Nuisance provisions of the Public Health etc (Scotland) Act 2008: guidance

SECTION 2 - FLIES ( DIPTERA)

Classification

Flies, from the insect order Diptera, constitute a major group of nuisance species in rural and urban environments worldwide. Some 120,000 different species of flies have been described and they inhabit almost all marine and non-marine ecosystems. Flies are common in rural areas where there are poultry farms, stables and piggeries, which provide an abundant supply of manure in which they can breed especially in summer and autumn months.

The major urban and agricultural species of pest fly in the world is the housefly ( Musca domestica). The housefly is important because it is ubiquitous, prolific and large populations can develop very quickly. The autumn fly ( Musca autumnalis), the false stable fly ( Muscina stabulans) and the lesser housefly ( Fannia canicularis) behave like houseflies. The lesser housefly is one of the most abundant flies found in human dwellings in many parts of the world.

Calliphorids, such as the green blowfly ( Lucilia sericata), the blue blowfly ( Calliphora vicina) and Chrysomya spp are usually associated with animal carcasses, refuse and faecal material; they will, however, enter structures and land on food.

A number of species of flesh flies, in the family Sarcophagidae, can be present in urban areas being attracted to animal carcasses and decaying meat, and many deposit living larvae instead of eggs. The major biting fly in urban areas is the stable fly ( Stomoxys calcitrans).

Housefly Life cycle - Adult females do not exceed 10-14 days of age and can produce 1000 or more eggs in their lifetime in clutches of 100-150. The life-cycle from egg to adult can be as short as 6.5 days at about 33°C and up to a month or more when temperatures are much lower. Under optimum conditions, eggs hatch in 12-18 hours and the larval stage complete their development in 3-5 days. Subsequent pupation and adults can emerge after another 4-5 days of pupal development.

Habitat

Houseflies are associated with conditions that exist in rotting, fermenting or moist organic matter with a high protein content. Flies are often attracted to sites because of a breakdown in standards of hygiene. Occasionally, the problem may be localized due to a dead bird or rodent, or due to external causes, such as a nearby farm or cattle in an adjacent field. Thus the most important aspect of fly control is to trace the cause of the problem and correct it. Only then can preventative measures be undertaken.

Houseflies tend to disperse randomly and may move from contaminated to clean substrates several times in the course of a day. Their flight speed without wind, is 8 km an hour and their known daily flight range is between 3 km and 30 km, but wind, animals, and vehicles can also distribute them. As adults, houseflies overwinter in a quiescent state and become active intermittently when temperatures exceed about 15°C. Adults remain active year-round in protected environments, such as animal housing. Populations can grow to large numbers over the winter in animal housing and the adults disperse to nearby urban areas in the spring, when the housing is opened and cleaned out.

Health Impact

Flies can become contaminated with more than a hundred different pathogens that cause human disease developing and feeding in and on animal manure, human excrement, waste and many types of decaying organic matter. Most of the diseases caused by flies in urban areas are intestinal in nature, and victims may suffer a series of flu-like symptoms, including elevated temperature, diarrhoea and vomiting. Some bacteria, such as E. coli serotype 0157:H7, are extremely pathogenic and may cause death. It has been shown that houseflies transmit Salmonella typhimurium to people and there is strong evidence that flies play a role in certain human enteric bacterial infections; for example, flies can mechanically transfer pathogenic organisms, such as those that cause salmonellosis, shigellosis, and cholera.

Synanthropic flies (flies ecologically associated with humans) may carry bacteria resistant to a number of antibiotics possibly playing an epidemiological role in health facilities. They also have been identified as vectors of protozoan parasites, such as Toxoplasma and Cryptosporidium parvum. They have also been incriminated in the transmission of viral pathogens, including poliovirus, coxsackievirus and enteroviruses.

Flies are capable of transferring the eggs and cysts of various cestodes and nematodes particularly hookworms and ascarids.

Stable flies mainly affect livestock but can also be a nuisance as their bite is very painful. Some people have allergic reactions to the stable fly bite, some of which can be life threatening. It is presumed that biting flies are involved in the transmission of Lyme disease.

Flesh flies, notably the spotted flesh fly ( Wohlfahrtia magnifica), are known to cause myiasis (a disease that results from infestation of living tissue by fly larvae) in humans and animals.

Nuisance

Flies are prolific and it is difficult to quantify the emotional effects of large numbers of flies on people. The encroachment of urban development into the countryside has resulted in significant increases in housefly populations in communities adjacent to farms, even though the source of flies may be over 6km away. Flies can cause nuisance by restricting outdoor recreational activities, particularly those that involve cooking or consumption of food . Flies are also considered to be an indication of unsanitary conditions. In general, in domestic premises, it is likely that the nuisance threshold will be very low and control actions might be taken in cases of few house flies. As a guideline, an occupier will normally experience some irritation if there are five or more active house flies present in any one room at any one time on three successive days but the impact may also depend on the size of room, number of people /premises affected etc.

The most important aspect of fly control is to trace the cause of the problem.

Assessment

Flies can be monitored with baited traps, sticky ribbons, or spot cards. Spot cards are approximately 80mm x 125mm white index cards that are attached to a house-fly resting surface. A minimum of five cards should be placed in a suspect source facility and left in place for seven days. As a guide, a count of 100 or more faecal or vomit spots per card per week may be taken to indicate a high level of house fly activity and a need for control.

Controls

Physical prevention is preferred to pesticide usage. It may be preferable to control harbourage and breeding material rather than to treat an infestation once it is established. Larvicides can be used although adulticides should be the last line of defence. Premises need to adopt an integrated approach to house fly control that includes building design; effective management and systematic monitoring of house fly populations. Ordinarily, house fly control from 1 to 2 km around sensitive sites will prevent ingress into a sensitive area (containing dwellings, for example). In cases where no local breeding area can be identified, adult house flies may be flying long distances (i.e. several miles) from infestation sources of, for example, refuse tips or animal houses. Good sanitation, and elimination of breeding areas are necessary for good management.

Prevention

1. Proper sanitation is the key to fly control. Deny flies access to food, shelter and a place to lay their eggs.

2. Do not allow flies to come in contact with contaminated substances and thus contaminate themselves.

3. Although management of adult flies can provide temporary relief, the location and elimination of development sites for immature stages is the best method for long-term control.

4. Prevent flies from entering buildings, by keeping doors closed and window screens in proper repair.

5. If flies do enter structures, eliminate them with traps or other suitable methods as quickly as possible.

6. Wet straw should not pile up in or near buildings and, as one of the best fly breeding materials and is not recommended as animal bedding.

7. Fly traps may be useful in some house fly control programmes if enough traps are used, placed correctly, and used both indoors and outdoors. House flies are attracted to white surfaces and baits that give off odours. Lesser house flies are shyer of traps.

8. Dustbins, wheelie-bins, paladins and skips should have tight-fitting lids and be cleaned regularly. Dry and wet rubbish should be placed in plastic rubbish bags and sealed up. All waste receptacles should be located as far from building entrances as possible.

9. For control at waste disposal sites, refuse should be deposited onto the same area as inorganic wastes to reduce the capacity of breeding resources, or covered with soil or other inorganic wastes of around 15 cm consistent thickness.

10. Electronic fly killers that can attract insects to an electrified grid by using an ultra-violet light source are not generally effective against houseflies. If they are used, one trap should be placed for every 30 feet of wall inside buildings, but not placed over or within five feet of food preparation areas. Recommended placement areas outdoors include near building entrances, in alleyways, beneath trees, and around animal sleeping areas and manure piles.

Chemical control measures

1. Chemical treatment should be considered as a last resort, as it may only be treating the insects in the vicinity at the time of treatment and not the source

2. Although most pesticides do have a residual effect and may work on particular species throughout their lifecycle.

3. The use of pesticides near water bodies is risky and must be minimised.

4. For adult control, conventional knockdown or residual treatments will kill the majority of adult flies in spite of the development of high resistance levels in a number of housefly populations.

5. Residual insecticides applied to the house flies' favoured resting areas will control landing flies in some situations, although they should not generally be applied to breeding areas, as insecticide breakdown can be rapid and resistance may be encouraged.

6. In poultry houses, the use of mists, fogs or baits may be necessary for house fly control.

7. Residual wall sprays can be applied where the flies congregate. Resistance can develop more rapidly in house fly populations on farms on a continuous insecticide regime using a single chemical than on farms in which insecticides are alternated.

8. Residual insecticides may be applied to favoured resting areas for house flies. Breeding areas should be avoided as spray targets as, where the insecticide breaks down in an area where eggs are developing, it may encourage increased resistance in the house fly population.

9. Outdoors, house fly control can include the use of chemical treatments in the bottom of skips, and treatment of vertical walls adjacent to skips and other breeding sites, with microencapsulated or wettable powder formulation, and the use of fly baits near adult feeding sources.

10. Indoors, house fly control can include automatic misters, fly paper, electrocuting and baited traps that can be used in milking parlours and other areas of low fly numbers.