Authors: Christelle Guédot and PJ Liesch, UW-Madison Entomology
Revised: 01/29/2026
Item number: XHT1237

Overview of Spotted wing Drosophila

Spotted wing Drosophila (SWD), Drosophila suzukii, is an invasive vinegar fly (aka Drosophilid fruit fly) native to Southeast Asia.  It became established in Hawaii during the 1980’s, and was first discovered in the continental United States in California in 2008.  SWD quickly spread throughout the Pacific Northwest and Canada, and was found in Florida in 2009.  At least 45 states have now reported SWD, with Michigan and Wisconsin first reporting the insect in 2010.  Breeding populations and fruit infestations in Wisconsin were reported in 2012 and were most severe in fall-bearing raspberries. After the initial detection of SWD in Wisconsin, it only took a few years for SWD to become a widespread pest of fruits like raspberries in the state.

Vinegar flies (Family Drosophilidae) are part of a large group of insects that typically attack rotting or damaged fruit, but spare healthy fruit.  SWD are similar in size, shape and appearance to our common fruit flies seen around the kitchen fruit bowl, but they are able to attack ripe and ripening fruits that are in good condition.  To do this, adult female SWDs have a serrated ovipositor (i.e., egg-laying structure) that allows them to cut into healthy fruit to lay eggs.  Larvae feed within healthy fruit tissue causing tissue collapse within a few days; consequently crop loss can be severe.

Identification and Appearance of Spotted wing Drosophila

SWD adults are small, ¹/₁₆ to ⅛ inch long with red eyes and a light brown thorax and abdomen.  SWD males are identified by a single dark colored spot towards the tip of each wing, as well as two dark colored bands (brush-like structrures) on each foreleg.  SWD females lack the dark spots on their wings and are distinguished from other vinegar flies by their serrated ovipositor (which is only visible with magnification).  SWD eggs are tiny and white, and larvae are cream-colored, legless, maggots up to ⅛ inch long.

Host Range of Spotted wing Drosophila

SWD prefers thin-skinned, soft-fleshed fruit and is primarily a pest of berry crops, including brambles (e.g., blackberries and raspberries), strawberries, blueberries, and currants.  Grapes and tree fruits (e.g., cherries, peaches, nectarines, plums, and Asian pears) are also hosts for SWD, as are non-edible fruiting plants such as snowberry, pokeweed, dogwood, honeysuckle, and bittersweet nightshade. SWD is not generally a pest of fruits such as apples, but they can be associated with apples that have been compromised due to physical damage, disease, etc.

Symptoms and Effects of Spotted wing Drosophila

Initial symptoms of an SWD infestation are small scars or slits (left by females during egg-laying) on intact fruits.  Soft, sunken spots appear around the scars as larvae begin to feed.  Fruits soon collapse and become gooey.  Other organisms (e.g., fungi and bacteria) are often introduced during egg-laying and can cause additional fruit deterioration.  The effect of SWD on some hosts (e.g., grapes) may vary based on varietal preferences; the effect on other hosts (e.g., brambles) may be complete crop loss.

Life Cycle of Spotted wing Drosophila

SWD prefers moderate temperatures and can complete a generation in as little as eight to nine days.  SWD adults live for about two weeks and females can lay more than 300 eggs during this time.  Females lay from one to three eggs per fruit and several females can lay eggs in a single fruit.  Eggs hatch in as little as one to three days.  Larvae can complete feeding within several days (the exact length of time depends on temperature) and can pupate in the damaged fruit or in the top layers of leaf litter around infested plants.  Because of their short generation time and multiple generations each year, large SWD populations can build up, especially if the insect is left uncontrolled.

In Wisconsin SWD activity typically begins in early summer and builds over the course of the summer and early fall. For that reason, fall-bearing fruit crops tend to be at highest risk from SWD as they correspond to the peak populations of this insect.

Monitoring and scouting for Spotted wing Drosophila

The first and most important step in SWD management is to determine whether SWD is present.  Use trapping of adult flies for early SWD detection and to monitor trends in adult populations.  Start monitoring when fruits begin to ripen and until harvest is completed. 

You can buy commercially available traps, or make simple, inexpensive traps using a 32 ounce clear plastic container with a lid.  To allow SWD adults to enter the trap, drill or melt ten 3/16 inch diameter holes around the top of the cup.  Bait traps with one tablespoon active dry yeast and four tablespoons sugar in twelve ounces of water.  Alternatively (although less effective), you can use a two inch layer of apple cider vinegar in the bottom of the container.  Add one to two drops of unscented dish soap to the trap to break the surface tension of the liquid so that flies are more likely to be captured.  Hang traps in a shaded plant canopy where fruit is present.  For strawberries, place traps on the ground.  Check traps and replace liquid bait weekly, using a hand lens to identify trapped insects.  Be careful not to pour bait on the ground near the traps as this will confuse SWD adults and reduce the effectiveness of the traps.

If you suspect fruit are infested with SWD, use a fruit dunk flotation method to look for SWD larvae.  Place a random sample of fruit in a sealed plastic bag or glass dish and crush the fruit lightly to break the skin.  Add a mixture of ¼ cup of salt in four cups of water and let the fruit, salt and water mixture stand for one hour.  Look for larvae that float in the liquid.  Backlight the bag or dish to help with detection.

Management of Spotted wing Drosophila

Non-chemical management: A number of non-chemical approaches can be used to reduce the impacts of SWD:

• Removal of wild host plants: In the Midwest, a number of wild fruits can serve as a food source for SWD and may act as a source of SWD in your area. Thus, locating and removing wild brambles (raspberries and blackberries), wild plums, and wild grapes may help.
• Prompt harvesting: The longer fruits are present, the greater the window of time for SWD to attack. Timely harvesting (as soon as fruit are ripe) will help in this regard.
• Consume/process fruits in a timely manner: If SWD larvae are present in harvested fruit, they can continue to feed and cause damage. Thus, consuming or preserving the fruits (e.g., jams, jellies, etc.) shortly after harvest is one way to limit any further deterioration. Alternatively, immediately placing harvested fruit into a refrigerator or other cold storage can help arrest any further activity of SWD.
• Good cleanup: Damaged and fallen fruits can continue to serve as a food source for SWD larvae. Picking up and removing damaged and fallen fruits can be helpful in this regard. At the time of harvest, it can be helpful to have a container for “good” fruit and fruits that are damaged or compromised. It is important to take the compromised fruits and either seal them in a plastic bag or remove them from the site. If damaged fruits are placed in the nearby area (e.g., compost pile), the adults can emerge and travel back to the fruit crop.
• Mesh netting: Fine mesh netting (i.e., row cover) can be used in both small and large-scale settings to cover plants and physically block SWD adults from gaining access. Keep in mind that for plants requiring insect pollination or plants with thorns this approach may not be feasible. To maximize effectiveness of this approach, the netting should be secured to the ground to serve as a complete barrier.
• Trapping: Traps (described in the scouting section) can be used as part of a monitoring program. While the traps can help indicate when SWD becomes active in your area for the year, these traps do not provide meaningful control of SWD populations.
• Plant Selection: For new plantings, consider fruit types and varieties that may see less damage. For example, as SWD populations build throughout the growing season, fall-bearing raspberries can be hit especially hard. Plants that produce fruit earlier in the growing season may see less pressure from SWD (e.g., June-bearing strawberries and black raspberries). In addition, some research has suggested that some yellow/golden raspberry varieties may be less attractive to SWD than darker-skinned varieties.

Chemical management: If needed, a number of insecticides are registered for the management of SWD for both small growers (e.g., home gardeners) and commercial growers. Between the long seasonal activity of SWD and limited residual activity of many insecticides, regular monitoring and treatments may be needed to maximize protection. It is also important to recognize that insecticide treatments can help prevent fruit from becoming infested, but will not kill SWD larvae already within fruit.

Small-Scale: In small-scale settings (e.g., home gardens), organic products containing spinosad and pyrethrins are available. Of these two, spinosad has performed better against SWD in University research trials. While readily-available, insecticidal soaps and horticultural oils (e.g., neem) work poorly due to their very limited residual activity and are not recommended. Common conventional ingredients for small scale settings include malathion and a number of pyrethroid ingredients (e.g., zeta-cypermethrin, etc.).

Commercial growers: Commercial fruit growers have additional options available for managing SWD. Spinosad and pyrethrum are available for use in organic production. Conventional products containing ingredients from the carbamate, organophosphate, pyrethroid, spinosyn, and anthranilic diamide classes are available for use in conventional production. Neonicotinoids are not effective against SWD and should not be used. See the Midwest Fruit Pest Spray Guide for additional details.  

Be sure to choose a product labeled for use on the specific fruit crop that you are growing and make sure to follow all label instructions to ensure that you use the product in the safest, most effective manner possible.  Spray thoroughly in the plant canopy to kill adults before they are able to lay eggs in the fruit.  Because you are applying insecticides to an edible crop, be especially aware of any pre-harvest interval (PHI) restrictions of the product that you select—this is how long you are required to wait before fruit can be harvested.

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