Rev 10/12/2022

  Classification Biology and Ecology
Morphology and Anatomy Life Cycle
Return to Steinernema Menu Ecosystem Functions and Services
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        Steinernema Travassos, 1927
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Morphology and Anatomy:



  • Stoma collapsed

  • Esophagus with slightly swollen metacorpus, narrow isthmus, enlarged posterior bulb

  • Excretory pore at mid-esophagus level.

  • Diovarial, amphidelphic
  • oviparous or ovoviviparous with juveniles developing to J3 before emerging from body.


Ref: Nguyen and Smart, 1996


  • Smaller than female.
  • Single testis, reflexed.
  • Spicules paired.
  • Long gubernaculum
  • Bursa absent.
  • Tail rounded or digitate.

Infective Juvenile:

  • J3 dauer.
  • Stoma collapsed.
  • With or without second cuticular sheath.
  • Esophagus and intestine reduced.
  • Tail conoid or filiform.


Body size range for the species of this genus in the database - Click:
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Nematodes of the genera Steinernema and Heterorhabditis (family Heterorhabditidae) have been found on every continent except for Antarctica.

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 Thesymbiotic complex of entomopathogenic nematode (EPN) and bacterium actively searches, infects and kills the host, propagates in the host, and produces progeny to start a new life cycle after leaving the host (Gotz et al., 1981).

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Biology and Ecology:

The following criteria characterize entomopathogenic nematodes (a modification of Koch's postulates):

Ref: Dillman, et al., 2012; Ye et al., 2018).

Xenorhabdus is a genus of motile, gram-negative proteobacteria from the family of the Morganellaceae. Species of the genus are only known to live in symbiosis with Steinernema spp.

The nematode cannot establish within his insect host without the bacteria.

The tripartite Xenorhabdus-Steinernema-insect interaction represents a model system in which there is both mutualism and pathogenicity.

Some species of Xenorhabdus are virulent when injected directly intothe insect host while other species appear to need phoresy with the nematode into the insect (Gaudriault et al, 2014).


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Life Cycle:


For Ecophysiological Parameters for this genus, click 


In the dauer stage of the infective juveniles (IJs) in the soil, Xenorhabdus spp. are carried in a specialized region of the intestine.

The IJs invade the hemocoel of susceptible insect hosts. Bacteria are released in the insect hemocoel, where they overcome the insect's defense systems and produce numerous virulence factors such as hemolysin and cytotoxin. The insect host is killed.

The bacteria proliferate to high levels in the insect cadaver and produce diverse antimicrobial compounds that suppress the growth of antagonistic microorganisms. Xenorhabdus spp. also secrete an array of exoenzymes that stimulate macromolecular degradation.

Nematodes feed on the proliferating bacteria. When nematode numbers become high and nutrients become limiting in the insect cadaver, nematode progeny re-associate with bacteria and differentiate into colonized, non-feeding IJs that emerge into the soil to forage for new hosts. (Kaya and Gaugler, 1993).


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Ecosystem Functions and Services:

(Kaya and Gaugler, 1993; Shapiro-Ilan et al., 2002; Ye et al., 2018)


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Dillman, A.R., Chaston, J.M., Adams, B.J., Ciche, T.A., Goodrich-Blair, H., Stock, S.P., and Sternberg, P.W. 2012. An entomopathogenic nematode by any other name. PLoS Pathogen 8(3): e1002527, available at:

Gaudriault S., Ogier J.C.; Pagu, S.; Bisch G.; Chiapello H.; M�digue C.; Rouy Z.; Teyssier C.; Vincent S.; Tailliez P.; Guivaudan A. (2014). Attenued Virulence And Genomic Reductive Evolution In The Entomopathogenic Bacterial Symbiont Species, Xenorhabdus poinarii. Genome Biology and Evolution. 6: 1495�1513.  

Gotz, P., Boman, A. and Boman, H. G. 1981. Interactions between insect immunity and an insect-pathogenic nematode with symbiotic bacteria. Proceedings of the Royal Society of London Series B 212:333-350.

Kaya, H.K., and Gaugler, R. 1993. Entomopathogenic nematodes. Annual Review of Entomology 38: 181-206.

Nguyen, K.B. and Smart, G.C. 1996. Identification of entomopathogenic nematodes in the Steinernematidae and Heterorhabditidae. J. Nemtology 28:286-300.

Shapiro-Ilan, D. I., Gouge, D. H. and Koppenhofer, A. M. 2002. Factors affecting commercial success: case studies in cotton, turf and citrus, In Gaugler, R. (Ed.), Entomopathogenic Nematology CABI Publishing, Wallingford, pp. 333-356.

Ye, W. Foye, S., MacGuidwin, A.E., Steffan, S. 2018. Incidence of Oscheius onirici (Nematoda: Rhabditidae), a potentially entomopathogenic nematode from the marshlands of Wisconsin, USA. J. Nematology 50:9-26. DOI: 10.21307/jofnem-2018-004



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Copyright © 1999 by Howard Ferris.
Revised: October 12, 2022.