372 ENTOMOLOGY 



Low temperatures lengthen the cycle and may be fatal to prepupal 

 stages. Low humidity also increases the length of the cycle, and if 

 extreme is fatal in all stages of development. (Headlee.) 



Eclosion. Every one who has had experience in raising moths 

 from pupae knows that the pupae must have a certain amount of 

 moisture or they will dry out and die. Out of doors the rainfall sup- 

 plies the requisite moisture, but even there pupae may succumb to too 

 much or too little moisture. 



Moths and butterflies upon emerging from the pupa can not expand 

 their wings if the air is too dry, on account of the rapid evaporation of 

 moisture from the wings. Indoors the moisture must be supplied if 

 necessary. It has often been observed that moths emerge from cocoons 

 in greater numbers on damp days. In dry weather many insects emerge 

 at night, when the relative humidity is higher than in the daytime. 

 This incidentally protects the helpless insect from its diurnal enemies. 



Adaptations. Many thin-skinned larvae, as those of the house fly 

 and the plum curculio, that live in a moist environment of decaying 

 substance, die quickly if subjected to a dry atmosphere, when the tem- 

 perature alone is not sufficiently high to' kill them. On the other hand, 

 larvae with a thick integument, like the meal worm, resist evaporation 

 more successfully. 



An immense number of dipterous larvae, those of the Hessian fly 

 and the house fly, for example, when full grown retain the larval skin 

 instead of shedding it ; this skin drying and hardening to form a pupa- 

 rium, which retards evaporation from the developing pupa within. An 

 unusually hot dry summer will, however, kill most of the puparia of 

 the Hessian fly, excepting such as may be protected by their depth in 

 the soil. 



Some of our large silkworms smear the inner surface of the cocoon 

 with a waterproof gum or varnish which undoubtedly prevents the un- 

 due escape of water from the enclosed pupa. 



Larvae that burrow into the ground (for example many caterpillars 

 and maggots, white grubs, larvae of the plum curculio, Colorado potato 

 beetle, and numerous others) and make earthen cells in which to pupate, 

 secure thereby protection from evaporation as well as from other 

 influences. Larvae of the late fall brood of the bollworm (corn ear 

 worm) dig much deeper than those pupating earlier in the season. 

 (Quaintance and Brues.) 



The beetles of the subfamily Eleodinae (Tenebrionidae) that are 

 characteristic of arid and semi-arid regions, have a thick integument and 



