Between mid-April and early June, 43,124 acres of state forest land, state park land, and Pennsylvania Game Commission land in eight counties will be sprayed to control gypsy moth infestations.
Cameron, Clarion, Forest, Jefferson, Lycoming, Potter, and Tioga counties will be treated with Bacillus thuringiensis, which is a naturally-occurring biological insecticide All spraying will be accomplished with helicopters, and no chemical insecticides will be used. Additionally, 65 acres in Venango County will be treated.
According to the state Department of Conservation and Natural Resources website, the gypsy moth was first discovered in the U.S. in the 1860s and in Pennsylvania in 1932. It is one of the most destructive forest pests in Pennsylvania. When the insect's population peaks, it may strip trees of foliage, leaving them weakened and susceptible to disease, drought and attack by other insects. A tree begins to suffer when 30 percent or more of its leaf surface is lost. Spraying is considered successful when eighty percent of the trees have thirty percent or less defoliation. An additional goal is to avoid the need to spray the following year.
Although white, chestnut, black and red oak are preferred, gypsy moth caterpillars also eat hundreds of other tree and shrub species including apple, alder, aspen, basswood, birch, poplar, willow, hawthorn, hemlock, tamarack (larch), pine, spruce, and witch hazel.
To determine when spraying is indicated, District Forester Cecile Stelter explained, "There are evaluations done in the field, including counting egg masses. If the count reaches certain levels spraying may be done."
Egg masses are surveyed between September of the current year and March of the next year. According to the DCNR website, about 2,000 semi-permanent sample sites, one-fortieth acre each, or circles with a radius of 18.6 feet, are selected across the state each year. The number of overwintering egg masses found at each site is recorded. An increase in egg mass size, frequency, and average number of egg masses per site from the previous year usually indicates an increasing population that may lead to suppression efforts.
Egg masses counts are only one of several indicators that are used to predict potential defoliation and mortality. Soil moisture content can affect gypsy moth population levels and reduce defoliation because the fungus Entomophaga maimaiga, which grows in moist soils, kills young gypsy moth caterpillars before defoliation can occur, so spring weather conditions could be another important consideration.
The Allegheny National Forest, along with personnel from the Pennsylvania Department of Natural Resources and the Forest Pest Management Division, has been collecting egg masses data on state, federal and private lands. Egg mass counts for the area have been on the rise, although no defoliation was recorded last year.
The DCNR has a program for the spraying of private lands, through county conservation districts with the landowners responsible for a portion of the costs. Locally, District Manager Heather Wilcox said, "The (Warren County) Conservation District elected not to participate, in a decision made last fall by the Warren County Commissioners."
She explained that there is a considerable lead time where decisions must be made, certain requirements met, and funds collected, and a determination was made that the process was too cumbersome.
The fungus caused a collapse in gypsy moth populations after 2009, so suppression was not necessary in the following years.
Surveys were conducted in 2012 for other insect pests, including the Hemlock Wooly Algelgid, the Walnut Twig Beetle and the Emerald Ash Borer. Their presence was confirmed in nine new counties.