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Insect Parasitic (Beneficial) Nematodes
- Tiny worms that kill soil inhabiting garden pests -
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Summary: Entomopathogenic nematodes are microscopic worms that infect and kill certain insect pests in the soil. Some of these nematodes can now be artificially produced and applied like a pesticide against landscape pests.
Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
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What are beneficial nematodes?
 Nematodes are microscopic worms (right) that live in the soil. Most species feed on soil bacteria. Some nematodes, however, are plant pathogens, and a few are insect parasites, or pathogens.
Entomopathogenic is a fancy term for beneficial nematodes that parasitize certain insect larvae that live in the soil. Parasitized larvae (right, bottom) usually die before development is complete and dead larvae release large numbers of new nematodes.
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Insect parasitic nematode, highly magnified.
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Naturally occurring nematodes are normally not present in high enough numbers to control soil dwelling plant pests like root weevils or mole crickets. However, some insect parasitic nematodes can now be artificially produced and applied much like a pesticide. These nematodes are non-toxic and will not harm plants.
Using nematodes for insect control can be a bit tricky. The most important considerations are (1) adequate soil moisture, (2) proper soil temperature, and (3) product viability and specificity. Follow package instructions carefully to have the best chance of success.
Nematodes actually live on a thin film of water that covers soil particles. Nematodes are essentially aquatic organisms. Because of this the correct soil moisture is important. Too dry and the nematodes can't swim, too wet and they get washed away.
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Black vine weevil larvae, healthy (top) and infected with nematodes (bottom).
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Are the nematodes viable (alive)?
You can, and should, do a nematode
viability test before applying nematodes to be certain they are alive and able to function. Mix the nematodes as per package instructions. Wait 30 minutes then place a drop or two on a flat piece of glass or clear plastic. Carefully examine the drop under good light with a hand lens. You should be able to
see the tiny nematodes wriggling or bending back and forth. If they are
stiff, and not moving, they may not be viable.
Optimum soil temperature
varies but generally temperatures above 50 degrees are needed. Finally,
because these are living organisms care must be taken in handling and
packaging to deliver live nematodes to the target pest.
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Entomopathogenic nematodes are
available for a number of soil dwelling pests [more information]. Check labels carefully for appropriate use and always follow label instructions.
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