The eastern larch beetle, Dendroctonus simplex, is native to North America but is a pest to the tamarack (or larch), Larix laricina. The beetles colonize the phloem of the main stem, exposed roots and larger branches of one of the very few species of deciduous needled trees. Beetles aggregate on stumps, fallen trees and standing trees, burrow through the bark and mate within the phloem. Even trees in relatively good health can fall to larch beetle infestation. Outbreaks in North America have been recorded and monitored since the 1970s. Historically D. simplex has been thought of as a secondary pest that has only targeted hosts already weakened by advanced age, disease. previous pests, physiological stress, fire, drought, flooding or other mechanical damage.
The distribution of the eastern larch beetles extends throughout the range of the tamarack tree itself; including most of northeastern and north-central North America, western Canada and Alaska. While the western larch, Larix occidentalis and the subalpine larch, L. lyalli, are not known hosts, the eastern larch beetle has been found infesting exotic larch species planted within its range.
When viewed at close range signs of infestation are very clear; 1/2 inch diameter boring holes are initiated by adults and can be seen in bark reaching through to the phloem. Frass will accumulate below entrance holes, but some dust is left within the galleries. Egg galleries are vertical, winding tunnels visible beneath the bark which can extend 6 to 16 inches. During the growing season resin flows can be heavy and conspicuous, coating the bark when an attack is in progress. Late in the season chlorotic foliage on afflicted trees can be seen from afar. In the fall and winter, woodpeckers may forage on infected trees, removing large portions of bark in search of overwintering eggs, larvae and even adults.
Eastern larch beetles attack trees regardless of age, diameter or regional conditions; in wet lowlands to higher, drier uplands, in pure stands or mixed. Although stands affected by disease, stress, other pests or other damage are predisposed to infestation by larch beetles. Management strategies include silvicultural, mechanical and chemical methods or a combination thereof. Should you have any concerns about larches on your property contact your arborist and visit http://www.savatree.com/insect-management.html for more information and advice on control.