Spotted wing drosophila: protecting your home garden from this new pest
A new invasive pest, spotted wing drosophila attacks thin-skinned fruit and berries. This fly is native to Japan, but in recent years has spread quickly through many states and provinces in North America. It was first identified in British Columbia in 2009, but is now widespread in coastal and interior fruit-growing areas of B.C.
Spotted wing drosophila are close relatives of the fruit flies (pomace or vinegar flies) found in the home. Unlike the common fruit flies that normally infest overripe, fallen, and rotting fruit, spotted wing drosophila prefer sound, ripe fruit on the plant (before harvest!). The fruit softens and begins to collapse within two to three days after the female has laid eggs, and mould may grow from the wound where eggs were laid and maggots are feeding. Heavily infested fruit turns into a pulpy, wormy mess.
If you grow tree fruits (e.g. cherries, peaches, and plums) or berries (e.g. strawberries, raspberries, blackberries, and blueberries) in a home or community garden, here’s what you can do to reduce the impact of spotted wing drosophila on your own garden as well as help protect local growers.
Distinguishing spotted wing drosophila from common fruit flies
Like common fruit flies, spotted wing drosophila are small (two to three millimetres long) and have red eyes and an amber-coloured body. However, two key traits distinguish spotted wing drosophila from common fruit flies (use a magnifying glass or a hand lens). Adult male flies have a black spot near the leading edge of each wing tip. Females lack spots on their wings, but have a prominent, saw-like egg-laying device (ovipositor) on their hind end that is used to insert eggs into intact fruit.
Controlling spotted wing drosophila flies
- Trap adult flies (from May to December) using baited traps containing, for example, apple cider vinegar and unscented liquid soap. Also look for infested fruit.
- Harvest fruit on a regular basis to reduce egg-laying opportunities for females. Remember, spotted wing drosophila prefer to lay eggs in ripening (and overripe) fruit.
- Clean up leftover, fallen, and infested fruit. Use sanitation procedures, such as bagging, freezing, crushing, and solarizing before disposing of the infested fruit.
- Manage irrigation to avoid fruit splitting; a break in the skin or pulp of the fruit is a favourite place for egg-laying females. Do not allow plants to dry out between waterings, and do not overwater.
- Cover individual fruits or entire fruiting plants with a fine netting or paint strainer bag. Cover plants at the first sign of spotted wing drosophila adults in traps but after plants have finished flowering.
- Grow plants that attract beneficial insects, such as coreopsis, coneflower, yarrow, clover, and goldenrod. Some natural enemies (e.g. predaceous bugs, lacewings, and parasitic wasps) can be important biological controls for spotted wing drosophila.
- For current chemical control options, consult your local pest control representative. Follow closely the directions and cautions on the label.