278 



POPULATIONS 



gressively more susceptible to desiccation 

 as diapause disappeared during the winter 

 months. Although the eggs are most resist- 

 ant to desiccation during diapause in labo- 



Three further illustrations of ecological 

 mortality are in order. The first is based on 

 the data of BHss, Cressman, and Broadbent 

 (1935) and Cressman, Bliss, Kessels, and 



if) 



X 



I- 

 < 



Q 



Li_ 

 O 



cc 



UJ 



m 



100 



200 



DAYS 

 Fig. 77. Number of deaths (approximate) of Schistocerca gregaria during egg, nymphal in- 

 stars, and imaginal stages. ( From Bodenheimer. ) 



< 



UJ 



o 



1,000 



800- 



600 



400 



200- 



100 



200 



300 



DAYS 



Fig. 78. Death rate curve for Schistocerca gregaria. ( From Bodenheimer. ) 



ratory experiments, nevertheless the greatest 

 mortality in the field occurs during the dia- 

 pause stage, owing to the severity of the 

 drought and heat of the summer months 

 (Birch and Andrewartha, 1944). 



Dumestre (1935) on the camphor scale, 

 Pseudaonida duplex Ckll. This coccid ovi- 

 posits beneath the scale of the mother, 

 which is attached to the leaves of camphor 

 trees. The eggs hatch into nymphs known 



