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Blowfly Strike a Concern in Warm, Humid Summer Months

18 June 2015

GLOBAL - Whether you are in the southern or northern hemisphere, flystrike can affect flocks. European farmers contend with Lucilia sericata flies, while in Australia, South Africa and the US, the pest is Lucilia cuprina.

Elise Brown explores the condition as a global issue, the risks involved and how to combat cases. 

Knowing What Your Up Against

Blowflies can be identified by their medium-sized blue or green metallic bodies. The insects thrive in moderate and warm climates, and rainy conditions are especially favorable for blowfly strike.

The most common countries where blowfly strike can be found are Australia, New Zealand, the United Kingdom, Ireland and South Africa.

Strike occurs in late spring, summer and early fall when female blowflies are attracted to a sheep's wound, injury or soiled wool.

Shearing and dagging have a key role to play in avoiding flystrike

The blowflies lay hundreds of eggs on the sheep, and when the eggs hatch 12 hours later, the larvae begin to feed on the animal's skin. Larvae thrive when humidity in the wool is high and hatch when humidity is above 90 percent. Once the larvae mature, they drop to the soil, where they pupate, emerging as adults after two weeks.

Several body parts can be affected. Most frequent are the breech strike at the rear, with wrinkles and dags (dried feces on the wool) attracting flies, and body strike at the flanks and back, often caused by fleece rot or lumpy wool.

Most Damaging

The most damaging species are Lucilia cuprina, the Australian sheep blowfly. This blowfly is mainly located in Australia and South Africa, but can also be found in places such as North America. In Europe and New Zealand, sheep are most affected by Lucilia sericata, known as the common green bottle fly. notes that blowfly strike most affects ewes and lambs.

"The maggots virtually eat their host alive, which is highly stressing and annoying for the animals," the site stated. "Secondary bacteria infect the wounds and the hosts' organism. The maggots produce also ammonia, which is poisonous for sheep. As a consequence affected sheep are depressed, stop feeding, suffer from fever, inflammations, blood loss, etc."

Symptoms and Management

Other symptoms, according to Novartis Animal Health, include:

  • Agitation shown by stamping, shaking, gnawing or rubbing
  • A distinctive odour that attracts more flies
  • Matted and discoloured wool
  • Areas of skin with no wool (these areas can increase in size if left untreated)
  • The economic consequences of blowfly strike can be serious and include lower wool and leather quality, reduced lamb crops and increased lamb time to market. Extensive infestations can even lead to an agonizing death for the animals if the problem is left untreated. The impact was recently estimated to be greater than $250 million in Australia.

However, there are several ways blowfly strike can be counteracted, including:

  • Selective breeding: Genetics has been shown to play a part in blowfly strike, as sheep with certain conformational characteristics, such as excess skin wrinkles and narrow breeches that are often soiled, more easily attract blowflies. Sheep with fewer wrinkles, less wool in the breech and a low tendency toward developing fleece rot or lumpy wool are less likely to attract blowflies.
  • Shearing: Blowflies are attracted to long fleeces. Shearing also suppresses humidity, a factor in larval survival, in the wool.
  • Tail docking: Removing the tail helps prevent soiling of the wool in the rear.
  • Using pour-ons: These products should contain cyromazine or dicyclanil, insect growth regulators. It should be noted other products (listed below) are needed to cure blowfly strike once it happens.
  • Keeping wool as dry as possible: Expose sheep to sunny and windy conditions when possible to help reduce fleece rot and lumpy wool, two blowfly attractants.
  • Keeping flocks free from gastrointestinal worms: These worms often cause scouring and great soiling of wool in the breech. Female blowflies are then attracted.

Treatment Options

If blowfly strike does occur, dressings with various powders, lotions, ointments and other treatments containing synthetic pyrethroid, carbamate and organophosphate larvicides can be used for treatment. A diazinon-based plunge dip or a synthetic pyrethroid pour-on with alphacypermethrin or cypermethrin may also be used. These products also protect against further attack. Deltamethrin also can be used, but the product does not protect against future blowfly strikes.

Some blowflies may have become resistant to treatments used in that region. If a product is not working, the reason may be resistance of the blowfly strain to that particular product.

Shepherds in the United Kingdom can anonymously report flystrike by visiting Scotland's Rural College's Blowfly Strike Database. The database was developed to provide farmers with up-to-date information about flystrike problems in their area. This information can let farmers know how many treatments for a strike might be needed.

But as Scotland's Rural College notes on their database website, prevention is still key.

"The more effectively farmers treat ewes for flystrike the less flies will be about."

TheSheepSite News Desk