DIPTERA. 463 



Mr. Havens has alluded to "an opinion, entertained by 

 many observers, that there are three generations of this insect 

 in a year," "two" being completed "before harvest." This 

 opinion was revived, in 1821, by Mr. James Worth, of Sharon, 

 Petmsylvania.* According to him, the second brood of ilics, 

 which appears early in June, had been altogether overlooked, 

 or confounded with the spring brood. Their " eggs were lain 

 on the upper leaves of the weakest or stunted wheat, and the 

 larvre became lodged about the two upper joints, but most 

 about the upper." Being very numerous, and crowded to- 

 gether, many of the larvee perished for want of food, and 

 many also were destroyed by parasites. Enough, however, 

 remained alive to continue the race; and the flies were evolved 

 from them at irregular intervals, and continued laying from 

 the fifteenth of August till October, when the earliest of their 

 progeny entered on the fly state; thus making, during the 

 year, as remarked by Mr. Worth, "three complete broods, and 

 partially a fourth." Mr. Say, though he does not appear to 

 have been fully acquainted with the history of the insect, has 

 recorded the occurrence of the fly in June. His remarks are 

 these: "The perfect fly appears early in June, lives but a 

 short time, deposits its eggs and dies; the insects from these 

 eggs complete the history by preparing for the winter brood." 

 In the year 1833, Mr. Herrick saw a Hessian fly laying eggs 

 on the third of June, another on the fifth, and a third on the 

 seventh of the same month. The fact of the occasional ap- 

 pearance of the flies as late as the 12th of June, when Mr. 

 Worth found the insects in all their stages, seems to be well 

 established; while it is equally certain that ordinarily only two 

 broods are brought to perfection in the course of one year. 

 Various circumstances may contribute to accelerate or to 

 retard a portion of each brood; and, hence, some of the flies 

 may be found from the middle of April to the middle of June, 

 and others from the beginning of August till December. 

 These circumstances have been so fully considered by Mr. 

 Havens, that it is unnecessary to repeat them here. The 



* See " American Farmer," Vol. III., p. 183. 



