Mature eastern larch beetles are light to dark brown and about 4mm long. Adults emerge from dormancy in late spring and bore into the trunk to feed, mate, and lay eggs. After the eggs hatch, larvae tunnel throughout the phloem of the tree, creating feeding galleries that cut off water and nutrient flow, which eventually kills the tree.
On the trunk of the tree, vertical galleries with many perpendicular branches signal eastern larch beetle infestations. Infested tamarack often looks reddish in late winter, as woodpeckers remove outer bark to feed on beetle larvae in the reddish inner bark. Another sign of infestation is yellowing tamarack foliage in late July or early August.
Eastern larch beetle galleries under tamarack bark. Photo by Steven Katovich, USDA Forest Service, Bugwood.org
Tamarack infested with eastern larch beetles appear red.