Potential of two entomopathogenic nematodes for suppression of plum curculio (Conotrachelus nenuphar, Coleoptera: Curculionidae) life stages in northern climates

Plum curculio, Conotrachelus nenuphar, is a major pest of pome and stone fruits in North America. We evaluated the potential efficacy of two entomopathogenic nematode species for suppression of plum curculio in northern regions, targeting life stages that reside in soil during spring and summer. A strain of Heterorhabditis bacteriophora isolated from soil infested with plum curculio in northern Utah and a commercially available strain of Steinernema feltiae known to tolerate cool temperatures were tested in the laboratory against three life stages of plum curculio. Bioassays used the southern strain of plum curculio because availability of the northern strain from the field was inadequate. H. bacteriophora was more virulent than S. feltiae to all plum curculio life stages. Adults and pupae were more susceptible than larvae. Temperature bioassays were conducted with a surrogate host: last instars of Galleria mellonella. The two nematodes exhibited different, but overlapping, thermal activity ranges. Both species performed best at 20[degree]C: virulence and reproductive potential was higher; however, H. bacteriophora was superior to S. feltiae at 30[degree]C and vice versa at 10[degree]C. The reproductive potential of H. bacteriophora was >2.5 times greater than for S. feltiae, and H. bacteriophora required fewer individuals to initiate a successful host infection. S. feltiae was a better fit for temperatures expected in northern climates, but H. bacteriophora was more virulent to plum curculio and produced more infective juveniles that may benefit nematode recycling and continuation and spread of insect suppression in the field.