Gypsy Moth

The Gypsy Moth, Lymantria dispar (L.)

[image:] Gypsy moth larvaThe gypsy moth (GM) is an invasive nonnative insect with larvae that feed voraciously on the foliage of many North American plants. GM caterpillars prefer oaks and aspens, but do not eat conifer needles unless they are starving. Preferred hosts are concentrated in the Northeast, Midwest, and southern Appalachians and Ozarks. GM was introduced about 130 years ago near Boston and has chomped its way through New England and Mid-Atlantic regions; the current “invasion front” stretches from North Carolina across to Minnesota.

At the invasion front, trees are being attacked for the first time and are usually completely defoliated, sometimes for a second time if they re-foliate. Behind the front, GM live at various densities, and populations can quickly increase (or “erupt”) every 5 to 10 years. Defoliation reduces trees’ growth, vigor, and resistance to biotic and abiotic stressors and cause direct mortality. Although less than 20% of the trees in most forests will die, tree mortality can be heavy in some places. Tree mortality reduces timber value; residential costs are associated with GM defoliation and nuisance— caterpillar hairs cause allergic reactions in humans and caterpillar “frass” (essentially excrement) can literally rain down from trees.

Fortunately, in forests behind the invasion front, several of the biological controls that were introduced at various times generally keep GM populations at reasonable numbers, although outbreaks do occur. Chemical insecticides are no longer used for spraying, only biocontrol agents such as the lepidoptera-specific bacterium Bacillus thuringiensis (Bt); a viral pathogen (Gypchek); and mating disrupters are now mostly used. For over 100+ years, the GM has been the focus of intensive study as federal, state, and academic entomologists, ecologists, and other scientists have worked to control and understand this voracious pest and stop its spread.

Much of the biology and behavior of GM has been studied and reported in the scientific literature and many control measures have been developed; they will be discussed in the sections below. Currently, Northern Research Station research focuses on newer goals — (1) slowing the spread of this insect into new susceptible habitats; (2) developing and improving biological controls; and (3) determining what factors influence eruptions or outbreaks.

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Last Modified: August 17, 2015