Gypsy moth (Lymantria dispar) is one of the most significant exotic pests in the history of the US.  Introduced to Boston in the 1860’s, it has continued to spread throughout the eastern United States. The gypsy moth larvae defoliate trees leaving them weakened and vulnerable to secondary fungal and insect invaders.

Repeated defoliation of hardwoods can kill the tree directly and a single defoliation may cause severe dieback and decline on softwood species especially when coupled with drought or other abiotic stress. Gypsy moth will affect trees in natural settings, forest plantations, and urban environments often defoliating thousands of trees in a single outbreak.

Susceptible Hosts
Gypsy moth is known to feed on hundreds of woody plant species. Preferred species are oak, aspen, willow, linden, hawthorn, apple, and alder. Less preferred species include elm, maple, hickory, beech, hemlock, pine, spruce, cedar, and sassafras.  Less preferred hosts are usually fed upon when gypsy moth populations are high and preferred species become scarce.

Pest
Lymantria dispar

Symptoms
* Shot holes in leaves beginning in spring resulting in partial or complete defoliation by midsummer.  Crowns of trees will be thin initially and will be partially to completely defoliated under heavy pest pressure.

Signs
* White, 1 ½ inch long, webby egg masses on trunks and limbs.
* Young caterpillars are black with orange spots on the back.
* Mature caterpillars grow up to 2 inches long and have five pairs of blue spots and six pairs of red spots in rows across its back.
* Pupae are tear-drop shaped and brown.

Life Cycle
* Eggs hatch in spring and larvae emerge.
* Young larvae feed in April and May and Caterpillars feed in spring and summer.
* Caterpillars pupate early to mid-summer.
* In summer, hair covered egg masses are laid in crevices, under picnic tables, and on vehicles.
* Over wintering takes place in these egg masses.
* One generation per year.

Distinguish from Look-alikes
Lymantria dispar is the only tussock (furry) caterpillar with five pairs of blue spots and six pairs of red spots in rows across its back.

Apply Lepitect annually at or just prior to full leaf emergence in the spring of the year.  A second application 30 days later may provide additional control if larvae are still feeding.

Foliar sprays with Conserve and Up-Star Gold should begin at bud break 90 GDD to control young larvae, and repeat applications should be made through early June 448 GDD.  Egg hatch occurs as oak leaves begin to unfold in the spring of the year.  This also occurs as Magnolia X soulangiana is dropping petals or Amelanchier is blooming.

Expectations:
Lepitect applications provided control of gypsy moth larvae in less than five days on smaller trees.  Control on larger trees will not occur as quickly (2-3 weeks).  Lepitect soil applications last for 30-45 days after treatment.
Conserve has a short residual (4-7 days) but is softer on beneficial insects, whereas Up-Star Gold will provide slightly longer residual, but is broad spectrum.

Use Lepitect Infusible on trees that can’t be treated with a foliar or soil application.  Lepitect Infusible has a 30 day residual.

Other Treatment Practices:
* Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
* While aerial sprays with Bacillus thuringiensis cannot be counted on to provide acceptable levels of control on individual high value urban trees it is a tool for managing Gypsy moth infestations in locations where large numbers of susceptible tree species are growing in remote locations.  Bt is typically applied using aerial spray applications.
* Plant less favorable species like sycamore, ash, tulip poplar, holly, and/or walnuts.

USDA-FS

Virginia Tech

“Slow the Spread” Project

Purdue University

APHIS

Michigan State University