Ecology of entomopathogenic nematodes

This chapter provides an overview on the ecology of entomopathogenic nematodes with emphasis on recent developments. These nematodes, represented by the genera Steinernema and Heterorhabditis, are important natural mortality agents of soil insects. Since the 1980s, great strides have been made in understanding their ecology, but much more work needs to be done as most studies have focused only on a few model nematode species. In spite of this, major accomplishments have been achieved in understanding the infection ecology such as their foraging behavior and understanding their active and passive dispersal and the effects of abiotic factors on nematode survival, dispersal and infectivity. In foraging behavior, the infective nematode stage was classified as being an ambusher (sit-and-wait forager), cruiser (widely forager) or intermediate (having characteristics of both types of foragers). With abiotic factors, there is a large body of literature with a good understanding on the effects of temperature and moisture extremes on the model nematode species. Effects of soil texture on the nematodes are less understood as soil is complex and various factors such as the amount of sand, silt, and clay and other factors as temperature, moisture, biotic organisms, soil chemistry, etc. affect the nematodes' survival, dispersal and infectivity. Field studies have focused on biogeography, but our knowledge base in population ecology and epizootiology of the nematodes and their hosts has only scratched the surface and much more studies in this area are warranted.