696 REPORT UNITED STATES GEOLOGICAL SURVEY. 



by General Frauds A. Walker, from the Statistics of Agriculture, Ninth 

 Census, 1870. 



This insect is donble-brooclecl, as the flies appear both in spring and 

 autumn. At each of these periods the fly lays twenty or thirty eggs in a 

 creaseintheleaf of the young plant. In about four days, in warm weather, 

 they hatch, and the pale-red larvae (Fig. 2«) " crawl down the leaf, work- 

 ing their way in between it and the main stalk, passing downward till 

 they 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." 

 (Plate IV, Fig. Ic.) Here they imbibe the sap by suction alone, and 

 by the simi)le pressure of their bodies, they become imbedded iu the 

 side of the stem. Two or three larvre thus imbedded serve to weaken 

 the plant and cause it to wither and die. The larvaj become full-grown 

 iu five or six weeks, then measuring about three-twentieths of an inch 

 iu length. About the 1st of December their skin hardens, becoming 

 brown, and then turns to a bright chestnut color. This is the so-called 

 flaxseed state, or i^uparium. In two or three weeks the "larva"' (or, 

 more truly speaking, the semi-pupa) becomes detached from the old 

 case. In this puparium some of the larva remains through the winter. 

 Toward the end of April or the beginning of May the pupa (Plate LXV, 

 Fig. lb) becomes fully formed, and iu the middle of May, in New Eng- 

 land, 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 the wheat is coming up 5 they 

 lay their eggs for a period of three weeks, and then entirely disappear. 

 The maggots hatched from these eggs take the flaxseed form iu June 

 and July, and are thus found in the harvest time, most of them remain- 

 ing on the stubble. Most of the flies appear in the autumn, but others 

 remain in the puparium until the following spring. By burning the 

 stubble iu the fall their attacks may best be prevented. Among the 



parasites on this species are the egg-parasites, 

 Flatyf/astcr and Semiotellus {Ceraphron) des- 

 tructor Say (Fig. 3), the latter of which pierces 

 the larva through the sheath of the leaf. Two 

 other Ichneumon parasites, according to Her- 

 rick, destroy the fly while in the flaxseed or 

 semi-pupa state. The ravages of the Hessian 

 fly have been greatly checked by these minute 

 insects, so that it is in many localities not so 

 destructive as it was formerly. Dr. Fitch has 

 suggested that the European parasites of this 

 insect, and the wheat-midge, could be imported 

 Fig. 3.— Parasite of the and bred in large quantities, so as to stop their 

 Hessuin Fly. ravages. With proper pecuniary aid from the 



State this seems feasible, while our native parasites might perhaps also 

 be bred and multiplied so as to effectually exterminate these pests. As 

 regards the increase of parasites, B. ^Vagner, in his " Researches on the 

 new Corn [wheat] Gall-fly" (Marburg, 18G1), finds that the parasites of 

 the Hessian fly increase in a ratio corresponding to that of their hosts. 

 In the same year, he says, in which the hosts are very generally frequent, 

 they are so infested by parasites that the next year only a few of the 

 gali-flies appear. He also found that the parasites only infested the 

 summer brood of Hessian flies, but not the winter brood ; seventy per 

 cent, of the former were found to be infested. Thus far the Hessian fly 

 has not occurred west of the Mississippi Valley. 



Egg and larva : The egg is about one-fiftieth of an inch long and fonr-thonsandths 

 of an inch iu diameter, cylindrical, translucent, and of a pale-red color (Herrick). 



