384 



AN ECONOMIC ENTOMOLOGY. 



Most of these parasites have the disadvantage of not influ- 

 encing in the least the amount of injury done by the host ; they 

 simply prevent it from changing to an adult. It often happens 

 that spinning caterpillars even complete their cocoon, and in this 

 we find the mass of parasitic cocoons instead of the Lepidopter- 

 ous pupa. On the other hand, some of them complete their 



Fig. 442. 



Apa7iteles species. — Little mass of cocoons on leaf, replacing an infested larva ; a 

 single cocoon below, from which adult has issued ; much enlarged. 



development and kill the caterpillar before it is much more than 

 half-grown. Many of these cocoon-forming species belong to 

 the genus Microgaste7% and they are typical of a ver^^ large 

 series in the family. The plant-lice-infesting forms frequently 

 belong to the genus Aphidius. As in the previous family, many 

 of these insects have an external ovipositor. 



While the preceding series of parasites contain a very fair pro- 

 portion of large species, the next family, Chalcididcs , contains 



