Field cage studies of Laricobius osakensis Montgomery & Shiyake (Coleoptera: Derodontidae), a predator of hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae)

Laricobius osakensis Montgomery and Shiyake (Coleoptera: Derodontidae), first identified in Japan in 2005, was evaluated in the field for the biological control of hemlock woolly adelgid (HWA), Adelges tsugae Annand (Hemiptera: Adelgidae). Long-term (2 months) and short-term (15 days) cage studies were conducted to evaluate survival, reproduction and impact of this predator in Saltville, VA. For each sampling period 4 branches from each of 5 trees received one of two treatments: caged hemlock branches with predators (2 branches), or caged hemlock branches without predators (2 branches). L. osakensis adults survived from December to April. Survival was affected both by the climatic conditions, degree of disturbance during the trial and prey availability. Females laid eggs during the entire sample period, with the highest numbers being laid during March and April. Females produced up to a maximum of 34 eggs during a 15 day period. Adelgid densities on branches with predators were significantly lower than branches without predators through most of the sampling period. The impact was especially significant in the long-term cages where the impact of both adults and larvae was observed. In all the branches with predators, no A. tsugae adult survived, and only a maximum of 2 ovisacs (all eggs) were not completely consumed. All branches without predators had some percentage of A. tsugae adults alive, and all ovisacs were undisturbed. In the cages where enough prey were available, larvae were able to complete development. L. osakensis can survive, feed, and reproduce in Saltville, VA.