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Everything you always wanted to know... but were afraid to ask
Fruit flies, or as they are more properly known small vinegar flies, have become a major nuisance in restaurants, bars, grocery stores, bakeries, fruit markets, and offices. Heavy populations of these pests can develop from a single source. The Red-Eyed Fruit Fly is pale brown in color with bright red eyes. The adults are poor fliers and they prefer fruits and vegetables that are in the earliest stage of decomposition. The Dark-Eyed Fruit Fly appears blackish brown with dark red eyes. It is slightly larger than the red eyed fruit fly, tends to be a strong flier, and prefers late stage decomposition. The larvae are found burrowed deep into moist, smelly organic debris.
Fruit flies live naturally outdoors during the warmer months and are attracted indoors by food odors, garbage containers, and compactors. They can easily fly in through an open door or various life stages may be brought in on fruit and vegetable deliveries. Even fruits and vegetables in employee lunches can carry these flies.
Female flies search out micro environments containing moist, fermenting organic debris and may lay 500 eggs (about 30 a day during their life span) on the surface of this material. Here are some favorite locations: the accumulated sludge that sticks to the bottom of garbage cans, the "gelatinous scum" that builds up inside of floor drains, the rotten piece of fruit or vegetable that is stuck on the floor under a work table, the loose floor tiles under the dishwasher or sink, the dirty mop that is stuck in a closet, and the drain pan under a refrigerator.
The eggs hatch in about 24 hours into tiny larvae that feed near the surface of the fermenting food. After five to six days they crawl to drier areas to pupate. Several days later new flies emerge and are attracted to light where they mate and then resume the process of laying more eggs. With temperatures in the mid to upper 70's the whole process takes 8 to 10 days. Under cooler conditions it may take 18 to 21 days to complete the life cycle.
No, fruit flies do not bite humans. They do not have biting mouthparts. They can be quite a nuisance as they hover around in search of suitable breeding sites.
The key to control is to locate and eliminate the breeding sites. Improved sanitation and maintenance and the elimination of excess moisture are also critical steps to eliminate fruit flies. There are no magic sprays to solve the problem. This is a hands and knees job to pull out and remove the moist organic debris from under work tables and counters. The accumulated scum inside floor drains needs to be removed. Loose and broken floor tiles and coving must be repaired. Moisture and standing water must not be allowed to accumulate overnight. Aerosol mists or fogs containing pyrethrins will give good kill of the adult flies but will do nothing to eliminate or control the eggs and larvae that are located in the breeding sites. The results will be temporary at best. Repeated treatments with these aerosols will be needed to keep killing the newly emerging adults flies until the breeding sites are found and eliminated. Ultra violet insect light traps (ILT's) are of little help because fruit flies are more attracted to odor than to the ultra violet light. Pouring bleach into a drain will not work either. Bleach is a good disinfectant and sanitizer but will not dissolve the greasy organic material stuck inside a floor drain.
Recent research has shown that any of the biological products such as BioZyme, InVade, BioGel (containing .good bacteria) applied as a foam do a good job of digesting and removing the organic scum in cracks, crevices, under warped tiles, and in floor drains. Well placed bottle traps containing an effective attractant will capture adult fruit flies. However, traps by themselves will not solve fruit fly problems. The breeding sites must be found and eliminated!
Remember the basic biology. Fruit flies need moisture, rotting organic debris, and a little warmth. Search for and eliminate these conditions.