ICHNEUMON-FLIES — GELINAE : MESOSTENINI 



89 



Figure 33. — Localities for 

 Gamhrus extrematis. 



Neck," and Pittsburgh); South Dakota (Black Hills, Brookings, 

 Chamberlain, and Highmore) ; Utah (Salt Lake City) ; and Wisconsin. 



The great majority of the specimens are Imown or suspected to 

 have been reared indoors. The species is presumed to be adult 

 throughout the summer. As an illustration of the scarcity in the 

 field, we ourselves have never collected it. Specimens with host 

 records include 29 lots reared from Hyalophora cecropia, 2 from H. 

 Columbia, and 1 from H. euryalus kasloensis. 



There have been several publications on the biology of this species, 

 as noted under the synonymy. The papers by Marsh are partic- 

 ularly interesting. In the account given in "Ecology," he relates: 



As soon as cocoon spinning [of the cecropia] has progressed to a thin-shell stage, 

 females of the ichneumonid have been observed coming up the wind to it as Can- 

 thon beetles follow up wind to fresh horse droppings. The ovipositor is thrust 

 through the cocoon, and eggs are deposited on the inside of the cocoon or on 

 the surface of the larva. Over one thousand eggs have been counted in one 

 early-spun cocoon resulting from the oviposition of several females, while the 

 greatest number of cocoons of [(?.] extrematis in a single Cecropian cocoon was 

 172. As no starved larvae have been found, cannibalism is indicated. The 

 average infestation of Cecropian cocoons with [G.] extrematis was found to be 

 thirty-three. During oviposition, the host larva is thrust with the ovipositor 

 and invariably dies within a few hours. The larvae of [G.] extrematis move about 

 freely over the dead host larva at first feeding on cuticle, later burrowing down 

 and drinking body fluids. In cases of heavy parasitism all the host body is 

 eaten except the few chitinized parts. In the Chicago area [G.] extrematis is 

 double brooded, completing a cycle in about eighteen days. 



Overwintering is in the host cocoon. In spring or early summer 

 parasitized cocoons brought indoors begin to yield their parasites, 

 which emerge from a single cocoon over a period of about a week, 

 through several holes cut to the outside. A single cocoon may yield 

 all parasites of one sex, or some of both sexes. Parasitized host cocoons 

 are filled solid \^ath a mass of cocoons of the parasites. 



589900—62 7 



