SEKPHOID AND CHALCIDOID PARASITES OF THE HESSIAN" FLY 79 



strongly aeneous to blackish with only a slight aeneous tinge. The pedicel 

 and scape are always testaceous, as are also the femora, tibiae, and tarsi, but 

 the coxae may be either wholly concolorous with the thorax or wholly testa- 

 ceous. Frequently the front and middle coxae are testaceous and the posterior 

 pair more or less metallic. The wings are hyaline. 



Male. — Length 0.9 to 2.3 mm. Antennae more slender than in the female, 

 the flagellum increasing very slightly in thickness from base to middle of 

 club, the funicle joints a little longer than broad, except the sixth, which is 

 quadrate; club ovate, scarcely thicker than the funicle, subacute at apex; 

 funicle and club joints sparsely hairy. Wings varying from mere stubs to fully 

 developed and normal. Abdomen a little more distinctly petiolate than in the 

 female, the first tergite about as long as broad, apical tergites frequently almost 

 wholly retracted, the petiole not so long as broad and finely rugulosely sculp- 

 tured. Color varying as in the female, the subapterous form usually strongly 

 aeneous with testaceous coxae and the winged form most frequently darker 

 with dark or metallic coxae. The male antennae are entirely reddish testaceous 

 or fuscotestaceous in the subapterous form, and usually testaceous with the 

 last funicle joint and the club blackish in the winged form. 



REMARKS ON VARIATION 



The astonishing variability of the species is not easily accounted 

 for. The presence of both winged and subapterous forms of the 

 female was recorded by Riley, but without mention of winged males 

 and without reference to the variations in color of both sexes. Riley 

 remarked that the proportion of the wingless to the winged forms 

 varied at different seasons and in different parts of the country, a 

 statement that is borne out by the present study. In discussing 

 Riley's remark, Osborn expressed the opinion that there may be much 

 the same retardation of development in this parasite as in the host, 

 and that the appearance of adults in autumn or in the following 

 spring may be a matter of conditions. 



Any doubt that may have existed regarding whether or not the 

 subapterous and winged individuals were representatives of the same 

 species was dispelled by the work of C. M. Packard, who bred a 

 subapterous female from a winged parent and who also observed 

 subapterous males mating freely with winged females. In unpub- 

 lished notes on experiments conducted by W. R. McConnell at 

 Hagerstown, Md., a winged female with all red coxae produced five 

 males, the coxae of all of which were metallic, thus showing that this 

 difference is not specific. 



In line with Riley's and Osborn's statements regarding the appear- 

 ance of the different forms at different seasons and in different parts 

 of the country, it appears from study of the material at hand that the 

 development or nondevelopment of wings and differences in color in 

 this species are related, to a large extent at least, to the length of the 

 developmental period as determined by temperature and humidity. 

 The subapterous form is the common one in the Mississippi Valley 

 during the hot summer months of July and August and may occur 

 as far north as Ontario, Canada, in August. The winged form, on 

 the other hand, occurs in late autumn and early spring in the Missis- 

 sippi Valley and seems to be the commoner form in such sections as 

 North Dakota, Oregon, and the mountainous portions of the eastern 

 part of the United States, where the mean temperatures are rela- 

 tively low and the developmental period is correspondingly longer. 

 Overwintering individuals seemingly are usually, if not always, 

 winged. 



