Description

At least three similar species occur in Louisiana, the “white-marked tussock moth” (Orygia leucostigma), the “fir tussock moth” (Orygia detrita) and the “definite tussock moth” (Orygia definita). The larvae are medium-sized caterpillars that reach a length of approximately 1.5 inches (38 mm) when mature. Caterpillars are distinctive, bearing three long “pencils” of setae, two extending forward, well beyond the front of the head, and a third extending at an angle up and back from the rear of the abdomen. In addition, they bear a series of four dense, short, pale-colored tufts of hair along the midline in the front half of the body. A series of bumps or “warts” along the bodies varies in color with species and is important in distinguishing species. The ground color of the body and head also varies with species. The head may be red, yellow or orange, and the body varies from yellow to dark gray. The head of the white-marked tussock moth caterpillar is bright red or reddish orange, and the warts along the sides of the abdomen are yellow. The head of the fir tussock moth is also red, but the warts along the sides are orange. Caterpillars of the definite tussock moth are overall more yellow, with yellow heads and warts. Caterpillars pupate within a white or off-white cocoon surrounded and protected by the spiky hairs of the last larval exoskeleton. Adult males of all species are mottled brown or brownish gray, broad-winged moths up to 1 inch (25 mm) in length when at rest. The wings possess subtle darker bands, circular patterns and white highlights near the rear of each wing. Adult males of the three species are similar and require detailed inspection to separate. Adult females possess minute, stubby wings and are not capable of flight. They cannot be identified to species without genetic analysis. Egg masses are protected by hairs from the female’s cocoon and are covered by a frothy secretion produced during egg laying.

Life Cycle

All species overwinter as eggs. During early spring, at bud break, the eggs hatch into tiny, hairy caterpillars that disperse and feed on a wide variety of deciduous tree and shrub hosts with preferences depending on species. Larvae feed individually and they wander extensively as they approach maturity, typically during late April and May in the southern U.S. Depending on species, they may go through one to three generations in Louisiana. First generation adults emerge in June and July, are short lived, and only mate and lay eggs. Males fly and are attracted to the flightless females via pheromones. After mating, the females produce egg masses at the pupation site and die shortly thereafter.

Ecological Significance and Pest Status

In Louisiana, tussock moth caterpillars are among the most abundant early spring caterpillars in forest and urban settings. Although all three species may be present in one area, the dominant species is often the fir tussock moth due to its preference for oak foliage, especially live oaks. The common name “fir tussock moth” is an unfortunate artifact, since the species does not feed on fir trees, and fir trees do not occur in Louisiana. An alternate common name, the “live oak tussock moth,” is more appropriate, but fir tussock moth persists. Despite the number of fir tussock moths that feed on oaks in Louisiana, the damage is typically not noticeable, although significant defoliation can occur during outbreak years. Many trees are able to generate a new flush of foliage following defoliation, and variations in population densities mean many trees are not defoliated annually. The feeding activities of larvae perform a valuable ecological service by recycling a portion of tree biomass back to the soil via their abundant droppings. These provide nutrients that promote herbaceous growth and improve overall floral diversity in forest and urban park ecosystems. Tussock moth caterpillar infestations are an annual spring event in Louisiana along with buck moth (Hemileuca maia) and tent caterpillars (Orygia spp.). The hairs of tussock moth caterpillars are associated with venom glands and can cause skin irritation, especially in children and sensitive individuals or with rough handling. The wandering habits and irritating hairs of mature tussock moth caterpillars in search of pupation sites can pose a nuisance to homeowners. Children should be taught to avoid handling the attractively marked caterpillars and cocoons.

Control

Control is typically not required or feasible given the large scales involved in treating entire trees. Trees can generally withstand limited defoliation, though repeated annual defoliations can weaken trees and make them more susceptible to other problems. For control options on high value trees and shrubs, contact your local extension agent or LSU AgCenter entomologist.

References

Lee, H. S., G. H. Tan, Y. M. Khoo, G. Balasubramaniam, P. L. Ooi, and K. T. Goh. 1991. Tussock moth dermatitis: evidence for histamine involvement. Reviews on Environmental Health 9: 11-15.

Wagner DL. 2005. Caterpillars of Eastern North America. Princeton University Press. Princeton, New Jersey. 512 pp.