It’s certainly been cold this winter, but current low temperatures, combined with the recent effects of the polar vortex, may deliver unexpected benefits this spring. Foresters and scientists in New York have been fighting against the rapid expansion of the Emerald Ash Borer, an invasive insect which kills ash trees in alarming numbers. The long winter freeze may provide a much-needed advantage against these tiny invaders.
The emerald ash borer is a beetle which arrived in the United States on untreated wood pallets used for shipping from China. In Asia and Russia, the emerald ash borer is kept in check by predators and the natural resistance of ash trees which have had thousands of years to adapt defenses against this parasitic insect. American ash trees, however, have no defenses against this exotic species.
Since they were first identified in Michigan in 2002, emerald ash borers have expanded across the Northern and Eastern United States and killed over 50 million American ash trees. In 2009, these pests were first identified in New York’s Cattaraugus County, posing a new and potentially devastating threat to New York’s forests.
Emerald ash borers kill ash trees by boring underneath the bark into order to lay their eggs. Once hatched, larva feed upon the tree’s living tissue, killing it slowly over the course of 2-3 years.
In wintertime, ash borer larva shelter underneath the bark of ash trees, however, extreme cold temperatures, like we have been experiencing, can freeze the larva even underneath the bark layer and slow down the population growth of this pernicious pest. However, it takes more than just a few hours below zero in the morning to hurt EABs, but sustained sub-zero temperatures could potentially kill a significant portion of the Emerald Ash Borer population. Because EAB larvae shelter deep under the tree’s bark at the base of the trunk and even in the upper roots, where a snow layer can keep them insulated from extreme cold and the tree itself regulates their temperature, they are relatively adept at surviving in cold climates.
For example, this winter at Taughannock State Park near Cayuga Lake, the temperature was never recorded below -8°F (-22°C) and we found Hemlock Wooly Adelgid, another pernicious invasive insect, mortality to be about 88%. On the other hand, at Mine Kill State Park in the northern Catskills, temperatures got to -24°F (-31°C) and we found only about 72% mortality.
For this reason, we can expect the polar vortex to temporarily slow down the expansion of EAB, but management and surveying efforts will continue to be necessary into the future.
Invasives and Cold Weather in NY, Cornell University Cooperative Extension.