514 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



FOREST INSECTS 



A certain amount of insect injury is occurring in almost every 

 great forest all the time, while from time to time particular 

 forests are devastated by the outbreaks of certain insects that 

 kill practically all of the trees in the affected regions. In some 

 instances these outbreaks have spread over 50,000 square miles, 



FIG. 245. Work of a bark-borer, Phlceosiniis cristatus, on Monterey 



cypress. (Reduced.) 



and trees that would have produced millions of feet of lumber 

 have been destroyed. Each year there are lesser outbreaks 

 when, although comparatively few trees may be killed, many are 

 retarded in their growth or so distorted or injured that they 

 make only second- or third-class lumber. Altogether the 



