Beneficial Organism — Nematodes
Common Name: Nematode
Nematodes are microscopic, whitish to transparent, unsegmented worms. They occupy almost
every conceivable habitat on earth, both aquatic and terrestrial, and are among the most common
multi-celled organisms. Nematodes are generally wormlike and cylindrical in shape, often tapering
at the head and tail ends; they are sometimes called roundworms or eelworms. There are thousands
of kinds of nematodes, each with their particular feeding behavior. For example, there are bacterial feeders,
plant feeders, animal parasites, and insect parasites, to name just a few feeding behaviors.
The body of a nematode is long and narrow, resembling a tiny thread in many cases, and this is the
origin of the group's name. The word "nematode" comes from a Greek word "nema" that means thread.
The epidermis (skin) of a nematode is highly unusual; it is not composed of cells like other animals,
but instead is a mass of cellular material and nuclei without separate membranes. This epidermis
secretes a thick outer cuticle which is both tough and flexible. The cuticle is the closest
thing a roundworm has to a skeleton, and in fact the worm uses its cuticle as a support and leverage
point for movement.
Long muscles lie just underneath the epidermis. These muscles are all aligned longitudinally along
the inside of the body, so the nematode can only bend its body from side to side, not crawl or lift itself.
The head of a nematode has a few tiny sense organs and a mouth opening into a muscular
pharynx (throat) where food is pulled in and crushed. This leads into a long simple gut cavity
lacking any muscles, and then to an anus near the tip of the body. Food digested in the gut is not
distributed by any specialized vascular system, and neither is there a respiratory system for the
uptake or distribution of oxygen. Rather, nutrients and waste are distributed in the body cavity,
whose contents are regulated by an excretory canal along each side of the body.
Beneficial nematodes aggressively pursue insects. The beneficial nematodes can be used to
control a broad range of soil- inhabiting insects and above ground insects in their soil inhabiting
stage of life. More than 200 species of pest insects from 100 insect families are susceptible
to these nematodes. When they sense the temperature and carbon dioxide emissions of
soil-borne insects beneficial nematodes move toward their prey and enter the pest through
its body openings. The nematodes carry an associated bacterium (Xenorhabdus species)
that kills insects fast within 48 hours.
They have such a wide host range that they can be used successfully on numerous insect pests.
The nematodes' nonspecific development, which does not rely on specific host nutrients, allows
them to infect a large number of insect species.
Nematodes kill their insect hosts within 48 hours.
Nematodes can be grown on artificial media. This allows for commercial production which
makes them a more available product.
The infective stage is durable. The nematodes can stay viable for weeks when stored at the
proper temperature. Usually 3 weeks when refrigerated at 37o to 50° F. They can also
tolerate being mixed with various insecticides, herbicides and fertilizers. The infective juveniles
can live for some time without nourishment as they search for a host.
They are harmless to plants, pollinators, pets and humans.
Because grubs are constantly on the move to find over-wintering sites in the soil during
September through October, they become easy targets for beneficial nematodes. Nematodes
use symbiotic bacteria as weapon to kill Japanese beetle grubs or pupae and
Early October is the best month to kill Japanese beetle grubs with beneficial nematodes
Nematodes travel through the soil the thin film of water that coats soil particles. They search for
insect larvae using built-in homing mechanisms that respond to changes in carbon dioxide
levels and temperature. They also follow trails of insect excrement. After a single nematode finds
and enters an insect through its skin or natural openings, the nematode release a toxic bacteria
that kills its host, usually within a day or two.
Once inside the larva the nematodes excretes specific bacteria from its digestive tract before it
starts to feed. The bacteria multiply very rapid and convert the host tissue into products that the
nematodes take up and use for food. The nematodes multiply and develop within the dead insect.
As soon as the nematodes are in the infectious stage, they leave the old host and start searching
for new larvae.
The life cycle of beneficial nematodes consists of six distinct stages: an egg stage, four juvenile
stages and the adult stage. The adult spends its life inside the host insect. The third juvenile
stage, called a dauer, enters the bodies of insects, usually the soil dwelling larval form. In less
than two weeks the nematodes pass through several generations of adults, which literally
fill the insect cadaver. Steinernema reproduction requires at least two dauer nematodes to enter
an insect, but a single Heterorhabditis can generate offspring on its own.
Most nematodes species are compatible with pressurized, mist, electrostatic, fan and aerial
sprayers. Hose-end sprayers, pump sprayers, and watering cans are effective applicators as well.
Fertilizers should be avoided roughly 2 weeks prior to and after nematode application, because
they may be adversely affected by high nitrogen content.
Since beneficial nematodes are susceptible to UV radiation, it is recommended to apply them in
Nematodes need a film water for their easy movement in the soil, apply them when there is
enough moisture present in the soil. It also recommended applying irrigation after application
of nematodes so that irrigation water will wash them from grass blades into soil.
Repeat applications if the insect is in the soil for a longer period of time.
Because they leave no residues, application can be made anytime before a
harvest and there is no re-entry time after application.