Steinernema

 

Contents

 

Rev 05/10/2024

  Classification Biology and Ecology
Morphology and Anatomy Life Cycle
Return to Steinernema Menu Ecosystem Functions and Services
Distribution Management
Return to Steinernematidae Menu Feeding  References
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Classification:

 
Chromadorea
  Rhabditia
    Rhabditida
      Rhabditoidea
        Steinernematidae
        Steinernema Travassos, 1927

   Type species of the genus::  Steinernema kraussei (Steiner 1923) Travassos, 1927

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Morphology and Anatomy:

 
Source: nematology.ifas.ufl.edu

Female:

  • 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

Male:

  • Smaller than female.
  • Monorchis, 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:

Based on the sequences of the internal transcribed spacer (ITS) region of the rRNA, the species of the genus Steinernema are phylogenetically grouped into 12 clades;  nine multiple species clades: "Affine", "Bicornutum", "Cameroonense", "Carpocapsae", "Costaricense", "Feltiae", "Glaseri", "Karii", "Khoisanae", "Kushidai", "Longicaudum", and "Monticolum"; and three monospecies clades: S. neocurtillae, S. unicornum, and S. rarum (Spiridonov and Subbotin, 2016).

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Distribution:

Nematodes of the genera Steinernema and Heterorhabditis (family Heterorhabditidae) have been found on every continent except for Antarctica.

Because of their potential as entomopathogens, there are hundreds of isolates in different laboratories around the globe, which have been assigned to one of the more than 100 Steinernema species described so far (Bhat et al., 2020). Many isolates still await being assigned to formal taxonomic studies, and it is very likely that they also represent new, undescribed species (Machado et al., 2022).

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Feeding:

 The symbiotic 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).

Steinernema spp. are associated with entomopathogenic bacteria of the genus Xenorhabdus which occupy a specialized receptacle structure within the digestive tract of the free-living infective juveniles (IJs) (Chaston et al., 2011). The infective juveniles search for insects, and once inside the hosts, they release their bacterial symbiont into the hemocoel. During the multiplication of the bacteria in the insect host, toxins, enzymes, and other insecticidal compounds are released that kill the insect (Bhat et al., 2023)..

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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. Unlike in the genus Heterorhabditis, the first generation of adults developing from the IJs are amphimicitic, not hermaproditic; they reproduce sexually. Subsequent generations of adults are also amphimictic. 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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Management:

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References:

Bhat, A. H., Chaubey, A. K., and Askary, T. H. 2020. Global distribution of entomopathogenic nematodes, Steinernema and Heterorhabditis. Egyptian Journal of Biological Pest Control 30:1-15.

Bhat, A.H., Machado, R.A.R., Abolafia, J., Askary, T.H., Puza, V., Ruiz-Cuenca, A.N., Rana, A., Sayed, S., Al-Shuraym, L.A. 2023. Multigene Sequence-Based and Phenotypic Characterization Reveals the Occurrence of a Novel Entomopathogenic Nematode Species, Steinernema anantnagense n. sp. J. Nematology 55:  | DOI: 10.2478/jofnem-2023-0029

Chaston, J. M., Suen, G., Tucker, S. L., Andersen, A. W., Bhasin, A., Bode, E., Bode, H. B., Brachmann, A. O., Cowles, C. E., Cowles, K. N., Darby, C., Leon, L., de Drace, K., Du, Z., Givaudan, A., Tran, E. E. H., Jewell, K. A., Knack, J. J., Krasomil-Osterfeld, K. C., and Goodrich-Blair, H. 2011. The entomopathogenic bacterial endosymbionts Xenorhabdus and Photorhabdus: Convergent lifestyles from divergent genomes. PLOS ONE 6:e27909. https://doi.org/10.1371/journal. pone.0027909

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: https://doi.org/10.1371/journal.ppat.1002527.

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.

Hunt, D.J. and Nguyen, K.B. 2016. Advances in Entonmopathogenic Nematode Taxonomy and Phylogeny. Nematology Monographs and Perspecives 12 Brill, Leiden.

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

Machado, R.A.R., Bhat, A.H., Abolafia, J., Shokoohi, E., Fallet, P., Turlings, T.C.J., Tarasco, E. Puza, V., Kajuga, J., Yan, X., Toepfer, S. 2022. Steinernema africanum n. sp. (Rhabditida,Steinernematidae), a New Entomopathogenic Nematode Species Isolated in the Republic of Rwanda. J. Nematology 54: | DOI: 10.2478/jofnem-2022-0049

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.

Spiridonov, S. E. and Subbotin, S. A. 2016. Phylogeny and phylogeography of Heterorhabditis and Steinernema. In: Hunt, D.J. & Nguyen, K.B. (Eds). Advances in entomopathogenic nematode taxonomy and phylogeny. Nematology Monographs and Perspectives 12 (Series Editors: Hunt, D.J. & Perry, R.N.). Leiden, The Netherlands, Brill, pp. 413"427. DOI: 10.1163/9789004285347_007

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: May 10, 2024.