156 THE AMERICAN NATURALIST [VOL.LV 



to parasitize both eggs and larvae, although the poly- 

 morphic and widespread Eupelmus among the Chalcis- 

 flies appears to be an exception. As the eggs and larvae 

 of manv insects frequently occur together at the same 

 time, this fact is rather surprising and shows that the 

 parasitic association must depend greatly upon gross 

 form, as well as upon the factors of environment and 

 specific physiological reactions, which we have already 

 mentioned. One case which comes to my mind in this 

 connection is quite instructive and there are no doubt 

 others of a similar nature. All the several genera in- 

 cluded in the EvaniinsB are, as previously mentioned, 

 parasites in the egg-cases of cockroaches, with the excep- 

 tion of a single reliable record (Picard, '13) of the rear 

 ing of Zeuxevania from the body of the blattid itself. 

 Quite likely the future may bring forth other similar ob- 

 servations on Evaniines, but this one shows that parasit- 

 ism has been transferred to the cockroach from the 

 ootheca, which is of course carried about by the female 

 for some time before deposition. 



Larval parasites have been more extensively reared 

 than those living in eggs and their habits are conse- 

 quently better known. Many observations upon indi- 

 vidual species of hosts show that the larval stages harbor 

 a far more extensive series of parasites {e.g., Howard 

 and Fiske, '12) than the eggs or pupae, while hymen- 

 opterous parasites of the adult are almost unknown. 

 Among larval parasites it is easy to recognize two gen- 

 eral series, so far as the number of hosts utilized. Some 

 species are very conservative in this respect and others 

 extremely versatile. These two terms are equally suit- 

 able for genera and larger groups, and the difference is 

 more important when it involves all or most of the species 

 of quite extensive groups. Thus the highly modified 

 members of the family Dryinidae (Perkins, '05) are re- 

 stricted to several families of Homoptera. A few which 

 parasitize Membracids are insects of quite ordinary ap- 

 pearance, but the remainder affecting Tettigoniellids and 



