Efficacy and timing of entomopathogens against plum curculio (Conotrachelus nenuphar) in Michigan

Tree fruit growers are seeking alternatives for managing plum curculio, Conotrachelus nenuphar Herbst (Coleoptera: Curculionidae), in organic, IPM, and conventional orchards. Researchers have demonstrated the virulence of entomopathogenic nematodes (families Steinernematidae and Heterorhabditidae) and fungi (Metarhizium anisopliae and Beauveria bassiana) to various life stages. These and other alternative management tactics to organophosphate insecticides may require precise timing, and thus a better understanding of plum curculio phenology. We investigated the degree day timing of 4th instar emergence and the proportion of life stages (egg, 1st-4th instar, exited 4th instar) in cherries and apples in Michigan in 2008. We also tested the efficacy of two nematode species (Steinernema riobrave and Heterorhabditis bacteriophora) and one fungus species (B. bassiana) applied to orchard soils, with introductions of plum curculio larvae to soils -10, -5, 0, 5, 10, 15, or 20 d from entomopathogen application. The S. riobrave treatments resulted in significant reduction of adult emergence at the -5 and 0 d timings, and were especially effective in sites with sandy soils with low organic matter. Other treatments were not effective (α=0.05). Comparisons in degree days among crops, regions, and dropped vs. nondropped fruit are discussed. Efficacy results are compared to previous findings and applicability of combining a phenology model with pathogen efficacy for orchardists is discussed.