. Bulletin. Insects; Insect pests; Entomology; Insects; Insect pests; Entomology. 18 SOME INSECTS INJURIOUS TO FORESTS. depredations })y insects in adjoining forests, and the relation of time of fellino; tind)er in re<2;ular loi2:^inp; operations to attack by Dendroc- tonus and other bark and wood borin^; insects. Accordingly, investigations were begun by the writer on May 17, 1905, with headcpiarters at Centerville, Idaho, and continued until October 10, 1905. DEATH OF THE PINE CAUSED BY THE WESTERN PINE- DESTROYING BARKBEETLE. Observations by the writer served to confirm the conclusion of
. Bulletin. Insects; Insect pests; Entomology; Insects; Insect pests; Entomology. 18 SOME INSECTS INJURIOUS TO FORESTS. depredations })y insects in adjoining forests, and the relation of time of fellino; tind)er in re<2;ular loi2:^inp; operations to attack by Dendroc- tonus and other bark and wood borin^; insects. Accordingly, investigations were begun by the writer on May 17, 1905, with headcpiarters at Centerville, Idaho, and continued until October 10, 1905. DEATH OF THE PINE CAUSED BY THE WESTERN PINE- DESTROYING BARKBEETLE. Observations by the writer served to confirm the conclusion of Mr. Burke that the primary enemy was a barkbeetle identified by Doctor Hopkins as the western pine-destroying barkbeetle (Dendroctonus hrevicomis Lee). CHARACTER OF THE INSECT AND ITS WORK. The adult insect is a stout, brownish-winged beetle (fig. 7) from one-eighth to three-sixteenths inch in length, which attacks the Jiving trees in swarms, and burrows into the living bark, through the inner layer of which each female excavates wind- ing galleries (fig. 8 and Pfs. II, 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 tht^ primary 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 cork}^ bark (fig. 12, a) where they excavate little cells in whicli 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 about 60 or 70 days—they bore out through the l^ark and fly to other trees to repeat the process and con- tinue their depredations. The presence of this destructive insect i
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