Heterorhabditis

Heterorhabditis	Contents	Rev 05/10/2024
	Classification	Biology and Ecology
	Morphology and Anatomy	Life Cycle
Return to Heterorhabditis Menu		Ecosystem Functions and Services
	Distribution	Management
Return to Heterorhabditidae Menu	Feeding	References
	Go to Nemaplex Main Menu	Go to Dictionary of Terminology

Classification:

Chromadorea Rhabditia
Rhabditida
Rhabditoidea
Heterorhabditidae
Heterorhabditis Poinar, 1976

Morphology and Anatomy:

Source: nematology.ifas.ufl.edu

Hermaprodites, amphimictic females and males occur.

Hermaphrodites and females:

Wide but shallow stoma; posterior part of stoma surrounded by esophagus.
Esophagus without metacorpus, slender isthmus, swollen basal bulb.
Excretory pore near basal bulb.
Vulva median. Amphidelphic; ovotestis (in hermaphrodites), uteri and ovaries in females.
Pointed tail, longer than anal body diameter.

Males:

single testis;
paired, separate, slightly curved spicules;
gubernaculum present.
Bursa peloderan with nine pairs of genital papillae.

Hermaphrodites and females oviparous when young, ovoviviparous when older.

Infective juvenile:

is the J3 dauer stage
usually encased in a second cuticular sheath
mouth and anus closed, esophagus reduced.
Tail pointed.
Symbiotic bacteria in intestine.

Body size range for the species of this genus in the database - Click:

Ref: Nguyen and Smart, 1996

Species can be grouped in three caldes: "Indica", "Bacteriophora" and "Megidis" (Dhakal et al., 2021).

Distribution:

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

Biology and Ecology:

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

Carry a pathogenic bacterium (Photorhabdus spp.) in the dauer juvenile (infective, IJ) stage.
Photorhabdus is a genus of bioluminescent, gram-negative bacteria living symbiotically within Heterorhabditis spp. Photorhabdus is pathogenic to a wide range of insects.
Dauer IJs actively seek and penetrate insect hosts aminly through natural openings..
Release the bacterium in the insect host.
There is rapid death of the insect host accompanied by exponential increase of the bacterium..
Both nematode and bacterium reproduce within the insect host; the IJ develops into a third-stage feeding larva and mainly into hermaphrodite adults in the case of Heterorhabditis. (In Steinernema they develop into male and female adults).
The bacterium is re-associated with new generations of the nematode.
Infective juvenile nematodes emerge from the cadaver of the insect host

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

Life Cycle:

For Ecophysiological Parameters for this genus, click

In the dauer stage of the infective juveniles (IJs) in the soil, Photorhabdus 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, usually within 24-48 hours post-infection.

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

Nematodes feed on the proliferating bacteria. They complete one to three generations within the cadaver. In species of Heterorhabditis, the IJs develop into self-fertile hermaphrodites which prduce the next generation. The secomd and subsequent generations in the cadaver are amphimictic and offspring are produced by cross fertilization involving males and females. In contrast, in species of Steinernema, with an exception of one species, all generations are produced by cross fertilization involving males and females (amphimictic).

Subsequent to the first generation, adult female body sizes of the nematode become smaller as nutrients are depleted. 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:

Nematodes of the genera Steinernema and Heterorhabditis are often entomopathogenic and are used as bio-control agents in suppression of insect pests (Kaya and Gaugler, 1993). They are available as a commercial product in Europe and the USA.
With their associated bacteria, they are lethal to a wide variety of insect pests.
They represent useful biocontrool agents because they can be reared in incubators and readily applied in field situtaions.

(Kaya and Gaugler, 1993; Ye et al., 2018)

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Management:

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References:

Dhakal. M., Nguyen, K.B., Hunt, D.J., Ehlers. R-U., Spitidonov, S.E., Subbotin, S.A. 2021. Molecular identification, phylogeny and phylogeography of the entomopathogenic nematodes of the genus Heterorhabditis Poinar, 1976: a multigene approach. Nematology 23, 451-466.

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.

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: 181ï¿½206.

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

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