Evaluating a Potential Area-wide IPM Strategy for Managing Hemlock Woolly Adelgid in the Eastern United States

The insecticide imidacloprid, has been found to be highly effective in suppressing hemlock woolly adelgid, Adelges tsugae. Laricobius nigrinus is a predatory beetle released as a biological control of adelgids in the eastern U.S. This project was designed to develop a pest management strategy that utilizes both tactics concurrently within the same site. It will assess the efficiency of this strategy in reducing HWA populations and improving the health of hemlock forests. The project was started in 2010 and data were collected annually through 2016. The project spanned three sites in three different states (KY, WV, and TN). Results show that tree health has generally declined across all sites for each year. HWA population index values are highly variable and are more strongly influenced by the occurrence of low winter temperatures than by treatment effect. Cross-correlation analysis of tree health and HWA population, revealed characteristics of their temporal relationship. In two of the three sites, tree health lagged up to three years behind changes in HWA population, and HWA populations lagged approximately one year behind changes in tree health. L. nigrinus did not establish at any site as of 2016. The lack of sustained recovery of the beetle may be attributable to the occurrence of extremely cold temperatures during the winters of 2014 and 2015 which produced subsequent crashes in the HWA population at two of the three sites. In TN, the L. nigrinus population may have never established due to a decline in the HWA population shortly after release.