44 



PARASITES. 



Surprisingly little of a definite and accurate character lias been 

 published on the parasites of this interesting and important insect, 

 and nearly all the facts now current have been derived from almost 

 the first competent observer of the fly in America. The only species 

 carefully described is Semiotellus destructor, first noticed by Say, and 

 studied, as to its habits and life history, with some care by him, 

 and especially by Prof. Herrick, of Yale College in 1833. One other 

 parasite, Platygaster error, has been described by Fitch, but its life 

 history has been only imperfectly worked out and inaccurately 

 stated. A few other forms have been mentioned, without names or 

 full descriptions, by Herrick, Fitch and Cook. 



The data herein presented are in themselves very incomplete, but 

 are as full and definite as I have been able to make them, with 

 two years study, in respect to the life histories of the parasitic 

 species found to affect the Hessian fly in Illinois in any important 

 way. 



The common Semiotellus destructor is here redescribed in detail 

 and descriptions are given of three new species bred from infested 

 wheat, and mention is made of two others not fully studied, — and 

 for all these species I have given full abstract of our breeding cage 

 records. 



It is proper to say that, as my studies were made with principal 

 reference to the life history of the Hessian fly itself, I was especially 

 solicitous to depart as little as might be from the natural condi- 

 tions of the species, and hence did not remove the flaxseeds from 

 the straws, as would have been desirable for the breeding of the 

 parasites only. From this it results that some of the parasitic 

 species may have infested other wheat insects than the Hessian fly. 

 Indeed, as Eupelmus allyni appeared quite frequently in these breed- 

 ing cages, and as this species has been supposed to be parasitic on the 

 wheat straw worm only, it is not impossible that some of our straws 

 were inhabited by this last species also, and that some of the new 

 parasites herein mentioned belong to Isosoma.* 



Semiotellus destructor. Say. 



Order Hymenoptera. Family Chalcidid^. 



This is far the commonest of the parasites of the Hessian fly in 

 Illinois, 85 per cent, of those appearing in our breeding cages (ex- 

 cluding Eupelmus) belonging to this species. It has been repeatedly 

 described by Say, Fitch and Packard, but so imperfectly or inac- 

 curately that I have not found it easy to identify the species posi- 

 tively. ' Not doubting, however, that our most abundant form belongs 

 here, I give a fresh description of both sexes, carefully drawn from 

 alcoholic specimens. 



*Prof. Riley writes me that he lias I'epeatedly bi"ed Evpebiius allyni from the Hessian 



fly. 



