Reported July 2007

BACKGROUND: Biocontrol agents are becoming more popular as both the public and regulators recognize the environmental and human health risks associated with chemical pesticides. One type of biocontrol agent is nematodes, which have proven to be highly effective against a wide variety of plant, animal and human pests.

WHAT ARE THEY? Pest-killing nematodes are tiny roundworms that can be applied through sprayers or irrigation systems to do the same job as chemical pesticides – minus the potential pollution. Unlike parasitic nematodes, which cause disease in plants, animals and humans, beneficial nematodes are used to fight costly insect and slug pests in vegetables, turf grass, citrus, strawberry, cranberry and ornamental crops. They have also shown promise against fleas, ticks and lice. For instance, citrus growers in Florida rely on the microscopic worms to combat the root-feeding citrus weevil.

Nematodes eat grubs and rid lawns and groves of other common insect pests, such as black vine weevils, beetles, leas, and cutworm, by releasing a bacterium that kills the pest. Nematodes are best applied when soil conditions are wet – right after it rains, for instance – with a soil temperature of at least 60 degrees F. They should be applied late in the day, or when it is cool and overcast, since exposure to ultraviolet light will kill them. Nematodes are non-toxic, and start becoming effective within 72 hours of being released into the soil.

THE ABCS OF NEMATODES: There are more than 15,000 known species of nematodes, and a single handful of garden soil may contain thousands of the creatures. They can lay more than 200,000 eggs in a single day. The nematode has an unusual skin that secretes a thick outer shell -- called a cuticle -- that is tough yet flexible, and is shed four times in the nematode’s lifetime before it reaches adulthood. The head has a few tiny sense organs, and a mouth so food can be pulled into the throat and crushed. Because they have no discrete circulatory or respiratory system, they are vulnerable to environmental conditions. Many nematodes can exist in a state of suspended animation (called cryptobiosis) in order to survive extreme conditions, such as dryness, heat or cold, returning to life when the environment becomes more favorable.

If you would like more information, please contact:

Dr. Parwinder Grewal
Department of Entomology
The Ohio State University

grewal.4@osu.edu

DID YOU KNOW?

The word “nematode” comes from the Greek word nema, meaning “thread,” because their long narrow bodies resemble threads.

Insect Parasitic Nematodes