Leucoma salicis (L.)
Severe defoliation of eastern cottonwood and other ornamental poplars by caterpillars of this European insect has been common in the Northeast since 1920. Woodland infestations in much of this country are uncommon. Since 1967, however, noticeable woodland defoliation of both bigtooth and trembling aspen has been reported in several areas of central and eastern Maine. In 1968 these infestations covered over 10,000 acres of woodland poplar in Maine with smaller but similar areas in New Brunswick. Scattered, but relatively short-lived infestations, have occurred periodically since then. Most have encompassed less than 5,000 acres.
The larvae (caterpillars) of the satin moth feed on a variety of the poplars and willows but are most common on: eastern cottonwood (Carolina poplar), white poplar, Lombardy poplar, bigtooth aspen, trembling aspen and balm-of-Gilead.
Description and Life Cycle
With the onset of warmer weather in May, the small overwintering caterpillars emerge and begin feeding on the foliage of host trees. They increase in size and by mid-June are producing very noticeable defoliation. The full-grown caterpillar is about 1 1/2 inches long and varies from mottled gray to black in color with a black head and a row of large conspicuous white spots down the back. The body bears tufts of yellowish-brown hairs coming from reddish-brown warts which are arranged in several rows (image). Mature caterpillars also become a nuisance through their wandering about over nearly everything in the area in search of food or a place to spin their cocoons. Most caterpillars have finished feeding by late June.
The cocoons are made of loosely woven silk and the black hairy pupa is visible inside. Cocoons are found attached to a wide variety of objects in the infested area from tree trunks to fence posts and the sides of buildings.
The moths begin appearing in early July and become most numerous around mid-July. As the name implies, the white moths are satiny in appearance. The body of the moth itself is black but is covered with a dense covering of white scales and hairs (image). The wingspan is about 1 1/2 inches. Moths are attracted to light and are often so numerous that they coat objects in the vicinity of lights like snow. Egg laying takes place in July and the tiny caterpillars hatch from the eggs in August. After feeding for a time the still small caterpillars crawl to a crack or crevice in the bark of the trunk or larger branches of the foodplant in late August or early September and spin a silken hibernating web (hibernaculum). These webs closely resemble the bark and are difficult to notice. The caterpillars overwinter within these webs and emerge in the spring to resume feeding and development.
The satin moth caterpillars may be controlled by spraying the foliage of host trees with Bacillus thuringiensis (Bt), carbaryl or cyfluthrin in the spring as soon as the foliage is out and caterpillars are starting to feed. Be sure to follow the application instructions on the container label.
*NOTE: These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Pesticide recommendations are contingent on continued EPA and Maine Board of Pesticides Control registration and are subject to change.
For your own protection and that of the environment, carefully read the label on the insecticide container and apply the insecticide only in strict accordance with use directions and precautions.
MAINE DEPARTMENT OF CONSERVATION
Maine Forest Service - Forest Health and Monitoring Division
More information on the Satin Moth