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, Adelges tsugae Annand, were studied in the laboratory. The two specialist predators are part of a biological control program that has been initiated for A. tsugae, and the potential for competition among these species and polyphagous established predators is unknown. Laboratory assays were evaluated in environmental chambers at two conditions: (1) early spring, 9:5°C (D:N), 12:12 (L:D) h, and 50–75% RH; and (2) late spring, 18:10°C (D:N), 16:8 (L:D) h, and 75–90% RH. Predator feeding trials using conspecific and heterospecific eggs showed that L. nigrinus and S. tsugae eggs were consumed by all species, and predation was decreased with increased A. tsugae density. Eggs of H. axyridis were eaten almost exclusively by conspecifics, at high rates, regardless of A. tsugae density. Survival, feeding on A. tsugae, and net egg production of single predators and groups of three conspecifics and heterospecifics were also examined. Survival for all species was not significantly affected by the presence of additional predators. In conspecific groupings, only H. axyridis showed significant reductions in feeding on A. tsugae, whereas all species had significantly reduced net egg production with conspecifics. In heterospecific groupings, no significant effects on A. tsugae predation or net egg production were detected. The only significant negative competitive interactions detected in these assays were among conspecifics, whereas heterospecific combinations showed noninterference.
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