The white-marked tussock moth is native to eastern North America and parts of Canada. This species of tussock moth overwinters in the egg stage. Eggs are laid by females in groups of approximately 300 in a white frothy mass on the cocoon from which the female moth emerges. When temperatures warm in the spring and as host plant leaves are emerging, the eggs of the white-marked tussock moth hatch by approximately April until June. This depends upon location and temperatures. Young, newly hatched larvae will balloon to their host plants and skeletonize the leaves as they feed. As the caterpillars age and grow in size, they are capable of eating the entire leaf with the exception of the major veins and petiole. Fully grown caterpillars are approximately 1.22 inches long. These caterpillars are conspicuously colored - they have red/orange head capsules and a mostly yellow body with tufts of white to yellow hair. The tufts are found on abdominal segments 1 through 4 (four tufts total) and the caterpillars have a black stripe in the middle of their back that has a yellow stripe on either side. Caterpillars also have two bright red glands near the back-end. Once mature, the caterpillars pupate in a gray colored cocoon that they form, creating it with hairs from their bodies. Cocoons can be found on host plant twigs, branches, or the bark of the trunk. There may be 1-3 generations of the white-marked tussock moth per growing season, depending upon location and seasonal temperatures. Adult male moths are 1.0-1.2 inches in wingspan and gray/brown in color. Adult female moths are wingless, a drab white color, hairy, and only 1/2 inch in length. Caterpillars of this species may be common in the late summer when other species of caterpillar's activity has ended.
Avoid touching these caterpillars or their cocoons: they may cause allergic reactions, especially if their hairs come into contact with sensitive skin (ex. back, stomach, underside of arms) (Wagner, 2005). Contact dermatitis (itching) as a result of interacting with these insects has been reported from schools and daycares. Teach children how to identify and avoid handling cocoons and caterpillars. These caterpillars have urticating (irritating) hairs. Welts may appear on the skin within minutes, but subside the next day; however itching can last for several days depending upon the sensitivity of the individual.
Feeds on at least 60 deciduous host plant species and some conifers, the most common of which as listed by Johnson and Lyon (1991) and Wagner (2005) are included above. At least 116 genera of possible host plants for this insect have been noted in the scientific literature (Heppner, 2003). This pest can appear frequently throughout the Northeast. It may cause problems for several years when population outbreaks occur, and then almost vanish from that area, only to return years later. White-marked tussock moths may be occasional pests of Christmas tree farms. Usually, however, large trees can tolerate feeding by these insects and chemical management options are unnecessary. They may be an issue for smaller ornamental trees and shrubs.
Sex pheromones produced by the adult female white-marked tussock moth (who is wingless) to attract the winged males have been identified by researchers. The pheromone is: (Z,Z)-6,9-heneicosadien-11-one (Z6Z9-11-one-21Hy) (Grant et al., 2006). However, to make it stable for field and trapping use, researchers have experimented with a pheromone "precursor", which they have identified as: (Z,Z)-6,9-heneicosadien-11-one ethylene ketal. Field tests in 2004 and 2005 showed that sticky traps fitted with an autonomous pump delivering the ketal (0.1-1 microg/microL in heptane) at 10 microL/hr to a cotton pad soaked with the hydrolyzing solution were attractive to male white-marked tussock moths (Grant et al., 2006). Visual monitoring for these insects can include searching susceptible host plants for cocoons (be careful not to touch them as they contain the hairs of the caterpillars), overwintered frothy egg masses on the cocoons, and the caterpillars themselves any time between approximately April (young larvae) through the late summer.
If overwintering egg masses on spent white-marked tussock moth cocoons are found, they can be removed and destroyed. Avoid direct handling or touching the cocoons; wear gloves and appropriate clothing. Wash any clothing that comes into contact with the cocoons separately. Cocoons contain the irritating hairs of the caterpillars and can cause allergic reactions.
Birds may be significant predators of the older white-marked tussock moth caterpillars. Mortality of younger-instar caterpillars may be due to the inability to find a suitable host plant when initially ballooning to disperse. Predation of young larvae can also occur by invertebrate predators. Larger ground beetles and Polistes spp. wasps have also been reported to predate upon these caterpillars. Caterpillars in the Orgyia genus are known to be infected by nuclear polyhedrosis viruses and cytoplasmic polyhedrosis viruses. If killed by these pathogens, they hang from the substrate limp, attached by their prolegs (in a shape similar to the spongy moth, Lymantria dispar, caterpillar when it is killed by an NPV virus). An abundance of tachinid fly parasitoids (Arnaud,1978) as well as braconid, ichneumonid, eulophid, pteromalid, and scelionid wasp parasitoids (Krombein et al.,1979) have also been reported for the white-marked tussock moth. Typically, the natural enemies of the white-marked tussock moth keep their populations at manageable levels.
Abamectin (NL)
Acephate (larvae) (NL)
Azadirachtin (NL)
Bifenthrin (NL)
Carbaryl (L)
Chlorantraniliprole (NL)
Cyfluthrin (larvae) (NL)
Emamectin benzoate (L)
Gamma-cyhalothrin (larvae) (L)
Indoxacarb (L)
Lambda-cyhalothrin (larvae) (L)
Neem oil (NL)
Spinetoram+sulfoxaflor (N)
Spinosad (larvae) (NL)
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), azadirachtin (injection, soil drench), chlorantraniliprole (soil drench), emamectin benzoate (injection), and neem oil (soil drench).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
