Gypsy moths not seen as major threat this year
The gypsy moths are here, but not in overwhelming numbers.
Allegheny National Forest (ANF) Forest Ecologist Collin Koers gave a report to the Warren County Intergovernmental Council on Wednesday, stating that the gypsy moth infestation would not be as strong as expected.
“This past fall the ANF, assisted by state and private forestry Forest Health Protection staff, conducted gypsy moth egg mass counts in areas that experienced moderate to heavy defoliation in early summer of 2013,” Koers said. “Egg mass numbers are used to predict future gypsy moth populations, and therefore defoliation potential.”
“The results showed new egg mass counts to be low at most sites,” she said.
That’s good news. Fewer eggs now means fewer hungry caterpillars next year.
“We saw some very extensive mortality this spring,” said Cecile Stelter, forest district manager for the Pennsylvania Department of Conservation and Natural Resources.
“Overall, new egg mass counts, and therefore potential gypsy moth populations next year, are low – less than 250 egg masses per acre,” ANF Silviculturist Andrea Hille said.
A count of 250 egg masses per acre will generally result in a level of defoliation that is considered a “nuisance,” according to Hille. At that level, the agency would consider some kind of countermeasures in recreation and residential settings.
Spraying costs about $40 per acre, but there’s a lot of costly preparation that goes before, including flight plans and environmental assessments, Hille said. The costs are picked up by state and private forestry.
Not spraying here frees up dollars for gypsy moth suppression elsewhere, including Ohio and the Great Lakes states, she said.
In Warren County, there were areas with higher densities, but those places were “few and far between,” Hille said, “and likely due to natural gypsy moth population variation.”
In some of those areas, workers conducted follow-up studies. “The intensified sampling effort also showed generally low egg mass counts,” Koers said.
The sizes of the egg masses and the number of new and old masses “indicate a reduced gypsy moth population for next year,” she said. “Given this, we are not anticipating the degree of defoliation next year that we experienced earlier this year, and we do not have any gypsy moth suppression activities planned for next year.”
The Forest Service provided two reasons why the population didn’t boom. “We attribute these low egg mass numbers to two naturally occurring gypsy moth enemies – a fungus in the soil and a virus carried by gypsy moth caterpillars themselves. Both the fungus and virus thrive in the moist conditions we experienced this past growing season and caused gypsy moth mortality before the caterpillars pupated, meaning they did not develop into moths, and were unable to lay new egg masses that would hatch next spring.”
“The counts are lower than last year’s because the population essentially collapsed due to the entomophaga maimaiga fungus and nucleopolyhedrosis virus (NPV) because environmental conditions – moist and warm with high population levels – were right for those natural controls to be effective,” Hille said. “The fungus occurs in the soil and thrives when conditions are warm and moist. The NPV is carried by gypsy moths themselves. The NP virus appeared to control populations the most, given the large numbers of dead, inverted gypsy moth caterpillars we observed in July and August.”
“The cool, wet spring that we had last year really helped contribute to the development of the virus and fungus that allowed the collapse of the population,” Stelter said.
The places where the gypsy moths were prevalent this year will probably not be problem areas next year. “We do not expect those areas to have a significant gypsy moth population,” Stelter said. “There may be some areas that did not have high populations last year that do have higher populations this year. There are probably going to be some small pockets where people are going to see some gypsy moths maybe even some defoliation.”
“While there may still be localized defoliation events next spring, we do not anticipate heavy defoliation in areas that experienced moderate to heavy defoliation in 2013 and the ANF will not proceed with NEPA (National Environmental Policy Act assessment) for a spring 2014 gypsy moth suppression program,” Koers said. “The ANF will continue to work adaptively and monitor gypsy moth populations across the forest next year.”