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(519) As pig farms have become more intensive over the last ten years and animals have been kept in a controlled environments a variety of flies, spiders, cockroaches and other insects have established themselves in these warm places. The most important of these is the house fly of which there are two types; the common house fly (Musca domestica) and the lesser house fly. Other flies that occasionally cause problems are the blue bottle (Calliphora), the stable fly (Stomoxys calcitrans) and the fruit fly (Drosophila). An understanding of the different life cycles from egg to adult is important in their control.

The life cycle

The common house fly, which is world-wide in distribution is by far the greatest problem in farrowing and weaner houses. It has a life cycle from egg to egg of 7 to 14 days. The adults lay up to 400 eggs. The fruit fly has a slightly longer life cycle, from 8-30 days and is a more prolific egg layer producing up to 900 eggs. The eggs of all species hatch into larvae which develop into pupae and finally adults. The common house fly breeds in slurry, in manure heaps and any damp moist places, particularly if food is present. The fruit fly breeds in damp feed.

Disease risks

Flies make contact with faeces, skin and discharges from all surfaces of the pig. It follows therefore, that if the number of flies in the environment reaches a high enough level they can become major transmitters of disease organisms, not only within a building, but also between buildings and sometimes between pig herds. Such infections include pathogenic strains of E. coli, Brachyspira hyodysenteriae which causes swine dysentery, salmonellae, streptococci, rotavirus and TGE. In a laboratory test, a large number of flies from a farrowing house were cultured to determine the bacteria present. Bacillus bacteria, moulds, staphylococci, yeast's, streptococci and coliforms were isolated. This illustrates the potential for the dissemination of organisms. Major outbreaks of greasy pig and coccidiosis can be maintained by very high fly populations. When sows are sick with mastitis, flies are attracted to the udder and skin surfaces in great numbers and they can be responsible for enhancing severe outbreaks.

They have also been shown experimentally to transmit Streptococci suis type 2 which causes meningitis and because adult flies can live for up to four weeks and travel up to 2.4km (1.5 miles), transmission between farms becomes a possibility. They can be responsible for piglet diarrhoea persisting in farrowing houses.

If fly populations are allowed to build up, particularly in farrowing houses, they cause annoyance to pigmen and distress to sows and piglets. Fly dirt causes heavy contamination of surfaces, particularly around warm areas, lamp surfaces and lights.

Large fly populations on a pig farm can also be a nuisance to nearby communities.

Management control and prevention

  • Keep the numbers low. This is the most important factor in the control of flies, to prevent the build-up of the population. In countries with warm summers, fly control should commence at the onset of the breeding period and be maintained throughout.
  • Break the breeding cycle. Flies require a minimum temperature, moisture content and light in order to breed. Eggs hatch best at 35ºC (90-100ºF) and multiplication is reduced when the temperature is below 16ºC (63ºF). Moisture is a major requirement and humidity between 25-65% is ideal. It is interesting that the breeding activity is impaired when light levels are reduced.
  • Identify the breeding grounds. This is an important part of control because if the breeding grounds can be removed, or the conditions for breeding changed, the reproductive cycle will be broken or much reduced. Waste feed that accumulates in and around pens, particularly where there is moisture, provides an ideal environment for flies to lay eggs. Crust on top of slurry becomes a major breeding grounds especially if slurry tanks are not completely emptied. Cracks and crevices in walls are an attractive area for flies to breed in, as are solid manure heaps. Farrowing houses harbour large populations that become sources of infection for other houses.
  • Use all-in all-out systems with cleaning and washing of the houses between batches of pigs.
  • Identify resting sites. Where contact insecticides are to be used for control it is important to identify the resting sites of the flies. These are creep lids, lamp tops and walls where it is warm. For the fruit fly this can be a problem, because this species does not move around the building, but lives on roofs, walls and in cracks where there is moist feed at ground level. Residual sprays are of value.
  • Hygiene. Having identified the breeding grounds, keep them clean by pressure washing frequently and applying a residual insecticide. Where flies have built up to large numbers it is necessary to completely empty slurry channels and remove the crust material. Bedding used in farrowing houses that contaminates slurry will exaggerate the problem and provide better breeding conditions. Solid muck stored on the farm is a prime breeding site and should be moved well away regularly each week.
  • Creep feeding. Creep feeds contain high levels of milk products and sugar which provide nutrition and encourage both breeding and feeding. Delay creep feeding until pigs are at least 14 days of age (they probably do not eat much anyway before that age). This will reduce breeding levels.
  • Monitoring the population. A useful technique is to hang a white card of approximately 150x200mm in size from the roof of each house. This card should be soaked in a sugar solution and dried. Weekly, over a 48 hour period the dots of the fly faeces should be counted. This will give an indication of the build-up over a period of time and predict a population explosion so that intensive prevention and treatment routines can be carried out.
Methods of control

These include electrocution, sprays (either daily or residual), paints and baits, larvacides, fly traps and biological predators such as other flies, beetles and wasps. In-feed medication using insecticides that pass through the sow have also been reported. The main chemicals used include pyrethrins, organophosphorus compounds (OPs), lindane and BHC. Some of the products available and their uses are listed Fig.11-14.

The following procedures can be used:

  • Pulse medication - This involves use of an automatic, battery-powered spray that ejects insecticide into the environment on a periodic basis. This is carried out every 10-20 minutes and is a very good method of keeping fly populations at low levels.
  • Contact baits - These are one of the best methods of controlling flies, because they have immediate access to the insecticide as soon as they hatch. Such surface baits can either be sprayed on the ceiling or painted on the walls, particularly over warm areas where the flies rest. Some products contain a fly attractant. An excellent method of control is to sprinkle small crystals containing the fly attractant and the insecticide over the top of creep lids or other flat surfaces every other day. When selecting the insecticide look at the history of use on that farm and as soon as there is evidence of resistance developing change to an alternate chemical. Make sure the manufacturer's instructions are followed and in particular, that the siting of the insecticide is to best advantage.
  • Sprays - There are many products available; but if they have to be used daily for control, the battle is lost because large numbers of flies will have built up.
  • Electrocution - These fly traps are a promising addition to the range of controls.
  • Sheep dip - This successfully kills maggots and small amounts can be added periodically onto slurry crusts provided there are no contraindications to the product being used as such. Waste oils will have a similar effect.
  • Larvacides - These are substances such as neoprene which inhibit larval development and thus stop the cycle. They are sprayed or applied to the breeding grounds such as faeces heaps and slurry. Alternate contact baits every three days with knock down sprays.
  • Biological control - House flies can be controlled using the predator fly, Orphyra. This fly is attracted to the areas where the house fly deposits its eggs. Its larva cannibalise the house fly larva and then cannibalise themselves thus the life cycle is a limiting one. This method of control is also effective against the fruit fly. Artificially produced pupae are placed in the contaminated houses in small trays and allowed to pupate over a 10-14 day period. It takes 3-6 weeks to achieve control and the populations are maintained at a low level by periodic inputs of further pupae. The production of pupae on the farm using purpose built culture chambers and special media is the most cost effective method. For further information contact Salus QP Ltd. Predator wasps have a similar action.

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