Gypsy moth virus can stop outbreaks with time


ROCHESTER, N.Y. (WROC) — Property owners with maple, pine, aspen, and oak trees are still seeing their land under attack by an invasive and hungry bug. Yet natural and manmade barriers may be able to help keep the threat at bay.

During gypsy moth outbreaks, caterpillar density can be so high that some trees may be completely stripped of leaves by mid-summer. Fortunately, defoliation caused by gypsy moth caterpillars rarely kills trees. The large, hairy caterpillars, however, often annoy people living or recreating in areas where an outbreak is underway.

Gypsy moth larvae—large, aggressive, hairy caterpillars—take over many kinds of trees in forests and yards alike, gorging on their leaves. Frequently they damage the tree, with populations growing so quickly that they can strip a tree by mid-summer.

Sometimes, they even kill the tree. Plus, just touching the bugs could harm your skin, according to the Department of Environmental Conservation (DEC). But nucleopolyhedrosis virus (NPV) could push back their populations.

Since first reporting an outbreak of gypsy moths on her maple tree, Sue McCarthy of Irondequoit has seen their impact spread to every leaf. But little is left of the caterpillar culprits due to the NPV Virus. “My understanding is that it is really the only known predator in North America is this virus,” she said. “It is not like any other bugs are going to go after them, so I am happy to hear the virus has come out.” 

The virus is naturally occurring at low levels throughout gypsy moth caterpillar populations already. When there is a lot of competition for food and space—like after a few years of a population boom—the stress affects their immune response, and the virus can become lethal.

“They do not usually come up very quickly in the first year of an outbreak,” Rob Cole of the Environmental Conservation said in a Facebook Live in June. “So you must let that build for a couple of years. What we end up with is a two- to three-year infestation before the population builds up and really knocks it back.”  

The NPV virus takes some time to eradicate infestations. In the meantime, landowners can apply for aerial spray applications and get contractors to unleash an insecticide known as BTK to kill the caterpillars alongside the virus. Beware that pesticides can also eradicate beneficial creatures.

“They sprayed the tree twice,” McCarthy said. “They did say you want to wait until they are ready to hatch then you want to spray the tree. We caught it close, but as you can see, they have been out eating it so we should have done it a little sooner.” 

As the gypsy moth caterpillars hatch, sticky material placed around trees and on any surfaces they crawl on can trap them and prevent infestations. The DEC also suggests attaching burlap to trees to keep them off.

Michigan State University says that gypsy moth outbreaks usually collapse within four years because of natural enemies like mice, birds, and other insects or mites. Highly specialized wasps or flies called parasitoids can decimate gypsy moth eggs, larvae, and cocoons. The entomophagy mamaliga fungus is also a natural gypsy moth predator. However, due to dry spring seasons, this fungus has difficulty thriving.

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