Competitive interactions among two specialist predators and a generalist predator of hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae)

Competitive interactions among two specialist predators, Laricobius nigrinus Fender and Sasajiscymnus (Pseudoscymnus ) tsugae Sasaji and McClure, and a generalist predator, Harmonia axyridis Pallas, of hemlock woolly adelgid were evaluated in the laboratory and field. The two specialist predators are part of a biological control program for Adelges tsugae Annand, and the potential for competition among these species and previously established generalist predators is unknown. In addition, detailed studies of predator behavior and activity patterns were completed using video methods.; In laboratory assays, predator feeding on conspecific and heterospecific predator eggs was tested at three A. tsugae densities. Eggs of L. nigrinus and S. tsugae were preyed upon by all species, and predation decreased with increased A. tsugae density. Eggs of H. axyridis were consumed almost exclusively by conspecifics, at high rates, for all A. tsugae densities. Predator survival, net egg production and feeding on A. tsugae were evaluated for single- and multiple-predator conspecific and heterospecific groupings at simulated early and late spring conditions. Survival was not significantly affected by the presence of additional predators or environmental conditions. Net egg production was significantly reduced in conspecific groupings, but was unaffected by heterospecifics. Conspecific groupings did not significantly affect feeding on A. tsugae by L. nigrinus or S. tsugae, but H. axyridis showed significant reductions. In contrast, feeding on A. tsugae by all species was not significantly affected by heterospecific groupings. Each species showed increased net egg production and feeding on A. tsugae at higher temperature assays, but this was proportionately greater for S. tsugae and H. axyridis. The only significant negative competitive interactions detected were among conspecifics, while heterospecific combinations showed non-interference.; In field assays, adult predators were evaluated using branch cages during spring and summer at two field sites infested with A. tsugae. Using females only in 2003 and sexual pairs in 2004, we examined predator survival and net reproduction as well as predator feeding and impact on A. tsugae in single- and multiple-predator conspecific and heterospecific groupings. Predator survival was high overall and not affected by the presence of additional predators during either evaluation. Net reproduction per predator was negatively affected by conspecifics, but unaffected by heterospecifics. (Abstract shortened by UMI.)...