Howardula		Contents		Rev: 05/18/2024
		Classification		Biology and Ecology
		Morphology and Anatomy		Life Cycle
Return to Howardula Menu				Ecosystem Functions and Services
		Distribution		Management
Return to Allantonematidae Menu		Feeding		References
		Go to Nemaplex Main Menu		Go to Dictionary of Terminology

Classification:

Chromadorea

Chromadoria

Rhabditida

Tylenchina/Hexatylina

Sphaerularioidea

 Allantonematidae

       Howardula Cobb, 1921

Type species: Howardula benigna Cobb, 1921

    Synonyms:
     

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Morphology and Anatomy:

Characteristics of Howardula apini (Sharga, 1932) Wachek, 1955, as an example of genus

 Adult parasitic female:

•  body enlarged but shorter than free-living female.
• Body surface mostly smooth.
• Anterior end conoid ; stylet not retracted into inner body,
• Tail end narrows quickly, resembling free-living female tail.
• Esophagus and intestine degenerate. Anus not apparent.
•  Oviparous; gonad fills body cavity and usually has two flexures; ovary with numerous hexagonal oogonia arranged about a central rachis;
• Spermatheca highly specialized, in pouch-like structure in wall of oviduct that contains individual sperm received from male during free-living stage. V
• Vulva1 lips slightly protruded.

Free-living female:

• Body slender'
•  Stylet robust, with large lumen; basal knobs well developed.
• Esophagus allantonematoid, strongly swollen at level of subventral gland orifices, glands extend far posteriorly, filled with coarse globules, dorsal gland not as well developed as subventrals.
•  Gonad monodelphic, prodelphic; ovary with few cells; no eggs produced in this stage; small postuterine sac-like area present; v
• Vulva small, round; vulva1 lips not protruded.
• Anus difficult to see.
• Tail wedge-shaped, rounded at the end.

Free-living male :

• Smaller than female.
• Stylet absent, stoma weakly cuticularized.
• Esophagus weakly developed.
• Gonad outstretched, reaching into esophageal region; vas deferens containing individual sperms.
• Tail rounded at tip, enveloped by narrow, peloderan caudal alae.
• Spicules slightly curved, distally acuminated, tylenchoid.
•  Gubernaculum appearing as a shepherd's crook in lateral view.

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Distribution:

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Feeding:

Insect-parasitic nematodes, many species are parasites of flies although the type species was described from the cucumber beetle (Diabrotica) (Cobb, 1921)

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Biology and Ecology:

Like the genus Parasitylenchus, nematodes of the genus Howardula have a direct life cycle; there is no intermediate host. However, unlike Parasitylenchus, there is only a single amphimictice generation in the host, which is similar to most other genera in the Allonematidae (Poinar et al., 1997).

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Life Cycle:

Direct parasites of Drosophila with no ntermediate host.

As an example of the genus, Welsch (1958) described his research on the life cycle of Howardula aoronymphium, whiich he considered simialr to that of most known Allantonematidae:

•  Since the nematode has a stylet, he assumed that the fertilized female nedatodes enter the Drosophila host larvae by penetrating the cuticle. Although entry might be achieved through the mouth or the anus, he was unable to find nematodes in the esophagus or intestine; all were found in the host haemocoele.
• The inseminated female increases in size, forms eggs, and discharges approximately 500 larvae into the host haemocoele.
• The larvae move about in the host abdomen, and occasionally in the head and the thorax. Eventually they leave the host through the genital or the intestinal tract, or both.
• Larvae exit the host at or near their oviposition sites.
•  Before mating, males undergo the final molt and the females the penultimate molt.
• Males die after copulation, and the females enter the final host to commence another cycle.
• Three molts were observed in the development of the female and two in that of the male. Welch considered that that the females are fertilized as fourth-stage larvae and that a final molt might occur before host penetration.

In another species, Howardula husseyi, Richardson et al. (1977). reported that:

•  mature females were in the adipose tissues of the body cavity of the dipteran Megasella halteratahe
• The nematodes deposit up to 850 eggs during the insects pupation.
• The first juvenile stage is completed in the egg, hatch from the eggs and feed in the haemocoel. 
• Hatched lLarvae migrate to the ovaries of the fly and continue development.
• Larvae are liberated during oviposition into mshroom compost. 
• The nematodes grow and develop using stored reserves. 
• Fourth stage juvenile females s are fertilized and penetrate the host flies.
• Males probably die after copulation.
• The nematode life cycle is completed only in female flies; parsitizing larvae in male flies die without completeing development..

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Ecosystem Functions and Services:

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Management:

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References:

Cobb, N.A. 1921. Howardula benigna, a nemic parasire of the cucumber-beetle (Diabrotica). Science, 54: 667-670i

Nickle, W.R., Wood, G.W. 1964. Howardula aptini (Sharga, 1922) parasitic in blueberry thrips in New Brunswick. Cn. J. Zool. 42:843-846

Poinar, Jr., G.O., Jaenike, J., Dombeck, I., 1997. Parasitylenchus nearcticus sp. n. (Tylenchida: Allantonematidae) parasitizing Drosophila (Diptera : Drosophilidae) in North America. Fundam. Appl. Nematol. 20:187-190.

Richardson, P.N., Hesling, J.J., Ridoing, I.L. 1977. Life Cycle and Description of Howardula husseyi N. Sp. (Tylenchida: Allantonematidae), a Nematode Parasite of the Mushroom Phorid Megaselia Halterata (Diptera: Phoridae). Nematologica 23:217-231.

Sharga, U.S. 1932. A new nematode,Tylenchus aptini n. sp. parasite of  Thysanoptera (Insecta: Aptinothrips rufus Gmelin). Parasitology 24:268-279.

Wachek, F. 1955.. System und biologic der entoparasitischen Tylenchida. Parasitolog. Schriftenreihe. Fischer Verlag, Jena. 119 pp.

Welch, H.E. 1958. Taxonomy, life cycle, developmentand habits of two new species of Parasitylenchidae (Nematoda) parasitic in drosphilid flies. Contribution No. 3755, Entomology Division, Science Service, Department of Agriculture, Ottawa, Canada;

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Copyright © 1999 by Howard Ferris.
Revised: May 18, 2024.