Patchiness in Populations of Entomopathogenic Nematodes

The distribution and abundance of entomopathogenic nematodes within and among sites were investigated by taking soil samples along transects at several locations in southwestern New Jersey and by assaying for nematodes using the Galleria -bait method. Entomopathogenic nematodes were found at 12 of 13 sites (92.3%) and in 72 of 600 soil samples (12.0%). Heterorhabditids (probably Heterorhabditis bacteriophora ) were found in 60 samples from 12 sites. Steinernematids were rarer, with Steinernema glaseri being found in 8 samples from 3 sites, S. feltiae (=bibionis) in 4 samples from 2 sites, and S. carpocapsae in 2 samples from 2 sites. Heterorhabditids differed significantly in abundance among sites with from 0 to 47.5% of samples from individual sites proving positive. Overall, heterorhabditids were equally abundant in turf and weedy habitats but significantly less abundant in closed-canopy forest where no positive records were obtained. Within sites, heterorhabditids were aggregated, with individual soil samples being much more likely to contain sufficient nematodes to infect multiple Galleria larvae than predicted based on the total number of positive soil samples and a random distribution. However, this patchiness occurred on a relatively small scale since the occurrences of nematodes in successive soil samples taken at 4-m intervals along transects were statistically independent of one another. Spatial heterogeneity is probably a fundamental aspect of the population biology of these species and has important ramifications for their population dynamics, population genetics, and community structure.