Extension > Garden > Yard and Garden > Fruit > Integrated pest management for home stone fruit growers > Spotted wing Drosophila
Spotted wing Drosophila
Discoloration on a 'Meteor' chery with spotted wing Drosophila maggots
Thaddeus McCamant, Central Lakes College
The spotted wing Drosophila (SWD) (Drosophila suzukii) is a new pest in Minnesota that has been found throughout the state. It has a wide host range, including some plums, cherries and most berries. Tart cherries appear to be one of the preferred hosts of SWD.
SWD adults look very similar to the fruit flies that accumulate near overripe fruit during late summer. They are about 1/8th inch long, have a tannish body, red eyes, and brown bands on their abdomens. Male SWD can be recognized by a distinct black spot near the tip of each wing. The female SWD can only be distinguished from other species by looking at the tip of their abdomen under a dissecting microscope; you need to examine their distinctly serrated ovipositor to properly identify them.
The larvae (maggots) are white, with a body that tapers at one end. They only grow as large as 1/8 of an inch long. If you are unsure whether SWD larvae are in cherries, place four or five cherries in a water and salt solution (one tablespoon of salt per one cup of water) in a small container. Gently crush the cherries to break the skin. After 30 minutes, any larvae that are present will float to the surface. Infested cherries typically have multiple larvae.
SWD turn cherry fruit flesh brown, making the fruit unappealing for both fresh consumption and for processing. The white maggots are easy to see in the red flesh of the cherries, and the maggots will grow even after the fruit is picked. Cherries with maggots decay rapidly. Tart cherries are commonly attacked; there have been reports of SWD infestation rates exceeding 50% of the fruit on some trees in central Minnesota.
SWD have multiple generations per summer. They overwinter as adults in brush near orchards and fruit trees. SWD adults first appear during late June or early July, and the numbers may increase rapidly during the middle of summer, the time the first cherries start to ripen. A female lays several eggs in each cherry. The eggs hatch quickly, and maggots turn into mature SWD rapidly. During warm weather, SWD can go from egg to mature adult in seven days.
Management of SWD can be challenging but is best achieved through a combination of detection, sanitation, and insecticides. The best control appears to be when gardeners destroy infested fruit to kill larvae, while using an insecticide to kill the adults at the same time.
Gardeners who are concerned about SWD should monitor for the presence of adults. Take a large clear plastic cup with a cover. Make several holes, 3/16 in diameter, near the top on one side of the cup. Larger holes will allow larger flies and other insects such as sap beetles to enter the trap, making detection of the SWD more difficult. The easiest way to make the holes is to heat a small (8 or 10 penny) nail, which can melt the right size hole in the cup. Pour one to two inches of apple cider vinegar into the bottom of the cup. You can then either add a yellow sticky card slightly above the vinegar or a little bit of liquid soap such as dish soap. Hang traps on branches in a shaded location near fruit. Replace the sticky card and apple cider vinegar bait at least once a week for SWD, disposing of the apple cider vinegar away from the trap location. Checking traps more often can be beneficial for early detection of adult SWD, especially early in the growing season.
Remove and dispose of all infested fruit to keep SWD numbers low. The larvae can be killed by microwaving the fruit, cooking the fruit or placing the fruit in a sealed plastic bag that will be put in the trash. Do not bury infested fruit or place fruit in a compost pile as the adults can still emerge.
Apply insecticides as soon as adults are caught in a trap. Repeat applications will probably be necessary; continue to monitor the trap throughout the growing season. Insecticides should be applied in the evening to avoid killing honeybees and other pollinators. Available insecticides to kill adult SWD are permethrin, carbaryl, malathion, spinosad and pyrethrin. Spinosad and pyrethrin are approved for organic production. Always read and follow labels when spraying pesticides, and follow the pre-harvest interval for all products.