Is the bark on that tree moving?
It’s a question one must ask while walking through the woods of Rothrock State Forest lately. A close inspection of those trees reveals heavy numbers of caterpillars slowly crawling their way upward.
They are European gypsy moths, or Lymantria dispar, and an outbreak of the crawlies are affecting not only forests in Centre County, but also across the commonwealth.
Allyson Muth, a member of the Ferguson Township Tree Commission, said the insects are “a serious forest pest.”
In a township press release, she said the outbreak, in combination with repeated defoliation events or other tree stressors such as drought, has been responsible for killing millions of oak and other species of trees in the past.
According to the Department of Conservation and Natural Resources, gypsy moths and their larvae may prefer oak species, but they will also feed on several other tree and shrub species, including deciduous and evergreen species.
Gypsy moths were first documented in Pennsylvania in 1932 in Lackawanna and Luzerne counties, 63 years after their arrival to North America from Europe. The gypsy moth has been causing significant forest damage in Pennsylvania since the 1970s.
Since then, DCNR has worked to use suppression tactics to reduce their abundance. DCNR suppression efforts twice surged during the early 1980s and 1990s when the number of state acres treated approached 1 million for each three-year period.
Although peak years were again witnessed in 2001, 2008 and from 2013 to 2015, according to DCNR, the number of acres defoliated (and then needing to be treated) paled in comparison to the extremes seen in the 1980s and 1990s — testifying to the success of the program and the effect of a new ally in the form of gypsy moth fungus disease.
DCNR said it did not see a need for suppression spraying in 2020, but was expecting this 2021 outbreak, so spraying was conducted this season.
At this point in the gypsy moth life cycle, Muth said, the only thing that local landowners can do is physically remove the insects themselves “and hope the destruction isn’t that bad.”
“Mature caterpillars, what we mostly are seeing around town, are distinctive in appearance, with five pairs of blue spots and six pairs of red spots running down the body,” Muth said. “Many landowners and homeowners are worried about what these insects are doing to their trees. With the current size of caterpillars in our area, the defoliation is readily apparent.
“Unfortunately, we are at a stage in the life cycle where there is not much to be done — any treatment, other than mechanical removal, is going to kill off beneficial insects and not help the trees.”
Muth said that as long as there are no other additional stressors, most trees can handle a year of defoliation; however, defoliation can use many of the tree’s resources and make it more susceptible to stressors in the future. She noted conifers are especially susceptible because, “if they are attacked and their needles are completely lost, the conifers will not re-leaf and will die.”
“Currently, we are waiting to see what the effect of these insects will have on our tree canopy,” Muth said. “We may see a bigger outbreak next year based on the growing population of gypsy moths. We hope for a cool, wet spring next year to help a fungal pathogen or virus decrease the population. We are starting to see some effect of these bio-controls — perhaps they will decimate the population before they pupate into adults.”
Muth suggested landowners look at resources from Penn State Extension and DCNR on how to prepare for the future and may also contact the township arborist at (814) 238-4651.
This story appears in the July 1-7, 2021 edition of The Centre County Gazette.
