BIOLOGICAL ACTIVITIES OP THE VETCH BRUCHID*
Bruchus brachialis Fahraeus

By
Elvis Arnie Dickason

A THESIS

Submitted to the School for Advanced Graduate Studie
of Michigan State University of Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Entomology

August 1959
i
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Appr ov ed

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ACKNOWLEDGEMENTS

The writer wishes to express his sincere appreciation
for the help and guidance of Professor R. Hutson, Head,
Department of Entomology, Michigan State University;
Dr. H.
L. King, Professor, Department of Entomology, Michigan State
University; and Dr* G. Guyer, Associate Professor, Depart­
ment of Entomology, Michigan State University.
Sincere appreciation is also expressed to Dr* P* 0.
Ritcher, Chairman, Department of Entomology, Oregon State
College, for advice and suggestions during the course of
the investigation; and to Dr* C. H. Martin, Professor,
Department of Entomology, Oregon State College, for his
helpful criticisms and suggestions throughout the prepar­
ation of this thesis.
Acknowledgement is also extended to Mr. P. J. Spangler
and Dr. B. D. Burks, Insect Identification and Parasite
Introduction Laboratories, United States Department of Agri­
culture, for identification of insect specimens; and to Dr.
C. G. Thompson, Insect Pathology Laboratory, United States
Department of Agriculture, for examination of diseased
insects•

ii

BIOLOGICAL ACTIVITIES OF THE VETCH BRUCHID,
Bruchua brachialia Fahraeua

By

Elvis Arnie Dickason

AN ABSTRACT

Submitted to the School for Advanced Graduate Studies
of Michigan State University of Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

DOCTOR OF PHILOSOPHY

Department of Entomology

August 1959
/ /
Approved

/' I , < .. .

>' [

,/ _
l

L ■

,

ABSTRACT

A study of the biological activities of the vetch
bruchid, Bruchus brachialis Pahraeus, was conducted in
Michigan in 1956, and in Oregon in 1957 and 1956.

In ad ­

dition, an attempt was made to clarify the problem invol­
ved in the correct nomenclature for the seed beetles*

The

family name Bruchidae and generic name Bruchus are accep­
ted and defended, although strict adherence to the Inter­
national Code of Zoological Nomenclature apparently would
not permit the use of any of the commonly accepted names,
Bruchus, Mylabris, or Laria*
Adults were found to overwinter in vetch seed storage
facilities, and in the moss on oak trees*

Males entered

vetch fields approximately one month before pods appeared,
and a sex ratio of 1 : 1 was found prior to the appearance of
vetch pods.

Mating occurred from the first flowering of

vetch until males were no longer present in vetch fields.
An attempt was made, through adult dissections and cage
experiments,

to determine the biotic potential of the species.

The incubation period of the egg stage varied from
12 to 18 days.

The activities of the four larval instars

within the vetch seed are discussed.

These stadia, col­

lectively, required from i+5 to 67 days, and the pupal
stage 9 days*

Thus, from egg to adult required from 55 to
iv

91 days, with an average of 72 days.
A life table, and mortality factors, are presented for
the immature stages of the vetch bruchid.

Although several

mortality factors are presented, approximately three-fourths
of the mortality resulted from eggs being lost from the pod,
failure of first instar larvae to enter a seed, and m o r ­
tality of larvae within a seed.

This latter is to be expec­

ted, because several larvae enter a seed and only one adult
can be produced per seed.

v

TABLE OF CONTENTS

Page
Introduction,

..............................

1

Review of Literature, ..... •..............................

3

Methods and Materials....................................
Field Procedure..................•..................
Laboratory Procedure......... .............
Locations of Study
• •••
• ••••.. .c.........
Identification of Insects
.

5
5
5
7
7

Data and Discussion......... ..........
Systematic Position. ••••••••• ......
Nomenclatorial Controversy....................
Distribution..................
....*.••••.
Host Plants............
Injury to Seeds................................
Adult Activities........
Overwinter ing
.......
Spring Emergence .........
Sex Ratio.........
Mat ing
.............
Field Studies of Oviposition
......
Egg Development............................
Laboratory Studies of Oviposition............
........................
Egg Stage
Larval Stages.......
First Instar Larvae............................
Second and Third Instar Larvae........
Fourth Instar Larvae...............
Pupal Stage ............. ••••.......................
Adult Stage..............
Immature Mortality Studies
...................
Life Table for Immature Stages................
Paras ites
.............. •••••••.................

9
9
10
16
17
19
22
22
23
21425
27
28
30
38
38
39
Ij-0
lj.1
1|2
1+3
1+7
I4-8
58

Summary. •••••............ ••••••••.

59

Literature Cited.

.....

• • • •........ ••••

•••••.................

vi

62

LIST OF TABLES

Table

1.

Page

Summary of* species of vetch susceptible or
resistant to the vetch bruchid.......................

2 . A yield comparison of vetch bruchid from the
two common host species, Vicia villosa Roth,
hairy vetch, and V. dasycarpa Ten., woolypod vetch.,
...........

3.

18

20

Period in days between the first appearance
of vetch bruchids in hairy vetch fields and
the first appearance of vetch pods and
insect eggs......

21+

1+. Sex ratio computed from laboratory-reared
adults in 1957 and 1 9 5 8 ? and from fieldcollected adults during the 1 95 8 vetch bruchid
activity period....................... ........ .

25

5.

Summary of oviposition habits of female vetch
bruchids confined in cages in total darkness,
and in normal diurnal-nocturnal conditions.........

29

6 . Number of developed eggs (or oocytes) dis­
sected from female vetch bruchids during 1 9 5 8 *•••.♦•

30

7.

Number of eggs laid per female bruchid con­
fined in lamp chimney cages with vetch pods ..........

8 . Total eggs arranged by classes and total fe­
males laying normal (and non-viable) eggs in
each class.............

9.

31

3 l+

Minimum, maximum, and average length and
width measurement (in mm.) of male and female
vetch bruchids.........................................

1+1+

10. Life table and mortality factors for immature
stages of the vetch bruchid...........................

49

vii

LIST OF FIGURES

Figure

1.

2.

3*

Page

Scatter diagram showing adult size (by sexes)
of the vetch bruchid in relation to diameter
of hairy vetch seeds from which adults
emerged....... .................................. ..

1+8

Histograms showing frequency of mortality
factors for the immature stages of the vetch
bruchid on hairy vetch...........

51

Histograms showing the number of adult vetch
bruchids produced from hairy vetch seeds with
various combinations of larval entrance p o ­
sitions and numbers........

58

viii

INTRODUCTION

The vetch bruchid, Bruchus brachialis Fahraeus, is an
insect pest of Eur o p e a n •origin that was first found in the
United States in 1930 (Bridwell and Bottimer 1933)*

Since

that date it has become distributed throughout most of the
areas of the United States producing vetch seed (U.S.D.A.
1958).

It is generally believed to have been transported

from one area (or country) to another in infested vetch
seeds.

It is principally a pest of hairy vetch, Vicia

villosa Roth, although it attacks woolypod vetch, V. dasycarpa Ten., and at times other vetches and commercial lent­
ils.

In areas where it has become established, the vetch

bruchid Is usually considered one of the major insect pests
of vetch seed production.
Since the insect is so widespread in the United States,
and because of the economic importance of the insect to
vetch seed production, a study of the biological activities
of the vetch bruchid was undertaken.

The investigations

reported herein were initiated in 1958 in Michigan, and con­
cluded during 1957 and 1958 in Oregon.
During the course of these investigations major atten­
tion was given to evaluating those activities not previously
reported in detail by other workers.

As a result of this

particular research, a life table was established wherein
mortality factors were evaluated for each of the immature

2

stages, from egg to emerging adult.
A discussion of the nomenclatorial controversy over the
correct generic name (Bruchus, Mylabris, or Laria), and the
correct family name

(Bruchidae, Mylabridae, or Lariidae),

for the seed beetles is essential to an understanding of the
nomenclature accepted in this thesis.

3

REVIEW OF LITERATURE

The vetch bruchid was described as Bruchus brachialis
by Fahraeus in 1 8 3 9 (Schoenherr 1839)*

Insects, which were

later shown to be synonyms of the species, were described by
Mulsant and Rey (1858), Mulsant (1858), and Allard (1867-8):.
and generic changes for the species were first proposed by
Baudi (1886) to Mylabris, and Bedel (1889-1901) to Laria*
A controversy exists today over the choice of the proper
generic names
family name

(Bruchus, Mylabris, or Laria), and the proper

(Bruchidae, Mylabridae, or Lariidae) for the

seed beetles.

The literature concerning this controversy is

too involved to present in this review of literature, but is
discussed in the section on Ucmenclatorial Controversy*
The world distribution of the species was summarized by
Pinckney (1937) and the U. S. distribution by the United
States Department of Agriculture

(1956)*

There are two records of the vetch bruchid infesting
seeds of a plant outside of the genus V i c i a , the true vetch­
es (Zacher 193& an^ Schopp 1953)*

The common hosts for the

larval stages are Vicia villosa and V. dasycarpa, although
the susceptibility or resistance of other vetches was evalu­
ated by Bridwell and Bottimer (1933)* Pinckney (1937)*
Pinckney and Stitt (19I}.1)* Weimer and Bissel
Rockwood et al (1914-6),

Seed analysts

(1914-2) and

(Wertman 1951 and.

Pierpoint 1952) have attempted to classify bruchid injured

k
seed*
Various aspects of biological activities have been
described by several workers*

Adult overwintering was

discussed by Rockwood et al (19Aj-6) and Steinhauer (1955)*
The egg stage was described by Bridwell and Bottimer (1933 )*
Pinckney (1937 ) 9 Steinhauer (1955)# and Randolph and Gillespie
(1958)*

These writers all consider the biology or life his­

tory of the insect in a general way, and some workers consider
certain phases in detail*

Experiments to determine the bio­

tic potential of female bruchids were conducted by Steinhauer
(1935) and Randolph and Gillespie(1958).

Incubation period

of the egg stage and temperature relationships were studied
by Steinhauer (1955)*
The activities of larvae within the vetch seed have re­
ceived very little attention*

Bridwell and Bottimer (1933)

determined there were four larval instars, and Steinhauer
(1955) and Randolph and Gillespie (1958) confirmed this by
larval head capsule measurements*
The larval stages were first described by Pinckney (1937)»
and Bridwell and Bottimer (1933) have given the most complete
description of the adult stage.

These two references give

accounts of parasitic insect species reared from vetch bruchids*

5

METHODS AND MATERIALS

Field Procedure

Observations of the activities of the vetch bruchid and
its various life stages under natural conditions in hairy
vetch fields was the primary procedure followed in this study.
Adult populations were sampled and collected by sweeping
vetch plants with a standard 15-inch insect net.
All plant material was collected by carefully placing
the entire above-ground portion of the plant in individual
boxes for later sub-sampling of the desired materials.

This

procedure was necessary to prevent loss of insect eggs from
vetch pods during sampling and subsequent handling.

Samples

of vetch pods for vetch bruchid mortality studies were taken
immediately following the maturity of pods in the field, and
prior to dehiscence of the most mature pods.

Laboratory Procedure

During the 1957 season adults were maintained in cages
in an insectary.

The insects did not live under caged con­

ditions in the insectary any longer than they did under caged
conditions

(out of direct sunlight) in the laboratory.

For

this reason, all of the 1958 cage studies were conducted in
the laboratory where the insects could be kept under closer

6

and more constant observation*
Adults were confined in petri dishes, or in cages con­
structed by capping glass lamp chimneys with a double layer
of cheesecloth*

In either type of cage, the plant material

was maintained in a fresh condition by wrapping the stem with
cellucotton and forcing it into a shell vial filled with
water.

In the oviposition experiments a single pod (usually

the basal pod on the raceme) with a short section of stem
and adjacent leaf was placed in each cage with the adult.
For these experiments pods of uniform maturity were selected
and all field-laid eggs were removed.
Harvested seed samples for rearing studies of the vetch
bruchid (and parasite) were maintained in pint, or one-half
pint, cardboard cartons.
Material used for the mortality studies of the immature
stages of the vetch bruchid was collected in the field and
returned to the laboratory for examination.
amined under a microscope
of the eggs

Each pod was ex­

(i+OX) and the number and condition

(lost from pod, sterile, embryo dead, eaten by

female bruchid, or hatched), and the number of larval entrance
holes into the pod were recorded.

The seeds were harvested,

examined under a microscope, and the number and position of
larval entrance holes

(hilum or side of seed) recorded.

These seeds were kept separate in individual paper envelopes
and retained for adult emergence.
Field collected material was used in almost all dissections.

7

Early instar larvae were easily dissected from the soft im­
mature seeds.

Later instar larvae and pupae were dissected

from hardened seeds after softening the seeds for ten minutes
in boiling water.

This procedure prevented crushing the

insect stages during dissection, and permitted a study of the
pattern and extent of feeding within the hardened seeds.
All measurements were made under a dissecting microscope
(20X or I4.OX) with a callibrated micrometer disc in the eye­
piece.

Locations of Study

The 1956 study was conducted on material collected from
a hairy vetch field near East Lansing, Michigan.

The 1957

sind 1 9 5 8 phases were conducted in hairy vetch fields near
Corvallis, Oregon.

All observations and collections were

made in fields where no insecticidal control practices were
followed.

Identification of Insects

Confirmation of identification of Michigan and Oregon
collected material as Bruchus brachialis Fahraeus was made by
the Insect Identification and Parasite Introduction Laborator­
ies, U.S.D.A., Beltsville, Maryland.

This agency also iden­

tified the parasites reared from the Michigan collected bruchids

8

as Bruchobius mayri (Masi.), a member of the family Pteromalidae

(superfamily Chalcidoidea) and order Hymenoptera.

The Insect Pathology Laboratories, U.S.D.A., Beltsville,
Maryland, identified the fungus attacking some of the vetch
bruchids as an Entomopthorales•

9

DATA AND DISCUSSION
Systematic Position

The insect was originally described by Fahraeus in 1839
as Bruchus brachialis from specimens collected in France
(Schoenherr 1839, p. 79)*
The male of the species was described in two separate
publications by Mulsant in 1858 as Bruchus pallidicornis♦
The correct reference for the description is questionable.
Mulsant (1858) described the species in Opuscules Entomologiques, and Mulsant and Rey (1858) described it in Memoires de
L racadamie Imperiale des Science, Belles-Lettres et Arts de
Lyon.

There is no way of determining which publication has

priority, or why Mulsant chose to publish the same article in
two periodicals, or why Rey was included in one and not the
other.

The first workers to place B. pallidicornis in syn-

onomy cited Mulsant as the author of the species

(Allard

1867-8, Baudi 1886, Bedel 1889-1901), but some of the later
publications

(most recently, Bridwell and Bottimer 1933) cite

B. pallidicornis Mulsant and Rey.

Further,

they not only

cite Mulsant and Rey, but they also cite the Opuscules Entomologiques reference.

There was no explanation given for

Including both authors under the Opuscules Entomologiques
reference.
authors

The earliest reference found which cites both

(Mulsant and Rey) under Opuscules Entomologiques was

Hagen*s Bibliotheca Entomologica (1862, p. 562), and possibly

10

subsequent workers have cited from this well-known
publication*
Allard (1867-8, pp. 103-4) renamed Bruchus pallidicornis
Mulsant as B. ruficornis, stating the name B* pallidicornis
was occupied by a species (presumably a homonym) of Schoenherr*s.

According to Perris

(1 8 7 6 , p. 237), Allard later

acknowledged to him B. ruficornis Allard was the male of
B. brachialis Pahraeus*
Baudi (1886a, p. 16, 1886b, p. 3 9 3 )» for nomenclatural
reasons, changed the name to Mylabris brachialis Fahraeus=
ruficornis All., pallidicornis M u l s *

Baudi unexplainably

published the same article in two periodicals in the same
year; one in Italian in a Sicilian periodical (1886a) and
one in Latin in a German periodical (1886b).

According to

the Zoological Record for 1886 (Sharp 1888, p. 4)* the
Italian (Baudi 1886a) article has priority.
Bedel (1889-1901, p. 357) changed the generic name to
Laria and recognized the synonomy outlined by Baudi.

Other

than these questionable changes in the choice of generic
names, the original name of the species has not been placed
in synonomy.
In this thesis the species is recognized as Bruchus
brachialis Pahraeus, a member of the family Bruchidae and
order Coleoptera.
Nomenclatorial Controversy:
A summary of the nomenclatorial controversy is essential

11

to an understanding of the choice of nomenclature accepted
for this thesis.

There is considerable controversy, and

very little agreement, among entomologists as to the proper
generic and family names for the group of insects commonly
called seed beetles.

They have been referred to under the

family names Bruchidae, Mylabridae, or Lariidae; and accord­
ingly, under the generic names Bruchus, Mylabris, or Laria.
According to Heave's Nomenclator Zoologicus

(1939a,

1939b, and 1940) the history of these genera is as follows:
Bruchus
(as summarized by Neave, 1939a, vol. 1 , p. 491)
Geoffrey 1762, Hist. Insect Paris, I. I6 3 .
Mueller 1 7 6 4 , Fauna Ins. Fridrichsdal., XV- Col.
(Ptinid).
Linnaeus 1767, Syst. Nat. ed. 12, 604- Col. (Bruchid).
Laria
(as summarized by Neave, 1939b, vol. 2, P. 869)
Scopoli 1 7 6 3 , Ent. Carn., 21,- Col.
Schrank 1802, F. Boica, 2(2) ISO.- Lep.
Gray 1867, Ann. Mag. Nat. Hist. (3 ) 20, 276- Marnm.
Mylabris
(as summarized by Neave, 191+0, Vol. 3» P* 239)
Geoffroy 1762, Hist. Insect Paris, I, 266.
Mueller I 76 J4 , Fauna Ins. Fridriehsdal., XIV- Col
(Bruchid).
Fabricius 1775> Syst. Ent., 261- Col. (Meloid).
The name Bruchus was adopted by early workers as a r e ­
sult of the use of this generic name by Linnaeus in 1767.
According to Bridwell (1946), Bruchus was first used by
Baeckner in 1732 to describe two bruchids.

Bridwell points

out that Opinion 3 o! the International Commission of
Zoological Nomenclature states that names prior to 1738,

12

which are cited in synonomy in 1 7 5 8 or later, are not avail­
able; and that Linnaeus treating the pea weevil in the
genus Permeates in 1758 places Bruchus in synonomy and it is
no longer available.
The use of Bruchus Mueller in I 7 6 I4 was in reference to
the family Ptinidae, but this genus of spider beetles is
referred to as Ptinus at the present time.
The use of Bruchus Geoffroy in 1762 is invalid because
Geoffroy!s 1762 publication is included in the Official Index
of Rejected and Invalid Works in Zoological Nomenclature
(1958).

The publication was rejected by Opinion 2 2 8 of the

Commission because the author failed to follow principles of
binomial nomenclature

(International Commission of Zoological

Nomenclature 1954)*
The change to Mylabris was based on the 1762 publication
of Geoffroy.

As mentioned in the previous paragraph, this

publication has been declared invalid, thus invalidating the
name Mylabris Geoffroy.

Prior to this action of the Commis­

sion, some concern had been expressed over the validity of
Mylabris Geoffroy because the author did not designate a
genotype.

An exception to the origin of the use of Mylabris

in relation to seed beetles was noted.

Leng (1920, p. 3 0 l|)

uses Mylabris Mueller in his Catalogue of Coleoptera.
ever, Blackwelder (19^8, p.

How­

in the Fifth Supplement to

the Leng Catalogue of Coleoptera cites Mylabris Geoffroy.
Since Geoffroy’s 1762 genera are not available,

the

13

1763 publication of Laria by Scopoli has priority.

Some

entomologists accept Laria Scopoli and the family name
Lariidae.

However, Bridwell (1932) designated Laria

dulcamarae Scopoli=Pria dulcamarae auctorum as the genotype
for a genus of Nitidulidae.

This designation by Bridwell

has been accepted (Barber 19i+2, p. 9)> thus making Laria a
genus in the family Nitidulidae and the name is no longer
available for Bruchidae.
According to the rules of zoological nomenclature it is
doubtful if any of these generic names are available.

Brid­

well (1946) suggests the International Commission of
Zoological Nomenclature could invoke the plenary power to
suspend the rules and arbitrarily validate Bruchus Linnaeus
as of 1756.

A review of available publications of the

International Commission of Zoological Nomenclature did not
reveal any request in reference to Bruchus, Mylabris or Laria.
A ruling by the Commission offers the only valid solution to
the nomenclatorial problem.
As mentioned earlier, Bruchus and Bruchidae are the
designations chosen for this thesis.

These are the desig­

nations approved by the Entomological Society of America in
their list of approved common names of insects
32).

(1955* p. 18,

However, this list has no official standing outside of

the Entomological Society of America, and entomologists are
not obligated to follow this nomenclature unless publishing
in the Journal of Economic Entomology.

It is the designation

Ho­

used by the Insect Identification and Parasite Introduction
Laboratories, U.S.D.A., because specimens sent in for
identification during the present study were identified as
Bruchus brachialis Pahraeus*

The effect has been that the

majority of American writings in recent years have used
Bruchus and Bruchidae.

European writers have, for the most

part, considered Laria as the generic name, but Mukerji and
Chatterjee

(1951) published under Bruchus at the suggestion

of the Director, Commonwealth Institute of Entomology,
London.
Mayr, Linsley, and Usinger (1953* PP* 212-20) attach
considerable importance to usage as a criterion in acceptance
of names in their text on Methods and Principles of System­
atic Zoology.

Their attitude is that the majority of modern

systematic zoologists are quite conservative in suggesting
changes in well-known.name s.

Usage is an important factor

in nomenclature because it tends to establish stability, and
strict application of priority frequently results in greater
confusion than uniformity.
Bradley (191^6) published a paper with "Mylabridae seu
Bruchidae” in the title, with the explanation that the use
of Bruchus or Bruchidae had not been validated.
personal correspondence

However, in

(Sept. 6, 1957) Dr. Bradley suggest­

ed that Bruchus and Bruchidae could be used in this thesis
because the present attitude and ruling of the International
Commission of Zoological Nomenclature is that names of long

15

and almost universal usage should not be disturbed until
the Commission has ruled upon them.
The most recent textbook in the field of entomology
presents a nomenclature quite different from that presented
in this thesis.

Essig (1956, pp. i|82-i|87) gives the family

name as Lariidae, Lariidae Mylabridae

(Bruchidae).

Obviously

the author considers Bruchidae a synonym of Lariidae, but
the combination of Lariidae Mylabridae is unexplainable.
Although the text does not list the vetch bruchid, a generic
approach to the nomenclature of the seed beetles is present­
ed that differs from any previously found.

For example, the

pea weevil is cited as Mylabris pisorum (Linn.)(Bruchus,
Laria) and the broad bean weevil as Laria rufimanus
(Bruchus, Mylabris)♦

(Boheman)

This approach is unexplainable because

pisorum and rufimanus are congeneric species.

Hence, in

spite of this different approach in recent American lit­
erature, the use of Br uchus and Bruchidae is maintained in
this thesis for previously stated reasons.

16

Distribution

The vetch bruchid is believed to be a native European
species (Zacher 1936)♦

No recent literature was found on

world distribution, but Pinckney (1937) summarized the
world distribution, from literature and records of vetch
bruchids found in shipments of vetch, as follows: Algeria,
Asia Minor, Austria, Czechoslovakia, Prance, Germany, Italy,
Hungary, Palestine, Poland, Spain, and the United States.
Because of the ease with which this insect can be transported
in vetch seed, this known distribution is undoubtedly in­
complete.
The vetch bruchid was first found in North America in
1930 a-t Haddon Heights, New Jersey (Bridwell and Bottimer
1933)*

The insect was undoubtedly introduced in shipments

of vetch seeds from abroad.

Since this original recovery

the vetch bruchid has spread into many of the vetch growing
areas of the United States.

The following U. S. distrib­

ution, computed by the Economic Insect Survey Section
(U.S.D.A. 1956), is based on reports from state agencies and
Agriculture Research Service records: Alabama, Arkansas,
California, Connecticut, Delaware, Georgia, Idaho, Indiana,
Maryland, Michigan, Mississippi, Missouri, New Jersey, North
Carolina, Oklahoma, Oregon, Pennsylvania, South Carolina,
Tennessee, Texas, Virginia, and Washington.

17

Host Plants

Host plants, as used here, refer to those plants upon
which larval development of the vetch bruchid is completed.
Adult feeding,

if it exists, has not been reported and was

not definitely established during the present study*
Table 1 is a summary of host records compiled from
the literature and observed during the course of this study*
It is not a complete reference to the numerous accounts of
the insect attacking the two common hosts, Vicia villosa Roth
(hairy vetch) and V* dasycarpa Ten* (woolypod vetch).

There

is complete agreement between previous reports and the present
study on these two species of vetch.

The differences between

observations reported in the literature on V. pannonica
Crantz, V. atropurpurea Desf*, and V* sativa L. and the n e g ­
ative findings reported in this study are difficult to ex­
plain, because all of the species studied were in replicated
nursery-row plantings, and adults oviposited freely on pods
in rows containing the previously mentioned common hosts,
V. villosa Roth and V. dasycarpa Ten.
There are two accounts of the insect maturing in seeds
from plants in a genus other than Vicia, the true vetches.
Zacher (1936) recorded the species attacking Ervum lens L . ,
which is a synonym of Lens culinaris Medic.,
commercial lentil.

the common

Schopp (1953) published an account of

adults reared from lentil seeds

(presumed to be L. culinaris)

16

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ft
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1, Summary
Table

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of species

of vetch

susceptible

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19

in an area where vetches were delayed by late cultivation or
killed with herbicide sprays.
Although several of the vetches may be infested by the
vetch bruchid (Table 1), hairy vetch and woolypod vetch are
the most commonly and severely attacked.

Pinckney (1937)

stated that these vetches were both readily infested, but
only S O per cent of the infested seeds of woolypod vetch
produced adults in contrast to 80-90 per cent of the infest­
ed seeds of hairy vetch.
In 1957 pod samples were collected from a mixed stand
of these two species of vetch, identified as to species, and
seed harvested and saved for adult emergence

(Table 2).

In

the hairy vetch samples, 5 b Per cent of the seeds were in­
fested, and 61 per cent of these produced adults.

In the

woolypod vetch samples, 72 per cent of the seeds were infest
ed, and 3$ P©r cent produced adults.

The percentages of

adult emergences varied from those reported by Pinckney, but
the ratio of emergence for the two species was comparable.
Twice as many eggs were laid on pods of woolypod vetch
(Table 2) as on pods of hairy vetch when the species were
grown in a mixed stand.
Injury to Seeds:
Injured seeds were characterized by one or more larval
entrance holes, and when insect development was complete,
either a ring was cut on the inside of the seed coat for
adult emergence, or a cavity was exposed in the seed where

20

an adult had ©merged*

Table 2, A yield comparison of vetch bruchid from the two
common host species of vetch, Vicia villosa Roth,
hairy vetch, and V. dasycarpa Ten* woolypod vetch*
Hairy
vetch

Entry
Number of eggs laid on pods
(34 pods in sample)
(29 pods in sample)

174

Woolypod
vetch

288

Number of seeds in sample

52

65

Number of seeds with larvae

28

47

Number of larval entrance holes in seeds

47

99

Number of adults produced

17

18

Percent of infested seeds producing
adults

61

38

The effect of bruchid-infested seed on germination, and
the evaluation of inert matter in purity analysis, has been
a problem to seed analysts for several years*

Seeds from

which adults emerge are usually not viable and are consider­
ed inert matter.

Seeds having one or more larval entrance

holes, but incomplete larval development, present a problem
in evaluating injury.

Wertman (1951)* a seed analyst, con­

cluded it was not necessary to remove all infested seeds as
some seeds produced normal seedlings.

In an attempt to

classify seeds in which larval development was not complete,
Pierpoint

(1952) tested seed viability in relation to larval

21

entrance holes*

G-ermination tests showed the number of

normal sprouts decreased as entrance holes increased.

The

course traveled by the larvae after entering the seed, and
subsequent larval development, effected the resulting
damage to the seedling.

22

Adult Activities

Overwintering:
The vetch bruchid was found to overwinter as an adult
in seed storage facilities in association with harvested
seed or in moss on oak trees, which is presumed to be a
natural or innate habitat.
There are numerous accounts of adult recovery from h a r ­
vested seed.

Undoubtedly this habit of remaining in or

among harvested seed accounts for the wide distribution of
the insect.
Storage facilities in western Oregon were noted to have
adults overwintering among sacks of vetch seeds.

Further,

limited observations at seed-cleaning time in the fall of
the year suggested many adults fly free during seed process­
ing.

If these adults escape from the buildings it is pos­

sible they overwinter in natural habitats.
There are two accounts in the literature of habitats
other than those associated with harvested seed.

Rockwood

et al (19i}-6) found adults in lichens on trees, and Steinhauer
(1955) found adults under lichens and loose bark on trees,
cracks in fence posts, and in trash and weeds in fence rows.
Both of these records are from areas In Oregon where the
present study was conducted.

During this study adults were

recovered during winter months from samples of moss collected
on oak trees growing near hairy vetch fields.

Samples of

23

moss approximately one-half cubic foot by volume yielded
only one to three vetch bruchids per sample.

Adults were

collected from this habitat in 1957 and 1956 by forcing the
insects out of the samples with heat in a Berlese-type
funnel.
All of the previously mentioned habitats

(Rockwood and

Steinhauer) were sampled, as well as extensive sampling of
field debris in and adjacent to vetch fields, and no adults
were recovered*

Wo adults were found remaining in the seed

under natural conditions in surface debris in the field.
Because of the numerous negative recoveries, and low numbers
of adults found in moss on oak trees, an overwintering
habitat not detected or seed storage facilities must have
accounted for the large populations of insects that migrated
into vetch fields in the spring of the year.
Habitats, similar to those described, were sampled in
March and April of 1956 in Michigan.

No adults were re­

covered, but a possible limitation to the study was the
method of evaluating samples*

Samples were hand-separated

and inactive adults were possibly easily overlooked.
Spring Emergence:
Adults left their overwintering habitats and appeared
in vetch fields approximately one month prior to the first
appearance of pods, Table 3.

This emergence period was ap­

proximately 2 weeks prior to the appearance of recognizable
racemes, and 3 weeks prior to the development of open florets*

21*

Table 3* Period in days between the first appearance of
vetch bruchids in hairy vetch fields and the first
appearance of vetch pods and insect eggs*
First Appearance
Pods & Eggs
Adults

Period in
days

Year

Area

1956

Michigan

May 21

J une 21

31

1957

Oregon

April 29

J une lj.

36

1958

Oregon

May 5

J une 3

29

Sex Ratio:
The vetch bruchid,
However,

there was only

in general, had a 1:1 sex ratio*
a short period

during which this

ratio existed in the field during the activity period of the
insect.

Table 1+ includes a summary of 1958 male and female

recoveries in the field, as well as laboratory-reared
results for 1957 and 1958*

Steinhauer (1955) tabulated sex

ratios from mid-season on to the period of inactivity, and
these data agree with the data from mid-season to the period
of

inactivity presented in Table 4*
An approximate 1:1

ratio of sexes

was found immediately

prior to the first set of vetch pods (May 26, Table /|) under
natural conditions*

The percentage of females in the pop­

ulation increased from the period of pod appearance until
termination of insect activity.

An approximate 1:1 ratio of

sexes was obtained from laboratory reared adults in 1957 and
1958.

This ratio agreed, in general, with that found in the

25

field during mid-season of 1956, and the ratio reported for
reared adults by Pinckney (1937)*

Table i+, Sex ratio computed from laboratory-reared adults in
1957 and 1958, and from field-collected adults
during the 1956 vetch bruchid activity period*
Collection (or rearing)
Date

Male

Adults reared in the laboratory
from field-collected vetch. 1957

Percent
Female

k3

57

100
76
63
^9
23
23
28
2
9
0

0
21+
37
51
77
77
72
98
91
100

i+9

5l

Field-collected adults. 1956
May 5
May 12
May 20
May 26
J une 3
J une 10
J une 16
June 23
J une 30
July 5

Adults reared in the laboratory
from field-collected vetch. 1956

Mating:
There are two accounts of mating of the vetch bruchid
recorded in the literature.

Pinckney (1937) reported that

mating took place during the period of oviposition, and at
no other time of the year*

Steinhauer (1955) reported

mating took place before pods were formed, and at no other

26

time of the year.

The results of the present study agree,

in part only, with the above statements.
Mating during this study was noted to take place on
warm, bright days, from the first appearance of open florets
until males were no longer present in the field.

Thus, the

observations agreed with Steinhauer that mating took place
before the pods were formed, but did not cease with pod form­
ation as reported by Steinhauer.

The observations agreed

with Pinckney that mating took place during the period of
oviposition, but did not last because males were not present
the entire period.

As the numbers of males declined after

mid-season (Table Lj.) it undoubtedly altered the mating
activities.

It was not possible to observe any changes under

field conditions, and all attempts to determine mating under
laboratory conditions failed.

Adults maintained in close

contact failed to mate under caged conditions, even among
specimens collected when mating was common under field con­
ditions •
Mating then, during 1957 and 1958? extended from ap­
proximately one week before the appearance of pods until
three or four weeks after the appearance of pods, depending
on the year.

It is possible mating took place at an earlier

date in the spring because well-formed oocytes were dissected
(table 6} from females one week prior to pod appearance, and
a period of development following fertilization is usually
necessary.

However,

the observations on mating at flowering

27

time were approximate, because recognizable oocytes were not
round two weeks prior to pod formation (Table 6), which was
approximately one week prior to flowering of the vetch.
This period also fell during a time when an approximate 1:1
ratio of sexes occurred in the field (Table

Possibly

this ratio was not a requisite to mating, because field
observations did not reveal any maximum mating activity
period.
Field Studies of Oviposition:
Oviposition has been observed and described by Bridwell
and Bottimer (1933) > Pinckney (1937)5 Rockwood et al (1 9 ^ ) 5
Steinhauer (1955)5 and Randolph and Gillespie (1958).

These

accounts agreed, in general, with the observations made dur­
ing this study.

Briefly, the female assumed an immobile

position for a few seconds with the body parallel to the
longitudinal axis of the vetch pod.

The tip of the abdomen

was then curved downward, and by a rhythmic motion of the ab­
domen the egg was deposited.

The egg was covered with a vis­

cous substance, which upon drying, fastened the egg to the
surface of the pod.

Invariably the adult flew or crawled

away from the pod following oviposition, and then either re­
turned to the same pod, or another pod, for subsequent ovi­
position.

When females were confined in lamp chimney cages

in the laboratory they rarely laid more than a single egg
without leaving the pod and crawling about for 1 to 3 minutes.
A vetch pod from the time it appeared, or was even

28

visible in the drying floret, seemed apparently satisfactory
for adult oviposition*

Eggs were not found on any part of

the plant except the pods.

Vetch stems and leaves were

placed in lamp chimney cages with females, and no eggs were
deposited on the plant material.

Under confined conditions

in the laboratory eggs were sometimes deposited on the walls
of the cages, even when vetch pods were available for
oviposition.
The search by females for a suitable oviposition site
appeared to be related to some sense associated with the
labial palpi.

As the female crawled about on the plant the

palpi were kept in constant motion and erratic contact with
the surface of the plant.

A simple experiment was designed

which, by circumstantial evidence only, demonstrated the
possibility of this palpal sensory relationship or associa­
tion.

A single female was introduced into each of six cloth-

capped glass chimney cages containing vetch stems, leaves,
florets, and a single pod.

Three of the cages were immed­

iately covered with cardboard cylinders closed at the top to
insure complete darkness within the cages*
2l± hours,

At the end of

eggs were found on the vetch pods in all six cages,

and on no other plant parts (Table 5)*

Thus, in complete

darkness the females were capable of determining the correct
oviposition site.
Egg Development:
An attempt to determine egg development in 1957 failed

29

Table 5* Summary of oviposition habits of female vetch
bruchids in total darkness and in normal diurnalnocturnal conditions.
Total Eggs Deposited
Stems, Leaves,
Pods (by cages)
or Florets
I
II
III

Condition
Complete darkness

none

Ik

5

7

Diurnal-nocturnal 1/

none

0

12

3

T T

Eggs were noted, but not counted, during the first
few hours of the experiment under natural daylight*

because alcohol preserved specimens were not satisfactory
for dissection.

Female bruchids were collected in the field

in 1958 and dissected while fresh.

This procedure neces­

sarily limited the number of specimens that could be dis­
sected because of the limited time available for immediate
dissection during the period of activity of the insect.
Steinhauer

(1953) dissected females and found that they

contained as many as 20 mature eggs in the oviducts and a
great many more developing.
Considerable difficulty was encountered in determining
which eggs to include as fully-formed or fully-developed.
Strictly speaking, they were not eggs but ovarial oocytes,
and not fully developed until oviposited.

A decision was

made to score the series of larger oocytes in the lateral
oviducts, or egg chambers, as developed eggs.

There was

a distinct reduction in size between these oocytes and those
in earlier stages of development.

30

Table 6, Number of developed eggs (or oocytes) dissected
from female vetch bruchids during 1938*
Number of Eggs
Per Female

Date

Average Number Eggs
Per Gravid Female

0
0

0
0

-

Ik

k
k

9 .5
8 .0

12
0
10

ik»k

1 1 .5
1 0 .6

Average number per gravid female

10*9

May 12
May 20
May 26
J une 3 1/
J une 10
J une 16
J une 23

-

ITFirst

0
0
0
16

0
0
18

Ik

8
10
6

20

k

0
0
2:
10
10
8
12

6
28
Ik

10

pods noted in field where insects were collected*

Table 6 summarizes the results of the dissections.

The

first developed eggs were found approximately one week before
the pods appeared in vetch fields.

The average number of

developed eggs (as previously defined) per gravid female was
10*9.

These data are not a reflection of the egg laying

potential, but an indication of the number of eggs produced
by an individual female at given times throughout most of
the egg deposition period.

A later collection was made

(June 30, 1958), but there was no opportunity to complete the
dissections while material was still in a fresh state.
A series of adults was selected for collateral studies
from the population that was collected for dissection studies.
Laboratory Studies of Oviposition:
Adults selected for collateral studies were confined in
lamp chimney cages for oviposition studies

(Table 7 K

31

Table 7 >

Number of eggs laid per female bruchid confined in
lamp chimney cages with vetch pods*
Each entry
represents total number of normal appearing eggs
laid in lj.8 hours, and entries in parentheses refer
to non-viable eggs laid in a 96 hour period*

(Number of Eggs Laid with Males Present in Chimney Cages)
June 10

Av* 1/

J une 16

26
22
0(1)
4
14

2(2)
17(1}-)
0(1)
4
0(1)

16 *S

7.6

(Number of Eggs Laid Without Males Present in Chimney Cages)
J une 10
10
23
3
4
12

Av. 1/
T T

10*4

June 16

J une 23

3

28
13
22
24(1)
22
27(3)
0
8
17
34

8.14-

21.7

17
8
10
(1 )

J une 30
5
7
1
13
2
10
5
2
2
1
4.8

J uly 5
0
0
3
1

2

Average computed from number of female bruchids
laying normal appearing eggs*

A female was placed in each cage, and in two of the experi­
ments, a male was admitted with the female in one-half of
the replications.

This procedure was not possible in

subsequent experiments because males were, for the most

32

part, unavailable in the fields after mid-May.
The pods were examined under a microscope, after ex­
posure to the adults, at 21}., lj.8, 72, and 96 hours, and then
retained for several days to verify the number of normal, or
eggs which hatched.

The totals in Table 7 for normal eggs

are based on the lj.8 hour counts, and the totals for sterile
eggs are based on the 96 hour counts.

The counts for 4^

hours are given because adult mortality was very high under
artificial (caged) conditions.

Adult mortality was noted

prior to the 72 hour counts, and in one experiment

(Table 7>

June 16 experiment) all adults were dead at the 96 hour
count.

This 4$ hour limitation does not impair the vaLid-

ity of these data because 91*3 per cent of the eggs were
laid in the first 2 4 hours of all experiments, and in ap­
proximately 40 P er cent of the chimneys, adults survived the
life (96 hours) of the experiments.
The peak of oviposition occurred during the experiment
established June 2 3 , and following this date the rate of
oviposition dropped rapidly.

The peak period occurred

during a period when males were extremely scarce in the field
(Table 4).

The numbers in parentheses in Table 7 refer to

sterile, or non-viable eggs.

There were more sterile eggs

laid early in the season than at the peak of oviposition or
later in the season.

In the section on mating, the pos­

sibility was mentioned that late-season mating was not taking
place under field conditions, and could not be observed

33

under laboratory conditions*

The peak oviposition period

was also a period of low numbers of sterile eggs, as well as
a period of low male populations, and followed an extended
period (Table
ratio*

Thus,

) when males had been in an approximate 1:3
the data offered circumstantial evidence

supporting the suggestion that late-season mating may not
have been essential.
Females, which produced a single sterile egg, and no
normal eggs, did not oviposit the first 72 hours of confine­
ment.

Similarly, those which produced both normal and

sterile eggs, laid only sterile eggs after 72 hours of con­
finement *
The average number of eggs produced per female, laying
normal appearing eggs, was 10.2 in Lj.8 hours.

This figure

was surprisingly close to the average number of developed
eggs

(10.9) reported for the season from dissected individ­

uals

(Table 6).

However, this relationship existed only on

seasonal averages computed from Tables 6 and 7.

An average

comparison by dates, revealed that during the peak ovipo­
sition period twice as many eggs were laid as were noted in
dissected adults from the same population.

Possibly this

was a reflection of inadequate numbers used in both experi­
ments,
tions.

or an error in designating mature oocytes in dissec­
It was possible, because of the stress of the unfavor­

able environmental conditions, and presumed premature death
of adults, that females were stimulated to lay eggs more

3k

rapidly than normal.

The latter possibility was suggested

by the fact that unfertilized females in the oviposition
experiments laid sterile eggs after a long confinement
period.

Conversely, countless insects were killed and pre

served in various ways over the three year period and no
attempt to promiscuously discharge eggs was noted.

Table 8, Total eggs arranged by classes and total females
laying normal (and non-viable) eggs in each class.
(Data are adapted from Table 7)
Total Normal Eggs
(by classes)

Total
Females
6
16
6
4

none
1-5
6-10
11-15
1 6 -2 0
21-25
2 6 -3 0
31-35

k2

5
2
1

16
10
10
13
5
2

3

-

k

non-viable
(only egg laid)
non-viable
(plus normal eggs laid)

Percent of Total Ovi­
positing in Each Class

5

Table 8 is a tabulation of oviposition, arranged by
classes, to illustrate frequency of total eggs per oviposit­
ing female.

The grouping by classes simplified the present­

ation of data, and has no known biological significance.
The table illustrates the high percentage of females ovi­
positing in the 1-5 egg class

(1|2 per cent), and the

35

distribution of entries in the four subsequent classes,
which accounted for almost 50 per cent of the total of no r ­
mal eggs deposited.
Steinhauer (1955) caged adults and reported the number
of eggs deposited to range from 0 to 6 2 ,

with an average of

2 4 per adult, during a period of 3 to 13 days *

In a recent paper Randolph and Gillespie (1958) re­
ported the average number of eggs laid per female as 8 . 5
per day when caged in the field, and 5 per day when caged
in the laboratory.
adults

The results obtained for field caged

(8.5 per day) by Randolph and Gillespie approached

the results

(1 0 . 2 per i|8 hours with 91.3 P©r cent of 9 . 2

eggs laid in the first 2l\. hours) in laboratory studies
during this study, Table 7*

In comparing laboratory results

there were considerable differences in the number of eggs
laid per day in their experiments and the present study.
Although the workers did not describe their procedure,
they mention eggs present on the walls of vials that were
used for isolating female bruchids.

Thus, it is possible

the oviposition of vial-confined adults cannot be compared
to the lamp chimney technique employed in the present study
because of the obviously great differences inthe physical
factors of the two environments.
It was not possible, as a result of the data collected
during this study, to resolve a valid egg-laying potential
for the vetch bruchid.

It would be possible, however, by

36

extrapolation of the presented data to compute a hypo­
thetical egg-laying potential for the insect.

This is of

questionable value because it would assume that an individ­
ual would live and oviposit during the entire season in an
uninhibited environment.

If computed from results presented

in Tables 3> U* and 7, it would not consider the possible
necessity of a recovery period following oviposition and
prior to subsequent oviposition.

Egg Stage

The egg of the vetch bruchid has been described in
detail by Bridwell and Bottimer (1933)> Pinckney (1937)>
Steinhauer (1955)* and Randolph and Gillespie (1958)Observations on the descriptive phase of the egg stage
agreed with published accounts.

The freshly laid egg was

pale yellow, the chorion was delicately sculptured with a
network of fine, irregular reticulations,

and ranged from

0.6 mm. to 0.7 mm* in length and from 0.2 to 0.25 nim. in
width.

About 72 hours after oviposition two dark trans­

verse bands appeared visible through the chorion, and as
the embryo developed, these bands lost their identity and
the head of the developing embryo appeared as a darkened
area through the chorion.

As pigmentation continued the

head became clearly visible through the semitransparent
chorion.

37

The incubation period was 18 days under field con­
ditions in Oregon in 1957 (average temperature, 60° P.),
and 12 days under field conditions in Oregon in 1956
(average temperature, 6l.j_j° F.).

Both of these accounts

refer to the duration of time required for the first laid
eggs to hatch,

incubation time for eggs subsequently laid

was not satisfactorily determined.

In spite of difficulties

in scoring hatching under field conditions, it appeared
quite definite that no eggs hatched in less than ten days
after oviposition.

This was considerably different than

the i|“5 day incubation period reported from Texas

(Randolph

and Gillespie 1958), or the eight day average reported from
North Carolina (Pinckney 1937)*
The most extensive studies and experiments on incubation
were made in Oregon by Steinhauer (1955)•

This worker con­

ducted incubation trials early and late in the season, and
found that eggs deposited early in the season hatched in
(average) lii-.6 days, and eggs deposited late in the season
hatched in (average) 11.9 days.

Upon plotting incubation

period against mean temperatures he obtained a straight line
relationship, suggesting that increased temperatures reduced
the incubation period.

These durations agreed closely with

the results obtained during the present study.

Possibly the

temperature relationship to the incubation period is an ex­
planation, or a factor in an explanation, for the wide
differences in incubation period reported in the literature.

38

Larval Stages

Bridwell and Bottimer (1933) were the first to estab­
lish that there were four larval instars in the developmental
period of the vetch bruchid*

Steinhauer (1955) and Randolph

and Gillespie (1956) confirmed the number of instars by head
capsule measurements of the various stadia*

During this

study the average width of the head capsule of the four lar­
val instars was found to agree within 0.02 mm. of published
accounts

(1= 0 . 1 3 mm., 11= 0.25 mm. , 111= 0.1*2 mm., IV=

0.62 mm. )•
The activities of larvae are mentioned by Bridwell and
Bottimer (1933)* Pinckney (1937)* Steinhauer (1955)* and
Randolph and Gillespie (1956).

Discussions on activities

are limited to statements, in effect,

that larvae completed

development by feeding within a vetch seed, and that the last
instar larva cuts a cap in the seed prior to pupation to
permit the escape of the adult.
is mentioned in two articles.

Duration of larval stages
Pinckney (1937) found the

four instars required two weeks for development in North
Carolina, but no mention was made of the duration of indi­
vidual stadia.

Steinhauer (1955)* working in western Oregon,

found each stadia to average about two weeks in duration.
The writer conducted a series of dissections of fieldcollected vetch seeds in 1957 and 1956 in an attempt to
extend the known data on larval activities and duration.

39

Any attempt to investigate or observe individual larvae
(such as opening a pod in the case of first instar larvae,
or dissecting a seed in the case of second, third, or
fourth instar larvae) killed the individual, or individuals,
thus exposed and terminated the observation.

As a result,

this discussion is necessarily based on the population
under observation at any one time.

Inference related and

interpreted from observations, such as these, can be subject
to large errors.
First Instar Larvae:
It was found that the first instar larva chewed its way
through the ventral surface of the chorion and into the
valve of the pod.

Thus, the larva did not leave the egg to

the outside, but remained protected by the egg as it bored
through the valve into the pod.

Based on the first appear­

ance of recognizable frass in the egg shell, until larval
entrance into the pod, the period from eclosion until pod
entry was at least three days.
Once inside the pod the larvae crawled about, ap­
parently at random, before gaining entry into a seed.
Larvae appeared capable of entering at any point on a seed,
including the hilum.

Observations indicated that a point

of purchase was necessary for seed entrance.

That is,

larvae appeared to enter where seeds were adjacent to each
other, or where seeds touched the walls of the valve.
Those which entered through the hilum mined in the

lj-0

funiculus, which afforded an excellent point of purchase for
boring into the seed.
The period from boring through the valve until seed en­
trance varied from overnight (less than 12 hours) to 2 or 3
days.

Larvae in premature pods, collected in the field and

maintained under laboratory conditions, mined in the inner
surface of the valve.

This type of mining was never obser­

ved under field conditions.
Following entrance into the seed, the first instar
larvae either molted and immediately tunneled into the seed,
or mined from 1 to 3 days between the seed coat and endo­
sperm.

These mines were never over 1 mm. in length.

The

duration of the first larval instar, based on these obser­
vations, ranged from 1| to 9 days.

However, since some

larvae did not mine in the seed before molting, it is pos­
sible they had a longer free-living period in the pod.
This conclusion, if valid, would make the duration of the
first stadia range from 7 to 9 days.
Second and Third Instar Larvae:
The study of activities of subsequent instars had to be
based on inference because if a seed was opened the larva or
larvae within soon died.

All attempts to rear larvae in any

habitat other than entire seeds failed.

Seeds were easily

dissected in early stages of their development, but after
they had hardened it was necessary to immerse them in
boiling water for at least ten minutes to soften them enough

41

for dissection*
Second instar larvae bored towards the center of the
seed, almost at right angles to the seed wall.

If larvae

entered through the hilum they usually remained oriented in
the area between the cotyledons and fed on both cotyledons.
If the larvae entered from any other point on the seed,

they

fed a short distance inwards and turned to feed parallel to
the seed wall, or fed in the area where the cotyledons were
contiguous•
Third instar larvae continued feeding in the central
portion of the seed.'

The feeding during this stadia was

more general and a central cavity was formed in the seed.
This latter pattern of feeding suggested that the larvae no
longer burrowed or tunneled, but fed on the perimeter of the
central cavity.
The collective duration of second and third instar
larvae was 25 days.

Difficulty was encountered in deter­

mining the duration of individual stadia.

The second stadia

apparently exceeded 13 days, and it appeared that the third
stadia ranged from 12 to 15 days.
Fourth Instar Larvae:
Fourth instar larvae continued to enlarge the central
cavity.

This stadia ranged from 13 to 23 days, with an

average duration of 18 days.

When ready to pupate, larvae

cemented frass around the wall of the cavity to form a
pupal cell.

They also cut a circular groove or ring in the

k2

seed coat which produced the "cap” or "lid" by which the
adult escaped from the seed.

This groove was apparent

externally as a narrow light green ring.

Occasionally a

small circular area in the center of the cap was thinned
out, which gave the appearance of a light green circular
area, surrounded by a dark green and a light green con­
centric rings.

Based on an examination of 150 seeds, the

cap was cut at a point along the line of cleavage of the
cotyledons

(other than in the hilum) in 80 seeds; and at a

point other than the line of cleavage (or hilum)
maining 70 seeds.

in the re­

The cap was never cut through the hilum

or around an existing larval entrance hole.
Prior to pupation, fourth instar larvae went through
a transformation stage.

The abdomen became greatly dis­

tended and it gradually assumed pupal characters.

The

initiation of these late-stadia characters was not clear-cut.
There were recognizable, gradual changes, and then suddenly
an apparent assumption of pupal characters in a period of
less than l±8 hours.

Pupal Stage

The pupal stage lasted 9 days.

The fourth instar

larval exuviae remained as a small disk, or pad, on the
ventor of pupae throughout pupation.

The newly formed adult

body was teneral for approximately one day, and then hardened

43

and assumed adult colors.

Adult Stage

Newly matured adults forced open the previously de­
scribed cap or lid, which the fourth instar larvae had cut
in the seeds, and then remained quiescent within the seed
or left the seed.

Frequently adults left the seed for a

short time, and then returned to the same seed, or another
seed, and remained quiescent.

Adults were unable to escape

from the pod unless the valves dehisced.
The total time for development from egg to adult ranged
from 55 to 91 days, with an average duration of 72 days.
Steinhauer (1955) worked on the vetch bruchid in Oregon and
found the duration to be 67 to 75-plus days.
Gillespie

Randolph and

(1958) found the development period to range from

22 to 43 days in Texas, and Bridwell and Bottimer (1933)
found the development period to be 30-plus days in New
Jersey.

The exact developmental period for the material

collected in 1958 in Michigan was not satisfactorily de­
termined, except that the minimum duration was in excess of
41

days.
Previous workers noted the great range in size of vetch

bruchids.

Bridwell and Bottimer (1933) gave the adult range

in length as 2.0 to 3.5 mm., and Pinckney (1937) gave the
length as 3.0 to 3*5 mm., however neither paper reported

■which, sex was measured.

Steinhauer (1955) gave the range

in length of the female as 2 . 5

to 3 * 5 mm*, and stated the

male was similar to the female.

Randolph and Gillespie

(195$) gave the following average sizes: male, length 2.92
mm., width 1 . 8 I|. mm*; female, length 3 * 0 1 mm., width 1.90 mm.
During the present study a sample of 36 males and 37
females was measured (Table 9)*

Although there was con­

siderable variation in size, the average fell within meas­
urements reported in previous accounts.

The female was

larger than the male in all measurements.

Table 9# Minimum, maximum, and average length and width
measurements (in mm.) of male and female vetch
bruchids•
(in m m . )
Measurement

Male

Female

Minimum length
Maximum length
AVERAGE LENGTH

2.3
3*5
3*02

2 .8
3*7
3*15

Minimum width
Maximum width
AVERAGE WIDTH

1*3
2.0
1.78

1 .6
2 .1
1.9

Bridwell and Bottimer (1933) noted that small, poorly
developed seeds, produced small adults.

Similar observations

were made during this study, and Figure 1 is a scatter dia­
gram of adult length (by sexes) and maximum diameter meas­
urements of hairy vetch seeds from which the adults emerged.

b5

These data were not calculated for regression coefficience
because of the low population involved.

However, the

measurements revealed that adult size was related to the
size of seed in which development took place.

There ap­

peared to be a closer relationship between seed size and
adult size among the males than among the females

(Figure 1).

The males tended to fall along a straight line from lower
left to upper right of the scatter diagram, whereas females
produced from seeds in excess of 3*4* rrB31* tended to be
grouped along a line perpendicular to adult length.

The re­

lationship of increased insect size to increased seed size
was reversed in large seeds, and smaller adults of both
sexes were produced from seeds in excess of 4..2 mm.

1+6

4.5
4.4H

00#

0
•
• 00
• • o ••
• o#
o •
• •
••
o •

4.3
42.

4.1 *

0= MALE
• = FEMALE

4.03.93.83.73.6'

•
o

38'

• 000## o •

3.4-

O

38i

•

00 0

o# o

o# •
0 o

00

• ••

o#
o •
3.2
0 0 0
3.1 o
3.02.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7
A D U L T LENG T H (MM.)

Figure 1 , Scatter diagram showing adult size (by sexes) of
the vetch bruchid in relation to diameter of hairy
vetch seeds from which adults emerged*

47

Immature Mortality Studies

Tile literature in all fields of biology contains teliological-like statements concerning the wasteful or haphazard
methods nature has in perpetuating herself.

The oviposition

habits of the vetch bruchid appeared, by man-made observa­
tional standards, to be very wasteful and inconsistent with
the presumably advanced type of host relationship previously
described.

As a result of this observation, a study of mor­

tality and mortality factors of the immature stages was
conducted in 1957 a n d 1958.

Only the 1958 data are present­

ed because of refinements in methods

adapted from knowledge

gained In the initial (1957) study.
There are previous accounts of mortality observations
on the vetch bruchid reported in the literature.

In vetch

pods caged in the field, Pinckney (1937) obtained a 75*7 per
cent hatch of bruchid eggs

(53 out of 70 eggs), and a 70 per

cent hatch in the laboratory (58 out

of 80 eggs).

(1955) reported an 82 per cent hatch

in laboratory rearing

trials

(271 out of 331 eggs).

Steinhauer

Steinhauer also noted that

under field conditions as high as 50 per cent of the eggs on
some pods dried up a few days after being laid.
Pinckney (1937) noted that some larvae died within the
pod before finding a seed, or while effecting entrance into
the seed.

He commented on more than one larval entry per

seed, and stated that generally the stronger and more

1+8

aggressive larvae destroyed the weaker specimens when they
met in a seed*

Bridwell and Bottimer (1933) noted up to

7 larval entries per seed*

Randolph and Gillespie (195 &)

reported that out of 297 larvae removed from seeds, in only
a few instances was there more than one per seed, and they
were not developed beyond the second instar*

All of these

accounts agreed with the present study in that only one
adult was produced per seed*
Life Table for Immature Stages:
Data for life tables of natural populations are ex­
tremely difficult to obtain.

Deevey (19ij-7), in a review of

life tables as a tool in the study of natural populations,
outlined various methods of obtaining life table data.

The

procedure followed in this study, direct observations of
the number of survivors out of a definite initial population,
was considered by Deevey to be the most valid approach*
Table 10 is a summary of immature mortality factors
and numbers dying in the finite population under observa­
tion.

It was not possible to measure mortality after adult

emergence from the seed, but It was not necessary to meas­
ure all factors in order to obtain a useful picture of the
delimited population mortality.

Some limits, for practical

experimental procedure, had to be imposed*
In this study approximately one-third of the total
mortality was caused by eggs dropping off the pods.
data collected showed that 29.7 per cent of the eggs

The

Table

10, Life table and mortality factors for immature stages of the vetch
bruchid*
(Based on 4,333 Qggs on 188 pods and 359 out of 620
seeds infested.)

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50

(Table 10) or 1,266 eggs out of the initial population of
4*333 were lost from the pod.

Eggs which drop from the pod

could have exhibited any of the mortality factors given in
Table 10,

It was impossible to designate these factors

after the eggs were lost, but fortunately it was not essen­
tial to these data.

The dropping of eggs from pods, re­

gardless of their condition, was the major mortality factor.
Some of the factors found to cause eggs to drop from
the pod, were adults brushing or knocking the eggs off the
pod as they crawled about during oviposition, and some eggs
appeared to be weakly cemented to the pod and fell off
shortly after oviposition.

Possibly a great many were

brushed off by any factor that brought about plant movement
and plant contact in the field.
Identification of this mortality factor was based on
examinations of field collected pods under binocular (1|0X)
magnification.

The presence of a slightly chewed area,

sometimes darkened, or remnants of the dried and somewhat
shiny adhesive substance easily indicated a lost egg.

If

there was a completed larval entrance hole in the valve,
the egg was not scored as lost from the pod because this
type of loss was not a mortality factor.

It indicated a

larva had successfully entered the pod before the egg was
los t •
Figure 2, B, indicates the frequency at which this mo r ­
tality factor occurred.

The importance of this factor was

Figure

2, Histogram showing frequency of mortality factors for the
immature stages of the vetch bruchid in hairy vetch.

51

52

established, since only 3 out of 1 8 8 pods retained all eggs.
Fro m 3 to 9 eggs were lost from 135 out of the 1 8 8 pods in
the sample (Figure 2, B), or by comparison to histogram A
(Figure 2), approximately one-third of the total eggs in
the samples.
Eggs with dead embryos accounted for 8*3 per cent of
the mortality, or 370 of the initial 4*333 eggs had dead
embryos

(Table 10).

determined.

The cause of embryo mortality was not

Possibly it was a result of some physical

factor in the environment, or a genetic feature of the
particular eggs.

This factor occurred in small numbers

among approximately two-thirds of the pods sampled
(Figure 2, D).
Sterile, or non-viable, eggs accounted for a 4 per
cent mortality,

or 173 eggs out of the initial 4*333*

frequency of sterile eggs was low (Figure 2, E) in contrast
to the previously mentioned factors.

In these eggs no

embryonic development took place, and the eggs were empty
and transparent.
Individual females eating their eggs following ovi­
position accounted for 1.7 per cent of the initial mortal­
ity.
1958.

This phenomenon was not observed until mid-season
However, eggs typical of those fed on were noted

throughout the study in Michigan and Oregon, but it was
earlier assumed to be the result of unaccountable predatory
insects•

53

Eggs laid b y certain females were immediately eaten
by the ovipositing insect.

In caged experiments, ij. females

that had been noted by observation to eat their eggs, were
confined in petri dishes, and they ate 3 I4. out of the J| 3 eggs
deposited in 2 I4. hours.

The fate of uneaten eggs, deposited

by females that ate most of their eggs, was not determined,
but in laboratory experiments the uneaten eggs did not
hatch*

There was no explanation for this activity, although

some insects are known to require a protein feeding to de­
velop their ovaries, and frequently eat their own eggs.
The 2,i|-30 eggs that survived the above mortality
factors

(Table 10) hatched and the larvae entered through

the valves Into the interior of the pod.

Only two pods

were without larval entrances, and the majority of pods had
many more entrances than seeds (average of 3 * 3 seeds per
pod) as illustrated in histogram P (Figure 2).
The initial occurrence of larval mortality within the
pod was due to failure of larvae to gain entrance into a
seed.

This accounted for a 21.7 per cent mortality of the

initial population, and a 3 I+ .6 per cent mortality of the
larval population (Table 10).

It appeared, by observation

of dissected material, that the principle cause of the
mortality was failure of larvae to find a point of purchase
in order to enter the seed.

This type of mortality was

confined to the early stadia of first instar larvae.
Failure to mature within the seed accounted for a 2 3 . 5

5b

per cent mortality of the initial population, or a I4.I•9
per cent mortality of the total larval population.
Destruction of one individual by another (as mentioned
by Pinckney 1937) was found in only one seed; and then both
larvae

(third instar) were dead in a common central cavity.

However, in other dissections, larvae (second and third
instar) were alive in a central cavity and apparently had
not attacked one another.

Until the tunnels or burrows

in the seed opened into a central cavity, there was never
an instance of tunnels contacting each other.

In spite of

this lack of physical contact by first and second instar
larvae, many of them were dead in their isolated burrows.
The cause of this mortality was not determined.
cumstantial evidence,

By cir­

it appeared that the presence of

older larvae within the seed caused the death of younger
individuals.

Possibly they altered the micro-environment

or secreted a toxin of some type.

Late entry into a seed,

when the seed was mature and quite hard, was not the cause
of mortality.

This was easily observed in seeds in which

there were no early-season entries.

And yet, in similar

seeds, all late entering larvae soon died within their
tunnels if a later and more mature instar larva or larvae
(third instar for certain, and possibly late second instar)
were feeding in a central cavity.

This association might

have accounted for some of the mortality within a seed,
particularly of the early instars.

55

There was very little difference in success of larvae
between those which entered the seed through the hilum, or
those which entered along the side of the seed*

Figure 3

is a series of histograms showing these relationships*

It

was significant that there was a 25 per cent mortality
when a single larva entered a seed through the side of the
seed (Figure 3> A) t and was the only individual in the seed;
and there was a 2 8 per cent mortality when a single in­
dividual entered the seed through the hilum (Figure 3, B),
and was the only individual in the seed*
surprisingly,

Thus, quite

there was an approximate 25 per cent mortality

of single individuals within a seed, presumably developing
free of larval competition*

Although this observation, or

the possibility of environmental toxicity, did not explain
the cause of larval mortality within a seed, they did
confirm the observation that the suspected cannibalism
was not a significant factor.
There must have existed a large group of innately
"weak*1 individuals in the larval populations*

This was

suggested because the higher the larval population within
a seed, the greater the chances were for an adult to be
produced from the seed (Figure 3> A, B, C, D, F)*
The 155 seeds which did not produce an adult during
the experiment were dissected.

Six of the seeds contained

a dead prepupa or late fourth instar larva, and four of the
seeds contained a dead adult (Table 10).

Combined,

these

56

NO E N T R I E S

ilii.

A

I 00
hi l

90 4

eo

a

m

ENTRIES

7 06060
40 -

■

NUMBER

OF

SEEDS

□

NUMBER

OF

ADULTS

3 020-

IO

0

0
NUMBER

1
OF

r

1- - - - - 1—

2

3
LARVAL

—
4

i- - - - :- - - - - r ~
6

ENTRIES

(EXCLUSIVE

OF

6
ON

7
SIDE

i- - - - - 1
8

OF

SEED

HI LUM)

Figure 3, Histograms showing the number of adult vetch
bruchids produced from hairy vetch seeds with
various combinations of larval entrance p o ­
sitions and numbers*

57

two mortality factors accounted for less than 1.0 per cent
of the total mortality.
None of the previously mentioned dissected seeds con­
tained a dead pupa.

It appeared that any larva that

pupated successfully transformed into an adult.
The total mortality of 89.1 per cent (Table 10) was
only slightly greater than a calculated mortality would
have been for the conditions of the experiment.

Based on

the 4,333 ©ggs in the initial count, and a total of 620
seeds in the sample, a calculated mortality would have been
85.7 per cent.

Thus, under the conditions of the experiment,

approximately one adult was produced for each ten eggs de­
posited on the pods of hairy vetch.
The mortality rate of 89*1 per cent in 1958 (Table 10)
was similar to the total mortality obtained in a prelim­
inary study in 1957.

At that time a 91 per cent mortality

was obtained, but it was undoubtedly higher than that
because a different

(and not as sensitive) procedure was

used in scoring eggs lost from the pod.
No parasitic insects were reared from any of the
material collected in Oregon.
been recovered,

However, had parasites

they would have comprised an additional

Immature mortality factor.

58

Parasites

Material collected in Michigan in 195& was infested
with a chalcid parasite, Bruchobius mayri (Masi.).

Spec­

imens were identified by Dr. R. D. Burk, Insect Identi­
fication Laboratories, U.S.D.A., Beltsville, Maryland.
Bridwell and Bottimer (1933) reared six species of
chalcid parasites from vetch in New Jersey, and Pinckney
(1937) reared five species from vetch in North Carolina,
including Bruchobius mayri (Masi.).
In a shipment of hairy vetch pods and seeds from
Michigan in 1957 many fungus-covered adults were found
dead within the seeds.
lid or cap on the seed.

The adults had failed to open the
Dr. C. G. Thompson, Insect Path­

ologist, Insect Pathology Laboratory, U.S.D.A., Belts­
ville, Maryland, identified the fungus as Entomopthorales,
but could not identify it further because the specimens
were so overrun with saprophytic fungi.

No apparent fungus-

killed bruchids were found in Michigan material examined
in 1958*

59

SUMMARY

The results of field and laboratory studies in Michigan
during 1956 and in Oregon during 1957 and 1958 with the
vetch bruchid, Bruchus brachialis Pahraeus, on hairy vetch
may be summarized as follows:
The insect was reared from infested seeds of Vicia
villosa Roth and V. das year pa Ten., but it was not found
to infest seeds of V. pannonica Crantz, V. atropurpurea
Desf., or V. sativa L*

A higher percentage of infested

hairy vetch seeds produced adults than infested woolypod
vetch seeds.
The vetch bruchid was found to overwinter as an adult
in storage facilities in association with harvested seed,
or in moss on oak trees adjacent to hairy vetch fields.
Males left their overwintering habitats and appeared in
vetch fields approximately one month prior to the formation
of pods.

A sex ratio of 1:1 was found immediately prior

to the appearance of the first pods in hairy vetch fields.
Mating was observed in the field from the first ap­
pearance of florets until males were no longer present in
the field.
conditions.

The insect never mated under caged (laboratory)
The average number of developed eggs

(or de­

veloped oocytes) dissected per gravid female was 10.9*
Females confined in lamp chimney cages in the laboratory

60

laid an average of 10*2 eggs per lj.8 hours, but so much dif­
ficulty was encountered maintaining females in confinement,
and the data were so varied,

it was not possible to determine

a valid egg-laying potential for the species.
The incubation period of the egg stage varied from 12
to 1 8 days, depending on the season, for the earliest depos­
ited eggs.

It was found that the developing embryo required

approximately 3 days from eclosion until entry into the pod.
The first instar larva was found to spend from less
than 12 hours to 3 hays in order to gain a point of purchase
and enter a seed.

The seed was entered at any point, in­

cluding the hilum.

The first instar larval stadia lasted

from 7 to 9 days•
The second and third instar (collectively) lasted ap­
proximately 25 days.

The fourth instar larva had an average

duration of 18 days.

During these three stadia a large

chamber was eaten out in the center of the seed, and the
fourth instar larva cut a circular ring in the seed which
afforded an escape lid for the adult.
The pupal stage lasted approximately 9 days.

Thus,

from egg to adult required a period ranging from 55 to 91
days, with an average duration of 72 days*

The newly emer­

ged adult either left the seed or remained quiescent within
the seed.
associated,

The size of the emerging adult of either sex was
up to a maximum size, with the size of the seed

in which it developed.

61

A chalcid parasite, Bruchobius mayri (Masi.), was
reared from Michigan material collected in 1956.

No para­

sites were reared from Oregon collected material.
Life table data were collected on immature stages, from
egg to emerging adult, with an initial population of 4,333
eggs producing 461 adults.

Thus, in the 1958 studies ap­

proximately one adult was produced for each ten eggs laid.
Mortality in the egg stage resulted from: loss of egg from
pod (29*7 pep cent), embryo dead in the egg (8.5 per cent),
sterile, or non-viable eggs

(4*0 per cent), and female

bruchids eating their own eggs (1.7 per cent).

21.7 per cent

of the larvae failed to find a point of purchase and enter
a seed.

2 3 * 5 per cent of the larvae died within the seed.

Mortality within a seed was expected because more than one
larvae entered a seed, and only one adult was produced per
seed.

The factors responsible for mortality within a seed

were not satisfactorily determined.

There was no mortality

in the pupal stage, and less than 1 per cent mortality in
failure of prepupa to pupate or adults to escape from the
seed.

6a

L IT E R A T U R E

C IT E D

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63

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64

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65

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