U.S. entomologists from the University of Minnesota and the Minnesota Department of Agriculture (MDA) have confirmed the return of spotted-wing drosophila, an invasive species that feeds off of soft-skinned fruit like blueberries, raspberries and strawberries.

University entomologist Bill Hutchison encouraged growers to monitor for the pest and begin management practices.

"SWD was first officially detected in Minnesota last August by the MDA, and the pest was a real challenge for our berry growers, statewide," Hutchison said in a university statement.

"Everywhere we looked last fall, either flies or maggots [in fruit] were detected – a total of 29 counties were positive last year."

The pest of Asian origin was first detected in California in 2008 and has since spread to a number of U.S. states.

"SWD looks similar to small fruit flies found on overripe bananas. However, unlike these other flies, which typically feed on overripe or deteriorating fruits, SWD feeds on healthy, intact, ripening fruits," the Minnesota Department of Agriculture said.

"Sometimes the symptoms won’t show until after the fruits are harvested and sometimes not until the fruits are in possession of the consumers. In addition to the damage caused directly by the larvae, the feeding makes the fruits susceptible to infestation by other insects and rot fungi and bacteria."

Entolomogist Mark Asplen - hired with emergency funding to control the pest - suggested growers adopt three control measures: yeast-based or apple cider-vinegar traps for early detection of adult flies, clean and timely harvests to avoid over-ripe fruit or fallen fruit, and insecticidal sprays.

Photo: male Drosophila suzukii, Martin Hauser Phycus via Wikimedia Commons

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