COLEOPTERA 



393 



the egg usually resembles the adult in many respects, differing 

 chiefly in the absence of wings. This is usually called the 

 nymph stage. The insect is then active and feeds abundantly. 

 It goes through several moulting periods and gradually develops 

 wings like the adult. Eggs are laid during the adult stage, but 

 feeding may be continued as during the nymph stage. The chief 

 orders of insects having incomplete metamorphosis are: True 

 locusts, grasshoppers, katydids and crickets; true bugs, such as 

 squash bug, chinch bug and numerous others. 



Orders of Insects. The farmer is chiefly concerned with six 

 orders or main divisions- of the insect class, but entomologists 

 classify insects into twenty-one orders, many of them being of lim- 

 ited economic importance. The most destructive and most 

 beneficial insects belong to the following six orders : 



Orthoptera (straight winged), or true locusts, grasshoppers, 

 (Figs. 272 and 273) katydids, crickets, roaches, and others. All 

 this group have biting mouth parts and the metamorphosis is in- 

 complete. 



FIG. 272. The "Rocky Mountain" locust (left) and the "lesser locust" (right) are 

 two of the most destructive of the locust group. The former has wrought destruction in 

 the western states several times. The latter is often vejty injurious to alfalfa, clover and other 

 crops in eastern states. (Economic Entomology.) 



FIG. 273. The American grasshopper or locust showing the first and last stages in 

 its development (metamorphosis). A destructive species of the southeastern states. (Econ- 

 omic Entomology.) 



Hemiptera (half -winged), or bugs, include many kinds of plant 

 bugs (Fig. 274), plant-lice, San Jose* scale (Fig. 275) and other 

 scale insects, cicada and leaf hoppers. The mouth parts are con- 

 structed for piercing and sucking juices. The metamorphosis is 

 incomplete. The order includes many of the most destructive 

 insects. 



Coleoptera (horn-winged), or true beetles. Some of the bene- 

 ficial insects of this order are ground-beetles, tiger-beetles, water- 



