HYMENOPTERA 



925 



Fig. 1 1 53. — Megarhyssa lunator. 



four North American species are easy to distinguish. Megarhyssa 

 atrdta has a black body and yellow head. The northern species 

 M. nortoni has yellow circular spots on the sides of the abdomen. 

 M. hmdtor and M. greenei have brownish abdomens with angulate 

 yellow stripes on the sides (Fig. 

 1 1 53). M. lunator has an ovi- 

 positor twice as long as its body 

 while that of M. greenei is 

 about one and a half times as 

 long as its body. 



The tribe Polysphinctini 

 comprises small species usually 

 without an areolet in the fore 

 wing and with a rather short 

 ovipositor. They are parasites 

 of spiders. The female tempo- 

 rarily paralyzes a spider by 

 stinging it and then glues an 

 egg to its abdomen . The spider 

 recovers and resumes its nor- 

 mal activities. The maggot- 

 like parasite larva hatches and 

 keeps its tail end attached to 

 the egg shell to maintain its 

 position on the spider's abdo- 

 men. It feeds through the skin of the spider and finally kills it and 

 then spins a cocoon and soon emerges as an adult. 



The tribe Pimplini includes robust species with stout ovipositors 

 about half as long as the abdomens. In the genus Theroiiia are species 

 that are almost entirely fulvous in color. The other three genera, 

 Pinipla, Apechthis, and Itoplectis are black and can usually be dis- 

 tinguished from other Pimplinas by the hind tibia which is white at 

 the middle and has the apex and base (including the extreme base) 

 black. Members of this tribe are parasitic upon pupae of Lepidoptera. 

 Each species parasitizes a great variety of hosts differing considerably 

 both in size and relationships. Due to the varying sizes of the hosts 

 the adult parasites have a remarkable variation in size. Usually 

 males develop in the smaller hosts and females in the larger so that 

 males average smaller than females. This is a frequent phenomenon 

 among parasitic Hymenoptera but no satisfactory explanation for it 

 has been advanced. Itoplectis conqnisitor is a common parasite on 

 tent caterpillars and Theronia atalantce is a common hyperparasite of 

 Itoplectis conquisitor. Sometimes Itoplectis is itself a secondary 

 parasite. Species of Pinipla and Apechthis give off a strong pungent 

 odor when captured. 



The tribe Lissonotini includes species with a tiny notch near the 

 tip of the ovipositor and a single bulla or weak place in vein M2. 

 The propodeum usually has a single semicircular carina. The larvae 

 are internal rather than external parasites, a biological characteristic 



