Assessment of the potential for hybridisation between Laricobius nigrinus (Coleoptera: Derodontidae) and Laricobius osakensis , predators of the hemlock woolly adelgid (Hemiptera: Adelgidae).

In 2003,Laricobius nigrinusFender was introduced into the eastern United States as a biological control agent of the hemlock woolly adelgid (Adelges tsugaeAnnand). Following its release, it was discovered thatL. nigrinuswas hybridising and producing viable progeny withLaricobius rubidusLeConte, a species native to eastern North America. Recently,Laricobius osakensisMontgomery and Shiyake was imported from Japan into the USA as a potential biological control agent of hemlock woolly adelgid. Hybridisation betweenL. nigrinusandL. rubidusled to interest in the outcome of interactions betweenL. osakensisand the other twoLaricobiusspp. The purpose of this study was to determine ifL. osakensiscould mate withL. nigrinus, if they could produce hybrid progeny, and whether mating interferes with reproductive output.Laricobiusspp. were observed mating directly following emergence and found to be capable of producing sterile eggs in the absence of a mating event. Laboratory and confined field studies found no evidence thatL. osakensisandL. nigrinuscould produce hybrid progeny and the interaction between the two species did not result in a lower reproduction associated with interspecific mating attempts. Interbreeding should therefore not have an impact on biological control using these species. Fecundity experiments showed thatL. osakensisproduced eggs earlier in the season and at a higher rate thanL. nigrinus, suggesting thatL. osakensismay have the potential to be an even more successful biological control agent thanL. nigrinus. [ABSTRACT FROM AUTHOR]