ECONOMIC ENTOMOLOGY. 



Hessian fly, which have done a great deal of late years to 

 check its ravages. 



The predaceous beetles, swallows and martens destroy 

 many. 



Changing or rotating crops is advantageous. 



THE BLACK ONION FLY. 



(Ortalis flexa. Wied.) 



The fly is approximately half an inch in length, each 

 wing having three whitish, oblique, crescent-shaped bands 

 or stripes 



\ 



Fig. 40. Black Onion Fly. (Lines show real size.) 



There are two yearly broods. 



The maggots of the first brood may be found during the 

 month of June. They remain from twelve to fourteen days 

 in the pupa state. 



The imagos are rather slow of flight and do not fly any 

 great distance. 



Remedies. The only remedies that have as yet been 

 tried with any success are the careful removal of all infested 

 onions, and the use of the kerosene emulsion (see Chapter 

 VIII). 



The application of salt, in the proportion of three or 

 four bushels to the acre, has proved useful. 



