An exotic predator, Laricobius nigrinus (Coleoptera: Derodontidae), shows promise as a biological control agent of the hemlock woolly adelgid (HWA), Adelges tsugae (Homoptera: Adelgidae). An exclusion study was conducted over two field seasons at 3 selected sites in Virginia to assess the survival, reproduction, and impact of L. nigrinus on HWA populations under field conditions. In the first year, 162 HWA-infested branches received one of three treatments: caged with two predators, caged without predators and uncaged branches. L. nigrinus adults survived from February to April, producing up to 41 progeny per female. Based on the first year's results, a similar experiment was conducted from November to April in year two, with some modifications. Predators were left on caged branches for a longer period of time and were exposed to a larger quantity of prey. All 72 branches were caged and received one of three treatments: same predators throughout the study, predators changed between sample periods, and cages without predators. Throughout the study, both groups of predators had 76% survival. Of the 45 predators that remained the same throughout the experiment, 23 were alive in April. Predators began oviposition in January and continued through April. Up to 182 progenies were found in a single cage. Adelgid populations on branches exposed to L. nigrinus suffered significantly higher mortality than branches without predators in both field seasons. In conclusion, L. nigrinus can survive, reproduce and shows potential of reducing HWA populations in Virginia.
Species 1: Coleoptera Derodontidae Laricobius nigrinus
Species 2: Homoptera Adelgidae Adelges tsugae (Hemlock woolly adelgid)
Keywords: predator exclusion
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