Field efficacy and persistence of the entomopathogenic nematodes Heterorhabditis bacteriophora 'Oswego' and H. bacteriophora 'NC' on alfalfa snout beetle larvae (Coleoptera: Curculionidae)

Abstract

Field efficacy of 2 strains of entomopathogenic nematode, Heterorhabditis bacteriophora Poinar, were examined against alfalfa snout beetle larvae, Otiorhynchus ligustici (L.), in an established alfalfa field. Both strains were applied at 2.5 and 15 billion IJs per hectare using 2 different spray nozzle configurations. H. bacteriophora 'NC' reduced the insect larval population to 0.33-2.3 larvae per 54,900 cm3, significantly below the levels in the untreated controls, and reduced the incidence of snout beetle larval feeding and alfalfa stand death. NC occurred in 23-70% of the soil cores during the 1st growing season, but did not persist beyond the 1st growing season. The high rate of H. bcateriophora 'Oswego' reduced the insect larval population to 1.3 larvae per 54,900 cm3, significantly below the levels of the untreated controls but not as low as NC. Oswego also reduced the incidence of snout beetle larval feeding and alfalfa stand death. Oswego could be found in 73-99% of the soil cores during the 1st growing season and persisted for the entire 700 d of the trial. After 700 d, Oswego could be found in 24-44% of the soil cores taken within the treated plots. Evidence of nematode recycling was observed in both nematode strains. Data suggests that the NC strain would be more appropriate in situations where a biopesticide is desired, and the Oswego strain is more appropriate where long-term insect suppression is desired within more stable ecosystems.