THE OAT APHIS. 



15 



the oat aphis after it has once gained much headway in numbers and 

 diffusion, but by proper precautions it is possible to prevent serious 

 outbreaks. 



Fig. 8. Syrphus americanus, whose larva destroys the oat aphis, a, Female fly ; b, second 

 abdominal segment' of male. Enlarged. (From Webster and Phillips.) 



DESTRUCTION OF BREEDING PLACES. 



As has been observed by the writer and other assistants of the 

 Cereal and Forage-Crop Insect Investigations, the plant-louse under 

 discussion thrives best in rank-growing wheat, for instance in spots 

 where manure piles or straw stacks have stood, as well as in the 

 vicinity of straw 

 stacks where the 

 growth of grain 

 is usually luxu- 

 riant. In fact, 

 observations 

 show that the lat- 

 ter place is the 

 usual center of 

 infestation, for 

 during the colder 

 winter months 

 the plant-lice 



may be found here when it is impossible to locate them elsewhere. 

 Such locations also provide much better protection from inclement 

 weather, and reproduction may continue, more or less, throughout 

 the winter. Therefore it is evident that if the growth about straw 



Fig. 9. — The convergent ladybird {Hippodamia convergens) , 

 an enemy of the oat aphis : a, Beetle ; b, pupa ; c, larva. 

 Enlarged. (From Chittenden.) 



