Gypsy moths have been making the news recently, as their population in some regions of the state is causing a lot of defoliation. According to the New York State Department of Environmental Conservation website, they are causing noticeable defoliation in both central and western New York.
Gypsy moth populations can remain at almost undetectable numbers for a number of years, and then for some unknown or unexplainable reason the population skyrockets. When populations are high, there are an estimated one million caterpillars per acre in some forests. While a single year of defoliation will not kill hardwood trees, there is decreased fall foliage.
As you may already suspect, the gypsy moth is not native to the United States. They were brought here from France in the late 1860s with the intent of developing a silk industry in the United States. The experiment was not successful and some of course escaped, becoming established in Medford, Massachusetts, and since spreading.
By 1981, the gypsy moth was found throughout New York state, and they are now considered to be naturalized in New York’s forests. It is not the adult moth that causes the problem. It is the larvae (caterpillars) that hatch from overwintering egg cases in April and May that start eating the emerging young leaves of many tree species. The early damage from the tiny caterpillars often goes unnoticed. Once the caterpillars are close to an inch in length, their huge appetites kick in and become visible with thinning tree canopies. The caterpillars will grow to just over 2 inches.
The list is long of tree species that gypsy moth eat. They have a preference for oak, but will feed on over 300 different species, including alder, apple, aspen, basswood, birch, hawthorn, maple, mountain ash and willow. These trees are deciduous and will regrow their leaves next year. They will also go, as a second choice, to evergreens such as pines, spruce and hemlocks. Evergreens cannot tolerate the defoliation, as they do not regenerate their leaves and may die from heavy feeding.
Gypsy moth larvae have distinctive markings. They develop five pairs of raised blue dots on their back followed by sixth pair of raised red dots. The adult moths are fairly plain, with the female being mostly white with brown markings, and the male moth is browner. The egg masses, containing between 100 and 700 eggs, can be found in the fall and through the winter.
Finding the egg masses allows for the easiest control. When identified, the egg mass can be scraped off where it was laid and dropped into a container with detergent. Controlling egg masses is practical when populations are low. In addition to tree trunks and branches, the female moth will also lay eggs on firewood, fence posts and rock outcroppings, and they have been found on lawn furniture and the sides of buildings. The state DEC’s website has a link to egg mass sampling protocol to help determine if there is potential for a large outbreak or if an insecticide spray is warranted on smaller larvae.
Spraying for gypsy moths can be expensive, plus timing is everything. The caterpillars are also controlled naturally by birds, rodents, parasites and disease. It has also been determined that temperature extremes will reduce populations. The cold temperatures this spring actually delayed their hatching in some areas until the middle of May into early June.
It takes about seven weeks for the newly hatched larvae to mature. As they reach maturity, they can eat approximately one square foot of leaf surface in a single day. Once mature, they go into a cocoon and emerge from July into August as adults. The female does not fly, but the male does. As they mate, the female lays the eggs, which then overwinter, and the cycle starts over again.
Don’t become confused if you see a lookalike, as eastern tent caterpillars look similar to the gypsy moth caterpillar. It is the red dots on the gypsy moth caterpillar that sets them apart from the tent caterpillar. Both are destructive pests; however, the tent caterpillar tends to be a localized outbreak, while the gypsy moth is widespread.
If you want to sample your woodlot or forest to determine next season’s potential for an outbreak, the DEC provides sampling protocol and the data you collect is valuable to them, if you want to share it for the annual tracking.
More information on gypsy moth management and control can be found on the Cornell University Insect Diagnostic Laboratory's website at idl.entomology.cornell.edu/wp-content/uploads/gypsy-moth.pdf.
Judy Wright is the senior agriculture specialist with Cornell Cooperative Extension of Seneca County. For more information, visit senecacountycce.org or call (315) 539-9251 ext. 109.
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