Evaluation of the establishment of predatory beetle, Laricobius nigrinus (Coleoptera: Derodontidae) in Virginia, and assessment of its impact on hemlock woolly adelgid (Hemiptera: Adelgidae) at release sites in the eastern U.S.


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Virginia Tech


The predatory beetle, Laricobius nigrinus Fender (Coleoptera: Derodontidae), has been released in the eastern U.S. since 2003 for the management of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae). The establishment of L. nigrinus at release sites in Virginia was assessed in 2017 and 2018. Sampling was performed in both years to determine presence or absence L. nigrinus. Stand level HWA densities, tree health, predator-prey ratios, and Laricobius spp. identifications were also assessed at each site. Laricobius nigrinus established at 82% of sites and was the primary species recovered. HWA densities appeared to decline, and tree health appeared to improve in year two. Predator-prey ratios were lower than those indicated in the native range, however much is left to be understood about the dynamics of this system in its introduced range. A separate two-year study to assess the impact of L. nigrinus on HWA was initiated in 2014 (Phase One) at nine sites in the eastern U.S. Significant predation of HWA sistens ovisacs was demonstrated during this period, therefore, it was continued from 2016-2018 (Phase Two) to provide longer-term evaluations. Predator exclusion cages were used to monitor predator and prey populations. In Phase Two of the study, mean ovisac disturbance rates on no-cage branches were significantly greater than caged branches and were as high as 80%, suggesting that L. nigrinus can have a significant impact on the sistens generation. Microsatellite analysis of Laricobius larvae indicated that L. nigrinus was the primary species recovered at study sites.



Laricobius nigrinus, Adelges tsugae, biological control, impact assessment, establishment