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Annals Entomological Society of America [Vol. X, 



are active immediately after the temperature is raised. Such 

 insects can be reared all the year round in the greenhouse and 

 may be exemplified by Drosophila, Noctua iinipimcta, the 

 cockroaches, Musca domestica and others. In fact, we have 

 every degree of development of this periodicity. 



The factors which have determined the variability of this 

 characteristic may be seen from a survey of some insect life 

 histories. These factors are of three kinds: 



1. Climate. — As there is no cold period in the tropics, insects do 

 not hibernate there. This lack of periodicity persists in insects 

 introduced into the temperate regions. This is probably the case with 

 Drosophila which cannot be induced to hibernate. 



2. Food. — Insects which feed upon materials constantly available 

 do not show a definite periodicity. Thus the house fly female will 

 oviposit at any time of the year when the temperature is appropriate. 

 Pictet has pointed out that insects which feed on evergreen trees are 

 not as rhythmical in their hibernation as those which feed on deciduous 

 trees. 



3. Exposures. — The degree to which insects are each year exposed 

 to the conditions of winter may also determine the elasticity of their 

 periodicity. Thus the Woolly Bear, which hibernates under stones in 

 rather an exposed condition, has a definitely established period of 

 hibernation, whereas the Anny Worm, which hibernates deep in the 

 earth, is less exposed to the effects of winter and hence hibernates 

 only upon direct stimulus. 



These three factors may also determine the stage or stages 

 in which different species of insects hibernate. The data on 

 life histories contained in Judeich and Nitsche^ are more 

 available than any others, because the life cycles of different 

 species are tabulated in a system of which I show a modification 

 below. This method makes it possible to record scattered 

 observations on different stages of the life cycle of an insect 

 and finally to read the whole history at a glance. It would be 

 a great advance if a repository for such data could be established 

 at some university or other institution. 



Dist. — Mid. Europe, S. France. 



Larvae — Skeletonize oak leaves, from one side only, working in a tunnel under roof 



of pes. of leaves. 

 Pupae — In cocoon under ground. 



Judeich u. Nitsche, 1895, p. lOfiO. 

 Symbols A, E, L, P stands for adult, egg, larva and pupa respectively. 



