Propagation, synchrony, and impact of introduced and native Laricobius spp. (Coleoptera: Derodontidae) on hemlock woolly adelgid in Virginia.

Abstract

Synchrony and impact of the predators Laricobius nigrinus Fender and Laricobius rubidus LeConte, on hemlock woolly adelgid, Adelges tsugae Annand, were studied in an eastern hemlock field insectary in Virginia. First, a field insectary for propagation of the introduced L. nigrinus was established by planting hemlocks in 2001, infesting them with hemlock woolly adelgid in 2002 and 2003, followed by releasing 258 L. nigrinus in 2003. Initial sampling showed that the native L. rubidus was present in the area. Hemlock woolly adelgid and both Laricobius species populations increased annually, from which 305 F3 L. nigrinus adults were collected and redistributed to forests in 2007. Second, the phenology of hemlock woolly adelgid and Laricobius spp. life cycles were monitored in 2005 and 2006. Adult L. nigrinus (F2) and L. rubidus were active on hemlock from fall through mid-spring and overlapped with second-instar sistentes nymphs through progredientes eggs. The predators' eggs were oviposited and larvae developed (i.e., F3 L. nigrinus) from late winter to mid-spring on progredientes eggs, indicating synchrony with suitable prey life stages. Third, a predator exclusion experiment was used to examine the relationships between the predators and prey in 2005 and 2006. When exposed to L. nigrinus (F2 adults and F3 larvae) and L. rubidus, hemlock woolly adelgid survival and ovisac density were lower and ovisac disturbance was higher than hemlock woolly adelgid protected in cages. The establishment and production of L. nigrinus at a field insectary, synchronization with, and impacts on hemlock woolly adelgid after a small release 2 yr earlier makes it an important potential biological control agent of hemlock woolly adelgid.