CORVALLIS, Ore. —Two Oregon State University researchers have discovered a microscopic, soil-dwelling nematode on the Corvallis campus that could become an important tool against invasive slugs responsible for billions of dollars in agricultural damage worldwide.
“If we can provide evidence it’s native, that makes a strong case for developing it as a bio-control. But we want to make sure there are no effects on native slugs or snails. We don’t want bio-control gone awry."
In Oregon, at least half of the state’s top 20 agricultural commodities suffer from slug damage, including the grass seed industry, which loses an estimated $60 million annually, according to Rory Mc Donnell, associate professor in crop and soil science in OSU’s College of Agricultural Sciences and slug specialist for the OSU Extension Service. Although figures aren’t available for the state’s $1 billion nursery industry, Oregon’s top commodity, slugs and snails also cause substantial losses there, Mc Donnell said.
The parasitic nematode Phasmarhabditis hermaphrodita could help reduce those losses significantly, said Dee Denver, professor and head of the OSU Department of Integrated Biology in the College of Science and a nematode specialist. The nematode has been used in Europe for more than 25 years as a bio-control product under the brand name Nemaslug, but it is not yet registered in the United States by the Environmental Protection Agency (EPA).
“The thought process is that if it works in Europe and we find it here, it might be easier to get it registered by the EPA,” Mc Donnell said. “If we can provide evidence it’s native, that makes a strong case for developing it as a bio-control. But we want to make sure there are no effects on native slugs or snails. We don’t want bio-control gone awry. That’s very, very important.”
The results of their work have been published in the journals PLOS One and Biological Control.
Limitations of chemical control
Currently, growers rely on expensive chemical pesticides that achieve only 10% to 60% control, Mc Donnell said. These products can also have unintended effects on non-target organisms and contaminate waterways.
“The damage slugs cause is a massive issue,” Mc Donnell said. “We surveyed 200 growers throughout the Willamette Valley about using pesticides to control slugs, and only 30% were satisfied with the performance of chemicals.”
For three years, Mc Donnell — whose position was originally funded by the Oregon Legislature to find solutions to the state’s slug problem — searched across Oregon for P. hermaphrodita. The breakthrough came unexpectedly on the OSU campus in Corvallis.
The discovery is the first in North America outside of California, where Mc Donnell and researchers at the University of California, Riverside, found the nematode in 2014.
Finding it was no easy task. With thousands, if not millions, of nematode species in existence, the comma-sized P. hermaphrodita is almost invisible to the untrained eye. Denver identified it by extracting and sequencing its DNA, then comparing it to samples in a national repository.
How the nematode kills slugs
To locate the nematode, Mc Donnell’s team set and checked traps at the edges of agricultural fields, looking for gray field slugs (Deroceras reticulatum) that may have succumbed to nematode infection. The nematodes invade the slug through a hole at the back of its mantle — the saddle-shaped area at the front of the slug. Once inside, the nematodes kill the host, feed on it and reproduce rapidly, with one nematode producing thousands of offspring within one to two weeks.
“When a slug is infested with nematodes, it liquefies,” Denver said. “You end up with a swarming pile of worms. It’s pretty gruesome.”
The gray field slug, a major pest for home gardeners and commercial agriculture, has spread across most of the world. In Europe, P. hermaphrodita can reduce crop damage by slugs by up to 90%. In addition to direct feeding damage, D. reticulatum can spread plant diseases and leave slime trails and feces that reduce crop quality.
Future research directions
As their research continues, Denver and Mc Donnell are cultivating other nematode species to study genetic relationships and identify additional species with bio-control potential.
“Nematodes are abundant and diverse — there are millions of them in every aspect of the earth’s biosphere,” Denver said. “They are really understudied, and with Rory’s lab as one of very few in North America devoted to slugs and snails, we’re in a good position to do this research.”
Previously titled Microscopic worm that liquefies slugs may be answer to controlling this invasive pest
