366 ENTOMOLOGY 



Estivation. In the case of the potato beetle, hibernation and (esti- 

 vation, or the condition of dormancy in summer, are practically the same 

 as regards the life history of the insect, according to Tower. In the 

 tropics, where there is no hibernation, aestivation occurs over the dry 

 season. Though aestivation is associated mainly with heat, relative 

 humidity is also a factor, and " undoubtedly has the most important 

 influence upon the time of emergence of forms in aestivation during 

 the summer or in arid regions. (Sanderson.) During intense heat (95 

 to 122 F.) the boll weevil aestivates temporarily on the ground under 

 protecting objects. 



Drought. Brought accompanies heat and affects animals and 

 plants through evaporation. It affects them directly, by desiccation; 

 or indirectly, by drying out the food plants or other food substances ; 

 as with larvae of the boll weevil or the house fly. The range of dryness 

 within which insects can exist varies greatly with different species. 

 The chinch bug, unlike the Hessian fly, thrives in hot dry summers; 

 and species that inhabit arid regions are exceptionally resistant to 

 conditions of drought. 



Precipitation. Rainfall is direct or indirect in its influence on the 

 life and activities of insects. Eggs of the cotton boll worm are destroyed 

 in immense numbers by the mechanical force of the rain during violent 

 storms. The combined effects of rain, wind, and sandy particles 

 washed against the plants removes many eggs. (Quaintance and Brues.) 

 Young larvae of the boll worm feeding on corn early in the spring are 

 often washed down by rain and submerged for considerable periods. 

 Of twenty newly hatched larvae submerged for seventeen hours, a 

 but four survived the immersion. Larger larvae cannot stand sue 

 long periods, but when dropped into water become stupefied after a fe 

 minutes. Pupae could not withstand twenty-four hours' submergence 

 in rain water at normal summer temperatures, but at a temperature of 

 from 50 to 60 F. they were unharmed by from four to six days' 

 submergence. (Quaintance and Brues.) In the case of the cotton boll 

 weevil, a pupa survived an immersion of six hours; and 60 per cent, of 

 adults, one of fifteen hours. Ten adults were floated for one hun- 

 dred and twelve hours, after which only one was dead, but only two 

 were normal; after floating for only twenty-five hours, however, six of 

 the ten were normal. The floating of adults and infested squares ex- 

 plains the appearance of weevils in great numbers along high-water 

 line immediately after a flood. (Hunter and Hinds.) 



Rains favor weevil increase in several ways. Frequent rains in 



