Fly Strike in Sheep
The most prevalent and important cause of flystrike in Australia is the sheep blowfly, Lucilia cuprina. This fly initiates more than 90% of all strikes on susceptible sheep. Prevention of fly strike relies on understanding the fly life-cycle and the institution of appropriate management and control measures.
The Lifecycle of Lucila cuprina
Lucilia cuprina breeds on living sheep, primarily. The incidence of flystrike is highest during the warmer months of the year. Generally, mid-summer is not favourable for fly strike, as the hot, dry conditions lead to dessication of the eggs and larvae before they are able to really take hold.
The female fly cannot lay any eggs until she has ingested a protein meal, usually from a carcass or dung. Following this, the female blowfly has the capacity to lay up to 200 eggs in a single batch and a female fly will live for up to 1 month and lay 2-3 batches of eggs during her life-time.
Under ideal conditions, maggots hatch from the laid eggs within 12 hours and may be fully fed and ready to drop off the sheep within 4 days of hatching. Once the maggots drop off the sheep, burrow into the top layers of the soil, where they form a cocoon and pupate, maturing to an adult fly. When conditions are favourable, an egg may develop through to an emergent adult fly within 12 days after being laid on the sheep.
If soil temperatures fall below 15° C, larval development may be suspended until the temperatures begin to rise again in the following spring. During the colder months, larval numbers in the soil may decrease as a result of natural predation, soil water-logging, etc.
As temperatures begin to increase again, larval development recommences in synchrony and the ‘over-wintering’ population will emerge as adults in synchrony. If these emerging flies encounter susceptible sheep, flystrike may occur. The next generation of flies produced from this emerging generation will be more numerous and if conditions remain suitable for flystrike to occur, a flywave may be produced. Although flywaves ‘move’, blowflies themselves do not travel long distances. Generally, flies tend to stay in one area. To a large extent, farms breed their own flies. Sheep blowflies do not move away from access to water and sheep.
What makes a sheep susceptible to flystrike?
A sheep's susceptibility to flystrike is primarily determined by the level of moisture in the fleece. Sheep that have been wet to the skin can develop a condition called fleecerot. Fleecerot develops from a severe inflammatory skin reaction that occurs following significant wetting. This inflammation leads to the release of serum from the skin (it 'weeps'). Blowflies are highly attracted to sheep with this condition.
Lumpy wool is also strongly attractive for blowflies. The flies lay their eggs in the affected wool and the hatched maggots feed on the lumpy wool before penetrating deeper and invading the skin tissues. A similar scenario occurs when eggs are laid onto daggy wool.
Blowflies are also attracted to urine or faecal stained wool, wounds, footrot, weeping eyes and sweat around the base of the horns of rams. In all cases, moisture is the common feature.
Prevention of Flystrike
An integrated approach consisting of strategic chemical control and non-chemical approaches is the most effective way to prevent production losses. Long-acting chemicals should be used at the beginning of the fly season (based on actual seasonal conditions, not calendar dates) to prevent fly populations from building up.
Tips to prevent a fly problem:
1. Improving the conformation through breeding – less wrinkled sheep
2. Improving conformation through surgery – mulesing, tail docking
3. Crutching to remove dags from the breach region
4. Strategic application of insecticides
5. Use of fly traps and home-made fly bait bins
6. Control of concurrent diseases that predispose to flystrike – e.g. drench to remove worms and prevent diarrhoea, treat footrot
If sheep are struck, clip the wool around the affected area and treat with a suitable knockdown product to kill the maggots.
If concerned please give us a ring.