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Winter Moths

No, those aren't snowflakes you're seeing out there—they're winter moths! The winter moth, an invasive insect from Europe that was introduced into the United States via Canada, has invaded eastern Massachusetts in huge numbers.

The adult winter moths (Operophtera brumata) emerge from the ground in November or December, but only the male is able to fly. The female climbs to the base of a tree or building and attracts the male through the pheromone (sex scent) that she exudes. After mating the female lays a cluster of approximately 150 eggs under tree bark or in tree crevices, and her life is now over. In March or April the eggs hatch into a smooth green inchworm with a narrow white-stripe running lengthwise on each side of the body. The caterpillar spins a strand of silk, which, with the help of air currents, takes it into tree canopies in a dispersal method known as "ballooning".

Once there, the damage to the tree begins as the caterpillars work their way into the tree buds and leaves to feed. In Massachusetts, the tree species frequently affected are maple, oak, ash, as well as fruits producers such as apple, crabapple, and blueberry. Winter moth caterpillars can also drop from trees to nearby ornamental shrubs such as roses. When feeding ends in mid-June the caterpillars migrate into the soil to pupate and emerge as moths.

In 2005 and 2006, in a cooperative effort by the Department of Entomology at the University of Massachusetts and the Forest Health Program at the Massachusetts Department of Conservation and Recreation, hundreds of parasitic flies known as Cyzenis albicans were released at Wompatuck State Park in Hingham and on town-owned property in Wenham, MA. Cyzenis albicans has been effective in combating winter moth populations in Nova Scotia, as well as other parts of Canada.

The fly lays its eggs on the leaves eaten by winter moth caterpillars during the spring. When the eggs are consumed, along with leaves, the eggs hatch inside the caterpillar and the larvae consume the caterpillar from within, eventually causing the moth to die. The fly pupates inside the carcass of the caterpillar and, the following spring, emerges as an adult fly to mate and begin the cycle again.

For more information:
http://www.umassgreeninfo.org/fact_sheets/defoliators/winter_moth.pdf*
http://www.umassgreeninfo.org/fact_sheets/defoliators/wm_id_man.html
http://www.umassgreeninfo.org/fact_sheets/defoliators/wm_bio_project_05.pdf*

Mass Audubon's Wildlife Information Line: 781-259-2150

*Requires Adobe Acrobat Reader; click here for more information.

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