Larch and Tamarack
Appearance and Life Cycle
The larch casebearer is a small, silvery to greyish-brown moth with a wingspan of approximately 9 mm. The wings are narrow and fringed with long, slender hairs. The adults may be present from late May to early July, at which time the females deposit their eggs on the needles of the host. The eggs are reddish-brown and resemble inverted cups with 12-14 ribs or ridges on the sides. Larvae hatch from the eggs and burrow into the needles, feeding until late summer. At this time, the larva constructs its case, by lining a hollow portion of the needle with silk and chewing the section free at both ends. The case is the colour of a dead needle and is an excellent camouflage. Larva continue
to feed by attaching its case to a needle and mining the inner contents as far as it can reach. The larvae fasten themselves to the base of a bud, branch or twig to overwinter. Larvae resume mining needles in the spring until they are full grown. Full grown larvae are dark, reddish-brown with black heads and are approximately 6 mm long. Larvae pupate within their cases and emerge after two weeks, completing the single generation a year life cycle.
Damage occurs when larvae mine the inner contents of the needles. Damage appears to be heaviest in the lower crown area. Feeding causes the tips of the needles to bend and turn light brown. If heavily infested, trees may appear reddened as though scorched by fire or damaged by a late spring frost. Later in the season, the trees regain their normal appearance, as larch have the ability to refoliate. However, repeated attacks cause a significant reduction in growth and weakening of the trees, making them susceptible to attack by other insects or diseases.
Native parasites are unable to hold the larch casebearer in check. In certain localities, birds play a major role in control. Trees can be sprayed with: Bacillus thuringiensis; carbaryl; chlorpyrifos; deltamethrin; malathion or permethrin. Spray larch foliage in May or in mid-July to August to destroy feeding larvae.
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