Nematodes with a taste for “insect guts” may offer cranberry growers a natural alternative to controlling pests of starving crops with chemical insecticides.

Scientists from the Agricultural Research Service (ARS) and the University of Wisconsin (UW) are currently exploring the possibility of field trials.

They’ve set their sights on red flea beetles, Sparganothis fruit worms and other cranberry pests that attack the cranberry itself or its tart-tasting fruits. Severe infestations can force growers to apply insecticides, increasing their production costs. Developing alternative controls as part of an integrated pest management approach can reduce or replace the need for insecticides, noted Shawn Steffan, an entomologist at ARS’s Vegetable Research Unit in Madison, Wisconsin.

For his part, he and his collaborator at UW, Shane Foye, are working on the formulation of a bio-insecticide composed of entomopathogenic nematodes (“insect killers”). One species they’re particularly passionate about comes from the same environment in which cranberries thrive: the swamps and bogs of central Wisconsin. Cranberries also happen to be the official state fruit, which produces 60 percent of the country’s total crop.

Every year, Americans consume 2.3 pounds of cranberries per person, mostly in the form of juice, but also in the form of dried fruit snacks and holiday dishes such as cranberry relish. However, the path from the bog to the juice bottle (or the table) can be perilous – not thanks to various pests whose appetite for destruction threatens crop yield, fruit quality, or both.

Nature, however, has seen fit to make these parasites a favorite food for the nematodes Heterorhabditis georgiana and Oscheius onirici. Both species have been found in moist, acidic bogs in central Wisconsin. Interestingly, H. georgiana was originally discovered by David Shapiro-Ilan (another ARS scientist) in Georgia. “O. onirici was originally found in caves in Italy, but it’s clear that there are populations living in the Wisconsin swamps,” Steffan said.

Researchers hope the two nematode species will prove to be a particularly useful ally for conventional and organic cranberry growers. Neither species poses a threat to humans, pets, or other vertebrate animals. But what they do to their favorite prey is not pretty. After entering a natural body cavity, nematodes release symbiotic bacteria that liquefy internal organs and the tissues of their prey. This creates a nutritious soup that the nematodes eat. They then mate and lay eggs inside their host’s remains. Eventually, juvenile nematodes wriggle freely in search of new hosts to infect, a cycle that lasts as long as their prey.

In field trials, spraying a nematode solution on the cranberry beds reduced the number of flea beetles by up to 93 percent. Average control levels were typically 60 to 70 percent, the equivalent of two insecticide applications, Steffan noted. In related laboratory experiments, O. onirici has also been shown to be fatal to the adult and larval stages of spotted wing drosophila, an invasive species from Asia that has become an established pest in the United States for many fruit crops. different.

Encouraged by the results, the researchers developed a method to breed nematodes by the billions and create a clean, highly concentrated mass that can be mixed with water and sprayed on cranberry plants.

In addition, “we are trying side-by-side trials with commercial nematodes this year,” Steffan said. “This will give us an idea of ​​how our native Wisconsin nematodes compare to ‘off the shelf’ varieties.”

The Agricultural Research Service is the principal in-house scientific research organization of the United States Department of Agriculture. Daily, ARS focuses on solutions to agricultural problems affecting America. Every dollar invested in agricultural research has an economic impact of $ 17.


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