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Gypsy Moths return in numbers

This female, with a partially formed egg mass, is much lighter than the male, but pheromone production rather than sight is the female’s tool in attracting a mate. Both sexes only live about a week after emerging from the pupae stage.
TRR photos by Scott Rando


July 24, 2013

People in certain parts of the region may have noticed a familiar looking caterpillar early this summer. It seems that the gypsy moth is back. An egg mass survey done last February in Pennsylvania by the Department of Conservation and Natural Resources (DCNR) indicated that egg mass density was light (40 to 200 egg masses/acre) at most sampling points in Pike County and isolated sampling points in Wayne County (see map at centrecountypa.gov/index.aspx?NID=217). Based on the number of moths flying around this week, however, there may be a more significant infestation for next year, assuming that most of these week’s moths are successful in breeding.

During the week of July 15, male gypsy moths have been observed flying about as they seek females. Males are darker than the flightless females and usually emerge first; the females find a spot near their emergence point and release a pheromone to attract a male to mate with, afterwards depositing an egg mass, containing up to 1,000 eggs, on the side of a tree or other vertical surface. The fibrous brown-yellow egg mass remains dormant until the following spring, when the tiny larvae emerge.

At this time of the moth’s life cycle, there is not much available in the way of control measures. Pheromone traps are sometimes used, but attract only the males, and a trap can get overwhelmed with so many flying around. After larvae emerge in the spring, spraying can be an effective tool to control large infestations, but timing is important to minimize the effect on native butterfly populations. Whether an area should be treated depends on the density of egg masses as determined by the winter survey. (PA DCNR uses 250 egg masses/acre as a trigger for intervention.)

Some natural parasites can impact gypsy moth populations including a fungus called Entomophaga maimaiga, and insects and birds as well.