8 



INSECTS INJURIOUS TO VEGETABLES 



Hymenoptera (Sawflies, ants, zvasps, bees, etc.). — In this order 

 there are two pairs of membranous wings with comparatively 

 few veins, the hind-wings being the smaller pair. The mouth- 

 parts of the adults are formed for both biting and sucking, 

 and those of the larvae, which are injurious, for biting. The 

 females are furnished with stings, piercers or saws. In this 

 order there are comparatively few noxious forms, and most 

 of these are confined to the sawflies whose larvae, known as 

 slugs and false-worms, consume vegetation, doing injury similar 



Fig:. 10.— Screw- worm (Compsomyia macetlaria). a. Maggot; b, head of 

 same; c, anal segment from rear; rf, puparium; e, adult fly;/, head from 

 side. All enlarged. 



to that accomplished by caterpillars. Some species of ants 

 are troublesome, both directly and indirectly, in the latter 

 case by acting as carriers of aphides or plant-lice, scales, and 

 some other insects. This order, however, contains many bene- 

 ficial forms, such as ichneumon and chalcis flies — parasites of 

 noxious insects, and wasps which also destroy insect pests. 

 One of these is shown in figure 7. 



Diptera, or Flies. — Insects of this order have a single pair 

 of wings which are borne on the mesothorax or middle por- 

 tion of the thorax. The metathorax or hind portion bears a 

 pair of knobbed thread-like processes called halteres, poisers, 

 or balancers. The mouth-parts are formed for sucking in the 

 adult condition, but in the larvse (called maggots) the mouth- 



