Entomopathogenic Nematode Facts / by Ganpati Jagdale

Entomopathogenic nematodes (EPNs) of the two genera Steinernema Travassos, 1927 and Heterorhabditis Poinar, 1976 in the order Rhabdita kill most insects but they are harmless to some beneficial insects (e.g. honey bees), higher animals and environment. Third-stage juvenile is the only free-living stage in the life cycle of the nematode known as the infective juvenile or dauer juvenile that found in soil and can seek, infect and kill their insect hosts.

These infective juveniles are mutualistically associated with symbiotic bacteria (Xenorhabdus spp. or Photorhabdus spp.) in the family Enterobacteriaceae, which are capable of causing disease in insect pests and killing them.

Species of genus, Xenorhabdus are specifically assocaited with the members of the nematode genusSteinernema and Photorhabdus species are associated with the members of nematode genusHeterorhabditis.

In this mutualistic relationship, the nematode infective juveniles provides protection for bacterium outside the insect host (as bacterium is unable to survive in the outside environment i.e. soil or water) and a means of transmission to new hosts and in return bacteria provides nutrients required for the nematode development and reproduction.

Infective juveniles are adapted to remain in the soil environment without feeding until they find a suitable host.

They are also resistant to unfavorable environmental conditions such as desiccation, heat and freezing.

EPNs can infect soil dwelling stages of butterflies, moths, beetles, flies, crickets and grasshoppers.

Infective juveniles of different nematode species employ different foraging strategy to find and infect their insect hosts. For example, Heterorhabditis bacteriophora is a cruiser forager meaning that it actively finds out or hunts its prey, Steinernema carpocapsae is an ambusher forager that sits and wait for a pray to pass by and S. feltiae and S. rivobrave are intermediate foragers.

EPNs are now commercially produced using both in vivo (in living host) and in vitro (in artificial medium) techniques.

Since EPNs have a wide host range, they are currently used as potential biological control agents to manage insect pests of many field crops, greenhouse and nursery plants, horticultural crops, turfgrass, and in some instances insect pests of animals and humans.

EPNs also have a potential to use as biocontrol agents against plant-parasitic nematodes.

Commercially produced nematode infective juveniles can be stored for extended periods and easily applied in aqueous suspensions in the field using traditional sprayers.

Also, EPNs are compatible with several chemical fungicides, insecticides, nematicides and herbicides, and therefore, they can be easily included in IPM programs.

Under current pesticide regulations, the U.S. Environmental Protection Agency has exempted these biological control agents from registration.