INSECT ECOLOGY 361 



there were some individuals that could endure a little more heat than 

 the others, and gradually a resistant strain of a species was built up. 



Hibernation. Temperature manifestly bears an important relation 



hibernation, the phenomenon of passing the winter in seclusion, 

 sually in a quiescent or inactive condition. The stimulus leading to 

 ibernation is usually decreased temperature in. autumn. Thus the 

 cotton boll weevil begins to hibernate with the decrease in mean average 

 temperature to about 55. (Hinds and Yothers.) Low temperature is 

 not always, however, the immediate incentive to hibernation. The 

 codling moth larva begins to hibernate before the temperature falls 

 and before food fails. The woolly bear caterpillars (Isia isabella) show 

 great regularity in the date at which they stop feeding, under con- 

 ditions of high temperature, different degrees of relative humidity, 

 and an abundance of fresh food. (Baumberger.) Mosquitoes begin to 

 hibernate before cold weather sets in. Among other influences there 

 may be a "tendency" to hibernate in many species. 



The period of hibernation i& prolonged by low temperatures. The 

 emergence of Cecropia moths from their cocoons may be delayed for 

 more than one year by placing the cocoons in cold storage with the 

 temperature a little above the freezing point. 



Warm periods during winter may arouse insects to more or less 

 activity. It is commonly thought by collectors that a uniformly 

 cold winter is more favorable to a subsequent abundance of insect life 

 than a winter interrupted by mild spells. 



Some insects do not awaken easily from the condition of hibernation, 

 while others respond readily to an increase of temperature. Examples 

 of the latter kind are the pomace flies (Drosophila), the house fly (Musca 

 domeslica) and other flies, and cockroaches. 



The temperature requisite to emergence varies with the species. 

 The boll weevil, in hibernation by the time of the first hard frost, con- 

 tinues to hibernate until the mean average temperature has been for 

 some time above 65 F. (Hunter and Hinds.) In the case of the brown- 

 tail moth 34 F. is the threshold above which the temperature accumu- 

 lates in determining the time of emergence of the caterpillars from their 

 winter nests. (Sanderson.) 



According to J. P. Baumberger, insects hibernate as (i) adults, 

 when their food habits are such that oviposition can take place on the 

 proper food at the earliest warm weather; (2) as larvae, when protected 

 from the cold and thus able to continue feeding to the latest date pos- 

 sible; (3) as pupae or eggs, because they are nonf ceding resistant stages. 





