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Predators of hemlock woolly adelgid in northwestern Oregon

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  • Hemlock woolly adelgid, Adelges tsugae Annand, is a serious threat to eastern hemlock, Tsuga canadensis Carriere, in the eastern United States. Infestations of A. tsugae are spreading rapidly and tree mortality caused by the insect is increasing yearly. As part of an integrated management approach, a classical biological control program is being implemented in eastern forests impacted by A. tsugae. Two insect predators have been released as control agents, but their impact on A. tsugae to date is uncertain. A priority of the USDA Forest Service Forest Health Techhology Enterprise Team (FHTET) is to identify additional potential control agents. The Pacific Northwest, where A. tsugae inhabits western hemlock (T. heterophylla), was identified as a region to survey for adelgid predators. Thirty-one T. heterophylla infested with A. tsugae in northwestern Oregon were sampled monthly for predatory arthropods from April 2003 to April 2004. Adelges tsugae development was monitored. In September 2003 and March 2004, trees were sampled to determine A. tsugae density. Development of adelgids on study trees was similar to development observed in the eastern U.S., with differences in timing between 2003 and 2004. Trees infested with A. tsugae had only a small amount of defoliation. Small numbers of several predatory arthropod taxa were collected from A. tsugae infested branches, including Laricobius nigrinus Fender, coccinellid beetles, minds, other hemipterans, pseudoscorpions, earwigs and lacewings. The abundance of L. nigrinus appeared to be positively correlated to the density of A. tsugae.
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