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Getting to know the Fruit Fly

The most common small fruit fly is Drosophila melanogaster, and it and D. simulans are known for their large, bright red eyes. A newer pest is the dark-eyed fruit fly (I am seeing more and more of this one, but manly in commercial kitchens), actually a group of related flies, including D. repleta, with darker red eyes and habits closer to phorid flies than fruit flies.

fruit flyAdult flies are tiny, about 1/8-inch (3-4 mm) long and rather chunky. They have short, 3-segmented antennae and a pair of large wings that overlap over the back and rest. The wings have a prominent cross vein that helps ID the fly. Eye color ranges from bright red to dark red. Body color ranges from brownish-yellow to brownish-black. The abdomen has darker cross-bands, appearing somewhat striped. D. melanogaster flies tend to hover in small circles; dark-eyed fruit flies rest more often on walls. The Drosophila larva is a legless, eyeless, white maggot, about 1/4-3/8 inches (7-8 mm) long when fully grown.

Red-eye fruit fly larvae feed on yeast and fungi growing in semi-liquid, fermenting or vinegary foods, especially overripe fruits and vegetables. Eggs are laid on the surface of fermenting material. Larvae feed near the surface for 5-6 days, then crawl to drier locations to pupate. The brown pupal cases have a distinctive pair of short “horns” on one end and can be confused with seeds. At higher temps, each life cycle takes only 8-10 days.

The Fruit Fly as a Pest

dark eyed fruit flyIndoors, Drosophila flies are attracted to foods or beverages with vinegary, yeasty, or fermenting odors such as overripe produce, wine, beer, cider, pickles, ketchup. They can be major pests in food processing plants, commercial kitchens, breweries, canneries, etc. where they can contaminate foods. Dark-eyed fruit fly larva are to be found in scummy drains or in animal feces than in fermenting produce.

Flies can enter buildings through screens or as eggs or larvae in overripe produce from gardens or farm stands. The flies may move from produce to infest scummy material in dirty garbage cans, floor drains, slop sinks or mop buckets, drip pans, under cracked floor tiles, recycling bins, beer dispensers, garbage disposals, and similar sites. Key to control is to find and eliminate (clean up) of the breeding sites. Deep cleaning of infested drains or hidden areas with microbial foam is useful. There are fruit fly traps available for monitoring or control. Adult flies can be killed with space sprays.

In residential kitchens I have found placing fruit in the refrigerator and pouring 1 cup of bleach in the drains at night works well. The bleach needs to sit over night, do not rinse drains until morning.

Key Points to Remember

Fruit flies are a very common, somewhat seasonal, indoor pest. They tend to hover over food or drink. Because they breed in such a variety of sites, you must be sure to inspect beyond the obvious Or you can always give us a call we would be happy to do it for you.