296 BEES AND WASPS 



All of these are distinctly parasitic in habit. Braconidce 

 and Ichneumunidoe are the more generalized kinds of para- 

 sites and parasitize such forms as the caterpillars of the 

 Lepidoptera in immense numbers. They constitute a very 

 important check upon a number of very important species. 

 It is hard to do much in the way of encouragement of them, 

 though they may be transported from one country to 

 another. One subfamily is pretty commonly parasitic on 

 plant lice. 



ChalcididcB form a specialized group with much reduced 

 venation for the wings and the Prodotrupidce are minute 

 and largely egg parasites. 



Family Ichneumonidse. — The Ichneumon flies include 

 many of the larger species of parasitic Hymenoptera and a 

 number of species which have important economic bearing 

 on the abundance of destructive species. Good examples are 

 to be noted in the species of Thalessa which parasitizes the 

 pigeon tremex and in species of Ophioii which attack a num- 

 ber of different kinds of caterpillars. The species of Pimpla 

 are also conspicuous members of the group and their attacks 

 are made especially upon injurious species of moths, so that 

 they are to be counted distinctly serviceable. 



Pimpla conquisitor is one of the parasites of the tent cater- 

 pillar and it is possibly due to this species that the tent 

 caterpillar is less destructive than it otherwise might be. In 

 this species the parasite lays its eggs in the cocoon of the 

 host and its larva develops within the pupa, so that it 

 serves to prevent the development of the adult and the 

 deposition of the eggs which would follow. 



Family Braconidae. — The family BraconidcF is quite similar 

 to the preceding but the species are on the average smaller 

 and many of the species parasitize the minuter kinds of 

 insects such as plant lice. A quite common species is Apan- 

 teles (jlomeratus which is a parasite of the common cabbage 

 worm and which no doubt serves as a quite important factor 

 in assisting to keep this pest in check. 



Perhaps one of the most important species is the little 

 Lysiphlehus tritici which is a very abundant parasite of 



