348 



THE STUDY OF INSECTS 



hole out through the bark if it does not find a hole already made by 

 the Tremex. Sometimes the adult Megarhyssa, like the adult Tremex, 

 gets her ovipositor wedged in the wood so tightly that it holds her a 

 prisoner until she dies. 



Among the more common of our larger Ich- 

 neumon-flies are those of the genus Ophion (Fig. 

 589); these have yellow bodies. One species 

 infests the caterpillars of the Polyphemus moth 

 and only a single egg is laid within each victim. 

 The caterpillar lives until it spins a cocoon, but 

 does not change to a pupa. The Ichneumon larva 

 when full-grown spins a dense brownish cocoon 

 within the cocoon of the caterpillar. 



Fig. 589. — Ophion. 



Fig. 590. 



Family Proctotrupid^e and Allies 



The Proctolrupoids 



There is a group of nine closely related families of the Hymenoptera 

 which together are known as the proctotrupoids. The group, as a whole, 

 is of great economic importance because the differ- 

 ent species are parasitic upon a great variety of 

 insects. 



The members of this group are slender insects 

 and mostly of minute size. Their color is almost 

 invariably black or brown without metallic luster. 

 The venation of the wings is greatly reduced and 

 in many foims the wings are veinless; there are 

 also many wingless species. Figure 590 represents 

 a proctotrupoid greatly enlarged. 



The proctotrupoids are all parasitic wasps; and very many of them 

 infest the eggs of other insects. The female proctotrupid bores a hole 

 with her ovipositor through the shell of an egg of one of the larger in- 

 sects, and deposits one of her eggs inside of it. Here the young parasite 

 when it hatches finds itself in the midst of food which is sufficient for it 

 till it is full v grown. The transformations are passed within the infested egg, 

 from which the parasite comes forth an adult. Other species are internal 

 parasites of larvae, and some are secondary parasites, that is, parasites 

 upon other parasites. None has been found to be injurious to vegetation. 

 Perhaps the most remarkable species of the proctotrupoids is Peleclnus 



polyturdtor, the only rep- 

 resentative in our fauna 

 of the family, Pelecinidae. 

 The females are common 

 in the regions in which 

 the species occurs and are 

 easily recognized by the 

 long and slender abdomen 

 (Fig. 591). The abdomen 

 of the male is club-shaped 

 and only about twice as 

 long as the head and thorax. This sex is very rare in this country but is 



Fig. 591. 



