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SECTION 2 - FILTH FLIES (DIPTERA)
Intoduction
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 can be a prevalent and important and their presence alone can be an indication of unsanitary conditions. Many flies bear the name filth flies because of their association with potentially contaminated substrates, such as food wastes, faeces, animal manures and carrion. Through this association, flying from contaminated to uncontaminated substrates and transmitting pathogens, filth flies can quite easily and accidentally become disease vectors. 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. There are many types of fly but the following are the most common cause of problems:
Common House Fly ( Musca domestica).
Lesser House Fly ( Fannia canicularis).
Autumn Fly ( Musca autumnalis).
Cluster Fly ( Pollenia rudis).
Houseflies can be classed as public health pests or pests of animal husbandry. They are associated with conditions that exist in rotting, fermenting, or at least moist organic matter, preferably of a high protein content, such as those that could be present at a sewage works.
Flies are almost certainly being attracted to the site because of a breakdown in standards of hygiene. Occasionally, the problem may be localised, i.e. blow flies ( Calliphora spp and Lucilia spp) may be attracted by 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.
Classification
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 and utilizes many proteinaceous materials, including garbage and human and animal faeces. Houseflies are very 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, being mainly a nuisance to people, but they have also been associated with a number of pathogenic organisms. The lesser housefly, especially, is one of the most abundant flies found in human dwellings in many parts of the world.
A number of species of flesh flies, in the family Sarcophagidae, can be present in urban areas, but rarely develop in pestiferous numbers. These flies are 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), which has a long, bayonet-style mouthpart designed for sucking blood. Stable flies also disperse at about 8 km an hour (Hogsette, Ruff & Jones, 1987) and have been shown to move long distances with synoptic (large-scale) weather systems, such as cold fronts. The known flight range is 225km (Hogsette & Ruff, 1985).
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. The life-cycle of the stable fly is slightly longer than that of the housefly and is about 12-13 days in length at 27°C. Its life-cycle is longer at cooler temperatures, and adults overwinter in a quiescent state, like houseflies. Stable flies are not as prolific as houseflies, laying 60-800 eggs during their lifespan. A number of species of flesh flies, in the family Sarcophagidae, can be present in urban areas but are usually attracted to animal carcasses and decaying meat, and many deposit living larvae instead of eggs.
Habitat
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 they can also be distributed by wind, animals, and vehicles. 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.
Calliphorids, such as the green blowfly ( Lucilia sericata), the blue blowfly ( Calliphora vicina) and Chrysomya spp are usually associated with animal carcasses, garbage and faecal material; they will, however, enter structures and land on food. This movement between contaminated and clean substrates makes them a potential pathogen vector. These flies can be very pestiferous at the outdoor or open meat markets still found in various parts of Europe. Females can land on unrefrigerated meat and quickly conceal large numbers of eggs in folds and openings in the meat. Other foods sold by outdoor vendors are also subject to attack, unless foods are properly wrapped and maintained at standard temperatures
Health Impact
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.
Filth 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. It has been shown that houseflies transmit Salmonella typhimurium to people and there is strong evidence that fkies 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. Adults can also carry enterohaemorrhagic E.coli serotype O157:H7 and Campylobacter spp..
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 are a pest mainly of livestock, but also of people in villages, in the suburbs of larger cities and in recreational areas near shorelines of lakes, rivers and larger bodies of water. Both sexes require blood to reproduce and are persistent in their feeding activities and continue to feed intermittently until replete. Their bite is very painful, because they inject no anaesthetic when feeding. Some people have allergic reactions to the stable fly bite, some of which can be life threatening. In urban areas, the preferred hosts of stable flies are dogs and people. When populations are large, flies will attempt to feed wherever they land and landing rates on people can exceed 100 stable flies a minute. There are presumptions 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 up to 6.4 km away. Flies can cause tremendous problems in these situations, by restricting outdoor recreational activities, particularly those that involve cooking or consumption of food .The nuisance factor is usually the main complaint. Flies are also considered to be an indication of unsanitary conditions.There are no objective levels at which a statutory nuisance exists or may be caused. In general, in domestic premises, it is likely that the 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. Just as noise nuisance is not a matter of decibel levels, insect nuisance is not a matter of numbers of insects. Impact may also depend on, e.g., size of room, number of people /premises affected etc. House flies do not damage property.
Flies can be monitored with baited traps, sticky ribbons, or spot cards. Spot cards are 3-inch by 5-inch white index cards which are attached to a house-fly resting surface. A minimum of five cards should be placed in a suspect animal 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 / reduce harbourage and breeding material than to treat an infestation once it is established. Larvicides are also used in animal husbandry although adulticides should be the last line of defence. Premises need to adopt an integrated approach to house fly control which 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. Chemical treatment is the last line of defence.
Physical prevention methods
i. Proper sanitation is the key to fly control. Deny flies access to food, shelter and a place to lay their eggs.
ii. Do not allow flies to come in contact with contaminated substances and thus contaminate themselves.
iii. 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.
iv. Prevent flies from entering buildings, by keeping doors closed and window screens in proper repair.
v. If flies do enter structures, eliminate them with traps or other suitable methods as quickly as possible.
vi. Wet straw should not pile up in or near buildings and, as one of the best fly breeding materials, is not recommended as bedding
vii. 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.
viii. 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.
ix. 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.
x. Electronic fly killers which 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 methods
a) 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
b) Although most pesticides do have a residual effect and may work on particular species throughout their lifecycle.
c) The use of pesticides near water bodies is risky and must be minimised.
d) 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.
e) 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.
f) In poultry houses, the use of mists, fogs or baits may be necessary for house fly control.
g) 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.
h) 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.
i) 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.
j) 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.
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