By Dr Comfort Phiri, technical services manager, Novartis Animal Health
Pig production is increasing in the world. As operations become larger and more complex, the issues of pest and odour control also increase in importance. Among pests, flies are a primary nuisance. Flies are not just a nuisance; they’re a major cause of disease, suffering and economic hardship around the world. All told, they are known to be involved in the transmission of more than 65 diseases to humans alone, including typhoid fever, dysentery, cholera, leprosy and tuberculosis. They are also responsible for significant reductions in the production of farmed animals. It is estimated that flies are responsible for global livestock and poultry production losses measured in billions of dollars. Modern methods of livestock farming often provide an ideal breeding environment for flies, making control a major challenge.
Municipalities have passed public health by-laws that amongst others, make specific provision for pest control in livestock operations. These can be used to enforce elements such as fly control on farms.Understanding the fly biology and behaviour
There are four distinct stages in the life of a fly: egg, larva or maggot, pupa and adult. The overall life cycle of the house fly can range from seven to ten days in the summer to about three months in cooler conditions. An adult female will lay a batch of 120 eggs on average and can produce four to six batches of eggs in her lifetime.
Adult flies are mainly active during the day, when they feed and mate. Although capable of movement up to several kilometers, house flies normally move no more than 3 km from their breeding sites. Flies disperse either across wind or into the wind with nuisance densities highest closest to the source.
Fly numbers are determined by abiotic factors (environmental factors such as temperature, moisture of breeding habitat and humidity) and biotic factors (natural enemies including parasites, predators and pathogens).
21st century fly control
Effective management entails a combination of insect control methods to reduce the mean level of flies to an acceptable level. Flies cannot be eliminated, but their numbers can be kept at a tolerable level. In the past, many relied on the application of a single broad spectrum adulticide to control flies. However, there have been major advances in our understanding of this pest in recent years, and this is no longer considered to be the most efficient approach. This, together with a greater awareness of the environmental issues surrounding adulticide use, and the mechanisms by which insects become resistant to such chemicals, has led to the development of more sophisticated control methods. Effective fly control on farm requires:
• Understanding of the various fly species (including their biology and behavior), parasites and predators of flies (biological control agents), manure management techniques, insecticides and insecticide application techniques.
• An integrated approach – Integration of products that tackle different stages of the fly life cycle with various cultural and biological techniques which reduce the amount of chemical treatment needed to achieve effective fly control in the first place. Integrated fly control is not only more cost-effective, it also helps prevent insect resistance and the build-up of insecticidal residues in animal tissues — two increasingly important factors facing farmers today.
• Targeted products – strategic and simultaneous targeting of the different stages of the fly life cycle will yield far much better results as compared to selective focus on adult flies. This reduces the rate of development of resistance.
Fly control principles
Using a mixture of cultural, biological and chemical control measures adapted to the farm, will always provide the most cost-effective solution.
The cultural control of flies is defined as the manipulation, insofar as possible, of abiotic factors (environmental conditions such as temperature, moisture of breeding habitat and humidity) that suppress fly numbers. In essence this means proper management of the manure, feeds, and facilities.
Some species of mites and beetles prey on fly eggs and larvae. The maximum benefit from predators and parasites is achieved with dry manure. In very wet manure, predators cannot move about effectively to find and consume fly eggs and larvae.
When using chemicals, it is important to use registered products and to adhere to label instructions. Insecticides are either adulticides (baits, spray-on, paint-on e.g. Agita®), or larvicides (spraying breeding sites e.g. Neporex®). Adulticides should be applied so that they will not contact and kill house fly predators and parasites. If using larvicides, ensure that these are compatible with commonly used biological control agents. In order to avoid the possibility of resistance to insecticides developing in the flies within the farms, it is vital to use insecticides from different chemical groups with different active ingredients in rotation during the span of the fly control programme. Suspected resistance should always be reported to the manufacturer.
If fly suppression by cultural and biological methods is maximised, then the effectiveness of insecticide treatments will be enhanced, and the rate of development of fly resistance to the insecticide will be reduced. The most effective insecticide use is as part of an integrated control programme, in conjunction with cultural and biological methods.
Fly control on farms is an issue which will continue to impinge on a large proportion of the population but by understanding the biology of the flies and implementing an integrated approach to the control of the flies the problems can be resolved successfully.