396 



ECONOMIC INSECTS 



The larvae of the injurious species or families have biting mouth 

 parts, but the adults have long sucking tubes, not adapted to 

 piercing tissues. In this stage they are harmless. 



Diptera (two-winged) flies and mosquitoes. There are a few 



FIG. 279. A male and female (left) of the white cabbage butterfly, 

 larva; 6, chrysalis or pupa. (Economic Entomology.) 



green, velvety 



beneficial flies: robber-flies, which prey upon other insects, and 

 a few which are parasitic upon other insects. Injurious diptera 



include mosqui- 

 toes, house-flies, 

 stable-flies, Hess- 

 ian fly (Fig, 281), 

 pear-midge, buffalo 

 gnat, horse-fly, ox- 

 bot, sheep-bot, 

 horn-fly, cabbage- 

 maggot, "sheep- 

 tick," and bee- 

 louse. The mouth 

 parts of mosqui- 



t np(5 r, rp aHorvrArl fr> 

 { 



piercinff and c UCk- 

 Su> '' i 



mg. This is also 

 true of many species of true flies, but in the case of the house-fly 

 and some others the mouth is not suited to piercing. The food 



FIG. 280. Grain moth, a, larva; b, pupa; c, moth; e, egg: 

 /, larva feeding in kernel of corn. In the middle and southern 

 states this pest is very destructive to stored corn. (Economic 

 Entomology.) 



