Needles begin to fall from infested trees the year following attack but becomes more noticeable the second year after infestation. Description of Life Stages Adult Douglas-fir beetles are stout, cylindrically shaped, and 4 to 6 mm. long. The whitish eggs are 1mm long. Eggs hatch into white, legless larvae with shiny, light-brown heads. Adult Douglas-fir beetle.
Mature larvae transform into pupae before becoming adults.
Pupae are white, mummy like, with some adult features, including wings that are folded beneath the abdomen. The Douglas-fir beetle has one generation per year. Broods remain in the tree and overwinter mainly as adult beetles, but also as larvae. Larvae that have overwintered complete their development and emerge as adults in the summer. Typically, late-season attacks account for less than 20 percent of all attacks in one season.