Microscopic worms rescue cranberries

• USDA Agricultural Research Service
• Oct 19, 2021 Updated Oct 19, 2021

Tiny wormlike organisms called nematodes that attack cranberry pests could offer a natural alternative to using insecticides. 

• Shawn Steffan

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Nematodes with a taste for “insect innards” may offer cranberry growers a natural alternative to fighting hungry crop pests with chemical insecticides.

Scientists with the U.S. Department of Agriculture’s Agricultural Research Service and University of Wisconsin are now exploring the possibility in field trials.

They’ve set their sights on redheaded flea beetles, Sparganothis fruitworms and other cranberry pests that attack the cranberry plant itself or its tart-tasting fruit. Severe infestations can force growers to apply insecticides, ratcheting up their production costs. Developing alternative controls as part of an integrated pest management approach can reduce or replace the need for insecticides, said Shawn Steffan, an entomologist with the Agricultural Research Service Vegetable Crops Research Unit in Madison, Wisconsin.https://1f1e72bdfae6591b8600816cafd353b4.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

For his part, he and UW collaborator Shane Foye are working to formulate a bio-insecticide that’s made of entomopathogenic — “insect-killing” — nematodes. One species they’re particularly excited about came from the self-same environment that cranberries thrive in — the marshland and bogs of central Wisconsin. Cranberry also happens to be the official fruit of the state, which produces 60 percent of the nation’s total crop.

Annually Americans consume 2.3 pounds of cranberries per person, primarily as juice but also in dried fruit snacks and holiday fare such as cranberry relish. However the path from bog to juice bottle can be a perilous one — no thanks to sundry insect pests whose appetites for destruction threaten the crop’s yield, fruit quality or both.

Nature, though, has seen fit to make the pests a favorite food of the nematodes Heterorhabditis georgiana and Oscheius onirici. Both species were found in the acidic wet bogs of central Wisconsin. Interestingly H. georgiana was originally discovered by David Shapiro-Ilan, who is another Agricultural Research Service scientist, in Georgia.

Steffan said, “O. onirici was originally found within caves in Italy, but clearly there are populations making a living in the marshlands of Wisconsin.”

The researchers hope both nematode species will prove to be an especially useful ally to both conventional and organic cranberry growers. Neither species is a threat to people, pets or other vertebrate animals. But what they do to their preferred prey isn’t pretty. After entering a natural body cavity, the nematodes release symbiotic bacteria that liquefy their prey’s internal organs and tissues. That creates a nutritious soup that the nematodes eat. Afterward they mate and deposit eggs inside their host’s remains. Eventually juvenile nematodes wriggle free in search of new hosts to infect, a cycle that lasts as long as their prey does.https://1f1e72bdfae6591b8600816cafd353b4.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

In field trials, spraying a solution of the nematodes onto cranberry beds reduced flea beetle numbers by as much as 93 percent. Average levels of control typically reached 60 percent to 70 percent — equal to two insecticide applications, Steffan said. In related laboratory experiments, O. onirici also proved lethal to the adult and larval stages of the spotted wing drosophila, an invasive species from Asia that’s become an established U.S. pest of many different fruit crops.

Encouraged by the results, the researchers have devised a method of rearing the nematodes by the billions and creating a clean highly concentrated mass of them that can be mixed with water and sprayed onto cranberry plants

“(And) we are trying some side-by-side trials this year involving commercial nematodes,” Steffan said. “This will give us some idea as to how our native Wisconsin nematodes compare to ‘off-the-shelf’ varieties.”

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This article originally ran on agupdate.com.