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William Pound, Ohio Department of Agriculture; Amy K. Stone, Daniel A. Herms, David Shetlar, Kelly Harvey, |
The gypsy moth life cycle begins with hatching of the eggs located within the egg mass. In Ohio, spring weather governs the timing of egg hatch, but it generally begins between April 15 to 20 each year. The young caterpillars (larvae) are black and approximately 1/8-inch long. The young caterpillars cluster on the egg mass for seven to 10 days, then disperse upward in the trees and begin feeding on the expanding foliage. During the next six to eight weeks, the larvae feed and undergo four to five developmental changes. Feeding during these latter developmental instars is when most of the leaf damage and defoliation occurs. The mature fifth- and sixth-instar caterpillars will be approximately 2 to 2.5 inches long.
Gypsy moth larvae are not the only caterpillars found in Ohio's trees. Fortunately, the identification of the gypsy moth caterpillars is simplified by the presence of 11 pairs of colored dots. Beginning at the head capsule, the first five pairs are blue, the last six pairs are brick red in coloration. No other forest insect pest in Ohio exhibits this pattern or coloration.
Approximately seven to eight weeks after egg hatch (mid June), the caterpillars transition into the pupal (resting) stage. Ten to 14 days later the adult moths emerge. The adult male moths emerge first and are distinguishable by their feathery, plumose, antennae and brown coloration. They depend on these antennae to locate the pheromone scent of the females. The female moths are white, larger, and emerge later than the males. The female moths do not fly. Therefore, successful mating is dependant on the male finding the female.
Neither of the adult moths feed, but simply live off their food reserves long enough to mate and for the female to lay an egg mass. The egg masses are laid in dense masses of brownish-tan, hairlike scales. Egg masses can contain more than 1,000 eggs with most egg masses containing 100 to 300 eggs. In Ohio, the laying of egg masses completes the life cycle and is usually accomplished by mid-late July or early August. For the next eight to nine months, the integrity of the egg masses protect and preserve the eggs.
Within the pests' annual life cycle, the damage to trees is initially due to the feeding of the larval stage of the gypsy moth, resulting in defoliation of the trees. Once defoliation occurs, the natural response of the affected trees is to refoliate and send out a new flush of leaves. This process depletes energy reserves and serves to weaken the health of the trees. Consecutive years of heavy defoliation eventually depletes tree reserves and often results in the death of the trees. Initially, the control strategy is focused on an integrated pest management (IPM) approach to suppress populations of the gypsy moth.
The foundation of IPM programs is the reliance on natural controls to reduce gypsy moth feeding and subsequent defoliation and tree loss. Unfortunately, gypsy moth is a nonnative insect and has very few natural controls. The populations of this insect can build very quickly and outpace corresponding increases in populations of these natural controls.
In wooded residential and forested areas where the gypsy moth has already defoliated target trees or is currently supporting populations capable of defoliating trees, the control programs should be selective aerial applications or ground applications capable of delivering recommended control products to the tops of the trees where active larval feeding is occurring. Treatments are most effective when applications are made to young larvae and after all eggs have hatched. In Ohio this is usually early May.