HYMENOPTERA 



353 



are yellow and some of the larger species have red markings. The head 

 is usually large (Fig. 597); the prothorax does not extend back on each 



side to the tegula; the ovipositor is 

 usually hidden, issuing before the apex 

 of the abdomen, but in some genera it 

 is very long. 



Fig. 597. — A chakid-fly, Aphycus emptor. 



Fig. 598. — Fore wing of a cha!cid-fly 



In most of the chalcids the venation of the wings is reduced to the 

 type shown in Figure 598; in a few, however, there are vestiges of other 

 veins; but in none are there any closed cells. 



The chalcid-flies constitute an exceedingly important group of insects 

 from an economic standpoint; and nearly all of them are beneficial, 

 being parasites that do much to keep in check noxious insects. A few 

 species, however, are phytophagous; among these are those of the genus 

 Isosoma, now known as Harmolita, that infest the stalks of growing grain, 

 and species of several genera that infest the seeds of various plants. 

 While these are noxious, the fig-insects, although phytophagous, are very 

 beneficial to man. 



Insects in all stages of their development suffer from the attacks of 

 chalcid-flies, eggs, larvae, pupae, and even adults in a few cases being 

 attacked by them. The larvae of chalcid-flies usually feed within the 



Fig. 598a. — A chalcid parasite, Aplielinus jucundus, emerging from the 

 geranium aphid. (Figure loaned by Dr. Grate H. Griswold.) 



body of their host, (Fig. 598a) but some species are external parasites of 

 other larvae. 



The plant-feeding chalcids are of considerable interest because they 

 are destructive to crops. The following are well-known. 



