ISO 



ENTOMOLOGICAL NEWS 



[April, 'i2 



a spontaneous production of young with wing pads. Many 

 species of Aphids increase until the condition of the plant 

 is wilted or curled, due to the poisonous effect of the lice 

 or the lack of water; then they produce winged forms and 

 free the plant entirely. 



There seem thus to be two possible explanations of wing- 

 production in these experiments ; first, there may be a stim- 

 ulative action due to the chemicals, or second, it may be 

 due to the slower development after hatching and after 

 feeding begins. This slower development of tissue gives 

 more opportunity for the development of wings, which 

 would otherwise be sacrificed to the development of such 

 'issue as the reproductive system under more favorable con- 

 ditions. This retarding in development is brought about by 

 the wilting efifect produced by several agencies, as drought, 

 excessive infestation of the plant by the lice, the prepara- 

 tion of the plant for winter conditions, or perhaps artificial- 

 ly by the presence of magnesium salts. 



The writer undertook to verify the determinations made 

 by Professor Clarke and obtained the following results : 



These results completely confirmed those obtained by Pro- 

 fessor Clarke, but bring out the additional fact that after the 

 first three days all the MgSO^ aphids developed wing pads. 

 This makes it possible to determine quite accurately the time 

 during the development of the insect at which the action of 

 magnesium became effective. 



A series of experiments were made by the writer to dis- 

 cover whether the determination of the future development 

 into winged or wingless aphids occurred before or after 



