February 20, 2009

The hemlock woolly adelgid has moved farther west and recently was found on trees at Natural Bridge State Park in Powell County and the Big South Fork in McCreary County. University of Kentucky Entomology Professor Lynne Rieske-Kinney is working to monitor, study and control the spread of the insect that can devastate Eastern hemlock trees.

"We are trying to learn to manage the hemlock woolly adelgid to preserve the Eastern hemlock because without intervention, this insect could certainly cause the loss of that tree species in Kentucky's forests," she said.

Eastern hemlock is a particularly important tree in the state's forests. It usually is found along stream banks and is crucial to stream health and water quality. Eastern hemlock trees regulate stream temperatures, control sedimentation and provide a resource for wildlife and stream organisms. If hemlocks were to disappear due to the adelgid, it would change the composition and structure of Kentucky's forests and irreparably alter watershed characteristics.

The hemlock woolly adelgid feeds at the base of a tree's needles, removing carbohydrates and photosynthates. Without these, trees begin to die. About the size of a pinhead, hemlock woolly adelgids are not easily detected until they settle on a host and begin secreting a white, woolly mass.

The pest is rapidly spreading and could be distributed throughout the state relatively soon.

Rieske-Kinney and UK Forestry Assistant Professor Songlin Fei are using remote sensing technologies to locate hemlocks in the state's forests and track the spread of the adelgid.

"The hemlock woolly adelgid spreads most readily by songbirds, and there are a number of songbird species that are hemlock dependent," she said. "It can also be transported other ways, including by wind currents or by latching onto other forms of wildlife."

Since the pest was first discovered in southeastern Kentucky in 2006, hundreds of trees have been treated by a systemic insecticide injection into the root zone. There have also been several releases of biological control agents including two species of predatory beetles.

Rieske-Kinney is also evaluating the adelgid's effects on forest structure and composition and watershed characteristics and exploring what characteristics of the Eastern hemlock make it so susceptible to the pest, with the goal of identifying specific mechanisms of host plant resistance. In collaboration with Entomology Assistant Professor James Harwood, she is also evaluating the role native predators may play in regulating adelgid populations, with the hope that the effectiveness of these native predators might be enhanced through forest management practices.

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