Impact of the biological control agent, Laricobius nigrinus, on hemlock woolly adelgid sistens generation and their ovisacs in the eastern United States

•Hemlock woolly adelgid (HWA), causes dieback and mortality of native species of hemlock (Tsuga spp.) in eastern North America.•Biologicalcontroleffortssince 2003have included releases of the predatory beetle, Laricobius nigrinus.•A field study with exclusion cages indicated that Laricobius nigrinus can have a significant impact on HWA ovisacs of the overwintering generation.•Low winter temperatures also tend to reduce overwintering HWA ovisacs with effects on next generation recruitment.•Genetic analysis revealed that Laricobius nigrinus outnumbered the native Laricobius rubidus, and hybrids of the two species.