Rev 07/25/2023
Female:
Stoma collapsed
Esophagus with slightly swollen metacorpus, narrow isthmus, enlarged posterior bulb
Excretory pore at mid-esophagus level.
Ref: Nguyen and Smart, 1996
Male:
Infective Juvenile:
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).
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).
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)..
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).
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).
(Kaya and Gaugler, 1993; Shapiro-Ilan et al., 2002; Ye et al., 2018)
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., Léon, 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.
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