Mercer County Horticulturist GYPSY MOTH 2008 Barbara J. Bromley Mercer County Horticulturist bbromley@mercercounty.org 609-989-6830

These are gypsy moth females These are gypsy moth females. Our concern is with the damage done by the caterpillar, the immature stage of the gypsy moth’s life.

Feeding Habits Preferred species: all oaks, apple, aspen, basswood, river birch, mountain ash, sweetgum, willow, hawthorn, hazelnut, hophornbeam, rose, serviceberry, witchhazel

Feeding habits, cont. Secondary (if preferred unavailable or for late instar caterpillars): beech, black and yellow birch, blackgum, yellow buckeye, butternut, sweet and black cherry, American and slippery elm, all hickories, boxelder, Norway maple, red and sugar maples, pear, black walnut, chestnut, hemlock, all pines, all spruce, blueberry, redbud, sourwood

Feeding habits, cont. Generally immune except in extremely heavy caterpillar pressure: ash, E. red cedar, American holly, horsechestnut, Kentucky coffee tree, black and honey locust, mulberry, sycamore, tulip tree, azaleas, dogwood, elderberry, grape, juniper, rhododendron, mountain laurel, spicebush, sassafras, and all viburnums.

Lymantria dispar Lepidoptera Complete metamorphosis 1 generation per year

Life Stage 1: Moths The life cycle starts in July or August with the mating of the day-flying brown male moths to the flightless white female .

Life Stage 2: Egg Mass After mating the females lay their eggs in “masses” of about 300 eggs. An egg mass is generally firm, oval shaped, about the size of a quarter, and buff or tan colored.

The egg masses remain on the tree, house siding, camper wheel well, shrub, rock, etc. through fall and winter. Photo: MN Tree Care

Controlling egg stage: Ideally, scrape these masses into a bucket of soapy water or into a paper or plastic bag to be thrown into the trash. May microwave egg masses for 2 minutes to kill the eggs. May thoroughly spray egg masses with dormant oil spray. Do not leave egg masses on the ground.

Sometimes eggs are parasitized by Ooencyrtus kuvanae, a tiny parasitic wasp that lays her eggs when the temp is ≥33°F

Life Stage 3: Caterpillar Caterpillars hatch from the eggs in late April or early May depending on weather.

A close-up of hairy first instar (growth stage) caterpillars. These hairs and silk threads enable the caterpillar to “balloon” on the wind.

First and second instar caterpillars can be carried from foliage a great distance by wind.  They can hang in trees on a silk strand and be blown away. First instars climb to the top of a tree before they start feeding in earnest. Gypsy moth caterpillars do not form a webby nest in a tree. (That’s Eastern tent caterpillar in spring and Fall webworm in late spring and summer.)

A full grown caterpillar – 1 ½ to 2 inches long and hard to kill with chemicals.

Males go through 5 instars (growth stages) before pupating, females through six. At the 4th instar, behavior changes dramatically. They then feed during the night, and descend at dawn to rest through the day. At dusk they climb the tree to feed again.

Migrating fourth and fifth instar caterpillars

Controlling caterpillar stage: Biological Pesticides: Spray second and third instars (caterpillars up to 1 inch long) with Bt (Bacillus thuringiensis is a naturally occurring microbial sold as Dipel, Bactur, Foray, Thuricide, et. al.) Commercial aerial sprays easy, but must be timely and arranged for in advance. Can spray from ground into trees. Use a professional for trees over 20 feet.

Chemical pesticides: Spray second and/or third instars with labeled chemical insecticides, such as carbaryl (Sevin), acephate (Orthene), or malathion. Less desirable, because non-target insects such as honey bees, ladybugs and other beneficials may be killed. Fourth and fifth instars are less likely to be effectively controlled.

Sticky barrier bands: Duct tape or two sided carpet tape with a sticky substance on it that will not drip onto the bark, such as Tanglefoot. (late April through June or mid summer)

Insecticide impregnated band (June through July)

Folded burlap strip Burlap should be 18 inches wide and long enough to fully wrap around the tree and overlap. Tie it in the middle with string. (early June through mid summer)

Caterpillars congregate under the burlap and should be hand picked or crushed.

There are naturally occurring parasites and predators on larvae that do not seriously reduce populations. Deer mice and shrews are known to feed on caterpillars. Some ants and ground beetles are also predators.

Nucleopolyhedrosis virus (NPV) is a known disease of gypsy moth caterpillars. It is quite effective at collapsing very large gypsy moth populations, but is not very effective with low populations.

Life Stage 4: Pupa Around July, mature caterpillars stop feeding and weave silk around their bodies to form a hard, brown shell or cocoon. 

The metamorphosis (or change) into the moth inside the pupa takes about two weeks. Moths, the adult stage of the life cycle, emerge from the pupal cases in mid-August.  The moths do not eat, and they live about a week.  This emergence of the moths starts the life cycle again.

Trees defoliated more than 40% become stressed by using next year’s energy reserves to grow new leaves during the same season. Keep trees watered and fertilized to lessen long term damage.

Gypsy Moth Management: Summary Plant resistant species Destroy egg masses (fall and winter) Microbial/Biological sprays (early May) Chemical sprays (May and June) Hand removal (anytime and any life stage) Tree banding with sticky barrier traps (early spring/June through mid summer) Tree banding with folded burlap (early spring/June through mid summer)

Evaluation in non-isolated situations Masses per tree Predicted defoliation Treatment 1-10 None Burlap trees near house, destroy life stages found, monitor late season caterpillars and eggs 11-50 Trace Problem a year away, monitor 51-100 30% Notify neighbors and authorities. Consider community-wide aerial spray application 101+ More than 30% Above plus spray, sticky bands on trees

Any Questions?