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[R] Nematodes (eelworms or roundworms) constitute a very homogeneous group as far as anatomical and morphological features are concerned, but exhibit very diverse living habits. Many of them live as parasites, especially hook-worms and other roundworms, which are enemies of Man and domestic animals. Others remain in the soil, some of them being phytophagous.
Nematodes are worm-shaped animals with a simple structure, and are composed of an external tube (cuticle) enveloping 2 internal superposed tubes, i.e. the digestive tract and the genital (male or female) tract.
At the anterior end of the digestive tract, nematodes parasitic on plants exhibit a piercing stylet and an oesophageal tract terminating in a muscular crop, which acts as a sucking and reversing pump. Once the plant has been pierced by the stylet, digestive enzymes produced by the salivary glands are injected in it through the pump. The latter then sucks up the digested substances and pours then into the intestine.
Direct damage consists mainly of a weakening of plants and sometimes distortion, discoloration and gall formation, etc.; indirect damage consists in a worsening of mycoses and introduction of virus diseases.
These phytoparasitic nematodes belong to 2 orders, the Dorylaimida and the Tylenchida. Only a specialist can identify a species.
Distinction should be made between:.
- root nematodes, in which the whole cycle is spent in the soil, some of them being mobile at all stages and external (Tylenchus) or internal (Pratylenchus) parasites, others sedentary (cyst nematodes: Heterodera, Globodera);.
- gall nematodes (Meloidogyne , etc.);.
- aerial parts nematodes (Ditylenchus, Aphelenchoides).

[R] Images

* Nematoda (INRA)
a: stylet; b; oesophagus: c: bulbe musculeux; d: gut; e: cuticula; f: sex organs; g: anus.
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