THE GENUS DENDROCTONUS. 



107 



mines extend at right angles from the main galleries and are exposed 

 in the inner bark, often marking the surface of the wood (figs. 66, 67, 

 68). The stout, whitish, grublike larvae transform to pupae and adults 

 in cells, either exposed or not, in the inner bark. The broods usually 

 work independently of the other species, and often occupy and 

 separate the bark on the lower to middle trunks of standing and 

 felled trees. The fresh attack on living or freshly felled trees is 

 indicated by red borings at the entrance to the galleries and lodged 

 in the loose bark on the trunk or around the base; the leaves of the 

 dying trees fade, turn pink- 

 ish yellow, or remain green in 

 the fall succeeding spring and 

 summer attack, but turn 

 brown during the winter and 

 spring. 



SEASONAL HISTORY. 



OVERWINTERING STAGES. 



The winter is passed in the 

 inner bark of trees, logs, etc., 

 attacked the preceding spring 

 and summer, principally as 

 developed broods of adults, 

 but also as young to matured 

 larvae and probably parent 

 adults. 



ACTIVITY OF OVERWINTERED 

 BROODS. 



Activity begins during the 

 first warm weather in April, 

 when the parent adults ex- 

 tend their galleries and de- 

 posit eggs. The young adults 

 of the developed broods be- 

 gin to emerge by the middle of 

 April, and continue to come out during June or July or later. The 

 overwintered, large larvae evidently complete their development and 

 emerge by the first of August, while the broods of young larvae of 

 the possible second generation from eggs deposited in the fall evidently 

 complete their development and begin to emerge in August, and 

 continue to do so until cold weather, when some will begin their 

 second hibernation as fully developed broods of adults. 



Fig. 65. — The Douglas fir beetle (Dendroctonus pseudo- 

 tsugae): Adult. Greatly enlarged. (Author's illustra- 

 tion.) 



