Heterorhabditis

Heterorhabditis is a genus of nematodes in the family Heterorhabditidae. These organisms are entomopathogenic nematodes that form a mutualistic association with bacteria of the genus Photorhabdus. The bacteria are essential for the nematodes’ ability to kill and digest insect hosts; each Heterorhabditis species carries specific Photorhabdus strains.

In their life cycle, infective juveniles (IJs) emerge from adults and actively search for insect hosts in the soil. IJs enter hosts through natural openings or directly through soft tissues. They release their symbiotic Photorhabdus bacteria into the insect hemocoel, where the bacteria multiply and produce toxins that kill the host within one to two days. The nematodes feed on the cadaver and reproduce, developing into new IJs that carry bacteria. After consuming the host resources, many IJs exit the cadaver and disperse in the soil to infect new hosts.

Heterorhabditis species have a broad but variable host range, including many soil-dwelling larvae and caterpillars, beetle larvae, and some dipteran larvae. They are widely used in biological control programs against agricultural pests. Mass-produced in liquid or gel formulations, they are applied as soil drenches or seed/soil treatments. Efficacy depends on soil moisture, temperature, and protection from ultraviolet light.

Representative species include Heterorhabditis bacteriophora, H. megidis, and H. indica. The symbiotic bacteria Photorhabdus spp. provide nutrition and help suppress competing microorganisms, making the combination effective under field conditions.