Drosophilid flies, Drosophila spp.
Adults are small flies with stout bodies, measuring approximately 3 mm (1/8 inch) long, and typically have bright red eyes. The abdomen often has bands and is darker than the tan-colored head and thorax. Larvae are small and legless maggots that have respiratory tubes (spiracles) on the abdomen, which allows for gas exchange while feeding in a semi-liquid medium. The pupae resemble brown cylinders with two extensions at one end.
Many different species of flies in this family can be found in Colorado and can become nuisance pests within the home. These flies are attracted to fermenting vegetables and fruit, residues in soft drink and beer containers. They can occasionally also feed on plant sap from trees infected with other pests. When their preferred food sources are available indoors, Drosophila spp. can establish a breeding population.
• Drosophila spp. are small flies commonly found indoors when potential food sources are allowed to accumulate, such as overripe fruits and vegetables. Regularly removing these food sources from the house will help reduce the likelihood of an infestation.
• Sealing possible entry sites is recommended. This can be done by keeping exterior doors closed, installing screen doors, and sealing any openings with caulking, weather stripping, door sweeps, or screens.
• Homemade monitoring traps can be easily constructed by placing a small amount of apple cider vinegar or mashed fruit in a cup. This will attract the flies to the liquid where they drown and can be easily observed.
Adult of Drosophila spp. These flies are a common household nuisance and can establish breeding populations indoors when abundant food and breeding sites are available. Potential food sources include fermenting or overripe fruit, vegetables, and sugary drink residues. These should be removed regularly and kept outdoors in a closed garbage can. Image credit: Pest and Diseases Image Library, Bugwood.org
Larvae of Drosophila spp. developing on an overripe banana. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Pupae of Drosophila spp. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Homemade trap for monitoring Drosophila spp. A glass is partially filled with vinegar, beer, or mashed fruit, and a funnel is inserted into the glass for capturing flies. Image credit: Whitney Cranshaw, Colorado State University, Bugwood.org
Life history and habits
Adults lay eggs directly on a food source, and the eggs hatch within a day or two. Larvae of Drosophila spp. feed on the surface, acquiring yeasts and other microorganisms from the fermenting plant matter. After feeding for five or six days, larvae migrate to a drier site to pupate. At continuous temperatures of 85°F, the entire life cycle can be completed in as little as eight days.
Infestations of Drosophila spp. result in homes when breeding sources are available. Therefore, identifying and removing food sources is essential. Any spilled material or unsealed compost containers can also serve as a breeding site for these flies.
Flies can be excluded from entering homes by installing screen doors, caulking, weather stripping, door sweeps, and screens, and by keeping exterior doors closed. Dumpsters can be kept a minimum of 50 feet from the building, and the lids of dumpsters and garbage cans should be closed.
These flies can be trapped with vinegar, beer, or mashed fruit. Place a small amount of the liquid in a cup or other container and insert a funnel so flies are directed into the liquid.
When maintaining the practice of eliminating breeding sites, the density of flies should decline within several days. After about two weeks, all remaining adults will have died. Continuing this practice is recommended to prevent reinfestation.
Colorado State University (n.d.). Small Fruit Flies (Vinegar Flies). Colorado State University – Extension: Colorado Insect of Interest. Available http://www.wci.colostate.edu/Assets/pdf/CIIFactSheets/FruitFlies.pdf
Utah State University (n.d.). Fruit Flies. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/fruit-flies