122 NORTH AMERICAN DIPTERA. 



abdominal tissues which surround them, until they are 

 consumed. They then escape to increase in size and pro- 

 duce another generation in the same remarkable manner. 

 These series of asexual reproductions are repeated until 

 finally, from the last brood, pupae are developed which 

 undergo their transformation into imagines, and from 

 which a new series of eggs, agamic broods of larvae and 

 pupae in their turn result. There are other instances cf 

 paedogenetic reproduction among diptera, but none so 

 interesting as this. 



This family contains some of the 'most destructive of 

 all insects in man's economy, and perhaps the most im- 

 portant of these is Cecidomyia (Mayetiola) destructor-, com- 

 monly called the Hessian Fly, from the belief, probably 

 erroneous, that it was first introduced into this country 

 in straw brought by Hessian troops during the Revo- 

 lution. 



The fly is very small, but little more than an eighth cf 

 an inch in length, of a prevailing black color, with the 

 abdomen pinkish or brownish. There are two broods, in 

 spring and autumn. The female deposits her eggs, one 

 or two at a time, on the upper side of the leaves of wheat, 

 to the number of from eighty to a hundred, or even more. 

 Hatching in from four to eight days, if the weather is 

 favorable, the yellowish red larvae crawl downward en 

 the leaves until they insert themselves between the leaf 

 and the stalk. Here they remain quiescent, growing by 

 means of imbibition or absorption of the juices of the 

 plant, until they reach the size cf a small grain of rice. 

 The larvae that are hatched in April, in a few 7 weeks as- 

 sume the pupa state, called the flax-seed stage. In Aug- 

 ust the second brood appears, the female of which deposits 

 her eggs in young winter wheat or other grain, where the 

 larvae soon hatch and acquire the flax-seed condition in 

 a few weeks, or by November, in which condition they 



