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A STUDY OF DEVELOPMENT OF THE
ANGOUMOIS GRAIN MOTH 0N
VARIOUS FOODS

THESIS FOR THE DEGREE OF M. S.

James M. Merritt
1932

 

 

 

 

 

 

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A STUDY CF Th5 DdeLOPmLKT OF TIE
ANGUUMQIS GRAIN MOTH

ON VAhIQUS FOODS

Thesis for
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Acknowledgment

The author wishes to express
his appreciation of the guidance
and counsel of Professors R. H.
Pettit, Fay Hutson, an E. I. Mc-
Daniel during the preparation of

this thesis.

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Object of Exeeriments ..........

Studj of Literature on Parasite
Production

Summary of Iethods ........

Factors Affecting Efficiency

Procedure .......................

Testing of Feasible Iethods

Data 00.000000000000000...
Method of Collection
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Discu sion of Results ....

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Literature Cited .........

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ILTKUDUCTIUN

The Angoumois Grain Moth (Sitotroga

 

cereallela, Olivier) has been Known for many
years as a pest of grains in the field and in
storage, (29), (13), and because of its economic
importance the field biology has been worked out
from time to time by various authors, (1), (5),
(5), (6), (7), (.3), (1’7), (19), (2O), (21), (22),
(25), (28), (51), (30).

Back, (2), in discussing the grain moth
as an economic pest, says that, "Under ordinary
climatic conditions ......, temperature seems to
be the most important controlling factor in dev—
elopment."

Back (2) also reports that, ”The An-
goumois grain moth has been bred from wheat, bar-
ley, oats, buckwheat, corn, sorghum, milo, rice,
beans, chickpeas, and cowpeas. It is a general
feeder upon all seeds of the cereal type. It
causes greatest loss to the wheat and corn in
this country, though instances of serious attack
are recorded frequently upon other grains." This

is substantially in accord with the statement of

Girault (17) that, "The grains attacked are

‘

wheat, corn, and other cereals less seriously.’
Other authors report that rye, popcorn, Sudan
grass, and possibly grass seed are attacked,
(6). (2-3), (10), (28)-

According to Back (2), the moths may
lay as many as three hundred eggs apiece, al-
though one hundred-fifty is probably a fair
average. King (25), also working on the field
biology of the grain moth in Pennsylvania, ar-
rived at approximately the same conclusions.

Recently (ll), (9), (24), this insect
has been selected as the host for the large
scale production of the tiny Hymenopterous para-
site, Trichogramma minutum Piley, for use in bi—
ological control of various insect pests. The
use of the Angoumcis grain moth was recommended
by S. E. Flanders (ll). Among the advantages
evidenced by the research of Flanders and others,
(9), (24), were the multivoltine type of life
history, (4), high biotic potential, (4), and an
environmental resistance made up of factors that
could be controlled effectively by laboratory

methods.

 

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ObJsCT or sxassrisnrs

The following experiments were carried
out in the study of the development of the Angou-
mois grain moth on various foods, to determine
the effect of this factor on the partial poten-
tial*, and were designed to enhance, without dis-
tortion, variations due to food to a point where

they could be measured and compared.

STUDY OF LITEfiATUhE ON PAEAQITfi PEUJUCTION

Summary of Methods

The procedure in the utilization of the
Angoumois grain moth as a host for the production
of Trichogramma minutum is to build up a large
colony of the host, from which eggs are obtained.
These are made available for the ovioosition of

the parasites, and in this way a large colony of

*Chapman, (Chapman, Royal N., Animal Ecology
P. 186), defines the "general term 'biotic poten-
tial'" as "a Quantitative expression of the dynamic
power of the species which is pitted against the
resistance of the environment in which it lives in
its struggle for existence". He further says that
because of the "serious difficulty ...... in deter-
mining ..... this absolute biotic potential ......
There is a practical advantage in introducing the
term 'partial potential' to represent the biotic po-
tential of a species under a given set of conditions"

L.

 

 

parasites is obtained, from which liberations
are made for the control of other insect pests,
(9), (ll), (12), (13), (14), (15), (24), (26),
(27), (54), (35). This procedure has been
highly developed, the optimum temperature and
humidity for the development of the moths has
been computed, (ll), (12), (19), (20), (21),
22), and very large colonies have been pro-

duced, (14), (15), (27), (24), (34).

Factors Affecting Eificienpy

 

However, Flanders (15) in a climate
approaching the optimum for the development of
the grain moth, reports that an infestation of
Plodia interpunctella increased to become a
very serious competitor and Very materially re-
duced the efficiency of the moth colony in the
production of eggs.

List, Daniels, and Bjurman (26) re-
ported a like reduction in the efficiency of a
colony upon the use of grain contaminated with

the harvest mite (Pediculoides ventricosus).

 

Wishart (34) developed elaborate breed-
ing methods patterned after Flanders' (14), but

modified to suit a more northern climate. His

results (34 show that the production of moths
by these methods was limited by the difficulty
encountered in providing, in a manner optimum
for the development of the moths, a food supply
uncontaminated by competing colonies of insects
or mites.

The results of the experiments pre-
viously reported,(15), (26), (34), show that
the greatest difficulty in the production of an
unlimited number of Angoumois grain moths under
controlled conditions of temperature and humid-
ity is the maintenance of an optimum food supply.
In other words, when reared under laboratory con-
ditions, that part of the environmental resis-
tance caused by temperature and humidity can be
governed, being only a matter of technique. The
factors controlling the efficiency of the colony
are those concerned with the prOper food or media
furnished the moths.

The host list for the grain moth, as
reported by Back (2), and others, indicates a
possibility that under uniform conditions except
as regards food, some preference among the dif-
feren grains might be exhibited. Wheat and
corn, for this reason, may be classed as preferred
hosts, from an economic status. The data on hosts

preferred by the moths when reared in the labora-

tory is limited. Wishart (34) reports that be
abandoned the use of wheat in the production

of moths and substituted corn, because of the
resulting increase in size of moths. List (27)
tried some ten different grains and decided

that corn and wheat were the most practical.

He says that the larvae seem to prefer the wheat,
or they are able to make entry into this grain
easier, but records that the moths produced are
smaller.

Therefore, if there are inherent fac-
tors in the grain eXposed for infestation by the
grain moth which affect the partial potential,
explanation could thus be made of variations in
infestation of different grains which occur in
the field. Also, as it has been shown that the

fficiency of a colony of moths reared in the
laboratory is governed by the partial potential
which is attained,it is obvious that any factor
affecting this would be very important, multi-
plied as it is by the multivoltine ty,e of life

history.

PROCEDURE

Testing of Possible Methods

 

The first problem was that of maintain—

ing colonies of Angoumois grain moths, under
laboratory conditions, of sufficient size to
conduct the desired experiments, but not yet
so large as to require elaborate equipment.
A flexibility of the population maintained
was necessary far in excess of that required
for cosmercial laboratory production.

As has been stated, the methods of
maintaining large colonies have been developed
in detail by various experimenters, (9), (ll),
(12"), (13), (14). (15). (24), 2'6), (2'7). (34,.
A study of these methods seemed to show that
by reducing the scale ofcperations it would be
possible to develop a method of handling a small
colony by the same technique, even under experi-
mental conditions. Therefore, a detailed study
of the various methods was made, and such of
these as seemed adaptable were tested on a small
scale. These are reported, with a summary of
the original method, and the results obtained in
testing their adaptability to these experiments.

The method used by Tishart (54) was to
rear the moths in a cabinet having a tier of
trays on one side sloping at a slight angle toward
the side, so that the front of the trays were
highest and opened into the cabinet. The trays

were separated by strips of wood which left one-

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eighth of an inch between them for the escape
of the moths. FrOn the open space in fron of
the trays, moths were collected daily by means
of a vacuum hose and were transferred to ovi-
position cages.

The ovipoeition cage used was cylin—
drical and closed on the ends by 20-mesh screen,
through which the moths laid their eggs when the
cage was placed on and in a dish of cornstarch.

The eggs were separated from the starch by sift-
ing through a 60-mesh bolting cloth.

These rearing cages were obviously not
adapted to rearing small colonies of moths, but
the apparatus used in oviposition was tested. A
few moths were confined in a small cage constructed
in the same way (plate 1). Eggs were obtained in
this manner, but it was found that the cO-mesh
bolting cloth was too coarse to separate the eggs
from the starch. Single eggs readily passed through
while such difficulty was experienced in sifting the
starch through, because of the tendency to form
lumps, 'hat it was evidently impossible to use a
finer grade of cloth. This was probably due to the
high humidity in the breeding chamber, but it was
decided that any hum'dity low enough to keep the
starch from becoming lumpy would be undesirable in

the Troduction of moths. The method was discarded

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too inaccurate on the scale desired.

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Another method that evidenced a pos-
sibility was thatrecommended by Flanders (lb),
who used a cone of metal, eight feet i1 diam-
eter, with the sides sloping at an angle of
22. 5 degrees for a rearing chamber. The moths
left tlis cage through an opening in the top
six inches across, and were collected in a cage.
The cone was filled with corn, then raised one-
eighth inch to allow he moths room to crawl out
over the corn. ”oths obtained in this way were
induced to lay eggs in the customary way.

This type of breedin: cage was dupli—
cated on a very small scale (Plate 2), using a
cone of the same angle about ten inches across,

but it w» found to be very unsatisfactory. The

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moths did not emerge freely from the cone, and
upon examination it was found that the moths were
unable to use more than the surface of the grain
to any advantage. Thos emerging in the deeper
parts of the cone were unable to crawl to the sur-
face. An added disadvantage of this method was
that observation of the moths was impossible.
Flanders (12), also developed an ovi-

osition case con isting of a smooth cylinder
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capped on each end with a 20-mesh wire screen.

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Roths were COUL in ed in this and stimulated to

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a current of air
up through the cage.

This was co~tined with the method
just described (Plate 7), not so much to test
its use as a device for measuring the oviposi-
tion rate as to see if the poths would oviposit
readily this way. A cylindrical cage, covered
with an inverted cone, was filled with infe .ted
grain. The cone was smaller than the diameter
of the cylinder, so the moths could escape
around the cone through the aperture at the top.
The moths were forced to descend through the
cone to another cylinder, capped at the end with
20~mesh screen, by the action of a current of
air passing down throus h the cone, and the eggs
were laid through the screen.

“v position was readily secured in this
manner, but considerable difficulty was encoun-
tered in separating the e_gs from the dead bodies
of the moths. The dead moths could not be separ-
ated fro» the live ones continually emerging, and
accumulated in the end of the cage. The apparent
possibility of premature death of the moths under

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these conditions, as well as the in accuracy 0

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data relative to the number of eggs laid by each

-11..

moth, prevented the use of teis method in these
experiments.

Another important part of the methods
cited, (24), (15), (34), (27), is the use of an
adaptation of a vacuum cleaner to move the moths
from cage to cage. This was done by using the
current of air to pick up the moths and transport
them to the next cage, where they were removed
from the air stream by baffles. The use of this
svstem has been necessary in the cosmercial wore,
but the smallest type of machine which could do
the work would be needlessly costly and elaborate
in these experiments. In the selection of a
breeding cage this had to he considered, and a
substitute devised.

These experiments were carried out in a
cabi-et designed to facilitate the maintenance of

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constant temperature and humidity. ihis was con-
structed in the College carpenter shop.
The cabinet was built two feet deep, four

feet hiqh, and eight feet long. The frsme is pine,

two inches squa

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, nd is covered with Nu-Wood, a
material of considerable insulating value. The box
rests on one of the long narrow panels.

Access to the interior is by means of
three large doors, each two feet, eight inches wide

and four feet highgand three small doors, each set

 

 

 

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in one of the large ones. The small doors are
fitted with glass windows to allow observation.

The interior is divided into two parts
by a horizontal shelf extending almost the full
length of the box. nee is supplied by two
electric elements in one end, controlled by a
centrally located thermostat. The humidity is
governed by the installation of a nitrogen-filled
bulb of the proper size, partially submerged in a
pan of water located under the heating elements.
Circulation of air is afforded by spaCes left at
either end of the shelf, and insured t
stallation of a fan. This was necessanr because
of the length of the cabinet, which is so sreat
that it precludes efficient circulation by con-
vection currents alone, allowing condensation if
the temperature falls to the dewpoint in the
cooler portions. A temperature of 80 degrees F.
and a relative humidity of about 70 per cent was
maintained.

The requirements for a rearing cage for
this work were that it should accomodate an amount
of grain sufficient for the development of the
colony without the possibility of lack of food; that
the grain should be readily available for entrance
by the young larvae; that it allow the ready emer-

gence of the adult moths; and that observation of

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the colony be easy. It was also necessary that
the temperature and humidity maintained in the
cabinet could be readily and equally maintained

in the cages.

plates, five by seven inches, of uniform thic.
ness prompted the construction of the rearing
cage (Plate 4), which was used in this work.
The cage was built with these glass plates for
the top, bottom, front and back. They were held
in olace by the ends, which were of "Prestwood",
grooved near the edges to accomodate the ends of
the glass plates. The tOp and bottom plates were

set in to allow the from t to slide up in the

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grooves giving ccess to the interior. The glass
plates were fastened in place with linoleum cement,
which was allowed to thicken aLd then applied like
putty in the corners.

Air circulation, necessary to keep the
cage conditions equal to those in the cabinet, was
afforded through circular openings in each end,
three and one-half inches across, which were cov-
ered with 40—mesh screen. When these cases we a
set one above the other across the<abinet and the

air circulation controlled by a fan, the velocity

of the circulating air varied little if any be-

tween the cages, thus insuring equal control
of temperature and humidity.

Rhile the larvae of the Angoumois
grain moth are reported to develop normally if
there are as many as four in a single grain of
corn (16), only one or two are produced from a
single grain of wheat. Therefore, there being
about four hundred kernels of wheat in one
cubic inch, ten cubic inches should be ample

for the development of the eves

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of twenty fe-
males, or three thousand larvae (2).
In the cages just described, ten cubic
inches of grain covered the bottom of the cage
to a depth of about one-third inch, making all
the grain available to the larvae, and facili-
tating the emergence of the adults, since they
were not hindered by having to crawl through
any amount of grain to reach the surface.
The use of a cage of this type neces-

itated a system that did not require that the

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adults be handled, as there was no provi-
sion made for the use of a vacuum apparatus.

Th

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s was accomplished b' handling the indivi-

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duals in the pupal stage. This prevented dam-
age to the moths in handling, insuring their
uninterrupted natural development. The pupal

stage was readily separated from other stages

by the presence of the emergence disc on the
kernel, which is formed just before the larvae
pupate. Isolations to obtain virgin females
were also possible by this method.

Eggs of the Angoumois grain moth
were secured from the New York Agricultural
Experiment Station through the courtesy of
Derrill M. Daniel. These were reared for
several generations on corn, and a fairly
large colony developed. One 0 ge, however,
was crowded out by an infestation of the les-
ser grain borer, ghizopertha dominica, which
had been introduced in the grain. The colony
of moths on corn has continued throughout the
experiments as a stock supply.

The following experiments were set
up to determine the effect of various foods
on the development of the moths. The points
selected for investigation were effect on the
sex ratio; effect on size of moths produced;
and resultant effect on the partial potential
of the various colonies.

Colonies were started on corn, wheat,
oats, buckwheat, and beans. Later colonies
were started on sorghum and Sudan grass. These
grains were selected because they represented

the variations in size of the grains that are

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recorded as being attacked bv tie grain moth.

lized in an

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The grains were eter
autoclave at fourteen pounds pressure ior
twenty minutes to eliminate any insect or mite
infestation that might be present.

A measured amount of each grain was

put into each cage and a knovn number of grains

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orn infested with the Angoumois grain moth
vas introduced into each cage to act as an in—
oculation.

When these moths died, they were re-
moved and the nunher of eacn sex recorded.

The breeding cages were Kept under
close observation, and when the female moths
began to emerge, sufficient oupae were removed
from the cage to inoculate another cage in the
same manner as the first. The rest of the fe-
male eoths were allowed to emerge at will. At
intervals they 1-"ere anaesthetised and removed
from the cage, those from each cage being iso-
lated for study in a seoarate vial in oicklene.

When all the moths had emerged, the
rain was discarded. This helpe’3 to con-
trol the infestation of mites, which be-

comes a serious difficulty if the grain is

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used for wore than one generation. lee pos-

-17-

sibility of this method for control of mites
has also been suggested by List (27).

This procedure allowe- the continu-
ance of the experiments for as many genera-
tions as desired without varying the cage con-
ditions, and the quantity and quality of grain

could be maintained uniformly.

DATA

Method of Collection

 

After the moths from each cage were
isokted, detailed observations were made as
follows: Three hundred moths from each cage
were measured and the sex ratio determined.
This was taken as an average for the test.
Measurement of the length of the moth was
made with the wings folded, from the front of
the head to the end of the wings. This per-
mitted a more accurate comparison than weight,
as the difference in size of the bodies of
the males and females would affect the weight,
as would variations of moisture content of the
dead moths. Counts were also made of the total

number of moths emerging from each cage to de-

-13..

termine the partial potential

Results

of the colony.

The results of the observations of

the colonies to determine the variation in

size, sex ratio, and partial potential are

recorded in Tables I, II, and III:

Table I - Length of moths, (mm.)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ee- . Aver- Fe- lAver-
male Male age male Male I age
.L» lst Generation 5rd Generation
aCorn 6.455 5.775 6.115 7.044 6.405 6.724
hheat 5.111 4.719 4.915 5.980 5.682 5.780
Oats 4.960 4.707 4.854 5.509 4.971 5.215
Buckwheat 4.923 4.672 4.799 5.173 4.765 4.969
Sorghum 4.864 4.450 4.657 -- -- --
“Sudan Grass 4.24 4.226 4.255 -- -- ~-

 

 

 

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Table II - Sex Ratio

 

5rd Generation

 

 

l
! lst Generation

 

 

 

 

 

Corn 145:155 177:141
Wheat 149:151 175:165
Oats 147:155 59 : 91
Buckwheat 158:162 2 :109
Sorghum 140:160 ------
Sudan Grass 156:144 -----

 

 

 

 

Sex ratio of 2904 moths, 1:1.059

Table III - Number of Adults

Produced Per Generation.

 

lst Generation

5rd Generation

 

 

 

 

 

 

 

 

 

Corn 40.4 47.0
[Wheat 154.9 129.5
l0ats 65.7 *25.46
Buckwheat 95.9 56.66
Sorghum 85.94 --—
udan Grass 100.65 --—

 

 

 

 

DIJCUoinN 0F hLoUTTS

The results in Table III were sub-
ject to considerable experimental error, because
any mortality of the larvae during the period of
development would affect it, as would also the
production of any sterile eggs. However, it
seemed that no more quantitative method was com-
patible with the conditions of the experiment,
and the results would be indicative of what
:might be expected if the work was repeated on a
larger scale.

During the course of the experiments,
difficulty was encountered in controlling factors
which affected the experimental error. It was
found that over-sterilization of the grain caused
a high mortality of the larvae, and in the case
of beans inhibited all development. This was
also true of oats when they were twice sterilized.
All grains were affected to some extent, so steam
sterilization had to be abandoned in the control
of other insects and mites. The test on beans
was abandoned, while the test on oats was continued
by the inoculation of a new supply of grain with
moths from the stock cage. In all other cases
there was sufficient emergence from the over-

sterilized grain to allow the experiment to con-

tinue.

The difficulty encountered with
sterilized grain detracts from the value of
the results, but the observations on toe size
and sex ratio of moths produced were made on
a number of individuals sufficient to give
veracity to the results. That is, observa-
tions of size and sex ratio of moths from one
kind of grain, mad on the first generation,
then again on the third generation, if all had
been subject to the same environmental condi-
tions, would have a value equal to that obtained
by making observations on all three generations
if enough individuals were examined.

The data in Table I shows that the
females produced during the course of the ex-
periment averaged .579 mm. longer than the
males, as might be anticipated. The data, as
recorded in Table I, also shows that these re-
sults were uniform, in that in all cases the
females were slightly larger than the males.

The largest moths were produced on
corn, and the difference in size of these and
any moths produced on the other grains was
striking. The size of the moths reduced quite

regularly on the different grains, in the fol-

loving order: Corn, wheat, oats, buckwheat,
sorghum, Sudan grass. The variations in size,
except for the moths produced on corn, was not
particularly large, but the results obtained
from the third generation are in accordance
with those of the first generation. The moths
produced in the third ge - ration were slifihtly

larger than those of the first. This difference

is so unifo m as to be significant, but could

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only indica e that the ffect 0.

ed is temporar", and furth: r research would
rec; ired to settle this question.

Sufficient variation in size is caused
by different grains to justify the observation of
Wishart (34), and List (27), that judging from the
size of moths produced, corn was a better host
than wheat for the commercial productio of An-
goumois grain moth.

The determination of the sex of the
moths (Table II) from each colony was made when
they vere measured, and in this way the sex ratio
was determined for 2304 moths. The ratio com-
puted was 1: 1.053, and while the males slightly
outnumber the fame es, this figure is in accord-
ance with the sex ratio as reported by Back (2).
The sex ratio as determined for the different

colonies is subject to con.iderable varia ion.

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The variation from 1:.919 in the case of the
colony reared on corn to 1:1.185 in the case

of the colony reared on oats, is not sufficient
to effect the efficiency of a colony reared on

any of the grails tested. The variation is not

would be eliminated, as it was when the results
were averaaed to obtain the ratio given above.

The results in Tatle III are, as has

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been pointed out, subject to a larger exp ri-

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mental error than those in the previous tabl
Certain deductions are justified by the results

tabulated, however. In the case of th\ figure

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given as the third generation result of the
colony on oats, as marked by an asterisk, moths
from the stock cage were used as inoculum, ac—

tually giving the figure a value comparable to

that of the first generation. It is listed
under the third generation because the cage

conditions for the figures in that column were
alike. The other figures represent results of
observations made on the first and third gen-

erations of a colony bred for three consecutive
generations on the same grain, each cage inocu-

lated from the one previous, as has b des-

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The results show that certain of
the grains attacked by the Angoumois grain
moth are more suitable for the development of
the moth than others. However, Table III shows
that there is no reason to believe tlat any
correlation exists between the size of the grain
and the increase in population of a colony of
moths reared upon it. The results obtained from
colonies reared on corn and sheet are respect-
ively very comparable. However, three times as
many moths were produced in the wheat colony.
The reason for this is shown by a consideration
of the data of Tables I and III taken together.

Table I shows a definite correlation
between the size of the moths and the size of
the grain on which they were reared, and this
might be taken to indicate that there would be
a correlation between the size of the grain, the
size of the noths and the number of eggs laid,
particularly as the moths are reported to lay a
varyiig number of eggs, (2). Table III contra-
dicts this by showing no correlation between the
size of moths and the number of adults produced

per moth.

CULCLQQIONS

The obvious conclusion is that some

inherent factor, structural or physiological,

L

irrespective of size, governs the desirability

\

of the grain for the development of the moths.
The first generation results in Table III are

all produced by inoculating the various cages
with moths from the same cage of corn. Approx-
imately the same nimber of eggs should have

been laid in each case, yet there was a varia-
tion of nearly one hundred in the number of
adults produced. List (27) says that "The lar—
vae seem to prefer wheat to the corn,or else

they are able to make entrance into the grains
more readily". These experiments show that the
larvae were able to gain entrance into the grains
.with varying ease. No decrease in size was found
in the moths produced in the third generation on
corn as compared with the first, yet the number
of moths produced was the same. Moths from the
same colony produced three times as many when
reared on wheat, and continued to do so. Even
when reared on Sudan grass, where the inhibition
of growth as evidenced by the smaller size of

adults was greater, two and one-half times as

many were produced. Therefore, the assump-
tion is reasonable that: regardless of the

size of moths or the number of eggs laid, the
number of moths reaching maturity is dependent
on the ability of the young larvae to enter

the kernel, in which the development is governed
by the size of the grain, at least insofar as
the grains tested in these experiments are con-

cerned.

(l)

(9)

<-~<>

(6)

LITLhATUhS CITED

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U. 3. D. A. Farmers' Bulletin No.

1023, page 6, 1313.

Each, 1. 1., Angoumois drain Both.
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Eritton, V. R., Insects Injurin;
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Chapman, Fcyal R., Animal Ecology.

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Cory, ?. N., and HcConnell, l. 9.,

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U

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‘I.’

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h
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(\

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r' r‘ f“):
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CH

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r-

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(19) Headlee, T. J., Influence of Atmos-

(0

pa ric Ioisture on Insect Tetabolism.

(“h

H.

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(20)

:13
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( L)
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‘0
F3
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O
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(+-

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'V"
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(D

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"1

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~" ' rv ‘3 r , —— .3 -: ~
.nart, Gnorbe, Larte ucale iroouct_on

 

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