180 
Journal of Agricultural Research 
Vol. XXXI, No. 2 
SUMMARY 
The common bean weevil, Bruchus obtectus , Say, has been used for ex¬ 
periments on supercooling and resistance to low temperature. Bach- 
met jew (2) has made the most extensive contributions to the subject 
of vital temperature in insects, and this study follows in a general 
way the lines laid down by him. While he believed that an insect’s 
temperature must be lowered again to its supercooling point after 
a rebound has taken place before death ensued, subsequent works 
show that an insect is killed if a rebound occurs. A rebound is evi¬ 
dence that heat of crystalization is given off. Crystalization of the 
lymph is believed to be responsible for the death of the insect. 
Comparing differences between individuals, it is found that pupae 
show more variation from the average trend. This is explained in 
the fact that pupae of all ages were used, and the physical properties 
of their lymph varied. 
It has been seen that larval, pupal, and adult weevils could with¬ 
stand lower temperatures when cooled uninjured than when the point 
of a thermocouple was thrust into them. Active adults withstood 
temperatures of —10° C., a temperature below the average super¬ 
cooling point, for a period of three hours. Pupae and advanced 
larvae withstood the same temperatures for seven hours. 
It has not been found possible to obtain the exact freezing point 
of Bruchus obtectus with present-day electrothermal methods. 
There is a distinct correlation between the supercooling point and 
the rebound point, but this is believed to be due to radiation from the 
insect to the air of the cooling chamber. The exact freezing point 
is actually much higher, then, than the rebound points recorded. 
The temperature-time experiments show that time is a factor in 
the resistance of Bruchus obtectus to low temperature. It is appar¬ 
ent, with freezing points as high as those of this insect must be, that 
supercooling takes place at temperatures of —10° C. or below. 
That being the case, the data imply that supercooling is possible for 
limited times only at certain temperatures. 
The relationship between supercooling and the rate at which the 
insect has cooled has been studied. There seems to be no correla¬ 
tion between these two factors. 
A condition of post-freezing development with ultimate death has 
been observed at temperatures just below the limits of resistance. 
This has been referred to in this paper as “ arrested development.” 
It manifests itself in the adults as failure to emerge, due to the loss 
of the insect’s capacity to cut its way out of the bean; pupae can 
metamorphose only to adult form in the head and thoracic regions, 
the abdomen remaining undeveloped; larvae are unable to emerge 
from the egg, or, if they do emerge, it is often through the side of 
the egg, not through the operculum. Many that emerge from the 
egg are unable to enter the bean. 
The limits of the fatal temperature-time zones have been deter¬ 
mined for four stages of Bruchus obtectus. This insect apparently 
has no capacity for hardening. 
The thermal constant, as described by Sanderson and Peairs (16), 
has not been worked out for this insect. A difference of less than 
10° F.—the difference obtaining between the temperature of the lab¬ 
oratory and a cool, dry basement at about 64°—almost doubles the 
