Parasitic Nematodes



Webmaster: Daniel Snyder

Last Edited: May 16, 2002

Introduction to Nematodes

What are nematodes and why are they important?

Nematodes are Economically Important to Agriculture!
"Annual crop loss estimates caused by plant parasitic nematodes are roughly $80 billion worldwide, with $8 billion in the USA"

Kingdom Animalia - Phylum Nematoda

Most abundant animal life form...
"If nothing but nematodes were present there would be an outline of the Earth and many of its features"

The Greek word nematode means "threadlike"

Nematodes are unsegmented roundworms.

Features of Nematodes:
aquatic, triploblastic, unsegmented, bilaterally symmetrical, roundworms, that are transparent, colorless, usually bisexual, and worm-shaped (vermiform), although some can become swollen (pyroform)

Only an estimated 3% of all nematode species have been studied.

Nematode Organ Systems
skeletal - exoskeleton (triple layered cuticle)
secretory/excretory -
nervous - nerve ring and longitudinal muscles
digestive - stoma, esophagus, intestine,
reproductive -
NO circulatory or respiratory systems - exchange of gasses through cuticle.

General Plant Parasitic Nematode Life Cycle
5 Stages-4 Molts
Egg - J1 - M1 - J2 - (Hatch) - M2 - J3- M3 - J4 - M4 - Adult

In all plant parasitic nematodes the first molt occurs in the egg.
The emerging second-stage juvenile (J2) is the most common infective stage.

Length of life cycle of plant parasitic nematodes can be anywhere from 20-40 days (on average 25 days at 22oC).

Nematode Modes of Reproduction
Amphimixis - cross fertilization (males and females)
Parthenogenesis- nonsexual, males not required for reproduction(clonal)
Hermaphrodism - male and female organs in one individual(some change sexes)

Reproductive Potential (Egg production)
Anquina 25,000 eggs (2,000/wk)
Meloidogyne 500-1500 eggs
C. elegans 250-350 eggs
Ascaris 2 million eggs/day

Nematode Groups
1. Marine, Freshwater, Soil
2. Animal Parasites
A. Vertebrate
B. Invertebrate
3. Plant Parasites
Marine, Freshwater, Soil (Trophic Groups)
Microbivores ("free-living")
Omnivores (feed on multiple sources)
Predators (on nematodes, protozoa,etc.)

Caenorhabditis elegans
- Model Metazoan for Study of Higher Organisms
free-living nematode
microbivorous (can culture on E. coli)
959 cells (302 are neurons)
genome completely sequenced (97 megabases)
six pairs of chromosomes
encodes more than 19,099 proteins

Animal Parasites - Vertebrate (50 species attack humans)
Hookworm (Anclyostoma) ) Strongylids (Strongylus)
Pinworm (Enterolobius) Trichinosis (Trichina)
Elephantitis (Wuchereria) Heartworm (Dirofilaria)
Ascarids (Ascaris)

Animal Parasites - Invertebrate
Nematode parasites of insects (entomopathogenic)
Used as a biocontrol for insects - Vector bacteria into insect hosts
- Steinernematidae (10 species)
- Heterorhabditdae (3 species)

Plant Parasites
197 Genera, 4300 species of phytoparasites
Obligate parasites (cannot culture axenically, but can culture monoxenically)