THE EFFECT OF LOW TEMPERATURES ON BRUCHUS 
OBTECTUS SAY, AN INSECT AFFECTING SEED 1 
By Walter Carter, 
Assistant in Animal Biology , University of Minnesota 
INTRODUCTION 
The common bean weevil, Bruchus obtectus Say, has been the sub¬ 
ject of considerable study. This is probably due to its economic 
importance and the fact that it is a fairly simple insect with which 
to work. It can be readily propagated in large numbers, ordinary 
laboratory conditions constitute a normal habitat, and there is 
freedom from complications due to periodicity in its life cycle. 
The investigation presented here covers two phases. The first is 
concerned with the general phenomenon of supercooling and freez¬ 
ing, as found in Bruchus obtectus . Working along the lines suggested 
by Bachmetjew ( 3 ) 2 , attention has been given to the individual 
freezing of larvae, pupae, and adults. The second phase deals with the 
control of this insect by means of low temperatures. It is generally 
known that temperatures such as obtain in midwinter in the Northern 
States are fatal to Bruchus obtectus . The upper limits of these 
temperatures have not previously been worked out, although data 
on the effect of continued cold storage on the bean weevil have been 
recently published (10). 
REVIEW OF LITERATURE 
Much of the earlier work on the freezing of living tissues was done 
by botanists. An admirable r6sum6 and bibliography of that work, 
together with a summary of the latest work on freezing of plant 
tissues, is given by Rosa (14). The outstanding worker on the 
subject of vital temperature in insects is Bachmetjew (1, 2). His 
first volume contains a review of the theories^ contributed up to his 
time, and then extensive data on supercooling and freezing con¬ 
sidered from the standpoint of the following influences: Rate at 
which the insect was cooled, sex and development, hunger, repeating 
the act of cooling the lymph, lymph coefficient, and season. In an 
appendix at the end of his first volume is a figure of the apparatus 
used. His second volume was published later (1907) and gives but 
little attention to the subject of vital temperature. 
Pirsch (13) reviews some of the earlier work on individual freezing 
of insect larvae, particularly with reference to bees. His citation 
includes references to the earliest users of the electrothermal method 
of taking insect temperatures. 
1 Received for publication July 18, 1924; issued September, 1925. Published with the approval of the 
director as paper No. 483 of the Journal series of the Minnesota Agricultural Experiment Station. The 
work on which this paper is based was done in the laboratories of the Division of Entomology, University 
of Minnesota, where all the apparatus mentioned herein is to be found. The writer gratefully acknowl¬ 
edges his indebtedness to the members of the staff. To Dr. R. N. Chapman, under whose immediate 
supervision the work was done, the writer is particularly indebted for constant guidance and much help¬ 
ful suggestion. 
2 Reference is made by number (italic) to “Literature cited,” p. 181. 
Journal of Agricultural Research, 
Washington. D. C. 
59837—25f-—5 
Vol. XXXI, No. 2 
July 15, 1925 
Key No. Minn-56 
(165) 
