THE CORREIvATlON OF STRUCTURE AND HOST- 

 REEATION AMONG THE ENCYRTIN^. 



By LELAND O. HOWARD. 



The student of the parasitic Hymenoptera cannot fail to be 

 impressed bj^ the uniformity with which parasites of certain 

 more or less restricted groups are parasitic upon insects of cer- 

 tain groups also of more or less circumscribed extent. Verj^ 

 broad and sweeping generalizations in this direction to which 

 there are, however, many exceptions, may be made. Thus, 

 while the Eepidoptera are parasitized by many representatives 

 of all of the four principal families of parasitic Hymenoptera, 

 those of the subfamily Ichneumoninse may in general be said 

 to be parasites of lycpidoptera. The species of the braconid 

 subfamily Euphorinse are, in the main, parasites of Coleop- 

 tera, those of the subfamily Microgasterinse are parasites of 

 Eepidoptera, those of the proctotrypid subfamily Platygas- 

 terinas are parasites of Diptera, mainly of Cecidomyiidse, and 

 those of the subfamily Dryininse of the Homoptera of the fami- 

 lies Membracidse, Jassidae, Tettigoniidse and their allies. In- 

 stances of this kind might be multiplied, but, at the same 

 time, groups in which much less uniformity exists are also 

 numerous. 



In the family Chalcididse, to which the subfamil}' which I 

 shall particularly discuss belongs, there is the same uniformity 

 in some groups and the same lack of uniformity in others. 

 Very few of the subfamilies may be said to possess any great 

 uniformity throughout their whole extent. The Tetrasti- 

 chinse, however, appear to be uniformly parasites of other 

 parasitic Hymenoptera, while the Elachistinse are parasites 

 (mainly external) of I^epidoptera, and the Toryminse are par- 

 asites of gall-insects, the preference of the latter depending 

 not so much upon the structure of the host as upon its posses- 

 sion of the gall-making habit, since they attack cynipid, ceci- 

 dom3'iid, trypetid, and even lepidopterous gall-makers. 



