The Minnesota Department of Agriculture (MDA) has confirmed a new fruit pest, the spotted wing drosophila (SWD), in Minnesota. SWD is an invasive pest of Asian origin that was first detected in the continental United States in California in 2008 and has since spread to several western and eastern states.
The first two detections of this pest in Minnesota were made by members of the public who reported the flies to the Minnesota Department of Agriculture (MDA). First, a homeowner from Hennepin County contacted MDA about flies found in a trap placed near a raspberry patch. Days later, MDA was contacted about an abundance of maggots in wild raspberries picked in Ramsey County. MDA followed up on both reports to confirm the identity of this new pest.
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. In particular, SWD will feed on thin-skinned, soft fruits such as raspberries, blackberries, blueberries, strawberries, grapes, plums and cherries. 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. The larvae will then leave the fruits to pupate and later emerge as adults.
The SWD is a small fly, only 2-3 mm long, with yellowish brown coloration and prominent red eyes. Male SWD have dark spots on the wing tips. SWD larvae are white with a cylindrical body that tapers on both ends.
The adult flies are difficult to distinguish from other small flies; however, if you find an abundance of small, white maggots in what were apparently healthy fruits at the time of harvest, contact the Minnesota Department of Agriculture at 1-888-545-6684 (voicemail) or Arrest.the.Pest@state.mn.us.
Current distribution of SWD in Minnesota and management information from the University of Minnesota.
Minnesota Department of Agriculture (MDA), 625 Robert Street N, St. Paul, MN 55155-2538, firstname.lastname@example.org