Impact assessment of Laricobius nigrinus (Coleoptera: Derodontidae), a predator of hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae)

Hemlock woolly adelgid, Adelges tsugae (HWA), is an exotic pest of eastern hemlock from Japan that has spread throughout much of the range of eastern hemlock in the eastern U.S. HWA causes hemlock decline and death. We are assessing the impact of Laricobius nigrinus (Ln) (Coleoptera: Derodontidae), a predator of HWA from the Pacific Northwest, on adelgid populations and tree health at several sites throughout the eastern U.S. In fall 2014, we identified nine sites from Georgia to New Jersey that had 1) releases of Ln at least four years prior to the beginning of the study, 2) documented recoveries of Ln in the past, and 3) a high density of HWA present. At each site, three treatments were tested on hemlock branches: closed bag (excludes Ln), open bag (allows for Ln to enter bag and to assess for cage bag effects), and no bag (an open branch). Upon initial set up, once HWA broke aestivation, we recorded the density of HWA on each of the test branches. We then removed samples of the test branches during the peak of oviposition period for HWA to assess Ln egg numbers and HWA mortality. The final sample was removed during peak Ln larval feeding and was then assessed for presence of Ln.  Results from this multi-regional study will be reported.