ESTABLISHMENT AND DEVELOPMENT OF RELEASED LARICOBIUS NIGRINUS IN THE EASTERN UNITED STATES

Abstract

The establishment of invasive species has affected biodiversity, biochemistry, and ecosystem functions worldwide. The hemlock woolly adelgid (Adelges tsugae), an invasive insect native to Japan was introduced to the eastern region of North America in 1951 and has reduced eastern hemlock populations throughout its native range. Laricobius nigrinus, a native western North American coleopteran predator of hemlock woolly adelgid was introduced as a biocontrol agent in 2008 by the Maryland Department of Agriculture. This study analyzed resulting field and lab data, which included evaluation of establishment and efficacy of the predatory beetle as a biocontrol and its possible impacts on hemlock woolly adelgid abundance. Evaluation of establishment on Laricobius nigrinus consisted of field collections at release sites and control sites using a beat sheet and collecting prepupae from clipped branches. Our results showed very low adult Laricobius nigrinus recoveries through beat sheet sampling and DNA barcoding prepupae collected from clipped branches. Efficacy of the beetle as a biocontrol consisted of microscopy to view disturbed ovisacs as well as abundance of hemlock woolly adelgids on each clipped branch. There was significant variation in the hemlock woolly adelgid abundance by site. Results support the establishment of Laricobius nigrinus in the central region of Maryland. However, the efficacy of the beetle playing a major role as a biocontrol for hemlock woolly adelgid is not supported by these findings.