i6 



SECOND REPORT ON ECONOMIC BIOLOGY. 



VI. SEASONAL HISTORY. 



Life Cycle. The duration of the various stages are subject to 

 some slight variation, due to weather changes, etc., the following 

 series represent those taking place under average conditions : 



As winged insects, most die before the winter sets in, but hyberna- 

 tion is by no means uncommon. 



Hybernation. It has been too generally assumed that in entering 

 hybernation insects are influenced solely by the falling temperature. 

 That this is not so has been shown by Tower 1 in his classical memoir 

 on Chrysomelid beetles. In the life-cycle a stage is reached when the 

 organism demands a period of rest before continuing reproduction. 

 That temperature is by no means the sole or dominant factor was very 

 clearly and conclusively illustrated by Weismann in his well-known 

 paper " On the Seasonal Dimorphism of Butterflies "; and important 

 investigations are at present being made on the subject by Prof. E. 

 Dwight Sanderson. 2 



Pegomyia betae hybernates one might say when it has become 

 exhausted, thus in 1909, in which year only two broods were general, 

 many hybernating females were observed, for the first time, on 



1 Carnegie Inst., 1906. Evolution in Chrysomelid Beetles. 



2 Journ. Kcon. Entom., 1908, vol. i, pp, 56-65, 2 figs. 



