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Photo courtesy of Ed Show

1.  There are 113 species of fruit flies. Why worry about this one? While most other fruit flies attack only overripe or damaged fruit, the female spotted wing drosophila can cut a slit and lay eggs in healthy fruit. Typically this insect will strike just as the fruit begins to color. It prefers such soft-skinned fruits as raspberries, blueberries, strawberries and blackberries.

2.  What’s been the regional damage so far? This native of eastern Asia, which began proliferating on the West Coast about four years ago, was first spotted in Michigan in 2010, where it has caused problems in cherries, blueberries, raspberries and strawberries. Untreated fruit will begin decay within three to four days of egg laying and have numbers of small white larvae (maggots) inside when harvested.

3.  What have we experienced in Wisconsin? Drosophila suzukii was first reported in adult fruit fly traps in Wisconsin in 2010, but no damage was seen until last August, with major crop losses in fall raspberries, blackberries and late strawberries in at least 15 counties. Cranberries, thankfully, have been spared so far, possibly due to the thickness of that fruit’s skin.

4.  What are the challenges of controlling this pest? The insect must be killed before eggs are laid in the fruit; eggs and larvae inside the fruit cannot be controlled by sprays. There are treatments that can be used to control this insect in organic production, but multiple sprays and thorough coverage are needed. We do not know if this insect is capable of surviving our winters or can be brought in on southerly winds or infested produce from out of state.

5.  What actions are we taking during the coming growing season? The use of vinegar-based adult fruit fly traps will help growers determine when the spotted wing drosophila first appear in their fields. Treatments must be started on sensitive crops when the first flies are captured.

Phillip Pellitteri is a distinguished faculty associate in the CALS Department of Entomology and a UW-Extension specialist. He runs the Insect Diagnostic Lab, which was established to identify insects and insect-damaged plant material from around the state and recommend controls to both county UW-Extension offices and commercial concerns. He also teaches in the Master Gardener program.