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2-29-08

Media Release

Species Discovered To Help Address Hemlock Pest Epidemic

CORVALLIS, Ore. – Forestry researchers at Oregon State University have discovered two likely candidates for biological control of a tiny, invasive insect that is devastating hemlock forests up and down the East Coast, disrupting ecosystems and in some places threatening the very survival of Eastern Hemlock as a tree species.

The findings may provide an important new way to address the growing epidemic of the Hemlock Woolly Adelgid – an insect about the size of a small ant that sucks the juices from tree needles, ultimately killing the tree. More research is still needed on safety and efficacy.

The findings are being published in Environmental Entomology, a professional journal.

Various other predators have been used in attempted biological control of this pest, so far with no proven success. The Adelgid, first found in eastern United States forests in the 1950s, is affecting trees in a vast area from Georgia to Maine, and is spreading west. It can cause 90 percent tree mortality in heavily infested areas, with major economic and ecological repercussions.

In eastern forests, hemlock is one of the few dominant conifer species in what are mostly deciduous forests. It can provide cover for grouse, turkey and deer, and is a food source, nesting site or shelter for almost 90 species of birds. Some bird species depend on hemlock forest habitats, and the trees’ shade helps cool streams, enhances fisheries, and provides a winter wind break.

The newest candidates for control are two species of Chamaemyiidae flies, which are similar to related species that have successfully been used for biological control of pests in Hawaii and Chile. It appears these flies prey only on Adelgids and have a life history that is closely synchronized with the pest.

“The potential of this species for biological control looks very promising at this point,” said Darrell Ross, a professor of forest science at OSU. “With biocontrol it’s always hard to predict what will work and what won’t, but flies very similar to these have worked well elsewhere.”

The insects previously used in attempted control of the Hemlock Woolly Adelgid have been beetles, Ross said. Some beetles imported from China and Japan have not worked well, and a beetle from British Columbia is now in early testing stages.

A native of Asia, the Hemlock Woolly Adelgid is found across North America but only causes serious problems in hemlock tree species in the East. Scientists believe it has been around considerably longer in the West, where hemlocks have more natural resistance and there are also a wider range of predators that appear to help keep the pest under control.

Glenn Kohler, a recent OSU graduate student, sorted through dozens of species and thousands of predators in work at 16 sites in Oregon and Washington to identify species that attacked the Adelgid and, more importantly, favored it. For biological control, researchers prefer a species that goes directly after the pest that is a concern, and not much else. The two Chamaemyiidae fly species fit that description.

Continued study of the host specificity and preferences of the Chamaemyiidae flies will be necessary before they could be released as a biological control agent, Ross said.

About the OSU College of Forestry: For a century, the College of Forestry has been a world class center of teaching, learning and research. It offers graduate and undergraduate degree programs in sustaining ecosystems, managing forests and manufacturing wood products; conducts basic and applied research on the nature and use of forests; and operates 14,000 acres of college forests.