species ▁of ▁Douglas - fir . ▁The ▁be et les ▁also ▁inf est ▁down ed ▁L arch ▁trees . ▁Out break s ▁often ▁occur ▁in ▁conj unction ▁with ▁dr ought , ▁root ▁rot ▁dise ases , ▁over c row ding , ▁damage ▁by ▁insect s ▁that ▁damage ▁fol i age , ▁and ▁environmental ▁disturb ance . ▁This ▁insect ▁is ▁part ▁of ▁the ▁western ▁forest ▁e cos ystem , ▁playing ▁a ▁role ▁in ▁thin ning ▁weak ▁trees ▁in ▁a ▁stand . ▁ ▁Ad ult ▁Douglas - fir ▁be et les ▁are ▁light ▁brown ▁when ▁young ▁and ▁become ▁dark ▁brown ▁or ▁black ▁with ▁re dd ish ▁wing ▁covers . ▁They ▁are ▁somewhat ▁hair y ▁and ▁range ▁in ▁size ▁from ▁ 4 . 4 ▁to ▁ 7   mm . ▁The ▁lar va e ▁are ▁small , ▁leg less , ▁the ▁size ▁of ▁gra ins ▁of ▁rice , ▁and ▁white . ▁P up ae ▁are ▁white ▁to ▁cre am ▁colored . ▁Vis ible ▁evidence ▁of ▁inf est ation ▁includes ▁patch es ▁of ▁orange ▁to ▁re dd ish - b rown ▁b oring ▁dust ▁in ▁the ▁b ark ▁or ▁at ▁the ▁base ▁of ▁the ▁tree . ▁Res in ▁stream ers ▁from ▁attacks ▁higher ▁in ▁the ▁tree ▁may ▁also ▁be ▁present . ▁Inside ▁the ▁b ark , ▁ 6 ▁to ▁ 3 0 ▁in ch ▁egg ▁gall eries ▁run ▁parallel ▁with ▁the ▁gra in . ▁E gg s ▁are ▁laid ▁on ▁either ▁side ▁of ▁the ▁gallery ▁and ▁when ▁they ▁h atch , ▁the ▁lar va e ▁mine ▁per