Responses of two introduced larval parasitoids to the invasive emerald ash borer (Coleoptera: Buprestidae) infesting a novel host plant, white fringe tree: Implication for biological control

Abstract

Emerald ash borer (EAB), Agrilus planipennis is a buprestid species native to Asia, where it is a pest of ash trees, Fraxinus spp. Since it was accidentally introduced to the United States in the 1990s, this beetle has become one of the most destructive invasive pests of North American ash trees. In 2015 it was found attacking the white fringe tree, Chionanthus virginicus, indicating the potential for host range expansion. This study evaluates the responses of two introduced larval parasitoids, Spathius agrili and S. galinae, to EAB larvae infesting this novel host plant. Third to fourth instar EAB larvae reared with tropical ash in the laboratory were inserted into green ash and white fringe tree bolts. Infested bolts were exposed to gravid females of both Spathius spp. under no-choice and S. galinae under choice testing conditions. No-choice testing indicated no difference in parasitism rate on EAB larvae between white fringe and green ash for either parasitoid species. Two-choice testing with S. galinae also indicated no difference in parasitism rate when green ash was an option. Sex ratio and brood size were unaffected by host substrate for EAB, but both species emerged sooner on EAB in white fringe tree under no-choice conditions. EAB larvae can be successfully parasitized in white fringe tree under laboratory conditions. These results indicate that S. agrili and S. galinae have potential to attack EAB larvae infesting white fringe tree.