THE LARCH CASEBEARER
(Lepidoptera: Coleophoridae)

The larch casebearer, Coleophora laricella, is an insect native to Europe and Asia. It was first recorded in Canada in 1905, and has since spread throughout eastern Canada and the Northeastern and Western United States.

The larch casebearer is a pest of larch also known as tamarack (including american, common, Dahurian, Dunkeld, japanese, tibetan, and western larches). Caterpillars of this insect cause damage by mining the larch needles, resulting in the hollowed needles to turn brown. Most damage occurs to the tree when the new foliage is developing. Several seasons of attack will result in severe reductions in growth. Branches may die during outbreaks but tree mortality is rare.

The larch casebearer has one generation per year. Winter is passed as an immature third instar larva in a case made from a hollowed out needle lined with silk. The case is attached to the base of needle fascicles (bundles) after the tree has shed its foliage. The majority of overwintering larvae are clustered on the tips of branches. As the temperature increases in early spring, the larva becomes active again and passes through the fourth and last instar, which is the most destructive stage. Full-grown larvae are about 6 mm long. After three to four weeks of needle mining, the larva fastens the case to a twig or needle with silk and changes to a pupa.

In late May and early June the tiny adult moths emerge. The adult is silvery grey and has narrow wings with a fringe of long hairs. The wingspan is approximately 9mm (3/8 inches). Natural dispersal occurs by moth flights until August.

Moths lay eggs singly near the tip of the needle, usually on the lower surface. The eggs are very small, reddish-brown, and resemble inverted jelly molds with 12-14 ridges. Hatching occurs in 2-3 weeks and the newly emerged larvae enter directly into the tissue of larch needles. The first two larval instars are spent in leaf mines with several needles being mined during this period.

CONTROLS

A number of species of parasites have been imported from Europe and have now established populations in North America. These have kept the casebearer at low numbers in forests, but where larch is grown as an ornamental, chemical control may sometimes be warranted. Spray the tree with malathion or carbaryl in May and again in September. Carbaryl is toxic to bees and should not be sprayed around other plants that are in bloom. Commercial recommendations for the larch casebearer can be found in Ontario Ministry of Agriculture and Food (OMAF) Publication 383, Nursery and Landscape Recommendations. This publication can be ordered through your local OMAF office, or through the OMAF website.

Follow label directions to ensure the safety and efficacy of each product

B. Smith/W.A. Attwater

PDCF-105 (Revised 2003/11/07)