Assessing Performance and Competition Among Three Laricobius (Coleoptera: Derodontidae) Species, Predators of Hemlock Woolly Adelgid, Adelges tsugae (Hemiptera: Adelgidae)

Predation, egg production, and survivorship of Laricobius nigrinus Fender, L. rubidus LeConte, and L. osakensis Montgomery and Shiyaki, predators of hemlock woolly adelgid, Adelges tsugae Annand, were investigated in the laboratory and in the field. In individual assays in the laboratory, L. rubidus oviposited fewer eggs than either L. nigrinus or L. osakensis. In assays containing congeneric or conspecific groups of adult Laricobius, L. osakensis preyed upon the greatest number of ovisacs. The number of ovisacs preyed upon was not different between treatments with all three species and those with only L. osakensis or L. nigrinus. Adult predators fed on few predator eggs and when they did no species preference was observed. The numbers of A. tsugae ovisacs fed upon did not differ significantly by groups of congeneric or conspecific Laricobius larvae. Laricobius adults and larvae had high survival rates throughout all experiments. In the field, L. nigrinus and L. rubidus were enclosed in sleeve cages with both high (>120 ovisacs) and low (<90 ovisacs) A. tsugae densities for 1 wk. All branches with caged beetles had significantly greater numbers of ovisacs preyed upon than branches caged without beetles. No differences in predation or egg production were found among the conspecific and congeneric groupings. Predation was uniformly greater on high prey-density branches than on low prey-density branches. Survivorship among predators did not differ significantly at either prey density. Results from both laboratory and field experiments suggest that these species are able to coexist and can be released in the same location for biological control of A. tsugae.