374 



DIPTERA. 



It does not change its condition and become a true pupa until 

 a few days before it discloses the winged insect." 



The pupa resembles that of the fungus-eating Tipulids, 

 such as Sciara. The bases of the antennae are often produced 

 into horn-like points, which aid the pupa in working its way 

 out from the gall before assuming the fly state, and for the 

 same purpose the back of the abdomen is spinose, and often 

 there are a few bristles at the tip. 



According to Dr. Harris, the Cecidomyia destructor Saj^, or 

 Hessian-fly (Fig. 279), has two broods, as the flies appear in 

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



twenty or thirty eggs in a 

 crease in the leaf of the young 

 plant. In about four da}'s, 

 in warm weather, they hatch 

 and the pale red larvae (a) 

 "crawl down the leaf, work- 

 ing their way in between it and 

 the main stalk, passing down- 

 w r ards till they come to a joint, 

 just above which they remain, 

 a little below the surface 

 of the ground, with the head towards the root of the plant" (c). 

 Here they imbibe the sap by suction alone, and by the simple 

 pressure of their bodies they become embedded in the side of 

 the stem. Two or three larvae thus embedded 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. About the first of December 

 their skin hardens, becomes brown and then turns to a 

 bright chestnut color. This is the so-called flax-seed state, or 

 puparium. In two or three weeks the "larva" (or more truly 

 speaking, the semipupa) becomes detached from the old case. 

 In this puparium the larva remains through the winter. To- 

 wards the end of April or the beginning of May the pupa (Fig. 

 279, b) becomes fully formed, and in the middle of May, in New 

 England, the pupa comes forth from the brown puparium, 

 "wrapped in a thin white skin," according to Herrick, "which 

 it soon breaks and is then at liberty." The flies appear just as 



- ?79 - 



