4 MISC. PUBLICATION" 17 4, U.S. DEPT. OF AGRICULTURE 



to be less selective in the matter of hosts. Several are quite poly- 

 phagia the 3 species of Eupelmidae being especially so. Eupelmella 

 vesioularis (Retzius) is recorded from no less than 68 different hosts 

 ranging through several orders of insects and embracing species 

 having a wide range of food habits. Eupehnus allynil (French) is 

 recorded from 29 widely different hosts, and E. atropurpureus Dal- 

 man from 16. Among other surprising records, both Eupehnus 

 dllynii and Eupelmella vesicularh are said to breed successfully upon 

 the eggs of Oecanthm. 



Aside from the eupelmids, most of the chalcidoids seem to be 

 guided by the character of the plant and the location of possible 

 hosts in it, rather than by taxonomic relationship of the species 

 attacked. Many of the species having as their preferred hosts one 

 or more of the joint worms that live in the stems of grains and 

 grasses attack the hessian fly occasionally; and, conversely, many 

 of the species which normally attack the hessian fly will at times 

 develop on the jointworms. Likewise, parasites of such wheat- 

 infesting insects as Oscinella frit (Linnaeus), Meromyza amemcana 

 Fitch, Slayetiola arenae Marchal, Contarinia tritici (Kirby), Cephus 

 cinctus Norton, G. pygmaeus Linneaus, and Trachelus tabidus Fab- 

 ricius are at times reared from the fly. 



Among the most interesting of these host records are those of two 

 species of Aphelinidae attacking the fly. As is well known, the 

 vast majority of the species of this large family are parasitic upon 

 scale insects. However, the species of the genera Centrodora and 

 Tumidiscapus, to which these fly parasites belong, are known to be 

 commonly, if not normally, parasitic upon eggs of Orthoptera, such 

 as Xiphidiuiii and Orchelimum, which insert their eggs in stems of 

 grasses and other plants. The occurrence of these aphelinids as para- 

 sites of the fly, therefore, is probably attributable to the same instinct 

 that seems to guide the oviposition of many of the other chalcidoids — 

 that of thrusting their eggs into any insect body which happens to be 

 suitably located in the type of plant which they habitually frequent. 



Contrary to the usual belief, none of the species involved in the 

 complex of hessian-fly parasites is strictly a secondary parasite, al- 

 though many, if not all, of the chalcidoicl species under certain cir- 

 cumstances will attack and successfully develop at the expense of 

 other parasites, in some instances even devouring those of their own 

 kind. Tetrastiehus carinatus Forbes was long supposed to be strictly 

 a secondary parasite, but it is now known to develop as a primary 

 parasite in the great majority of cases. The platygasterids rarely, 

 if ever, develop as secondary parasites. 



Superfamily SERPHOIDEA 

 Family PLATYGASTERIDAE 



PLATYGASTEH HIEMALIS Forbes 



(Fig. 1) 



Platijgaster sp. Her rick, Amer. Jour. Sci. and Arts 41: 157, 1841; Fitch, N.Y. 

 State Agr. Soc. Trans. 6: 334. 356, 1846; The hessian fly (private publication), 

 p. 43, 1847; N.Y. State Ent. Rpt. 7; 829, 1862; Harris, Insects, injurious to 

 vegetation, p. 587, 1862 (also 1890 ed.) ; Fitch, Cult, and Country Gent. 28; 354, 

 1866; Packard, Rpt. U.S. Ent. Conini., Bui. 4: 20, 1880, and U.S. Ent. Comrn. 

 Rpt. 3: 219, 1883; Riley, U.S. Natl. Mus. Proc. (1885) 8: 420. 1886. 



