Habitat heterogeneity enhances conservation of aboveground biological control organisms in agricultural systems and may conserve soil organisms, although this has rarely been examined.  Since few field studies have explored dispersal of soil-dwelling organisms, it is difficult to predict the extent of movement between crop and refuge habitats.  To address this, we compared the effect of simple (maize) and more complex (maize plus mixed annual plant refuge) habitats on the dispersal of entomopathogenic nematode (EPN) Steinernema carpocapsae, applied to soil as infected insect cadavers.  The experiment was conducted twice, in 2005 and 2006.  We quantified EPN dispersal by bioassay of soil samples collected at distances up to 3m away from the point of EPN application within and between crop and refuge habitats.
Results/Conclusions

We detected EPN at movement rates up to 33.3 cm/day, with EPN detection decreasing with distance away from the point of application.  In 2005, soil moisture and habitat type interacted such that EPN were detected further away in complex habitats, which had wetter soil.  In 2006, EPN movement was similar in both habitats, likely due to similar overall plant density that year.  Our results indicate that EPN movement is not necessarily dependent on plant diversity, but may respond to increased plant density, and subsequently, soil moisture.  We show that complex habitats may serve as movement corridors for EPN, particularly when there is low plant density within the crop area.