170 



ELEMENTARY ENTOMOLOGY 



small, slender, brown weevils, one eighth of an inch long, which 



are the most abundant pests of granaries. 



The engraver-beetles (ScolytidctR), or bark-beetles, live on the 



inner bark and sapwood of forest and fruit trees, the larvae of 



each brood tunneling out their little burrows in characteristic 



patterns, giving them the name 

 of 'engravers." They are small 

 brown or blackish beetles, often 

 microscopic, rarely over one eighth 

 and never over one fourth of an 

 inch long, and with the head very 

 slightly produced, so that they are 

 not readily recognized as snout- 

 beetles. They have stout, cylin- 

 drical bodies, obliquely or squarely 

 truncate at the tip. The larvae are 

 little white grubs, with brown 

 heads and strong jaws, which 

 riddle the inner bark of the food 

 plant and pupate in the burrows. 

 When the adults emerge, they make 

 numerous small holes through the 

 bark, which habit has given them 

 the name of ' shot-hole borers." 

 This family includes the most de- 

 structive of all our forest insects, 

 the losses due to them being es- 

 timated at over one hundred million 

 dollars per annum. Almost every 

 tree has species which commonly 

 attack it in different sections of 

 the country, some infesting only 

 sick or dead timber, while others 



FIG. 256. Typical woric of a scolytid, 

 the fruit-tree bark-beetle, showing 

 the main galleries, the side or larval 

 galleries, and the pupal cells. ( Slightly 

 enlarged) 



(After Ratzeburg) 



attack the healthy trees and sweep them off over large areas, the 

 trees dying and giving rise to forest fires. The fruit-tree bark- 

 beetle (Scolytns rugulosus] is a well-known example, infesting our 

 common fruit trees. 



