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 conver&ens) , 
an enemy of the oat aphis : a, Beetle ; ~b, pupa ; c, larva. 
Enlarged. (From Chittenden.) 
