Daily activity patterns of Laricobius osakensis and Laricobius nigrinus, two specialist predators of Adelges tsugae, and potential interactions.

Adelges tsugae Annand (Hemiptera: Adelgidae) is an exotic pest of hemlocks in the eastern US.  Control of this pest has focused on building a natural enemy community.  Laricobius nigrinus Fender, native to western North America, and Laricobius osakensis Montgomery & Shiyake, native to Japan, are highly specialized predators of A. tsugae already introduced or in the process of being introduced into the eastern US for the control of this pest.  Previous studies on potential interactions have focused mostly on whether the two predators impact each other’s effectiveness or not, but there are no studies on how L. osakensis interacts with its prey, with a congeneric specific predator and its daily activity pattern.  The behavior and daily activity patterns of both predators were examined using digital video recording in the laboratory.  The daily activity patterns of adult females and males of each species were recorded in single-predator and same sex paired-predators assays under simulated winter and spring conditions.  Behavior was qualitatively similar but varied quantitatively by species.  L. osakensis was more active than L. nigrinus and had a lower association to the tree host (the foliage).  Interactions between specimens were generally low and were not detrimental to either species.  A higher level of interactions was observed in male-female pairing, followed by male-male pairing, with the lowest level of interactions observed in female-female pairings.  Intrasexual copulation attempts were observed between males but also between females.  The presence of the other species did not interfere with the level of activity or of oviposition of either species.