is armed with
peculiarly sharp toothed edges which help the grub to bore
into the shell of the pod which the grub at once proceeds to do
and then eats its way into the seed.”

The quotations given above are with reference mainly
to the free-living forms. We have not yet had an opportunity
to study fully the process of penetration in the various free-
living forms; but if we may judge from the analogy of the
forms examined, any share in excavation, as 1s suggested by the
quotations given above, for the chitinous process in the
former, is highly problematical. ‘The apparatus is situated
immediately behind the head before the thoracic prominence
begins. In case the larva is supposed to work with the chi-
tinous process in the normal way, 7.e., ventrally, the hood
in which the process is situated has to travel over the head
down below, so far indeed that it will pass over the mandi-
bles. On the other hand, if the larva works on its back,
which is what one is likely to be Jed to expect from the in-
verted position in hatching, the chitinous process will, in its
work, encounter the thoracic prominence which will prove
thus a serious obstacle. Furthermore, the mandibles are
far more powerful than the chitinous process which is very
slender. It appears to us, therefore, that the function of
the chitinous process in Bruchid larva cannot be very different
in the various species from what has been described, at least
in those species in which the eggs are laid flat on the surface
of the seed and are attached to it.

In any case, in the light now thrown on the process of
excavation in P. chinensis, the behaviour of the post-em-
bryonic larvee of other species has to be examined, more
especially of the free-living forms. The chitinous structure
appears to vary a great deal. For each one of the species

es Lefroy. Indian Insect Life, Page 350. *
. Fletcher. Some South Indian Insects, Page 307.

i

studied by Chittenden the chitinous process figured differs
considerably. It has peculiarly sharp teeth in B. pisorum
in which the larva has got three “apparent joints” in each
leg. In B. obtectus which is said to deposit eggs on the
outside of the pods as well as inside, the teeth of the chiti-
nous process are blunter, but the legs are better developed.
The plate and legs in P. chinensis have already been described.
In B. quadrimaculatus, Chittenden says ‘the teeth are shar-
per and the thorax is armed on the lower portion of the plate
with three acutely pointed teeth on each side’.” If by this is
implied the lower teeth are absent in P. chinensis, Chitten-
den has failed to observe them in the latter species. In any
case there can be no doubt that there is a remarkable variety
in strength and form of the structure so peculiar to Bruchid
larvee which may help in explaining such apparently small
differences in the habit of egg-laying as oviposition on green
pods, dry pods, inside the pods, etc. It is proposed to dis-
cuss these in greater detail in the bulletin on free-living
forms.

THE SUBSEQUENT HIstoRY OF THE LARVA.

Soon after effecting entry into the seed, the larva
casts its skin. Before it does so it swells considerably, nearly
twice its size when hatched. The thoracic region is con-
siderably arched at the time and there is a kind of jerking
movement affecting the whole body, probably in order to
split the skin. The skin ruptures usually along the thorax,
but extends to the head as far as the triangular piece above
the labrum. The larva emerging from the skin is no longer
provided with the chitinous process. The legs are still
further reduced and appear only as conical prominences.
The mouth parts do not alter appreciably. The shape
assumed by the larva in the second instar, it continues to
have until pupation. The larva usually lies in a doubled up
condition. This enables it to move about in the chamber
with greater ease than if it lay along its full length. The
pupating chamber has as its boundary on one side, the seed
coat in which the larva cuts a ring. ‘The chamber is
smoothened with a secretion from the larva, apparently
similar to that out of which a cocoon is formed in Cary-borus
gonagra. The period of pupation varies from seven to twelve
days. The adult after emergence remains in the chamber for
about two days until the integument hardens. Afterwards it

‘, Chittenden, loc. cit. footnote page 247,

19

bitesthrough the ring so that the disc falls off,and then emerges
from the seed. The ring, though it is made by the larva,
does not appear to be necessary for the emergence of the
‘beetle. Beetles emerged successfully from cow-pea seeds in
which the position of the pupz was reversed and which were
glued on to the glass at the disc end of the pupal chamber.
There is also reason to believe that the larvee, which later
on turn into the beetles that hrbernate, do not cut a ring.
The larvee pupate just near the seed coat as usual and
the rings cut by the beetles in these chambers are as neat
as those cut by the larvee. The absence of the ring makes
the insect inside less subject to the changes of weather
and this is probably the reason why no rings are cut by
such larve. When seeds with such pupal chambers are
sown, the beetles make their escape as soon as the seed coats
burst.

The total period required to complete the life history
varies from nineteen days to as much as one month and
twenty-one days. The shortest period is during the warm
weather and the longest, during the cold weather. _

The life history described above is different in import-
ant details from that described by Fletcher. The figure of
the larva given by him is acknowledged to be after Chitten-
den. But he states that it has long slender thoracic legs “and
the prothoracic plate is armed with peculiarly sharp teeth*.”
Chittenden, on the other hand, says in regard to the larva
that it is, of course, smaller than that of the pea weevil, the
minute temporary legs are apparently not jointed and the
prothoracic plate bears blunt rounded teeth instead of acute
spines. There appears, therefore, to have been a mistake
which is in all probability one of identification. From the
description given later, Fletcher clearly looks upon the
species as a serious pest in the field ; for, he recommends that
“the insects may be caught with hand nets in the evening
when they are abundant.” It is clear, therefore, that he
regards the species as free-lving. On the other hand,
Chittenden? says “that eggs are laid both on the outside of
the pod in the field and upon dried seeds and notes that
beetles continue to develop in the dried and stored seed for
several generations until the seed becomes completely ruined
for any practical purpose and unfit for the sustenance of
this insect.” That is to say, the insect is more important
as a pest of stored grain. We have obtained eggs laid on the

1, Fletcher loc. cit. “Page 307.
2. Chittenden loc. cit. Page 244.

13

seeds in the open pods before harvest but have failed to
get the beetles to oviposit on the growing pods. The life
history described by Fletcher is, therefore, not that of a free-
living form. There is a free-living Bruchid which is common
in Mysore on red gram in the field and whose larvee are pro-
vided with legs. and thoracic armature of the description
given by Fletcher. The life history described by him, in all
probability, is of this species. This form is, however,
unable to multiply in the store as has been found by
experiment. | :

HaBIts OF BEETLES.

The adults appear to take no food during their life.
Beetles emerged on the same date died nearly about the
same time whether they were provided with ‘seeds or not.
Nor were any markings visible on the seeds even though a
fine powder was found deposited in the dishes in which
beetles were kept along with seeds. Dissection showed
the alimentary canal empty, except for a little white stuff
near the origin of the malphigian tubes, evidently the ex-
cretion from the latter.

Beetles may copulate and lay eggs soon after emergence.
The eggs are usually laid in the upper layer of seeds only.
When the topmost layer of seed is so riddled and excavated
that there is no more food for the larva, the beetles proceed
to the layer next below which is less injured, so that, on exa-
mining a lot of infested pulses long kept in store. the percent-
age of injured seeds is found to diminish gradually the further
they are below the top surface. It is clear, therefore, that
beetles always come up to the top, wherever they happen to
emerge in the receptacle. They generally remain there with-
out flying away if they are not disturbed. Usually, however,
when the store is opened they appear to be disturbed and a
number escape. This disturbance results apparently from
the difference in temperature, for itis higher in an infested
store than outside. When no lid is provided for the re-
ceptacle, most of the emerging beetles may remain on the
top without flying away.

The instinct of the beetles to seek the top surface on
emergence is of great advantage. The initial infestation at
the time of storing is only of a few seeds. It follows that
the few beetles emerging in different places in the receptacle
separated by several hundreds of seeds, cannot find one
another for purposes of copulation unless they all reach
a common place. Secondly, even if they happen to meet

BQ**

14

layers beneath the top surface, there cannot be any freedom
of movement required for the female beetles to travel over
a large number of seeds and deposit their eggs; for eggs
cannot be crowded on a few seeds without the risk of. ham-
pering the development of several, which, distributed over
a larger number of seeds, might have a better chance of
‘completing their development. On the top surface, there is
no pressure of surrounding seeds but on the other hand com-
plete freedom of movement.

To ascertain what exactly induces the beetles to come to:
the top, the following experiment was conducted. A tin
box was filled with infested gram so as to leave no space
above the top surface for beetles to move freely and lay
their eggs. Into the tin six large holes were bored, four at.
the sides at right angles, one in the middle on the lid above
and one on the bottom below. Into each of these holes
a glass cylinder six inches long was fixed. All the cylinders
were filled with uninfested gram for about half their length,
the seeds in the cylinder at the bottom being prevented
from falling by a paper disc fixed into it, with holes suffi-
ciently big for the beetles to pass through but too small
for the seeds (Fig. 8). This arrangement prevented the
possibility of any beetles emerging from the seeds inside
the cylinders themselves, but to make it absolutely certain,
the uninfested seeds were made to extend inwards into the
tin for a little way from the cylinders. The cylinders were
then corked to prevent beetles from escaping. When the
arrangements were complete, the gram from the cylinders
above and below A and D had a stiaight level but in the four
cylinders at the sides it sloped towards the cork B, C, E and.
F. It is clear that pressure is greatest on seeds in the bottom
cylinder D, less in the cylinder on top A and _ least in
cylinders B,C, Eand F. On emergence of beetles inside, by
far the larger number worked their way into the top cylinder,
a few were found in each of the four cylinders at the sides,
but none at all in the cylinder below. The beetles in two
of the side cylinders Band E. were now allowed to escape,
the grain was pressed back and kept at that level by means
of a paper disc with holes as in cylinder D. The result was
that irto these two. beetles ceased to come up while in the
other two C and F which were lett as in the first experi-
ment, they continued to appear. When the paper discs
Were removed from the cylinders C and F and inserted in
B and E instead. the beetles put in their appearance in the
former but not in the latter.

RS

15

These experiments appear to us to prove that beetles
work their way upwards on emergence ; secondly, that it
is to get relief from the weight of the seeds on top of them
that beetles move upwards. The presence of beetles in the
cylinders at the sides, B, C, E and F may appear to contradict

Fic. 8,—Cylindrical tin box containing infested gram and having tubes inserted as
described on page 14.

the conelusion drawn. The few béetles found in these are,
however, those that have been deflected from their upward
movement by the diminished pressure among seeds in the-
neighbourhood of the insertion of the cylinders. It will be-
recalled that, at the commencement of the experiment, the
seeds in these cylinders sloped and that therefore there

16

could not be the same pressure in them or in their neighbour-
hood inside the tin, as in cylinders Aand D. The beetles
working their way upwards to the top surface in the tin are
certain to feel the difference as soon as they come within
the area and make for the direction where pressure is’ less.
That it is so is proved by the fact that no beetles appeared
in those cylinders where the seeds were pressed hack by
paper discs. The negative geotropism exhibited by the
insects appears thus to be directly caused by the weight of
the seeds above them which they teel when they emerge.
As they move upwards this weight becomes less and less
until it disappears completely when they reach the top
surface.

The pest appears to be carried over from year to year
by the adults. Adults have been taken from situations near
which pulses were stored. They have also been taken in the
field in seasons of the year when the crops which they attack
are not yet ripe. At the time of harvest, a number of pods
are dry and open. The beetles get at the exposed seeds in
these pods and lay eggs on them. Infestation may also take
place during the interval between harvest and storage or in
the store itself. In one instance where multiplication had
ceased for over a year in a quantity of infested seeds kept
in a bottle, a fresh attack ensued in spite of the fact that the
jar was never opened during the interval.

Three species of parasites have been reared out, of which
two are black-bodied species, one large and the other small.
These do not multiply in large numbers proportionate to the
number of beetles until the infestation has advanced far.
- They are, therefore, of little use as checks. As many as six
have been reared out from one larva but the number varies
and probably depends on the size of the larva at the time of
oviposition. Boring has been observed to take place through
the egg shells and through the other parts of the seed far
removed from them. The following is an account of obser-
vations made by Dr. Coleman and kindly furnished for this
bulletin :— ;

‘Female parasite explored surface of seed with feelers
bent down. Then she raised herself and brought tip of
abdomen down between the hind legs in almost vertical .
position. The tip of the abdomen was then moved away
posteriorly leaving the tips of ovipositors in a vertical posi-
tion. Boring did not immediately take place, but tips of
Ovipositors were moved about on the surface of egg as
if seeking the most favourable point for penetration.

17

Frequently the process stopped here and parasite moved
again as if not satisfied with the position. This was
observed to happen in one case as often as five times.
“When the position was finally found, satisfactory boring
commenced (Fig. 9). This consisted practically of a vertical
drilling motion consisting of raising and depressing of abdo-
men. Small quantities of meal (borings) could be seen about
the ovipositors. The boring lasted in the two cases observed
about 15 minutes and at the end, the ovipositors were sunk
into the seed right up to the sheath and the top of the abdo-

Fia. 9.—Bruchocida orientalis ovipositing through seed of Cajanus indicus. Note
ovipositor between middle and hind legs. (From photograph.)

men was then pulled out and the parasite walked away.
During the act of drilling, the insect keeps up a jerky move-
ment of the outer antenne.

“Oviposition has-been observed to take place in the
centre of the hilum also. The following are the descriptions
of the two species :-—

BRUCHOCIDA ORIENTALIS, (CRAWFORD.) (Fig. 10.)

“ Female.——Length about 4 mm.; sheaths of ovipositor
exposed 1 mm.; bronzy, with tints of green, the scape of
antennze reddish, pedicel green, rest of antennze dark brown ;
first joint of funicle about one and one-half times as long as
the pedicel, the following joints successively decreasing in
length, the last somewhat longer than broad ; very similar
in sculpture to B. vuilleti; wings with white hair as far out
as the apex of submarginal vein; beyond this the hairs dark,
longer and more numerous than in vuilleti and the wings
somewhat infuscated; front and hind cox bronzy ; front

18

and middle legs and middle coxe reddish ; hind legs darker

with bronzy tints ; tarsi white.

-F1a. 10.—Bruchocida orientalis.

‘¢ Three females, Bangalore, India, reared from Bruchus
chinensis. (L. C. Coleman, Collector.)

BRUCHOBIUS COLEMANI, (CRAWFORD). (Fic. 11.)

“ Female.—-Length about 2°5 mm. Similar in color and
sculpture to B. laticeps, Ashmead, but the third ring joint
transverse ; marginal vein over half as long, as the sub-
marginal ; postmarginal shorter than the marginal (about

Fiqa. 11.—Bruchobius colemani.

as 12:17); stigmal shorter than postmarginal (about as
8:12); stigmal knob enlarged; femora dark, the hind
femora mostly greenish anteriorly.

‘* Male.—Length about 2mm. Similar to the female,
the antennw with two ring joints, the scape and pedicel
reddish-honey color, funicle somewhat lighter, club darker ;

19
first jomt of funicle as long as the second; legs reddish:
honey color; hind femora somewhat darkened and with a
small spot with metallic reflections; abdomen no longer
than propodeum.

“ Habitat.—Bangalore, Mysore, India.”

A minute egg parasite less than °3 mm _ has been noticed
recently in very large numbers. It hasa yellow body and
red eyes. The eggs attacked by this hymenopteran turn
blackish in a couple of days after oviposition and the deve-
lopment is completed in about ten days, the adult coming
out through a neat hole made at the broad end of the egg
shell. The species has not yet been identified.

Fie. 12.—Pediculoides ventri-
cosus? in an
early stage.

—

Fia. 13.—Pediculoides ventricosus ? a gravid female.

A fourth enemy is a species of mite, probably Pedicu-
loides ventricosus, described as a pest on the broad bean
weevil’, (Fig. 12) which attacks the larva, pupa and the adult
inside the pupal chamber. The enormously swollen abdo-
men of the gravid female (Fig. 13) all but conceals the rest
of the body. Before this advanced stage of maturity, the
female resembles the male mite which is very minute and both
may be found at times moving among the seeds in large num-
bers. The body is about thrice as long as broad and is

1, Chittenden. The Broad Boan Weevil. U. 8. Department of Agriculture,
Bulletin No, 96, Part V, 1912.

20

slightly swollen in the middle. The posterior. three legs
end in suckers. There are a pair of eyes. Some of these
may be found in the empty egg shells. Probably they
effect an entry through these and keep track of the larva.
This enemy is not found at all times and is by no means a
serious check on the pest.

ControL MEASURES.

The remedy universally suggested by Entomologists
is fumigation of the seed before storage or whenever the
seeds are found to be infested. This consists in exposing
the seeds to the fumes of carbon bisulphide or hydrocyanic
acid in an air-tight receptacle until the insects are dead.
A fumigation chamber can be made at a low cost out
of a tin-lned dealwood box. It is provided with a rim
in which runs a groove into which the lid fits. Water is run
round the channel after the lid is put on. The infested seed
is put into the receptacle and carbon bisulphide is placed on
the top of the seed in a shallow dish. The fumes of the
chemical are heavier than air and-descend to the bottom.
In doing so the insects and their various stages get killed.
The dose is at the rate of 2 lbs. per thousand cubic feet of
space but in small chambers of a few cubic feet, it is usually
doubled. The seed is removed after two days and
stored in a larger receptacle which should also be air-tight
to prevent the beetles getting in. Large quantities may be
fumigated in rooms; provided these can be made air-tight.
Great care has to be taken in the case of the chemical as it
is highly inflammable. No light of any kind, not even that of
a lighted cigar, should be brought anywhere near the chemical,
nor should bottles contaiming it be placed in the sun or in
any other warm place. Otherwise there is danger of serious
explosion. Hydrocyanic acid gas is also an efficient fumigant
but is even more dangerous to human life. It is prepared
by dropping crystals of potassium cyanide into dilute
sulphuric acid, the crystals beimg previously enclosed in
thin paper to avoid a too rapid-evolution of the gas. This
gas 1s one of the most violent poisons known and immedi-
ately the crystals are dropped, the lid should be put on and
the operator should withdraw. The dose for a 100 cubic feet
of space is the gas produced by dropping one ounce of
potassium cyanide | (98 per cent grade) into an ounce of sul-
phuric acid diluted with 3 fluid ounces of water. For fumi-
gating seeds hydrocyanic acid gas is, however, not usually

employed.

21

Both the chemicals mentioned are fatal to human life.
This does not, perhaps, detract from their value as fumigants
where the seed to be treated is a very large quantity and
fumigation done under intelligent supervision. But the
problem in Mysore is different where there are a multitude of
small producers who store their pulses for the greater part of
the year both for purposes of consumption and for seed and
who, moreover, live in houses in which fumigation cannot
be conducted under reasonable safeguards. (Frontispiece
Fig. 2) Their illiteracy is an even more serious obstacle in
the way of recommending the use of dangerous and highly
explosive chemicals.

Means, therefore had to be devised other than fumigation
to keep the stores of the raiyat from the beetles. From the
very beginning of the investigation the aim was kept steadily
in view of finding a remedy which was inexpensive and
at the same time adapted to conditions in which the raiyats
lived and worked. It was necessary for the realisation of
this object to study the methods already in practice among
the raiyat population.

The results of the enquiry have been very encouraging
and are briefly summarised. It is an essential preliminary
to all storage that the seeds should be dried in the sun for
three days. After thorough drying the seed is stored in large
earthen pots, bins made of split bamboo or in bags made of
gunny or matting. The capacity of the pots may vary froma
few seers’ to as many asa hundred or more. The bin is made
of split bamboo having a large bulging base with a narrow
neck. The seed is taken, when wanted, out of a small hole
large enough for the hand near the bottom. This is closed
by a cocoanut shell brought close against it by a string pass-
ing through the eye (Fig. 14). This arrangement obvi-
ates the necessity of disturbing the top layers. The dise
put on once remains closed except when the whole basket has
to be emptied. Bins may be made with interlaced bamboo
smeared over with clay. Bamboo bins may be also cylin-
drical, but pulses are not generally stored in such. The more
usual practice is to store them in bags, gunny or matting,
which are always kept one on top of another. A most
interesting method is to store in what are called ‘ moodais,”
which are made out of pelted straw and which when
completed are spherical (Frontispiece Fig. I). These
‘““moodais”’ are tightened further by means of ropes

1, A ‘seer’ is a local measure equivalent to about 1250 C.Cs,

22

all round. It takes as much as a day to make one so that
raiyats are tempted to abandon the method even though they
have a great deal of faith init. The seeds may be mixed with
sand, ashes, ragi husk, etc., before storage. In baskets they

are not so mixed, but the top layer may be smeared over
with castor oil. A practice which evidently prevailed among

the people but is no longer so, is the use of a small quantity
of mercury—little more than a few drops—which is placed in-

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Section of the
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Fig. 14.—Bamboo bin with narrow mouth shewing arrangement for withdrawing

seed from below.
side the excavated shell of a soapnut in the store. With the
exception of storage in “ moodais,” all these methods have

been tried in the Insectary. The admixture of sand, ashes, -
ragi husk, etc., was found entirely useless. The layer of

seeds smeared over with castor oi] was found, on the other
hand, quite effective though emergence was by no means
absolutely prevented. Similar results were obtained with
mercury which were quite unexpected. In small jars
of a capacity of a few seers, the presence of the metal

23

placed in a dish absolutely prevented emergence while the
check teemed with beetles. It made no difference whether
light had access to the jar or not. In large receptacles con-
taining 100 seers and more, the effect was not so marked even
though emergence was reduced by about three-fourths. To
decide in which stage of life of the beetles the mercury acted
as a poison, the following experiment was tried. Four lots
of seeds one in which the beetles had just laid eggs, second
in which the larvee were about half grown, third in which the
larve had pupated, and fourth in which the beetles had
emerged, were all exposed to the action of mercury with cor-
responding check in each case. It was found that the effect
was on eggs in which the protoplasm was apparently dis-
integrated and the shells became empty. It is possible that
no effect was produced on either the larve or pupe because
these stages are wholly spent inside the seed. A fresh
series of experiments was carried out which appears to show
that the mercury has no action on the eggs once the larve
are fully formed. Detailed results of these experiments
which are of scientific rather than of practical interest will
be published elsewhere. For the present it is enough to
state that, to preserve small quantities from attack, a little
mercury placed in the receptacle which need not be air-tight
will be quite effective. The treatment does not affect ger-
mination.

With regard to castor oil, the secret of its undoubted
efficacy was not revealed until the investigation had continued
for some time and the method of penetration by the larve
was discovered.

It will have become clear from the method of larval pene-
tration described, that the larva would be quite helpless if
the eggs were not firmly attached to the seed as its main hold
is on the egg shell. Jarve carefully dissected out of the egg
shell invariably fail to effect an entry into the seed. Now
we find that the smearing of the seeds with oil prevents the
close adherence of the egg to the seed. Eggs deposited on
seeds so treated fail to assume their normal form, and even
if they do hatch, fail to furnish the larva with the support
that it requires for boring into the seed. For, immediately
it starts the boring, the egg shell begins to move.

Observations on the effect of castor oil when smeared
on the upper surface led to the discovery of the instinct of
the beetles to seek the top surface. As has already been
stated, there was hardly any emergence in seeds which had
the top layer treated with the oil. In this case the beetles

24

had been introduced after the top layer was treated. There
was therefore reasonable ground to believe that the beetles
laid eggs on the treated seeds as being the first they met with.
In a subsequent experiment a quantity of infested seeds was
placed at the bottom of the pot, uninfested seed about four
times the quantity was placed on top of it and then the layer
of oiled seeds was introduced. In spite of it, the results were the
same. It appeared, therefore, certain that in this experiment
too, beetles had sought the top surface for egg laying even
though they must have emerged far below the surface. It
was this fact coupled with the observation that the percent-
age of infested seeds diminished directly with their depth
from the surface that established beyond a _ doubt
the instinct of the beetles to seek always the top
surface.

Once the discovery was made, the wisdom of some of the
methods adopted by the ratyats became clear at once. The
bamboo bin with a narrow neck and a hole at the side ap-
peared admirably suited to prevent serious damage by the
beetles ; for, in this arrangement, the top surfaceis very much
reduced and is left undisturbed. In the “ moodais ” there
is no level surface on top at all and the seeds are packed so close
together that there is little space afforded to the beetles to
proceed far from the place of emergence to find a male or to
lay their eggs. When the seeds are mixed with husk in these,
the interspaces between the seeds are still further reduced.
The practice of keeping these ‘‘ moodais,” bags, etc., one on
top of another is also to be recommended as the pressure so
exerted tends to reduce further the space between the seeds,
required by the beetles and hinder their multiplication.
With regard to oiling the top layer of seeds, the method,
though effective, does not entirely prevent beetles from
getting into the untreated layer below and laying their eggs
on the seeds there.

Another method that deserves notice is the storage of
pulses under ragi (Hleusine coracana) or savai (Panicum fru-
mentaceum). These grains are not attacked by pulse beetles.
When they are used as a top layer several inches deep, the
beetles, on emergence to the surface, do not generally get
back to the pulses below and the latter are usually saved
from attack.

There can be no question that these methods reduce
damage to a great extent. At the same time, without consi-
derable care, the few that manage to emerge may success-
fully reproduce and there is the chance of injury extending to

oe

& considerable percentage of the seeds. To effect improve-
ments, it was necessary to prevent the beetles that came to
the surface from getting back to the seed for oviposition.
The device first thought of was what may be called a paper
trap (Fig. 15). Anumber of semi-circular rings are cut into
the paper. The paper is closely adjusted to the surface of
the seeds, so that there is no space between them and the
paper. The beetles, on emergence, will get through the holes

Fia. 15 —Paper trap shewing discs cut into it.

on to the top of the paper, but fail to get back as the semi-
circular disc comes in contact against the seeds directly they
try to do so and unless the disc is lifted up or drawn a good
way, there is no hole sufficiently large for the beetles to pass
through. Properly adjusted, the paper trap was absolutely
effective. There were drawbacks, however, to an extensive
adoption of this device. In the first place, unless the bins
are standardised, the size of the paper will have to be varied
according to the size of the neck, or, if the bin is not full, to the
size required to completely cover the top layer at whatever
level this happens to be. Secondly, any careless adjustment

26

may afford sufficient room for the beetles below the paper
to move about as they please, and consequently to reproduce.
The idea was thus abandoned. The next idea that occurred
was to have a layer of seeds of castor, (Ricinus communis)
or of Abrus. precatorius on the top of the pulses.
Castor has got a very thick shell too hard for the larva to
penetrate and develop and Abrus precatorius has a very
smooth seed coat. When beetles were compelled to lay eggs
on these, no progeny followed even though a number of
larvee successfully penetrated. Unfortunately, however, when
these seeds were spread as a top layer, the insects while they
came above them on emergence, got back to the pulses below
instead of depositing the eggs on the seeds above. The last
idea was to spread a layer of sand. This had been tried pre-
viously mixed with pulses and had proved useless because, as
was found later, the beetles could work their way through
to the top where some of the seeds were lying exposed un-
covered by it. When used as a top layer it was found quite
effective, but the layer should be at least half an inch thick.
In thinner layers the insects displayed the remarkable habit
of bringing up the seed. Two or three of these jomed and
brought up seeds in which eggs were subsequently deposited.
Eggs were not laid, however, on the seed below the sand.

This is then the remedy that has occurred to us as equally
efficient, simple and within the means of the poorest raiyats.
The bin best suited for storage is the one already described,
having a narrow neck with a large base. The sand is put
as a top layer. The lid remains closed as a rule, the quantity
required being withdrawn from the hole at the side near the
base. The brood from the initial infestation will work their
way to the top of the sand layer and will die there without
being able to lay eggs. And since the lid remains closed
until the whole basket has to be emptied, chances of infes-
tation during storage are reduced to a minimum.

Before covering the top layer with sand, it is necessary
to see that the seeds are pressed down well in the basket.
Otherwise the gradual settling after storage may so disturb
the sand layer that gaps in it may be formed especially
along the sides of the basket exposing the seeds and allowing
the beetles to come up. It is further necessary that no seeds
should be withdrawn for at least a month after storage for
the removal may have much the same effect on the sand
layer. Assuming the seeds are infested at the time of storage
at least a month must elapse before the adults arising from
the infestation emerge and come to the top and die. Any

of

disturbance of the sand layer during this period may exposé
the seeds and so enable these beetles to reproduce. A third
precaution is to have the sand layer at least a couple of
inches thick to ensure that slight disturbances do not expose
the seeds in any way. It is also necessary to see at frequent
intervals that the sand layer is intact.

There is reason to believe that this remedy has a wider
application than to pulse beetles, for the instinct on which it
is based must be the means by which other stored grain
insects as well secure copulation and reproduction unham-
pered. The same instinct has been found to direct to the top
surface such widely differing species as T'riboliwm castaneum.
Lasioderma serricorne, Calandra oryze@, Gibbium scotias,
Rhizopertha dominica. Experiments have, however, not
progressed far enough, nor is this bulletin the appropriate
place, to record whether the sand layer would be effective

Fria. 16.—Bruchus analis.

against these and other species or whether other devices have
to be made to utilize this instinct in their destruction. It
may be stated, however, that the instinct is likely to
furnish in every case an easy means of controlling these

ests.
Since the discovery of the method described above, the
announcement has been made that it has been discovered
in Pusa also. We have not yet had any detailed description
of experiments which resulted in the discovery there. It
would be interesting to know the line of investigation carried
out there which has yielded the same result.

OTHER ForRMS IN STORED PULSES.

There are at least three other forms to be found in stored
pulses in the State. The more common one is B. anaiis,

28

(Fig. 16). The form in Mysore answers to the descrip-
tion given by Fabricius but there are variations as great
in this species as in P. chinensis. In the typical form as
described by Fabricius the elytra are shorter than in P.
chinensis, the portion of the abdomen exposed is greater and
has a black suffusion only interrupted by a median white
line. On each elyfron there is a black spot in the middle
which is tipped behind more or less conspicuously with
white. The scutellum is white. All the markings, white
as well as black, may be absent or the black may be present
in varying depths. So too with the black coloration of
the pygidium and the median white line, both of which may
be wanting. Even the white spot on the scutellum may be
inconspicuous. Owing to the absence of these markings,
some of the forms are with difficulty identified as B. analis.
There can be no doubt, however, of the range in variation in
the forms as most of these have been noted in the progeny
from the same parents.

The form attacks cow-pea by preference but may attack
other pulses also. There is little to be noted in the life history
which is practically identical with that of P. chinensis.

Fie. 17.—Bruchus quadrimaculatus.

B. quadrimaculatus, (Fig. 17).—This form is easily dis- -
tinguished by the markings on the elytra which together
assume the shape of X in white and by its slightly larger size.
The space enclosed by each of the limbs of the X is dark
brown. Chittenden describes the species as follows :—

«The ground colour is black, with black, grey and white
pubescence. The antenne are serrate and not pectinate in
the male. The basal lobe of the thorax is marked with white
pubescence only. The elytra are longer and the grey and

= 29

white pubescence is so arranged as to leave four large black
spots whence the species derives its name. These markings
are often, variable and lacking.”

Little need be added to the description save that the
four spots on which the name is based are more often
absent than present, and when present, always inconspicuous
in Mysore.

The species was taken in the field in seeds of lablab in
open pods. Multiplication continues in the store; but it ap-
pears to require a greater degree of moisture in the seeds so
that the infestation tends to diminish rather than increase in
the store. The life history does not differ in material particu-
lars, from those of the species already described.

An unidentified species, (Fig. 18)—This form multi-
plies in the store in seeds of lablab. It is much more common
than B. quadrimaculatus. The beetle is smaller being never
longer than 2°25 mm. ‘The markings on the elytra are some-
what similar to those in quadrimaculatus but the colour

Fia. 18.—An unidentified species.

is dull grey. The limbs of the X are, however, less
curved and more like those of the alphabet. The
portion enclosed by each limb varies from black to brown.
The limbs themselves are light brownish-grey and this is the
ground colour of the elytra. In very dark forms the elytra
may be tipped with black, but usually, there are only a few
scattered spots. The prothorax is much curved, the margin
has a slight rounded prominence. There is a faint double
ridge along themedian line and a large black spot in the
middle. The antenne are serrate. The terminal segments
excepting the last are usually dark. The coxe of the last
pair of legs is black. The pygidium has also a large black
marking. The range in variation is as great in this form as in
others and the markings may be well defined and very con-
spicuous or more or less absent,

30

The life history is much the same as that of other store
forms.
| The forms described above are identified as _ species
‘in accordance with the description given by either Fab-
ricius or Chittenden. With regard to each, as has already
been stated, there is a very wide range in variation so that
forms undoubtedly allied to the typical representative of the
species may nevertheless be regarded as not belonging to it
unless proved to be so by actual rearing. There is little
reason to believe that the different species in the store
are able to cross and successfully reproduce; but nothing
on this point can be definitely stated until more experi-
ments are carried out than has been done in the past. Until
this work is done—and it is being attempted in Mysore—the
identification of the species described above should be
regarded as only provisional,

SUMMARY.

1. There are no less than four species of Bruchids which
are responsible for damage to pulses in store.

2. Though varying in appearance and size, they have
more or less, the same life history.

3. The pulses are infested either in the-field when ex-
posed in dry open pods or in the store itself by the adult
beetles which alone appear to be responsible for carrying
the infestation over from one year to another.

4. Eggs are deposited on the surface of the seed. The
larve bore into the seed, inside which the further develop-
ment is completed, the adult beetles emerging out through
neat holes cut out of the seed coat.

5. The life history takes from three to six weeks, the
actual period depending on the season.

6. The beetles are directed by a remarkable instinct
to come to the top surface where alone eggs are deposited.

7. Advantage may be taken of this instinct by spread-
ing a layer of sand, a couple of inches thick on the top
surface which prevents the beetles which come to the top for
copulation from getting back to the seed.

8. Some of the methods practised by the raiyats are
to be commended though they do not completely prevent
injury. Among these, the practice of ‘‘ moodai” tying and
smearing the top layer of seeds with castor oil are the most
efficient. .

9. The closer together the seeds are packed in the

31

receptacle, the greater the difficulty for the beetles to come to
the top for oviposition.

10. There are féwenemies. There are three hymenop-
terous parasites and one acarid which are not efficient
checks.

11. The range in variation of the species is enormous.
The identification of the gy described should be
regarded as provisional.

Mono WD 091—GPB—2,006—22-5-19

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NIAN pment LIBRARIES i ae

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