Sheep parasites
Management of blowflies
Ken Wilson and Bob Armstrong, formerly of Department of Primary Industries and Fisheries
Reviewed
by Geoff Knights, Department of
Primary Industries and Fisheries
Key points
- The Australian sheep blowfly (Lucilia cuprina) is the primary sheep blowfly responsible for initiating most blowfly strikes.
- Hairy maggot fly (Chrysomya rufifacies) is a secondary blowfly that will only strike sheep after the Australian sheep blowfly has initiated a strike.
- Blowflies thrive in warm, humid conditions. They do not like cool weather (less than 17oC) or excessively high temperatures.
- For Lucilia cuprina to strike sheep there should be a moist protein source on either the fleece or skin to allow newly hatched larvae to become established.
- Blowfly control requires a practical combination of animal management, trapping and chemical control.
- The chemical used, as well as the method and timing of application, have a major bearing on the level and severity of residues in greasy wool.
Introduction
The dry climate of western Queensland means that blowflies present less of a problem than in other wool growing areas of the state. However, serious losses can occur in a very short space of time when conditions are suited to blowfly activity.
Modern day chemicals are effective in controlling and preventing blowfly strike but the use of these products needs to be tempered by the fact that chemical residue in wool is a problem for wool processors. Environmental contamination with chemicals is becoming increasingly less acceptable. This is a challenge that the Australian industry needs to address and manage.
Types of blowflies
There are basically two species of blowfly that cause problems in sheep.
- The Australian sheep blowfly (Lucilia cuprina) is a primary fly, which is responsible for initiating over 90 per cent of all strikes and virtually 100 per cent of all serious fly waves. It is a copper green colour with reddish eyes. The adult fly is approximately 10 mm long and produces a smooth skinned white maggot. Figures 1 and 3 illustrate the adult fly and maggot of Lucilia cuprina.
- The hairy maggot fly (Chrysomya rufifacies) is a secondary fly, which prefers to breed on carcases. It will also strike sheep after Lucilia has initiated a strike. It is blue green in colour, 10 mm long and produces the characteristic hairy maggots. Figures 2 and 3 illustrate the adult fly and maggot of Chrysomya rufifacies.
|
|
|
| Figure 1: Lucilia cuprina, the primary sheep blowfly | Figure 2: Chrysomya rufifacies, the secondary sheep blowfly |
Figure 3: Lucilia (smooth) and Chrysomya (hairy) blowfly maggots
Biology of Lucilia cuprina
Adult flies live for approximately two to three weeks and Figure 4 depicts the life cycle of the Australian sheep blowfly. Female flies have well developed sensory organs on the feet and legs, which are used to find a suitable environment for egg laying.
Mature females will lay two or three batches of eggs with about 200 eggs per batch. Eggs are laid individually at about 15 second intervals, which means egg laying takes about one hour per batch.
The number of larvae needed to establish a strike is at least 1500. Not every egg laid will produce a viable larvae and an established strike would be the result of egg laying by several flies.
Eggs usually hatch into larvae in 12-24 hours, although this can be as short as eight hours under ideal conditions. Larvae grow from pin head size to 10-15 mm in length in about three days, then drop off the sheep to commence pupation a day or two later. They usually fall off at night or in the early morning when ground temperatures are coolest, and burrow into the soil. This means that a large proportion will pupate and subsequently emerge as blowflies from around sheep camps.
Adult flies will normally not travel more than three kilometres from where they hatch during their life span.
After hatching, the female fly needs a feed of protein for her reproductive organs to mature. She needs a further feed of protein before egg laying. Common sources of protein are carcases, manure and existing strikes.
Some Lucilia will breed on carcases when conditions are not favourable for doing so on live sheep. This is one way that low level populations are maintained. Covert strikes (ie small strikes that go unnoticed) on a small number of animals are also common and is another way in which the life cycle is continued through cold and/or dry periods.
Figure 4: Lifecycle of Lucilia cuprina
Conditions that favour blowfly activity
Blowflies thrive in warm, humid conditions. They do not like cool weather (less than 17°C) or excessively high temperatures (more than 38oC). For Lucilia cuprina to strike sheep there needs to be a moist protein source on either the fleece or skin to allow newly hatched larvae to become established.
Breech strike in ewes and pizzle strike in wethers is the most common. Wet urine stained wool causes skin irritation and 'weeping' of protein rich fluids from the inflamed skin.
Dermatophilosis (lumpy wool or dermo) and fleece rot (water stain) are also a source of protein. Affected areas become attractive to Lucilia cuprina when they are wet by rainfall or prolonged humid conditions.
Lice infestations can lead to body strike. Sheep that bite or rub to relieve the discomfort caused by lice often break the skin, which exposes a moist protein source.
Fighting amongst horned rams also exposes an attractive egg laying site.
Lamb marking and mulesing wounds are susceptible to strike, as are other injuries and infected wounds.
Management and control
Animal management
Time of shearing and crutching are the main management practices used to combat flystrike. The peak blowfly periods are early spring and late summer/autumn. Shearing prior to one of these periods and crutching prior to the other will minimise potential problems. Lambing is also timed to start following either shearing or crutching to reduce breech strike associated with urine and afterbirth in long wool.
Mulesing will provide lifetime protection against 90 per cent of all breech strikes. When combined with shearing and crutching at high-risk periods, breech strike can be virtually eliminated in all but exceptional seasons.
Breeding and selection against conformation and fleece faults that predispose sheep to flystrike (e.g. excessive wrinkle, devil's grip, fleece rot) and culling struck animals in years of low blowfly activity will help breed for resistance against flystrike.
Trapping
The LuciTrap sheep blowfly trapping system consists of a unique trap and patented blend of chemical called LuciLure which, when combined attracts and captures Lucilia cuprina. The LuciTrap system is in adjunct to other blowfly control procedures and should be included in an integrated pest management program.
Using LuciTrap to trap blowflies can substantially reduce flystrike - particularly if carried out by several neighbouring properties. Trapping during the cooler months when numbers are low, will slow down the rate of population increase when conditions become favourable. It may even prevent strikes from being established in circumstances where favourable conditions are short lived and blowflies are unable to breed in sufficient numbers in the time available.
LuciTraps need to be located at watering points, along boredrains and creeks and at other regular sheep camps. This will take advantage of the fact that blowflies need access to water to survive and that most newly hatched flies emerge near sheep camps. Trapping can also provide an early warning of a build-up in blowfly numbers and allow appropriate control strategies to be implemented.
Chemical control
Where the incidence of flystrike is low, treating individually struck sheep in the paddock or yards is an option.
Application of chemicals as a preventative measure against body, breech and/or pizzle strike may be necessary in some years. The decision to resort to large-scale chemical usage should be based on:
- seasonal conditions
- attractiveness of sheep to flystrike
- blowfly numbers (observed in traps)
- timing in relation to other management practices (shearing, crutching, lambing, etc)
- ability to respond to a fly wave if preventative measures are not carried out.
Product choice
When choosing a product for jetting, there are three distinct types of chemical available.
- organophosphates (OP) eg Top Clip, Di-Jet, Jet Dip, Ectomort, Seraphos
- insect growth regulators (IGR) eg Vetrazin, Jetcon, Fleececare, Strike, Clik
- spinosyn eg Extinosad.
Organophosphates will kill most maggots on existing strikes but will only provide very limited protection (two to four weeks) against new strikes.
Insect growth regulators will not give immediate kill of maggots on existing strikes. However, they do stop maggots from feeding so that they die within two to three days. They also provide long-term protection (up to 14 weeks) against new strikes and pose less of a residue problem then OPs.
Spinosyn provides four to six weeks protection and has the advantage that it has a nil withholding period and can be used in long wool.
Where knockdown of existing strikes is required a spinosyn or an OP product can be used remembering that OPs should not be used on sheep with more than six months wool. For long term protection jet the whole mob with an IGR. Mixing an OP with an IGR for jetting is not recommended as this will lead to an unnecessarily high OP residue on the wool at shearing.
Where chemical usage is unavoidable, the type of product and method of application used will affect the level and severity of the residue.
Chemical application method
Hand jetting is the preferred method of application as the chemical can be applied only to those areas of the fleece that are susceptible to flystrike. It also provides the most effective control. Walk through spray races apply chemical indiscriminately and only achieve limited control.
Long wool backliners apply very high concentrations of chemical and result in some of the highest residue levels.
Wool growth
Chemicals applied to sheep with greater than six weeks wool growth will leave an unacceptable residue in the greasy wool at the next shearing.
Where chemicals are applied within six weeks off shears for lice control, only minimal residues remain at the following shearing. It is therefore important to effectively control lice at shearing to eliminate the need to mix an OP with an IGR for lice control when jetting for fly in long wool.
Do not dip (shower or plunge) sheep with more than six weeks wool growth.
Chemical residues in wool
Pollution and environmental controls in many of the wool processing countries are becoming increasingly stringent. To avoid the possibility of restrictions and regulations being imposed on the marketing and processing of Australian wool, the industry needs to voluntarily reduce the level of chemical residues in greasy wool. Being able to provide a residue free product would also give Australian wool a marketing advantage.
This is not to say that chemicals shouldn't be used at all. In fact, all registered products can be applied to sheep providing they are used in accordance with label directions. However, there is an urgent need for producers to take maximum advantage of non-chemical control measures and to limit the use of chemicals to situations where no other alternative exists. The use of integrated pest management strategies is recommended.
Further information
DPI&F Note Sheep parasites: Integrated pest management to control blowflies and lice.
DPI&F Note Sheep parasites: The LuciTrap sheep blowfly trapping system.
The book Blowflies and lice information manual: A practical approach to producing low residue wool (DPI&F Shop) takes you step-by-step through best practice management of blowflies and lice following an integrated pest management approach to reducing pesticide use and residues on wool.
The Quick guide to commonly used treatments for blowflies and lice describes the differences between chemical groups and lists commonly used pesticides.
For further information contact DPI&F on Telephone 132523 (Queensland residents) or (07) 3404 6999 (non-Queensland residents) between 8 am and 6 pm weekdays, or e-mail callweb@dpi.qld.gov.au.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
File No: SW0101
Last reviewed 03 March 2005