Abstract
Photorhabdus spp. are entomopathogenic bacteria that mutualistically associate with heterorhabditid nematodes. This chapter is devoted to reporting the toxic secretions of Photorhabdus bacteria and their efficacy against crop insect pests. Yet, because these bacteria are fairly similar to members of the bacterial genus Xenorhabdus, the two genera have been introduced together to show aspects of their similarities and differences. It is now well established that both genera of bacteria supply similar services to their different nematode hosts using matchless physiological and metabolic mechanisms. Distinctive phenotypic attributes for both Xenorhabdus and Photorhabdus are presented.