1! 



SOMl'] INSECTS INJURIOUS TO FORESTS. 



de])ro(lati()ns ])y insocts in ad joinini^; forests, and the relation of time 

 of felling tind)er in regular logging o])erations to attack by Dendroc- 

 tonus and other bark and wood boring insects. 



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

 1905, with lieadcjuarters at (^enterville, Idaho, and continued until 

 October 10, 1905. 



DEATH OF THE PINE CAUSED BY THE WESTERN PINE- 

 DESTROYING BARKBEETLE. 



Observations l)y the writer served to confirm the conclusion of Mr. 

 Burke that the primary enemy was a barkbeetle identified by Doctor 

 Hopkins as tlie western pine-destroying barkbeetle (Dendroctonus 

 hrevicomis T^ec). 



CHARACTER OF THE INSECT AND ITS WORK. 



The adult insect is a stout, brownish-whiged beetle (fig. 7) fi'om 

 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 wind- 

 ing galleries (fig. 8 and 

 Pis. il. III) in which to 

 deposit eggs. These 

 galleries serve to cut off 

 the natural movement 

 of the sap and com- 

 pletely girdle and kill 

 the tree. In the vicinity 

 of Centerville, Idaho, 

 the eggs, deposited dur- 

 ing June, July, or Au- 

 gust, in little niches in the sides of the galleries, hatch within 4 or 

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

 from the primary gallery through the outer layers of the inner bark 

 until they have completed their growth, which requires from al)out 

 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 genera- 

 tion have thus developed — in a})out 60 or 70 days — they bore out 

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

 tinue their depredations. 



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

 dead and dying trees scattered about or in chmips or large patches. 

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



Fig. 7.— Tlie western pine-destroying barkbeetle (Dcndroctimiis 

 brevicomis): a , adult female; 6, c, d, details of punetuation; e, 

 adult male. Natural size at left (original). 



