Gypsy Moth Management Starts at Home
The gypsy moth (Lymantria dispar) is a foreign pest with few native predators to keep populations in check here in the United States. It was introduced to Massachusetts in 1869 and has spread across the much of the northeast. Gypsy moth outbreaks began to occur in the lower peninsula of Michigan in the mid-1980’s. Caterpillars feed on tree leaves, preferring those of oak, aspen, poplar, and birch but will feed on over 500 types plants throughout the summer. Large populations can defoliate entire wooded areas. Caterpillars in large numbers (and their waste, frass) are a nuisance in residential areas. Gypsy moths cannot be eradicated, but they can be suppressed to tolerable levels.
What are the goals of suppressing them?
- Reduce high caterpillar populations to tolerable levels
- Reduce tree loss by preserving at least 60% tree foliage, to reduce stress on trees
- Prevent indiscriminate use of chemical controls
- Provide educational information
How are gypsy moth populations suppressed?
The main defense is an aerial application of Bacillus thuringiensis var. kurstaki (Btk), used to reduce high populations of gypsy moth caterpillars at sites that meet certain guidelines for treatment. Btk is a naturally occurring bacterium found in the soil and is not harmful to pets, birds, fish, plants, beneficial insects, or humans. Btk specifically targets only caterpillars of a certain age. It is applied when the caterpillars are young (usually in May) to ensure the greatest impact in reducing numbers. Alternative mechanical techniques, such as tree banding, egg mass scraping, and hormone traps to help reduce populations.
What is the gypsy moth life cycle?
The gypsy moth life cycle has four main stages: egg, caterpillar, pupae, and moth.
In mid-August, after mating with the male moths, the females lay their eggs in masses. Egg masses are generally firm, oval shaped, about the size of a quarter, and buff or tan colored. Egg masses are laid on any surface, such as tree bark, rocks, woodpiles, decks, buildings, and outdoor equipment. Since gypsy moths complete only one life cycle per year, eggs laid in mid-August do not hatch until spring.
The eggs hatch into caterpillars late April or early May. Hatch date is directly affected by weather. The colder the spring, the later the eggs hatch. A healthy egg mass can hold 1000 eggs, although the average is probably between 300 and 500. Once the eggs hatch, the caterpillars will remain on the egg mass for a few days before they leave to feed. In its short lifetime, a caterpillar can eat one square meter of leaves. Mature caterpillars are about 2” in length with long hairs grouped in bundles. They have 5 pairs of blue dots and 6 pairs of red dots running down their backs. Their heads are black with yellow markings.
In mid-July to mid-August, mature caterpillars stop feeding and weave silk around their bodies to form a hard, brown shell or cocoon. In this pupa stage, caterpillars start their metamorphosis or change into the moth stage of the life cycle. This process 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 only for a week. Female moths have white wings with brown chevron or ‘V-shaped’ markings and do not fly. Male moths have smaller brown wings and can fly. Attracted to a pheromone emitted by the female, the males can fertilize several females before dying. Female moths lay egg masses that remain dormant until spring.
How do gypsy moths travel?
Caterpillars hang in trees on a silk strand and can be carried a great distance by the wind. Humans also move egg masses or pupal cases on travel trailers, firewood, cars, etc. Make sure you do not give the gypsy moth a ride.
How do I know if I have gypsy moth?
Several MSU Extension bulletins can help you identify the gypsy moth and caterpillar.
What does gypsy moth damage look like?
Gypsy moth caterpillars feed on tree leaves creating ‘swiss cheese’ type holes. They do not cause pre-mature leaf drop, browning, or curling of leaves. They do not make a web or tent in trees. In addition to damage to the trees, gypsy moth caterpillars can be a nuisance if populations are high enough. Caterpillars and their frass (feces) can drop down from trees on to sidewalks, driveways, yards, porches, and vehicles. The hairs on the caterpillars can cause irritation or an allergic reaction to bare skin. Frass can stain surfaces, especially if it is rained on or becomes wet.
What happens when trees are defoliated?
Trees defoliated more than 40% become stressed by using next year’s energy reserves to grow new leaves during the same season. Healthy trees may withstand several years of defoliation. Evergreens are unable to replace their needles and may die when defoliated. Keep trees watered and fertilized to reduce any stress.
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