Establishment of Sasajiscymnus tsugae (Coleoptera: Coccinellidae), a predator of hemlock woolly adelgid, Adelges tsugae, in the Great Smoky Mountains National Park

Eastern hemlock, Tsuga canadensis (L.) Carrière, in the Great Smoky Mountains National Park is currently threatened by the hemlock woolly adelgid, Adelges tsugae Annand (HWA) (Hemiptera: Adelgidae). As part of a biological control program against this invasive insect pest, Sasajiscymnus tsugae (Sasaji and McClure) (Coleoptera: Coccinellidae), a predatory beetle native to Japan, was released (n=ca. 350,000) at ca. 150 sites in the Park from 2002-2007. Of these release sites, 56 sites were sampled using beat-sheets for four-man hours per site from March to July, 2008 - 2010. Sasajiscymnus tsugae adults (n=103) and/or larvae (n=152) were recovered from ten sites (17.86% of the release sites sampled) in the Park. Recovery of S. tsugae was significantly associated with older release sites, with the most beetles recovered from 2002 release sites. These results indicate that S. tsugae may require more time than anticipated for population densities to reach readily detectable levels in a forest setting. However, recent research using whole-tree canopy enclosures (i.e., cages) demonstrated that beetles can be released and readily recovered two years after beetle releases. The reasons for the longer time for recovery following releases in the forest are unclear. A multivariate model using selected variables which may influence establishment of S. tsugae will be discussed. The development of a suitable site-predictive model would assist land managers with selecting appropriate release sites.