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College of Food, Agricultural, and Environmental Sciences


Nematode Species Effective Biological Control of Slugs

March 6, 2002

WOOSTER, Ohio - A common European nematode has been found to be an effective parasite of grey garden slugs, and Ohio State University researchers are hoping to find the species in the United States or Canada for use as a biological control.

The nematode Phasmarhabditis hermaphrodita contains a bacterium that multiplies and kills the slug when the nematode enters its host. The nematode feeds on the bacteria that are produced, multiplies and produces more nematodes that seek and kill more slugs. Slugs die four to 16 days after infection, depending on the toxicity of the bacteria and their concentration in the host.

"It's a pretty neat little system," said Parwinder Grewal, an Ohio State University entomologist who conducts research on parasitic nematodes.

Grey garden slugs are mollusk pests that will feed on just about anything growing in an agricultural field - corn, wheat, soybeans, alfalfa -- and are especially problematic in no-till fields where residue provides food and shelter for the slugs to lay eggs and multiply. Stand loss in no-till fields from slug feeding can range from 50-90 percent. The juvenile stage of the slug is considered the most destructive phase.

Using nematodes, microscopic worms found abundantly in soil, as biological agents to control slugs is not new. Finding a parasitic nematode species that is effective against the grey garden slug is the challenge.

"There are different nematode species found in the U.S. as there are different slug species found, and each life stage of the slug has a different susceptibility to a parasitic nematode," said Grewal, who has been conducting surveys for over two years to determine if any species found in the United States is effective against the grey garden slug.

To date, 12 parasitic nematode species have been identified that show potential for biological control, but through comparative evaluations, Ohio State researchers found that they don't give that "one-two" punch the European nematode is capable of.

"The grey garden slug is a European species," said Grewal. "What better way to control the pest than to use its natural parasite?"

Grewal and his research associates are currently surveying areas in the United States and Canada in hopes of finding the European nematode.

"We are extending the survey for another year and are looking in more undisturbed areas like grasslands, wooded areas and prairies," said Grewal, who has received soil samples from Florida, Texas, Colorado, Michigan, Oregon and Vancouver, Canada.

If the researchers come up empty-handed, their next step may be to introduce the European species to the United States, a long process that requires government approval backed by solid research that the nematode is environmentally safe.

"We would have to make sure that the nematode is not dangerous to other creatures in the soil, like earthworms. Or if it can survive in water, it's not a threat to young fish or tadpoles," said Grewal. "If we can prove the safety of nematodes to non-target organisms, then it's our opinion that we have a case to bring it to the U.S. We are already able to demonstrate its potential use."

The introduction of non-native insect, plant and animal species, whether intentional or by accident, can potentially cause environmental damage, place native species at risk and drive up economic costs. The gypsy moth, intentionally introduced, and the zebra mussel, accidentally brought to the United States, are examples of problematic invasive species.

The U.S. Department of Agriculture, however, has seen some success in introducing non-native species to the United States for biological pest control. For example, USDA officials approved the introduction of a non-native predatory mite to help control wooly aphids that were destroying California's grape crop. Mite species are not harmful to people, plants or animals.

In other cases, introduction of non-native plant and animal species has been beneficial if not important to our livelihood. Corn, wheat, rice, cattle and poultry are examples of non-native plants and animals that are the backbone of our current food production system.

Candace Pollock
Parwinder Grewal