The spotted wing drosophila (SWD) is a small fly that was first discovered in the western U.S. in 2008. Since then it has colonized many fruit-growing areas in North America and has caused major problems for growers of cherries, berries, grapes, and tree fruits.
To manage the SWD, an insecticide called spinosad “is effective and has the least negative environmental effects of currently available products,” according to a publication by the University of California, Davis. Spinosad works well against flies like the SWD, but it carries a low risk of harming bees, which are needed to pollinate fruits and vegetables.
Now, according to an article by researchers at the Connecticut Agricultural Experiment Station, Rutgers University, and Cornell University that appears in the Journal of Economic Entomology, spinosad may be even more effective if a tiny bit of sucrose is added to the spray mixture.
“The addition of sucrose to insecticides targeting spotted wing drosophila, Drosophila suzukii (Matsumura), enhanced lethality in laboratory, semifield, and field tests,” the authors wrote. “In the laboratory, 0.1% sucrose added to a spray solution enhanced spotted wing drosophila feeding.”
It works because the sucrose acts as a phagostimulant — a substance that encourages feeding (“phago” is Greek for eating). Because of it, the flies are attracted to the liquid and they ingest it, making the spinosad more effective.
“Spotted wing drosophila flies are sensitive to and able to detect relatively low concentrations of sucrose presented on surfaces in their environment,” the authors wrote. “Their feeding on these deposits provides an opportunity that we can exploit for increasing their exposure to insecticides directed to manage their populations.”
The researchers found similar results when sucrose was used with other pesticides, but recommend that growers use reduced-risk insecticides like spinosad.
“The enhancement in activity of several reduced risk insecticides, such as spinosyns, cyantraniliprole, and acetamiprid, provided equivalent or superior protection of blueberry and strawberry fruits when compared with application of conventional insecticides,” they wrote. “Adoption of insecticide programs based on reduced risk insecticides applied with phagostimulants should reduce the broad spectrum environmental toxicity associated with the over reliance on organophosphates and pyrethroids for managing this pest.”
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