Beetles 



299 



almost invisible from above. The larvas are white and footless little grubs 

 with very strong jaws. The family includes 150 species in North America, and 

 because of the recently awakened interest in forestry is now being given special 

 attention by entomologists. The losses, by the death of trees and the rid- 

 dling of timber, caused by these obscure little insects are enormous. Pinchot, 

 chief of the United Slates Bureau of Forestry, has recently estimated the 

 annual forest losses caused by insects to be $100,000,000, and most of the 

 ravages are due to the Scolytidae. 



Among the most destructive genera are Dendroctonus and Tomicus, 

 each with numerous species. They often work in the same tree. For 

 example, the famous Monterey pines of California are attacked by Dcndroc- 



FlG. 408. — Galleries in MunUiey pine, with larva;, pupa;, and adults of the engraver- 

 beetle, Tomicus plastographus. (Natural size except the single beetle outside, 

 which is enlarged three times.) 



tonus valens in the lower three or four feet of the trunk, as many as four 

 hundred individuals (larvK, pupae, and adults) occurring in this limited 

 space in badly infested trees, while above this zone on up to the top of the 

 tree are the mines of Tomicus plaslographus (Fig. 408), from thirty to forty 

 pairs burrowing into each yard of trunk. It is plain that such a combined 

 attack on a single tree means death to it. 



The ambrosia-beetles, including half a dozen genera and many species, 



