ICHNEUMON-FLIES OF AMERICA: 1. METOPIINAE 5 



and single scraps of published information on four of the species. 

 There have been no detailed biological studies. Piecing together the 

 available information, some general conclusions about the biology of 

 the group may be developed. Though presentation of such generali- 

 zations is at the risk of glossing over a profound ignorance, they are 

 given for what they may be worth as starting points for future investi- 

 gators. 



The Metopiinae are all parasitic on Lepidoptera. There are a few 

 records of other hosts, but these need verification. Oviposition is 

 into the host larva, apparently a considerable time prior to pupation, 

 but emergence is always from the pupa. At its pupation the parasite 

 larva spins a few strands of silk to form a flimsy cocoon within the 

 host pupa. Emergence is by cutting off the front end of the host pupa 

 as a cap-like lid. A single adult develops in each host. 



Seasonal records of capture show that a few species have a single 

 generation in the spring or fall, but many are on the wing from late 

 spring to early fall and apparently have at least two generations a 

 year. Overwintering is always within the host pupa. 



The kinds of Lepidoptera that serve as host are correlated with 

 the size and habitat of the adult ichneumon-fly. Large species like 

 Metopius parasitize larger Lepidoptera, but most of the species of 

 Metopiinae are small, and their usual hosts are among the pyraloids 

 and tortricoids. Lepidoptera which live next to the soil or pupate 

 deep in it, or spin tough cocoons, or live in tunnels — these do not seem 

 to serve as hosts; but exposed larvae and larvae in leaf rolls or leaf 

 folds are commonly attacked. A single species of parasite usually 

 may be reared from a number of hosts that occur within its habitat 

 and size range. There are doubtless some cases of restricted host 

 specificity, but the rearing records at hand do not prove any. 



The larval morphology of the subfamily is known only through 

 illustrations of the mouthparts of Metopius and of Triclistus, published 

 by Beirne (1941, Trans. Soc. Brit. Ent., vol. 7, pp. 160-162). 



We have the impression that the metopiines locate their hosts 

 mainly by flying, hovering just to leeward of the hosts and finding 

 them by smell, rather than by crawling over vegetation and exploring 

 with their antennae as do the Gelinae and Ichneumoninae. 



Mating has never been observed in the field. Sometimes loose 

 groups of males have been found hovering around a bush or the ends 

 of a branch, just under the tips of the leaves. Possibly they were in a 

 primitive sort of mating swarm and waiting for females to appear. 

 This habit has been seen in several species of Exochus, in Colpotrochia 

 crassipes, and in Metopius krombeini krombeini. 



Many of the metopiines frequent more open, drier habitats than the 

 majority of ichneumonids. This is particularly true of Metopius, 



