Gypsy Moth Defoliation in Virginia - 2006

Click here to see a larger version of the map.Gypsy moth populations have resurged this year, and defoliation on approximately 14,330 acres was documented throughout the Commonwealth, compared to 5,000 acres during 2005. However, significant defoliation was concentrated in three main areas – about 7,000 acres along Poor Mountain near Roanoke, 4,000 acres scattered throughout Giles County near Pembroke, and 3,000 acres on Great North Mountain in Frederick County. All of these locations reported some defoliation last summer and heavy egg mass densities last fall, so it was not a great surprise that defoliation showed up. What is surprising to me is that defoliation was not more severe and widespread given that we have had two back to back years with a very dry spring. These conditions are not conducive to survival of the gypsy moth fungus, Entomophaga maimaiga, which can cause severe mortality of gypsy moth caterpillars during years when spring conditions are moist. What is even more surprising to me is that in many locations where defoliation was significant, E. maimaiga was found to be killing many caterpillars, despite the relatively dry conditions. E. maimaiga began having a major impact on gypsy moth in Virginia during the mid-’90s. We’re not sure how it got here, but nobody is complaining.

Although gypsy moth outbreaks will probably always be with us from time to time, some experts believe we can expect to see less intense outbreaks now that this natural mortality factor is out there helping to keeping populations in check. Perhaps a ‘bad’ gypsy moth year will mean tens of thousands of acres instead of hundreds of thousands of acres. Time will tell. In the meantime, we’ll take all the help we can get since next year’s funding to support gypsy moth suppression and the Slow-The-Spread Program is going to be cut drastically.