Natural Distribution of Entomopathogenic Nematodes (Rhabditida: Heterorhabditidae and Steinernematidae) in Oregon Soils

To determine the natural distribution of entomopathogenic nematodes (Heterorhabditidae and Steinernematidae) in Oregon, 255 soil samples were taken from 59 sites representing ecologically diverse habitats and different geographic regions of the state. The presence or absence of entomopathogenic nematodes in samples was determined using the Galleria mellonella (L.) bioassay. Entomopathogenic nematodes were recovered from 30 soil samples representing 14 different sites. Twenty-four soil samples from 10 sites contained Heterorhabditis spp. and seven samples from five sites contained Steinernema spp. We found significant association among geographic regions, habitats, soil textures, and genera of nematodes recovered. More Heterorhabditis spp. were recovered than Steinernema spp. at the high latitude of Oregon. Geographic region and soil texture may be the most important factors influencing the natural distribution of Heterorhabditis spp. in Oregon.