Larch casebearer

Overview

• Invasive – native to Europe.
• Larch casebearer was introduced to North America in the late 1800s.
• Its distribution stretches from the Maritime provinces to southern Manitoba, as well as the Rocky Mountains.
• Larch casebearer is a serious defoliator of native tamarack and exotic species of larch in Ontario.

“Invasive” refers to a species that has moved outside of its native habitat and threatens the new environment, economy or society by disrupting local ecosystems.

Host species

The larch casebearer prefers European larch (Larix decidua) and native larch or tamarack (Larix laricina).

Species identification and life cycle

• Larch casebearer adults are small grey moths.
• They emerge in June and deposit eggs singly on the needles.
• Larvae bore directly into needles, which they mine until late summer.
• At the end of their development, larvae attach their cases to a twig or a needle and change into pupae.
• In autumn, after the needles have been shed, the presence of cases can be easily detected on the twigs near buds.
• The case appears is tiny, light brown and cigar-shaped.

Symptoms and damage

• Heavy defoliation will reduce tree height and growth.
• The larch casebearer can be seen in the spring by the light brown colour of the foliage and the presence of tiny, cigar-shaped cases on needles.
• Damage caused by the larch casebearer is reflected in the drying out and browning of new needles.
• Trees weakened by larch casebearer can be susceptible to attack by secondary pests, especially eastern larch beetle (Dendroctonus simplex).
• Infestations by the species occur fairly regularly, usually on a cycle of about eight years.

Control measures

Two parasites were introduced to help control the larch casebearer: Agathis pumila and Chrysocharis laricinellae. Trees can also be protected using insecticides.