

INTERRELATIONS OF INSECTS 



273 



another large hymenopteron, Tremex columba (Fig. 30), upon whose 

 larvae the larva of Megarhyssa feeds. 



The enormous family Braconidae, closely related to Ichneumonidae, 

 is illustrated by the common Apanteles congregatus, which lays its eggs 

 in the caterpillars of various Sphingidag. The parasitic larvae feed upon 

 the blood and possibly also the fat-body of their host, and at length 

 emerge and spin their cocoons upon the exterior of the caterpillar (Fig. 

 2 79) , sometimes to the number of several hundred. Species of Aphidius 

 ransform within the bodies of plant lice, one to each host, and the imago 

 ruts its way out through a circular opening with a correspondingly 



PIG. 279. A tomato worm, Protoparce sexta, bearing cocoons of the parasitic Apanteles 



congregatus. Natural size. 



circular lid. Chalcididae, of which some four thousand species are 

 known, are usually minute and parasitic; though some are phytopha- 

 gous, for example, species of Harmolita (Isosoma) which live in wild or 

 cultivated grasses, and the clover seed-midge Bruchophagus funebris. 

 Chalcids affect a great variety of insects of one stage or another, such 

 as caterpillars, pupae, cockroach eggs, plant lice and scale insects; 

 while some of them develop in cynipid galls, either upon the larvae of 

 the gall-makers or upon the larvae of inquilines. Giard in France reared 

 more than three thousand chalcids (Copidosoma truncatellum) from a 

 single caterpillar of Plusia. Proctotrypidae are remarkable as parasites. 

 Most of them are minute; indeed, this family and the coleopterous family 

 Trichopterygidae contain the smallest winged insects known species 

 but one-third or one-fourth of a millimeter long. A large proportion 



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