. The Black Hills beetle : with further notes on its distribution, life history, and methods of control. Mountain pine beetle; Forest insects. exception to this is when the top portion of the tree or one side of the trunk is killed the first year and a brood develops in the remain- ing living bark the next year. This sometimes occurs, bul is never common enough to require special notice. Its occasional occurrence, however, explains why broods of the beetle are sometimes found in trees which appear to have been dead for two or three years. LIFE HISTORY. The insect passes the winter, or inactive
. The Black Hills beetle : with further notes on its distribution, life history, and methods of control. Mountain pine beetle; Forest insects. exception to this is when the top portion of the tree or one side of the trunk is killed the first year and a brood develops in the remain- ing living bark the next year. This sometimes occurs, bul is never common enough to require special notice. Its occasional occurrence, however, explains why broods of the beetle are sometimes found in trees which appear to have been dead for two or three years. LIFE HISTORY. The insect passes the winter, or inactive period, in all stages—as larvae, pupae, and adults—beneath the bark of trees attacked by the parent beetles during the previous summer and fall. Activity begins in the spring as soon as sufficient warm weather prevails, when the broods continue to develop and mature, but remain in the bark until about the middle of July (Black Hills, latitude 44°, altitude 7,000 feet), probably later northward and at higher altitudes, and earlier southward and at lower altitudes. When the adults (fig. 1) begin to emerge from the bark of the trees in which they had developed from eggs depos- ited the previous year, they usually fly in swarms, and attack the living trees, in which they excavate galleries through the inner layer of bark and groove the surface of the wood. Along the sides of these primary galleries excavated by the beetle, eggs are deposited for the next generation, which, as be- fore, hatch into grubs or larvae (fig. 5), which mine at right angles to the primary galleries through the inner bark, on which they feed. This feeding and growing stage continues during the first summer, some of the individuals completing their development before fall. so that all stages, including the pupae (fig. 6), may be found during the fall in the trees attacked in July. These with the younger broods remain dormant dur- ing the winter and complete their development the following spring in time
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