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

Field efficacy of 2 strains of entomopathogenic nematode, Heterorhabditis b acteriophora Poinar, were examined against alfalfa snout beetle larvae, Oti orhynchus ligustici (L.), in an established alfalfa field. Both strains wer e applied at 2.5 and 15 billion IJs per hectare using 2 different spray noz zle configurations. H. bacteriophora 'NC' reduced the insect larval populat ion to 0.33-2.3 larvae per 54,900 cm(3), significantly below the levels in the untreated controls, and reduced the incidence of snout beetle larval fe eding and alfalfa stand death. NC occurred in 23-70% of the soil cores duri ng the 1st growing season, but did not persist beyond the 1st growing seaso n. The high late of H. bacteriophora 'Oswego' reduced the insect larval pop ulation to 1.3 larvae per 54,000 cm(3), significantly below the levels of t he untreated controls but not as low as NC. Oswego also reduced the inciden ce of snout beetle larval feeding and alfalfa stand death. Oswego could. be found in 73-99% of the soil cores during the Ist growing season and persis ted For the entire 700 d of th trial. After 700 d Oswego could be found in 24-44% of the soil cores taken within the treated plots. Evidence of nemato de recycling was observed in both nematode strains. Data suggests that the NC strain would be more appropriate in situations where a biopesticide is d esired, and the Oswego strain is more appropriate where long-term insect su ppression is desired within more stable ecosystems.