No place to go: Establishment of multiple species of introduced predators against hemlock woolly adelgid, Adelges tsugae, on eastern hemlock using whole-tree canopy enclosures

Hemlock woolly adelgid, Adelges tsugae (HWA) (Hemiptera: Adelgidae), an invasive species from Japan, has caused extensive mortality of eastern hemlock in the eastern U.S., especially in the southern Appalachians where thousands of trees have died in the last few years. The biological control component of an IPM program involves the mass rearing and release of several biological control agents [Sasajiscymnus tsugae and Scymnus sinuanodulus (both Coleoptera: Coccinellidae), and Laricobius nigrinus (Coleoptera: Derodontidae)]. The long-term goal is to establish multiple species of biocontrol agents to enhance mortality of HWA. A study was designed and conducted to assess the feasibility of using whole-tree canopy enclosures (i.e., cages) (ca. 9 m tall) to evaluate the biology and establishment of biocontrol agents on HWA and assess their impact on pest populations. Three predatory beetle species (L. nigrinus, S. sinuanodulus and S. tsugae) were released inside each cage (one species/cage; three cages [replications]/species; release densities ranged from ca. 100 – 300 adult beetles/cage), and trees remained caged for about one year. One year following removal of the cages, larvae and adults of S. tsugae and L. nigrinus, as well as adult L. rubidus (a native predator), were recovered from previously caged trees. These three species also were collected from the same tree, suggesting that these three species can coexist on the same host tree. Results will be presented and discussed. These results indicate that whole-tree canopy enclosures may be a viable, more rapid method to establish localized populations of multiple species of introduced predators of HWA.