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Spotted wing drosophila in home gardens

Quick facts

  • Spotted wing drosophila (SWD), Drosophila suzukii, is an invasive small fruit fly (sometimes called vinegar fly).
  • In Minnesota, SWD primarily attacks raspberries, blackberries (and other cane berries), and blueberries but may also infest strawberries, grapes and stone fruit.
  • Native to Asia, SWD is currently found in most if not all of the primary fruit growing regions of the U.S.
  • The Minnesota Department of Agriculture monitors this invasive species. Please report any SWD you spot at Arrest the Pest.

How to tell SWD from other fruit flies

Adults

  • SWD is only 1/12 to 1/8 inch (2-3 mm) long.
  • Yellowish-brown.
  • Dark colored bands on the abdomen.
  • Prominent red eyes.
  • They can be difficult to distinguish from other species of small fruit flies.
spotted wing drosophila on its side, with 1 visible translucent wing with a dark spot at the top  edge of each wing, and large red eye
Male spotted wing drosophila. Note the dark spot on tip of wing.
  • Male SWD are relatively easy to identify as they have clear wings and a dark spot along the first vein near the tip of each of wing.
  • Female SWD also have clear wings, but they do not have any spots on them.
    • They can only be identified by their saw-like ovipositor, which has two rows of dark-colored teeth (the ovipositor is the structure used by the female fly to insert eggs into berries).
    • High magnification is needed to see the ovipositor.
tiny white larvae inside a strawberry
SWD larva in a strawberry

Larvae

  • SWD maggots are white with a cylindrical body that tapers on one end. 
  • They do not have legs or a conspicuous head. 
  • This is a small insect, only reaching 1/8th inch long.

Life cycle

  • SWD first appear during late June or early July, and the numbers increase rapidly during the middle of summer, with the populations peaking in August.
  • Adult flies insert eggs into soft fruit where the larvae develop.
  • The larvae leave the fruits to pupate and later emerge as adults.
  • SWD can complete its life cycle in as little as seven days.
  • Multiple generations of SWD can occur in a year, with populations building throughout the summer.
  • SWD overwinters as an adult.
  • There is evidence that some SWD are able to survive Minnesota winters.

Damage

tiny fruit fly on a black raspberry
Female SWD on a blackberry
  • SWD larvae feed 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.
  • SWD larvae feed within the fruits causing brown, sunken areas. 
  • It is possible that larval feeding symptoms won't show until after crops are harvested.
  • During egg laying, the female may introduce fungi that cause the fruit to rot, and infested fruit often develop a fermented or a sour smell.
  • If berries are stored at room temperature, larvae can hatch after the fruit has been picked. Fruit that was normal then may be soft and maggot-infested a day or two later.
  • Mature larvae often crawl out of fruit stored on the counter.
  • The feeding makes the fruits susceptible to infestation by other insects, rot fungi and bacteria.
  • During minor infestations, infested fruit can be processed into wine or jelly.
  • During severe infestations, fruit is too rotten to be processed.

Managing spotted wing drosophila

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Jeff Hahn, Extension entomologist and Suzanne Wold-Burkness, College of Food, Agricultural and Natural Resource Sciences

Reviewed in 2018

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