148 



APPLIED ENTOMOLOGY 



When the beetles have been formed there, they bore out to the surface of 

 the tree (Fig. 145) and soon begin to tunnel in again, to lay eggs for a 

 second generation which in the North becomes adult before winter, 

 thus giving two generations a year. In the South with its longer warm 



a 



FIG. 144. Fruit-tree Bark-Beetle (Eccoptogaster rugulosus Ratz.); a, Adult Beetle; b, 

 side view of same; c, pupa; d, larva. Hair lines show true length. (From U. S. D. A. 

 Farm. Bull. 763.) 



season, three or perhaps four generations may be produced each year, 

 the adult beetle in some cases at least, wintering in the tree, while in 

 others this season may be passed in the egg stage. 



Healthy trees are not often attacked except when the beetles become 

 so abundant that a sufficient supply of weak or dying ones is not available. 



FIG. 145. Exit holes of the Fruit-tree Bark-Beetle in bark of a young tree, about natural 

 size. (From U. S. D. A. Farm. Bull. 763.) 



In healthy trees the flow of gum sometimes prevents the development of 

 larvae but in time this becomes less and the insects then have a weakened 

 tree to attack. Trunk, branches and twigs are perhaps equally liable to 

 be injured. The burrows extending in all directions, partly in the outer 



