An Entomopathogenic Nematode by Any Other Name
Figure 1
Evolution of nematode–insect associations and the entomopathogenic nematode life cycle.
(A) The evolution of nematode–insect associations. Free-living: microbotrophic nematodes not known to associate with arthropods, vertebrates, plants, or fungi; only perhaps transiently associated with insects. Phoresy: a relationship where nematodes are adapted to use insects for dispersal or shelter but have no direct nutritional relationship to them. Necromeny: a relationship where nematodes are adapted to use saprophytic insect cadavers as a food resource but do not participate in insect death. Parasitism: a relationship where nematodes are adapted to use living insects directly for nutrition, likely inflicting some level of harm or even causing eventual death of the host. Entomopathogeny: a relationship where nematodes cooperate with insect-pathogenic bacteria to cause rapid insect disease and death and then feed and develop on the insect and bacterial resources. The distinction between parasitism and entomopathogeny is based on salient features including use of pathogenic bacteria and direction of selection (against virulence or avirulence), either making the nematodes more or less immediately harmful to their host. (B) The life cycle of entomopathogenic nematodes. The IJ stage is a developmentally arrested third larval stage and is the only free-living stage; all other stages exist exclusively within the host. EPN IJs carry symbiotic bacteria and search for potential insect hosts. They enter a host, gain access to the hemolymph, and release their bacterial symbiont. The symbiont plays a critical role in overcoming host immunity. The nematodes develop and reproduce in the resulting nutrient-rich environment until population density is high and resources begin to deplete, at which point new IJs develop and disperse, carrying the symbiotic bacteria to new hosts [5].