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Flies are a source of irritation for humans and animals, and can mean large production losses in livestock and a loss of income for producers. Dr Arno Moore of Bio-Insectaries South Africa (BISA) says the irritation flies cause often leads to animals using unnecessary energy while attempting to repel flies by swishing their tails, swinging their heads and kicking their legs.
Their feed intake decreases, along with production and growth rate. Milk production can drop by as much as a litre per day. Flies are also vectors of various eye diseases and certain biting flies are associated with Staphylococcus aureus mastitis, especially in heifers.
Celeste Meyer of Coopers Environmental Science says flies also create problems at feedlots and cause losses for food processors when contaminated food is rejected. According to Jannie Myburgh of Myburgh Equipment, it is difficult to calculate actual financial losses due to flies, but it is estimated that a 1 000-animal feedlot can lose around R10 000 per day.
Fly species and life cycles
According to Dr Moore, house and stable flies are species that can reach plague status. The housefly irritates livestock when they cluster around moist areas such as the eyes and teats. The stable fly is a biting fly that feeds on blood and can amass on the abdomen and legs of animals.
Flies are carriers of around 70 human and animal diseases, including cholera, gastric fever and Salmonella typhoid fever. Flies also spread worms such as hook- and tapeworm.
The housefly’s life cycle is similar to, but slightly shorter than, that of stable flies. A female fly lays up to 50 eggs at a time and can lay as many as 800 eggs in her lifetime. The eggs are white, approximately 1,2mm long and develop into larvae within twelve to 18 hours (yellowish-white maggots up to 12mm in length).
The larvae complete three stages that can last one to three weeks. After three days to three weeks they pupate and hatch. The pupae produce adult flies. One fly can produce ten to 30 generations of flies annually.
Biological fly control
BISA breeds a fly parasite, Muscidifurax raptor – a small wasp that targets fly pupae to feed on and to lay their eggs in. The wasp effectively prevents the hatching of a new generation of flies. An increase in wasp numbers means a decrease in fly numbers.
Fly larvae play a key ecological role as composters of protein- and energy-rich waste. This nutrient breakdown has a positive effect on compost. “Wasps allow fly larvae to play their part in composting, but the parasitisation of fly pupae prevents the excessive hatching of flies.”
This is a natural, chemical toxin free control method, and flies do not build up resistance. “The wasps are bred according to strict phytosanitary guidelines to ensure they can be used safely in all areas,” explains Dr Moore.
Integrated fly control
Regular manure removal, for example, will not break the life cycle of most flies. Coopers Environmental Science therefore applies an integrated pest management programme to control flies. “We look at various components that must work together to solve the problem. This includes breeding and resting places, as well as a combination of toxins. Wettable powders, residual and space sprays, hygiene, knowledge of flies’ habits and temperature play a role,” says Celeste.
Coopers offers a wide range of active ingredients and formulations, including granules, which are used as bait. Residual sprays for indoor use, and wettable powders for porous outdoor surfaces, are available.
Flycatchers
Myburgh Equipment, in turn, makes use of method that physically attracts flies and traps them in a mesh cage. This pyramid-shaped cage has a hole big enough for a fly to crawl through. The mesh cage is placed over a 20ℓ bucket of bait, which is placed on a pole erected in areas known for fly hatching activity.
For bait, for example, raw meat is submerged in water in the bucket. The water must cover the bait to reduce excessive odour and prevent flies from laying eggs on it. When the mesh cage is full, the frame is removed and the dead flies shaken out. The method is especially effective in kraals.
The goal of any control programme is to reduce fly numbers to below the economic threshold value and irritation level as quickly as possible, and to prevent fly numbers from becoming uncontrollable. Jannie says they annually start applying fly control in August, to keep flies from laying eggs.
Fly breeding grounds should be managed in a way that keeps hatching to a minimum. Manure should be kept as dry as possible, good drainage maintained, and effluent and spilled feed, silage and rotting hay removed, recommends Dr Moore.
For enquiries, contact Dr Arno Moore on 083 270 4866 or arno@bioinsectsa.com, Celeste Meyer on 066 288 7285 or cmeyer@cooperses.co.za, or Jannie Myburgh on 082 417 0175.
