Pine tussock moth and Eastern larch beetle

Pine tussock moth

Late June and early July pheromone trapping of male pine tussock moths, Dasychira pinicola, in southeastern Hubbard and northeastern Wadena Counties indicate that this forest pest is increasing. Annual trapping has been done since the early 1960's,and several spray operations in the 1960's, 1979, and 1980 in Pine County were necessary to control outbreaks of this pest.


pine tussock moth

Its caterpillar stage prefers jack pine, but it will also consume needles and buds of red pine, white pine, spruce and balsam fir. Full grown caterpillars are gray-brown, have four tufts of grayish or brownish hairs on their backs, and the first tuft has two black hair pencils on the front and three similar pencils on the rear.

Adults are gray brown moths with light and dark banding across their forewings and they are present from early July through early September. Eggs are deposited in irregular clusters on needles, trunk and dead twigs. Tiny larvae feed on needles until August or September when they spin silken threads about themselves and go into hibernation beneath rough bark edges or bases of needles. Feeding resumes in the spring on staminate flowers (male cones) and, later, on the needles. Defoliation of old and new needles, as well as buds can be nearly 100 percent. Full-grown larvae are about 11/2 inch long when they spin cocoons on twigs among the needles.

Eastern larch beetle

The eastern larch beetle, Dendroctonus simplex, is one of eight or more different tiny beetles that attack weakened or dying larch, but this bark beetle feeds exclusively on larch. Adults are about 3/16 inch long, emerge from the bark in May and seek and bore into suitable live larch. Their attack is marked by a flow of resin and dark brown boring dust. Eggs laid in inner bark tunnels called galleries hatch and complete development in about a month, then change into pupae and adults in the succeeding month. Parents and offspring adults then leave the trees and infest other larch trees.

Timely removal of dead or dying larch can control this and other bark beetles. Since they feed mainly on the live tissues of the inner bark, the wood behind the bark is only slightly scored, so larch trees killed by this bark beetle can be harvested and used for lumber, posts and other wood products. Another reason to utilize larch killed by bark beetles is that deep wood-boring beetles seem to avoid dying larch and larch are not easily decayed by wood-rotting fungi.


close up of decayed by wood-rotting fungi