Life stage influence on subterranean plum curculio, Conotrachelus nenuphar, susceptibility to microbial control agents

The plum curculio, Conotrachelus nenuphar (Herbst), remains an economically important pest of pome and stone fruit in the Eastern US. Traditional insecticide control options for plum curculio are becoming less available because of changes in legislature (FQPA 1996) and maximum residue limit concerns. Entomopathogenic nematodes, microbial control agents that kill insects by invading their host and releasing symbiotic bacteria that causes mortality, have demonstrated their potential as biological control tactic for plum curculio in soil. Our goal was to determine the efficacy of entomopathogenic nematodes against soil dwelling larval, pupal, and adult plum curculio. Laboratory experiments were established by incubating plum curculio in soil filled cups at the same temperature over different intervals so that the insects would be in their desired lifestages on the day of treatment. Cups were treated with four species of entomopathogenic nematodes: Heterorhabditis bacteriophora, Steinernema carpocapsae, Steinernema feltiae, Steinernema riobrave, and a water control. Cups were incubated for eight days and destructively sampled. Adult plum curculio cuticle status was noted as either scerlotized or unsclerotized and mortality due to nematode infection was confirmed via dissection. Survival of plum curculio pupae and teneral adults was reduced compared to larvae and the nematodes S. riobrave and S. carpocapsae were most efficacious. Survival of teneral adults with unsclerotized cuticles experienced was reduced compared to adults recovered with sclerotized cuticles. This research indicates that accurate timing of nematode applications is crucial for effective on farm adoption and the development of a phenology model for subterranean plum curculio is discussed.