404 ENTOMOLOGICAL SOCIETY 



HYMENOPTERA. The vast majority of the insects which are 

 parasitic upon members of their own class belong to the order 

 Hymenoptera, which contains one great series, comprising 

 several families, distinguished as Hymenoptera Parasitica. This 

 is composed, with an insignificant number of exceptions, of para 

 sitic forms embracing an immense number of species. So numer 

 ous are they, indeed, that although several thousand species have 

 already been described, these are but a very small portion of 

 those yet remaining to be described. The habits of all these 

 parasitic Hymenoptera are in many respects identical. The 

 female lays her eggs in, or upon, or near, the body of the intended 

 victim. The egg hatches, and the young larva, which is a white, 

 footless, maggot-like creature, issues, and, in what may be con 

 sidered the most perfect parasitism, lives within the body of its host 

 and bathes in its fluids, deriving its sustenance either from the 

 blood or the adipose tissue. The host-insect is not destroyed at 

 once, but frequently, when attacked in the larva state, is able to 

 transform to the pupa before succumbing ; yet the attack of one 

 of these parasites is invariably followed, sooner or later, by death. 



The Proctotrypid sub-family Scelioninae,and the Chalcidid sub 

 family Trichogramminas, are, so far as we know, composed en 

 tirely of egg-parasites, developing more particularly in the eggs 

 of Heteroptera. A certain number of Chalcidids, e. g., Pterom- 

 alus and Smicra, affect the chrysalis state, especially of butterflies, 

 though here the attack is doubtless made on the larva. The ma 

 jority of Hymenopterous parasites, however, infest the larvaa of 

 other insects, and so general is their attack that, in the fall of the 

 year, it is often difficult to get hold of a healthy larva of some of 

 the Lepidopterous species which are affected. 



In some restricted groups there is remarkable unity of habit in 

 the same genus, while in others there is great diversity of habit. 

 Thus the species of the genus Bassus are invariably parasitic 

 upon the larvae of the Syrphidas, while the species of Pimpla may 

 be parasitic upon Lepidopterous larvae, upon spiders' eggs, or 

 even upon saw-fly larvae. The little parasites of the genus Coc- 

 cophagus are invariably parasitic upon Coccids, and those of the 

 genus Aphidius (and in fact all the Aphidiinae) upon Aphidids ; 

 those of the genus Gonatopus always upon Tettigoniids, and 

 those of the genus Platygaster always upon the larva? of gall- 



