22 MISC. PUBLICATION 17 4, U.S. DEPT. OF AGRICULTUKE 



either in the egg of the host or in the very young larva. It also 

 seems probable, although data are too scanty for a definite conclusion, 

 that the species is single brooded, eggs being deposited in late spring 

 or early summer, and the adult emerging the following spring from 

 the puparium of the fly. 



DISTRIBUTION 



Not many records of this species are available, but it appears cer- 

 tain that it is widely distributed. Fitch recorded it from New York ; 

 Webster reared it at La Fayette, Ind. ; Ashmead recorded it from 

 Washington, D.C., and Arlington, Va. ; and Viereck recorded it from 

 West Haven, Conn. Besides the types and one of Webster's speci- 

 mens, there are in the National Museum collection 1 specimen from 

 Chambersburg, Pa., collected by C. N. Ainslie; 1 from Hagerstown, 

 Md., reared by P. R. Myers; 2 from New Castle, Pa., reared by 

 Myers ; and 7 from Mount Holly Springs, Pa., swept by Myers and 

 Fonts. It is not unlikely that the parasite occurs throughout the 

 range of the wheat midge. 



IMPORTANCE 



This species is normally parasitic upon the wheat midge and is 

 probably an important factor in the control of that insect. As a 

 parasite of the hessian fly it is of no importance. Only a single speci- 

 men has been reared from that host at the Carlisle, Pa., laboratory 

 of the Bureau of Entomology, where an extensive study has been 

 made of the parasites of the fly in the Middle Atlantic States during 

 the last 20 years. The species is included in this bulletin because of 

 that record and in order that it may be differentiated from the 

 other Platygasters attacking the hessian fly, with which it might be 

 confused because of its association with the wheat plant. 



TRICHACIS REMULUS (Walker) 



(Fig. 5) 



Platygaster remulus Walker, Ent. Mag. 3 : 239, 1836. 



Trichacis remulus Foerster. Hymenopterologische Studien, Heft 2, p. 115, 1856 ; 

 Ashmead, Psyche 8: 138, 1897; Marchal, Compt. Rend. Soc. Biol. [Paris] 

 49: 59-60, 1897; Ann. Soc. Ent. France 66: 84, 1897; Howard, Science (n.s.) 7: 

 247, 1898; Osborn, U.S.Dept.Agr., Div. Ent. Bui. (n.s.) 16: 29, 1898; Pospjelov, 

 Illus. Ztschr. Ent. 5: 262. fig. 3, 1900; Marchal. Arch. Zool. Expt. et Gen. (4) 

 4 : 548, pis. 19 and 20, 1906 ; Kieffer, Ann. Soc. Sci. Bruxelles 30 : 135, fig. 14, 

 1906; Marchal, Notice sur travaux scientifiques, p. 47, figs. 19 and 23, 1912; 

 Znamenski, Poltava Agr. Expt. Sta., Ent. Dept. Bui. 2: 1923 (abstract in Rev. 

 Appl. Ent. (A) 12: 291, 1924) ; Kieffer. Das Tierreich, v. 48. p. 712. 1926; Meyer, 

 Rpt. Appl. Ent. Leningrad 4 : 241, 1929 ; Blunck, Ztschr. Angew. Ent. 18 : 585, 

 1931. 



DESCRIPTION 



Trichacis remulus more closely resembles PI atyg aster herrickii 

 than it does any of the other hessian-fly parasites, but it may be dis- 

 tinguished at once from that species, as well as from all the others, 

 by the very distinct tuft of short gray hairs near the apex of the 

 scutellum. 



Female. — Length 1.4 to 1.9 mm. Head viewed from above transverse, about 

 twice as broad as long, scarcely narrowed behind the eyes, the temples nearly 

 or quite as wide as the eyes and broadly rounded, the occiput not concave ; ocelli 

 in a low triangle, the lateral ones more than twice their own diameter from the 

 eye margin ; viewed from the front the head is slightly broader than high, the 



