18 



SOME INSECTS INJUKIOUS TO FORESTS. 



depredations by insects in adjoining forests, and the relation of time 

 of felling timber in regular logging operations to attack by Dendroc- 

 tonus and other bark and wood boring inserts. 



Accordingly, investigations were begun by the writer on May 17, 

 1905, with headquarters at Centerville, Idaho, and continued until 

 October 10, 1905. 



DEATH or THE PINE OATJSED BY THE WESTERN PINE- 

 DESTBOYING BABKBEETLE. 



Observations by the writer served to confirm the conclusion of Mr. 

 Bm-ke that the primary enemy was a barkbeetle identified by Doctor 

 Hopkins as the western pine-destroying barkbeetle (Dendroctonus 

 irevicomis Lee). 



CHARACTER OP THE INSECT AND ITS WORK:. 



The adult insect is a stout, brownish-wiuged beetle (fig. 7) from 

 one-eighth to three-sixteenths inch in length, which attacks the living 



trees in swarms, and 

 burrows into the living 

 bark, through the inner 

 layer of which each 

 female excavates wiiid- 



f^^'^P* \M^lk^ ^^ galleries (fig. 8 and 



/«»{.^i-.fe-: .pv^ Jmmm/ Pls.II,III)inwhichto 



deposit eggs. These 

 galleries serve to cut off 

 the natural movement 

 of the sap and com- 

 pletety girdle and kill 

 the tree. In the vicinity 

 of Centerville, Idaho, 

 the eggs, deposited dur- 



, . ,.,„ • t. . , ^^o June, July, or Au- 



gust, m httle mches m the sides of the galleries, hatch within 4 or 

 5 days mto small whitish larva^ (fig. 9), which mine at right angles 

 from the prmiary gallery through. the outer layers of the inner bark 

 until they have completed their growth, which requires from about 

 20 to 30 days. They then bore into the outer corky bark (fig 12 a) 

 where they excavate little cells in which to transform, first to the pupa 

 (fig. 10) and later to the adult. When the broods of the first .venera- 

 tion have thus developed-in about 60 or 70 days-they bore out 

 through the bark and fly to other trees to repeat the process and con- 

 tmue their depredations. 



The presence of this destructive insect in a forest is indicated (1) bv 

 dead and dymg trees scattered about or in clumps or large patches 

 (The dymg ones, with fading yellowish and reddish foliage, are called 



Fig. 7.— The western pine-destroying barkbeetle {Dendroctonus 

 breviamis): a, adult female; 6, c, <Z, details of punctuation; e, 

 adult male. Natural size at left (original). 



