Since the early part of the 20th century in the United States, however,there have been no documented foodborne illnesses due to flies. A recent study of Israeli army camps with open latrines and nearby foodservice facilities implicated flies in the transmission of shigellosis within these camps (Cohen, et al, 1991). The problem in foodservice units, then, is aesthetic and relates to customer satisfaction. For any foodservice dispensing operation, the customer expectation standard is zero flies.

The number of flies found in a given foodservice establishment is influenced by the factors such as: the sanitation practices in the immediate vicinity; the activity of the city controlling the flies; the location of the facility; the neighborhood's attention to waste disposal; and general housekeeping.

Another reason that flies are difficult to control is their rapid rate of reproduction. One female fly can produce thousands of offspring in a single breeding season. Flies also have the ability to develop in small quantities of food. Flies also have the typical insect ability to enter through and hide in openings the size of a pinhead.

FAMILY MUSCIDAE: Musca domestica Linnaeus is the common housefly. Housefly eggs are laid in decaying organic matter (garbage). Houseflies rest on plants, the ground, fences, electric wires, and garbage cans near sources of food. At restaurant sites, this type of fly frequently is found in and around the garbage cans.

FAMILY CALLIPHORIDAE: These flies are known as blue bottle flies, green and bronze flies, and black flies. Garbage cans are the most significant sources for this family of flies, and can be breeding places for up to 30,000 flies during a one-week period. Newly hatched larvae feed for a short time on the surface of the decaying material on which the eggs were laid, and then burrow into the less decayed material underneath the surface. These flies have a relatively short life cycle of only nine to twenty-one days from egg to adult. Eggs are laid on decomposing vegetable debris. Larvae feed on this material from two to ten days, and then burrow into the ground to pupate. These flies survive during winter in the soil as fully grown larvae.

FAMILY DROSOPHILIDAE: This family is made up of fruit and pomace flies. Large populations can be found near foodservice establishments, close to fruit, dirty garbage containers, rotten vegetables, and slime in drains. Adult flies are known to travel as far as six and one half miles within twenty-four hours. They become abundant at harvest time and are attracted to ripened fruits and vegetables, fermenting products, empty bottles and cans, floor drains and garbage disposal areas.

FAMILY PHORIDAE: Known as humpbacked flies, the members of this family breed wherever warmth and moisture exist, such as drains in basements, kitchen areas, garbage containers, and crawl spaces.

Breeding Material
For flies to breed, the organic material must be loose and porous and have a high moisture content. The medium must be located in a shady place in the hot season.

Temporary Removal
Fly Swatter: This device is an inexpensive, effective old-fashioned way to remove a few flies.

Electrocuting Machines (Often Called "Zappers"): These boxes attract flies with an ultraviolet light in the 330 to 350 nanometer wavelength, then kill the flies with electricity. The only scientific study of their effectiveness was done in two cafeterias in San Antonio, Texas in 1986 (Gilbert, Insect Light Traps). These devices were shown to reduce the population of flies by 72 percent.

SELECTION CONSIDERATIONS: When selecting attractant lamps, one should shop for the best price from reliable sources, such as local electrical suppliers, manufacturers, pest control suppliers, and trap suppliers. The three currently available phosphors are Sylvania (barium silicate, lead activated), Philips (strontium floral borate, europium activated), and General Electric (strontium borate, europium activated) (Gilbert, 1984). The most successful industrial light trap design includes two forty-watt, straight-tube, black light lamps, each of which is forty-eight inches long, one and one half inches in diameter.

The lamp brightness, size of the UV bulb, reflecting area, and orientation of the bulb all influence effectiveness. Most flying insects do not respond to light traps at a distance of more than one hundred feet. Twelve feet is the maximum distance at which a housefly can respond to a fifteen-watt UV bulb. Fluorescent and incandescent lighting are not nearly as attractive as UV traps, and present no competition as attractants. They should not be used where their attractant light shines directly out through doors that will be opened after dusk.

For outside control of night-flying insects, one should place the light on a pole, thirty to fifty feet from an entrance over the door. If placed inside a back door, it should not be seen from the outside, so that insects will not be attracted in from the outside. The lights should not be placed where they are in direct competition with sunlight. Sunlight contains all of the wavelengths of energy that insects see as light, which makes the electrocuting machine ineffective.

Other concerns include whether the ultraviolet light source could cause acute or chronic health problems to people exposed to the device. Potential short term problems include skin burns. Long term exposure relates to premature skin aging, skin cancer, and hazards to the eye, such as cataract formation. The FDA has measured UV radiation emission, and has concluded that there is not a significant concern about acute health problems (FDA, 1987). The effects of long term exposure are still unanswered. For this reason, it would be prudent for operators to position these devices so that employees are not required to work continuously in close eye-level proximity to these insect electrocuting devices.

INSTALLATION: For effective fly control, one should use light devices twenty-four hours a day, and install traps so that the center of the traps are no closer than three feet (one meter) above the floor, since most flies are found at this level. The traps should be installed no closer than five feet from exposed items, and twelve to twenty-five feet inside the entrance. Only wall-type devices should be used because ceiling units are restricted and are not allowed in operations where food and food contact surfaces, equipment and utensils are exposed. Insects can bounce off of the electric wires, out of the unit, and into food. In other words, ceiling UV units are limited to receiving areas, corridors, and refuse areas.

When deciding where to place traps, one should look for bottlenecks, stairwells, foyers, and static areas, and find locations where exposure is long and distance is short. The traps should be placed so that they are protected from forklifts, traffic, water or sprays, dust, etc., and will not interfere with or cause any potential problems to the food process or the employees.

The food production area should have a trap near its entry. Because insects are cold blooded, traps need to be placed in warm areas where the insects will remain active. The optimum temperature for most insects is approximately 85oF. As the temperature lowers, they become less active. Below 50oF, insects become inactive and cease to fly. Installing traps in colder areas, such as shipping or loading docks, should be avoided.

Flies seem to follow a counter-clockwise route when first entering a new environment, which suggests that placing the traps to the flies' right as they enter is preferred (Gilbert, 1984).

Requirements in the Code of Federal Regulations are as follows:

1. Arcing equipment must be isolated from combustible material.
2. Electrically charged parts should be guarded so that people cannot be accidently shocked when working near the unit, if installed lower than eight feet, six inches above the floor.
3. The device must be properly grounded.
4. The equipment must be accepted, certified, listed, labeled, or otherwise determined to be safe by a nationally recognized testing laboratory such as, but not limited to, Underwriters' Laboratories, Inc. and Factory Mutual Engineering Corporation.

MAINTENANCE: Maintenance of these units is critical. In order to maintain a high intensity, lights should be changed once a year, prior to the spring season. Dead insects must be cleaned from the catch tray frequently because other insects feed on them. Also, eggs of dead insects may hatch and the larvae develop within an unemptied catch tray. These traps must be inspected and emptied at least weekly, and preferably twice a week. These traps are most effective if the number of flying insects is limited to a few.

Fly Paper and Insect Strips: These two methods of trapping insects are not permitted by health codes. Flies do not stick to fly paper 100 percent of the time, allowing them to fall onto food or food contact surfaces. Insect strips contain chemicals in a solid form that emit dangerous vapors.

Sprays: There are different types of chemical insecticide sprays used to remove flies. Use them with caution. They are no substitute for cleanliness.

SPACE SPRAYS: Aerosol bombs that contain 0.15 to 0.25 percent pyrethethrum plus a synergist will control flying insects. The room should be closed for one hour following a five to twenty second treatment. No one should be allowed into the room at the time, because they afford a slight health risk. All food must be tightly covered. All food contact surfaces must be thoroughly washed following spraying.

SURFACE SPRAYS: A surface treatment using 1 percent malathion or 0.5 percent diazinon can be used where flies cluster. These sprays discharge a mist into the air for killing insects. Because surface sprays can easily contaminate food, uses of this form of pesticide in foodservice facilities are limited. Food and food contact surfaces must be completely covered, and people should not enter the area during their use.

RESIDUAL SPRAYS: A residual spray is applied directly to surfaces and leaves a deposit that kills insects that contact it. It should be applied near favored fly resting and breeding places. To be effective, the spray must form a thin, uniform layer on the treated surface. It must be used by professionals, and not used anywhere near open or packaged food. Food contact surfaces must be completely covered during application or washed thoroughly following the application.

AIR SCREENS: For buildings where prevailing winds cause inward drafts, an air screen might be satisfactory. If the opening is against the prevailing wind, the air screen will probably be ineffective (American Institute of Baking, 1979).

Permanent Removal and Prevention
Good housekeeping, maintenance, and construction standards are the secrets to successful fly control. The following guidelines (American Institute of Baking, 1979; American Institute of Baking, 1987; Axler, 1974; Center for Food Safety and Applied Nutrition; Cichy, 1984; NIFI, 1985) can be used for permanent removal and prevention of fly problems.

1. Starve the insects through cleanliness. If there is nothing to eat, they will go somewhere else. During the fly season, cleaning should be frequent, once a day in the work and garbage areas, and twice a day where customers walk and spill food. A combination pressure hose with detergent cleaning and hot water rinse capability is excellent. In entrance areas, wash down all bushes, grass, blacktop, sidewalks, and gravel. Clean out customer waste containers. Cleaning must be intensive and thorough, with the use of brooms, hoses, soap, and hot water. Food that could be possible breeding sites must be removed before the insects are attracted. 
2. Equipment should have smooth surfaces with rounded corners so that hidden breeding places are not allowed, and cleaning is easily accomplished.
3. Accumulations of waste and garbage should be prevented. Standing pools of water should be eliminated. Garbage must be kept in tightly covered containers. If the problem is severe, one may need to rinse food from bottles, tin cans, and plastic wrap before putting them into garbage cans.
4. Garbage pick-ups should be made daily.
5. Garbage containers must be placed fifty feet or more from the building, and enclosed in a screened space on a solid pad with a drain. The entire enclosure and all containers should be cleaned daily with detergent and hot water. Determine breeding places by checking for maggots, which are white, moist looking, and approximately one half inch long.
6. If garbage must be stored indoors, put it in a 45oF refrigerated room.
7. Provide enough containers with tightly fitting lids to hold all of the garbage between pick-ups.
8. If necessary, put garbage in closed plastic bags to keep flies from their food sources.
9. Put sixteen mesh per inch or tighter screens on windows and vents. Seal pipes to the walls. Make all doors close fitting.
10. Drains should be cleaned daily or tightly plugged.
11. When receiving supplies, leave doors and screens open for the shortest time possible. All doors should be self-closing and tight. Air screens on doors or vestibules with two doors are also effective.

References 

1. American Institute of Baking. 1979., Basic Food Plant Sanitation 3rd ed. AIB. Manhattan, KS.
2. American Institute of Baking. 1987. Insect Electrocutor Light Traps. Manhattan, KS.
3. Axler, B.H. 1974. Focus on Kitchen Sanitation and Food Hygiene. Howard W. Sams & Co., Inc. Indianapolis, IN.
4. Cichy, R.F. 1984. Sanitation Management--Strategies for Success. Educational Institute of the American Hotel & Motel Association. Lansing, MI.
5. Cohen, G., and Cohen, M.E. 1982. Food Service Sanitation Handbook. Hayden Book Company, Inc. Rochelle Park, NJ.
6. Cohen, D., Green., M., Block., C., Stepon, R., Amber,
7. R., Wasserman, S., Levine, M. April 27, 1991. Reduction of transmission of shigellosis by control of houseflies (Musca domestica). The Lancet. 337:993-997.
8. FDA. Center for Food Safety and Applied Nutrition. Retail Food Protection Branch. HFF-342. 1987. Insect and rodent control--devices for electrocuting flying insects. Washington, D.C.
9. FDA. Center for Food Safety and Applied Nutrition. Retail Food Protection Branch. HFF-324. Retail food protection--program information manual. Washington, D.C.
10. Gilbert. 1984. Industrial insect light traps. Jonesboro, AR.
11. Gilbert. Insect light traps: operations testing of electrocutor traps for fly control in dining facilities. Jonesboro, AR.
12. Greenberg, B. 1973. Flies & Disease Vol II: Biology and Disease Transmission. Princeton University Press. Princeton, NJ.
13. NIFI. 1985. Food Service Sanitation. 3rd ed. National Sanitation Foundation.
14. Noetzel, D.M., and Cutkomp, L.K. 1980. Flies in the home. Agricultural Extension Service, University of Minnesota. St. Paul, MN
15. Truman, L.C., Butts, W.L. 1976. Scientific Guide to Pest Control Operations. Harvest Publishing Co. Cleveland, OH.