Confined field release of Laricobius nigrinus (Coleoptera: Derodontidae), a predator of the hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), in Virginia

Laricobius nigrinus Fender is a specialist predator of the hemlock woolly adelgid (HWA), Adelges Isugae Armand (Hemiptera: Adelgidae), a lethal pest of hemlock (Tsuga spp.) in the eastern United States. A release was conducted in 2003 in Virginia to evaluate survival and oviposition of L. nigrinus adults, egg development in the field, and their impact on HWA density. In March, April, and May, groups of zero, one, two, or three L. nigrinus females were caged on 64 hemlock branches. After 10 days, half the branches were removed to determine L. nigrinus adult survival, total eggs laid, and oviposition location with respect to prey abundance. Beetles on branches remaining in the field were recovered and recaged on new branches every 10 days. The estimated 10 344 eggs laid on branches left in the field represent the first field release of L. nigrinus in the eastern United States. The density of L. nigrinus adults affected the total eggs laid per female and oviposition site selection. Branches caged with L. nigrinus had lower densities of HWA than branches without predators. Although F, adults were not recovered from this release site in fall 2003, F, adults were recovered in fall 2004. Laricobius nigrinus shows promise as a biological control agent for HWA in the eastern United States.