i64 DISEASES OF THE SWEET PEA 



loses its natural color, then turns gray and 

 dies, remaining attached to the part of the 

 plant upon which it has been feeding. 

 When the larva is fully developed it 

 pupates and cuts a circular hole on the 

 top of the body of the now "mummied" 

 aphis, emerging as a winged insect to at- 

 tack other living aphids in the same way 

 as its mother. The circular hole cut by 

 the escaped parasites is always a sure sign 

 of the presence of these beneficial in- 

 sects. 



In the summer of 1911, the author no- 

 ticed that Aphiduis testaceipes alone de- 

 stroyed and kept in check what seemed an 

 epidemic of the sweet pea aphis. On the 

 other hand, in the summer season of 1912, 

 this beneficial parasite was rather scarce. 

 It is, therefore, interesting to know the con- 

 ditions which determine its presence or 

 absence. The following are observations 



