Heterorhabditis, Steinernema and their bacterial symbionts - lethal pathogens of insects

The entomopathogenic nematodes (EPN) Heterorhabditis and Steinernema togeth er with their symbiont bacteria Photorhabdus and Xenorhabdus, respectively, are obligate and lethal parasites of insects. EPN can provide effective bi ological control of some important lepidopteran, dipteran and coleopteran p ests of commercial crops and they are amenable to large-scale culture in li quid fermenters. They are unique among rhabditids in having a symbiotic rel ationship with an enteric bacterium species. The bacterial symbiont is requ ired to kill the insect host and to digest the host tissues, thereby provid ing suitable nutrient conditions for nematode growth and development. This review describes the general biology of EPN and their symbionts and gives a n overview of studies to date on EPN biodiversity, biogeography and phyloge ny. The impetus for research in EPN and their symbionts has come about beca use of their biological control potential, with much of the focus in EPN re search having been on applied aspects relating to pest control. However EPN and their symbionts are increasingly being viewed as exciting subjects for basic research in the areas of ecology biodiversity, evolution, biochemist ry, symbiosis and molecular genetics. Much progress has been made over the past 20 years in our understanding of the basic biology and genetics of EPN and their symbionts. We are now entering a new phase in which the tools of molecular genetics are being increasingly used to address a range of biolo gical questions in EPN research. The knowledge gained from this endeavour s hould ensure that EPN will become even more effective biopesticides and sho uld also ensure that EPN and their symbionts gain prominence as unique and intrinsically interesting biological systems.