Evaluation of hybridization between Laricobius osakensis and Laricobius nigrinus, predators of hemlock woolly adelgid, (Adelgidae)

The hemlock woolly adelgid (HWA, Adelges tsugae) is an invasive insect from Japan that has caused extensive mortality of eastern and Carolina hemlock (Tsuga canadensis, T. caroliniana). Releases of Laricobius nigrinus, a predator of HWA native to the PNW and Canada, began in the eastern U.S. in 2003. As of this time, L. nigrinus has been released in 18 eastern states. Laricobius osakensis, an additional predator of HWA native to Japan, has been released from quarantine and is pending field release. Due to the fact that L. nigrinus has been found to hybridize with Laricobius rubidus, a predator of pine bark adelgid (Pineus strobi) native to the east coast, it was necessary to address the possibility of hybridization between L. osakensis and L. nigrinus before L. osakensis could be released. The potential of hybridization between these two species has been assessed through lab mating studies and genetic analysis. Although they attempt to mate, viable eggs are not produced. Currently there is no evidence that the two species can hybridize.