ERIE, PA - Mercyhurst University biologists have received a $30,000 grant to study the impact of cold winter temperatures on the hemlock woolly adelgid, a small, aphidlike insect that is decimating the hemlock trees of eastern U.S. forests.
"The adelgid is considered one of the greatest threats to our eastern forests; already it has spread to 18 states, from Maine to Georgia," said Michael Elnitsky, assistant professor of biology, who wrote the proposal that earned Mercyhurst funding from the Pennsylvania Department of Conservation and Natural Resources (DCNR). "Pennsylvania is very much at the center of the range expansion of the adelgid, with infestation already across two-thirds of the state."
Although the invasive pest has not yet reached Erie County, Elnitksy said it is only a matter of time. Studies have documented the adelgid's vulnerability to the cold, so it seems reasonable that climate change trends, specifically this winter's warmer temperatures, may accelerate its distribution.
The adelgid feeds on the phloem of hemlock trees by inserting its stylet into twigs, injecting toxic saliva that weakens the tree, causing needle loss, reduced growth and eventual death within four to six years of infestation.
Although the adelgid has been in Pennsylvania for 40 years, there are no thorough studies that examine the low temperature tolerance and winter survival strategies of the species.
Elnitsky's research team, which he expects to include between five and eight students in each of the next two years, will identify 20 to 25 hemlock stands across the state and monitor the environmental conditions impacting them throughout the winter. Besides field work, researchers will also conduct lab studies to assess the species' cold tolerance.
Through the Mercyhurst research, it is hoped that the DCNR, the Bureau of Forestry and regional land managers will be able to predict insect population size and the likelihood of outbreaks, the potential impact of the adelgid and its rate of expansion.