ICHNEUMON-FLIES, PART 2 1 EPHIALTINAE 217 



positor the point of which is long and tapered. One genus (Laufeia) 

 has the areolet present but has the enlarged fifth tarsal segment and 

 ovipositor shape typical of the tribe. A few of the Pimplini (Zaglyptus, 

 Clisiopyga, and a few Tromaiobia and Acropimpla) lack the areolet 

 but do not have the enlarged fifth tarsal segment, nor except in 

 Clisiopyga, a long-tapered point on the ovipositor. 



The species of Polysphinctini are mostly small or very small. A 

 few are medium sized, and some species of Acrotaphus and Hymeno- 

 epimecis are medium large. They are worldwide in distribution. 

 In correlation with their small size and slender bodies, they are 

 commonest in damp habitats. All are parasitic on the bodies of 

 spiders. The adult parasite stings a spider to quiet it, then lays a 

 single egg, usually near the base of the abdomen on the dorsal side. 

 The hatching larva clings to the active spider and feeds on its juices. 

 In most species the larva rests curved over the base of the abdomen 

 on the dorsal side. It is attached to the spider by a saddle of its 

 egg shell and old shed skins, piled one on the other, into which it 

 has two or four pairs of projecting papillae, arising one pair each from 

 the under side of the median abdominal segments. The larva is 

 very securely attached to this saddle and the saddle to the spider. 

 Even if the spider molts, the skin beneath the saddle is not shed and 

 the larva remains in position. Growth of the larva is rapid. At 

 the last molt it acquires four to eight pairs of dorsal tubercles (one 

 pair per segment) covered with small hooks, which are one of the 

 main distinguishing features of larvae of this tribe. When the spider 

 succumbs, a narrow fusiform cocoon is spun, usually in the remains 

 of the web of the spider. The dorsal tubercles beset with hooks are 

 used by the larva for holding to the spider web while finishing off 

 its host and starting the cocoon. The cocoon of the Polysphinctini 

 differs from those of possibly all other Hymenoptera in having an 

 opening at the hind end. Through this the last larval excrement is 

 pushed, and often also the exuvia of the molt at pupation, leaving 

 the cocoon very tidy inside. 



The polysphinctines are evidently a specialized offshoot of the 

 Pimplini, and the steps in the biological and morphological change 

 from one tribe to the other are still well preserved. Most of the 

 Pimplini parasitize larvae living in plant tissue, and oviposition is 

 through the plant tissue into the host larva. Some genera, like 

 Sericopimpla and probably Acropimpla, however, parasitize larvae in 

 cocoons or silken cases and in these genera oviposition is through a 

 silken bag to reach the host. Iseropus is related to these and has the 

 same habit, but in Iseropus several parasites rather than one develop 

 from a single host. From Iseropus the change to the biology of 

 Tromaiobia is a small step. Tromaiobia selects spider egg cocoons 



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