ECONOMIC ENTOMOLOGY. 37 



CHAPTER IT. 



Injurious Dipteea. 



The order Diptera, (" two- winged ") includes the mos- 

 quito, the gnat and the common house-fly, the Hessian fly, 

 etc. Also the Syrphus and Tachina flies which are useful 

 because they destroy many injurious insects. 



The larvae of Diptera are called maggots. 



The distinguishing feature of this order is that the sec- 

 ond pair of wings are not developed as in other orders, but 

 are rudimentary, serving as " balancers." 



THE HESSIAN FLY. 



(Cecidomyia destructor. Say.) 



" This insect is double-brooded, as the flies appear both 

 in spring and in autumn. At each of these periods the fly 

 lays twenty or thirty eggs in the leaf of the young wheat 

 plant. 



" In about four days in warm weather they hatch, and 

 the pale-red larvae crawl down the leaf, working their way 

 in between it and the main stalk; passing downward till 

 ihey come to a joint, just above which they remain, a little 

 below the surface of the ground, with the head toward the 

 root of the plant. Here they imbibe the sap by suction 

 alone, and by the simple pressure of their bodies they be- 

 come imbedded in the side of the stem. Two or three larvae 

 thus imbedded serve to weaken the plant and cause it to 

 wither and die. 



" The larvae become full grown in five or six weeks, 

 then measuring about three- twentieths of an inch in length. 



