July 15,1925 Effect of Low Temperatures on Bruchus obtectus 
175 
Larson and Simmons {10) conducted an extensive series of experi¬ 
ments with commercial cold-storage conditions. They used three 
temperatures, 36, 32, and 20° F. Perfect control of the weevil in¬ 
festation was obtained with 56 days’ exposure to 32°. Loss of re¬ 
productive power was noted after exposure for 22 days or longer. 
Satisfactory control was obtained with 66 days’ exposure at 36°. 
Unemerged adults were found to be the most resistant, pupae next, 
and larvae the least resistant. No experiments with eggs of Bruchus 
obtectus are recorded. It is suggested that weevils put into cold 
storage from lower temperatures obtaining in February could resist 
longer than those put in at the higher temperatures of November. 
De Ong {8) used several species of insects in a study of cold-storage 
control. His findings are interesting here in that he reports that 
mature larvae were more resistant than any other stage studied. 
He also doubts the mortality of the egg at temperatures fatal to other 
more advanced stages. 
METHOD 
In these studies a constant-temperature cabinet was used with 
which it was possible to keep temperatures within less than 1° of the 
desired temperature for long periods. Glass vials containing beans 
infested with the several stages of weevil were placed in this cabinet 
and subjected to the temperatures as stated in the tables for the 
several periods. 
A difficulty experienced in dealing with the immature stages of 
bean weevil infestation is that of knowing just which stage was being 
dealt with when the cavity first became visible from the outside of the 
bean. The cavity may contain either a pupa, prepupa, or even a 
larva. Another difficulty is in the fact that when beans are heavily 
infested with weevils in all stages the last larvae to enter the bean 
often perish through lack of food. This act rather tends to stress 
a larval mortality which may not be due to the conditions of the 
experiment. In order to avoid this colonies of known data were used 
for getting definite data on larvae. The most complete data, how¬ 
ever, have been obtained from the use of beans where the weevils 
were showing black through the bean—in all cases unemerged adults— 
and those where the work of the weevil was visible from the outside, 
but the weevils were still cream-colored. The majority of these 
were early pupae, but larvae were sometimes found within these lig|it- 
colored cells. 
EFFECT OF FATAL TEMPERATURE ON THE APPEARANCE OF THE SEVERAL STAGES. 
Eggs shrivel up and the contents become clear. It is not always 
easy to ascertain whether the eggs were killed by the temperature or 
were simply infertile. For this reason total mortality and hatching 
have been the criteria used. Pupae when fatally affected turn rotten 
and brown. The same i^ true of larvae. With unemerged adults 
later emergence was the criterion, and for active adults recovery. 
An interesting condition met with was that called, for want of a 
better name, “ arrested development.” In this condition develop¬ 
ment proceeds for some time after return to normal temperatures, 
but the insect fails to mature and usually fails to complete the stage 
in which it was at the time of freezing. Pupae often continue their 
development until they are almost to the unemerged or quiescent 
