Flies

In Australia the flies of most concern to livestock producers include:

• buffalo flies
• nuisance flies in feedlots
• sheep blowflies.

Buffalo flies

The buffalo fly is primarily a problem for cattle producers in northern Australia. They are a small, biting fly that feeds on the blood of cattle and breed in the dung of the animals. Buffalo flies are found in hot humid regions of northern Australia from north-eastern New South Wales to northern Western Australia.

Buffalo flies have developed resistance to most of the chemicals used for their control such as in impregnated ear tags or back rubbers.

Conditions under which buffalo fly are likely to occur

The spread of buffalo flies between herds and between animals occurs when:

• newly emerged flies are seeking their first host – they can fly up to 10 km in search of a host
• flies are dislodged from an animal
• female flies return to a different host after laying eggs in dung
• movement of infested animals can be an important method of spread between herds
• dark-coated cattle, bulls, older cattle and those in poor condition usually attract more flies

Identification and diagnosis

Buffalo flies cause a number of problems. It is generally considered that infestations of more than 200 flies per animal are necessary to reduce production.

Clinical signs that would lead a producer to suspect buffalo flies include the following:

• Lower weight gain and lower milk production have been measured in heavily infested cattle.
• Heavy infestations result in severe skin irritation causing affected cattle to rub vigorously. This disrupts grazing, damages hides and can lead to skin ulcers.
• Many infested cattle develop sores in the inner corners of their eyes.
• Some cattle are ‘allergic’ to buffalo flies and are intensely irritated by as few as four or five flies. These cattle scratch and rub themselves constantly, which results in large sores on their necks and sides.

Prevention

An integrated approach to buffalo fly control should consider the following:

• understanding whether or not the cattle on a property need to be treated for buffalo fly – only treat when there are more than 200 flies per beef animal (100 per side) or more than 30 per dairy animal
• culling allergic or sensitive cattle
• using buffalo fly traps
• increasing the dung beetle population as dung beetles bury the cow pats and the fly larvae within the dung struggle to survive
• chemical control, including ear tags, sprays, pour-ons, back rubbers and dust bags.

Nuisance flies in feedlots

Flies are a problem in many feedlots due to the abundance of available food and breeding medium (dung). Only a few types of fly are of concern due to their numbers, annoying behaviour or disease-carrying potential.

Conditions under which nuisance flies are likely to occur in feedlots

• Increasing temperature and rainfall will increase populations.
• Fly larvae numbers will increase where a mixture of manure, vegetation and moisture are present, for example in hospital/induction areas, under the pen fence lines, drains and silage pits.

Identification and diagnosis

The four types of nuisance flies found in largest numbers on Australian feedlots include the house fly (Musca domestica), the bush fly (Musca vetustissima), the stable fly (Stomoxys calcitrans) and blowflies (Chrysomyia spp., Calliphora spp. and Lucilia spp.). Identification of  these four types of feedlot flies is necessary in the design of integrated feedlot fly control programs.

A key for identifying feedlot flies is included in the MLA Tips & Tools: Integrated pest management for nuisance flies on cattle feedlots. 

Prevention

An integrated approach to feedlot fly control should consider the following RULES acronym:

• Reduce fly breeding sites through strategies such as efficient waste management
• Use insecticides selectively
• Lotfeeding design principles
• Enhance populations of biological control agents
• Systematic monitoring of fly populations

Sheep blowflies

Flystrike is a significant health, welfare and profitability concern for Australian sheep producers. The species responsible for the majority of all strikes is the Australian sheep blowfly (Lucilia cuprina). The adult fly is a copper green colour with red eyes and produces a smooth skinned white/cream maggot.

The MLA-funded FlyBoss website is based on best practice parasite management strategies. It provides planning tools for optimal shearing, crutching and (if required) chemical treatment scheduling to reduce the risk of flystrike.

Conditions under which flystrike is likely to occur

Flystike can occur:

• when there is the presence of primary species (most commonly the Australian sheep blowfly)
• the risk of flystrike increases once the temperature is between 17-38°C, wind speeds are moderate (<30 km per hour)
• after recent rain. Susceptible sites on the sheep have been moist for about three days
• when there are susceptible sites on the sheep including wrinkles, urine and faeces to attract flies and sustain larvae.

Identification and diagnosis

Clinical signs that would lead a producer to suspect sheep blowflies include the following:

• Early strike signs:
  • small wounds with maggots present upon close inspection
  • sheep will bite or scratch at the affected area, may also duck head and stamp feet
• Advanced strike signs:
  • lethargy and inability to keep up with the mob. May lay down and refuse to get up
  • general depression with reduced grazing and drinking
  • strike will be large, inflamed and maggots will be visible
  • untreated flystrike can result in death.

Prevention

An integrated approach to flystrike control should consider the following:

• use the FlyBoss website and strategic planning tools to plan the optimal time of shearing, crutching and (if required) chemical treatment to reduce the risk of flystrike.
• integrating management options to reduce the attractiveness of sheep to flies
• long-term genetic selection for plainer-bodied sheep without daggy breeches
• strategic use of chemicals during high-risk periods
• using odour-baited fly traps to reduce fly numbers may also be helpful but is controversial.