Fruit flies, also known as vinegar flies, are annoying pests in the home. Found at any time of the year in our mild climate, they seem to come out exponentially in the fall as tree fruits begin to ripen.
A quick review of the lifecycle of these all-too-common pests will tell us why they grow in numbers at this time of year and what we can do to eliminate their bothersome visits.
Adult fruit flies are one-eighth of an inch long and usually sport red eyes. They have tan and gray bodies, some with dark banding on the segments, and transparent wings. The female uses an ovipositor to lay eggs on the surface of moist fermenting fruits and other rotting organic materials. The larvae or maggots will feed on the surface of a moisture source and in a week or less develop into adult flies. A female fruit fly can lay up to 100 eggs a day or about 500 eggs in her short 10-day lifetime.
Insecticidal sprays and fogs are available to kill adult flies on contact. But these products are poisonous; they must be used with caution and kept away from children, pets and livestock. Also, the larvae will continue to develop and new adults will continue to emerge unless potential food sources are removed.
The key to controlling these pests is to eliminate sources of moisture that serve as their breeding grounds. (See sidebar.) Because the maggots require only a small amount of moisture to become flies, even a wet mop could harbor growing larvae.
New threat, a fly named ‘Spot’
There is a new fruit fly in the neighborhood called the Spotted Wing Drosophila (SWD) and this is not the fairy tale of a cute little bug, but the terrifying reality of a red-eyed foreign invader. Originating in Asia, this pest first was discovered in Western Washington in 2009.
SWD look very similar to the fruit flies we refer to as vinegar flies. They favor our mild climates and are a real threat to local fruit crops.
Unlike everyday vinegar flies, SWDs attack healthy ripening fruit as well as damaged or split fruit. Their feeding larvae can quickly destroy soft fruit such as blueberries, cherries, peaches, plums, raspberries and strawberries. Furthermore, the SWD has a rapid reproduction rate and can hatch from four to 10 generations per season depending on environmental conditions, leading to a serious infestation of an entire crop.
The female is the dangerous one of the species as she dons an ovipositor that can lay eggs under the surface of undamaged fruit, still on the plant at pre-harvest. The fruit appears caved in where the ovipositor punctured the skin; larvae activity further destroys the fruit to complete the metamorphosis.
There are no registered insecticides that will control maggots within fruit, so chemicals must target adults with the intent to eliminate adult flies before they mate and lay eggs. Home growers are encouraged to start monitoring for adult SWD before fruit ripens to determine when to apply insecticides. (See cru.cahe.wsu.edu/CEPublications/FS049E/FS049E.pdf for more information.)
To reduce populations of flies that might infest next year’s crop or later-ripening varieties, pick fruit regularly. Remove overripe or damaged fruit which may attract SWD. Remove infested and fallen fruit from the garden.
Discard infested fruit in a sealed container or bury it at least six inches deep in an area that will not be disturbed.
For more
Get gardening inform-ation at a Saturday in the Garden presentation at the Master Gardener Demonstration Garden at 2711 Woodcock Road, Sequim. These free educational events are held on selected Saturdays. On Sept. 24 from 10-11 a.m., Lorrie Hamilton, Clallam County Master Gardener coordinator, talks about fall and winter ornamental containers.
Michele Mangiantini is a WSU-certified Clallam County Master Gardener.
Tips for controlling vinegar flies in the home
