Blowfly resistance to insecticides is widespread

Blowfly resistance to insecticides is widespread

Animal Health Science researcher, Narelle Sales of the DPI laboratories at Elizabeth Macarthur Agricultural Institute (EMASI) , Menangle, was guest speaker at the recent Macquarie Merino Lifetime Productivity Project field day,Trangie Agricultural Research Centre.

Animal Health Science researcher, Narelle Sales of the DPI laboratories at Elizabeth Macarthur Agricultural Institute (EMASI) , Menangle, was guest speaker at the recent Macquarie Merino Lifetime Productivity Project field day,Trangie Agricultural Research Centre.


Research continues on blowfly resistance, but free maggot sampling is to end on June 30.


BLOWFLIES don't recognise boundary fences, and are now more of a district or even a regional problem as graziers battle with insecticide resistance.

Animal Health Science researcher, Narelle Sales, told more than 80 attendees to the recent Macquarie Merino Lifetime Productivity Project field day at Trangie Agricultural Research Centre, funding for free maggot testing to assess the current level of pesticide resistance in fly populations on properties will end on June 30.

"Tests that would cost more than $3500 are currently being offered free through joint funding by NSW Department of Primary Industries and Australian Wool Innovation," she said.

Ms Sales is one of a long line of researchers at the NSW DPI laboratories now at Elizabeth Macarthur Agricultural Institute (EMASI) , Menangle, who has conducted thousands of tests on maggots for more than 30 years.

Tests are conducted only on the Australian sheep blowfly Lucilia cuprina, the major pest blowfly species responsible for initiating 90 per cent of all flystrike.

Ms Sales said the project aimed to determine the resistance profiles of blowflies across all wool producing states, and gather baseline data on newer chemicals for future reference.

"Everything we have received in NSW so far has been resistant to dicyclanil and cyromazine which belong to the same group of insecticides, so make sure you check the insecticide group the chemical you use belongs to, not just the trade name," she said.

Dicyclanil and cyromazine are both insect growth regulators (IGR).

"Make the opportunity where possible to rotate between insecticide groups when you treat, and plan to minimise the number of treatments applied in a season."

It is also important to consider the treatments used for worm and lice control.

"Blowflies will also come into contact with the products used to control when it's on the backs of sheep.

"Apply insecticide treatments carefully and according to the label instructions, and monitor flystrike frequently.

"Importantly, when cleaning strikes, make sure you kill the maggots, because that's the only way to stop them becoming the next generation of flies causing flystrike."

Maggot testing for resistance has been carried out in NSW DPI laboratories since the 1950s.

"While not much changed for a long time during the 1980s, 90s and 2000s, blowfly resistance has more recently changed significantly enough that graziers need to think more strategically about flystrike, especially now there has been rain," she said.

"It may not have been on the agenda during drought, but this will now change."

When the laboratory receives a sample, the maggots are cultured for two generations.

"We need to breed them up so we have enough to test," she said.

Chemicals which represent all the major chemical groups registered for blowfly prevention and control are tested at the laboratory.

They are spinosad, imidacloprid, Ivermectin, cyromazine, dicyclanil, diazinon and diflubenzuron.

Ms Sales said resistance to organochlorines (OC) took about three years to develop, while organophosphates (OP) took just eight years.

"Benzoylphenyl urea (IGR) also took eight years while butacarb lasted just 12 months.

"Current registered chemicals like the triazine (IGR) and cyromazine (the active in products like Vetrazin) has lasted 32 years, while the pyrimidine (IGR), dicyclanil (such as in Clik) which was introduced in 1998 had resistance detected in 2011, about 13 years.

"The synthetic pyrethroid (SP) cypermethrin (as in Vanquish) was introduced in 1988; the avermectin (ML) ivermectin, such as in Coopers Blowfly & Lice, was introduced in 1993; the spinosyn, spinosad (as in Extinosad) was introduced in 2003, while the neonicotinoid, imidacloprid (as in Avenge + fly) was introduced in 2019."

Overseas tests have found that the Lucilia cuprina blowfly can fly up to 16 kilometres looking for food, while Australian research has reported that the fly can travel 10km.

"But basically they won't travel far if they can find everything they need close by," Ms Sales said.

"Once they find what they need, that's where they will stay to carry on their life cycle.

"For blowflies to breed they need susceptible sheep and the breech area is a prime spot with urine staining, dags and scouring.

"Predisposing things for body strike include fleece rot, lumpy wool (Dermatophilus congolensis) and conformational issues such as 'devil's grip', which should now be bred out of the Australian Merino.

"Other flystrike susceptible areas include the pizzle, poll, wounds and footrot.

"They like weather conditions with temperatures between 17 to 39 degrees Celsius, wind speed less than 30kmh and they need moisture."

Reduce insecticide reliance

"Reducing insecticide reliance is hard, but strategic use of treatments. either with a longer protection period or two treatments with shorter protection periods, may enable farmers to carry out the other activities that need to be done on their property," Ms Sales said.

"You need to know when the greatest risk period for flystrike is in your area, and to do this you should use the 'Flystrike Decision Support Tool' available on the FlyBoss website.

"To try and reduce reliance on insecticides you should breed sheep that are resistant to flystrike, shear or crutch at times that maximise protection against flystrike, dock tails to the correct length, and manage scouring."

She said that breech modification may need to be used until sheep were genetically resistant to breech strike, and to drench, crutch and shear strategically.

Graziers can obtain a maggot collection kit from their local Local Lands Services office or from the EMAI.

Chemical groups and how they work.

Organophosphates (OP): diazinon, propetamphos, temephos are Acetylcholinesterase inhibitors which interfere with nerve signal transmission in the insect's nerves causing paralysis.

Synthetic pyrethroids (SP): alphacypermethrin, cyhalothrin, cypermethrin, deltamethrin prevent the closure of sodium channels in the insect's nerves causing paralysis.

Insect growth regulators (IGR's): benzoylphenyl ureas, triazine and pyrimidine derivatives - diflubenzuron, triflumuron, cyromazine, dicyclanil - interfere with the moulting process of larvae and prevent them developing into flies.

Macrocyclic lactones (ML): ivermectin, avermectin, abamectin, - block nerve signals.

Spinosyns: spinosad - excite the insect nervous system causing paralysis.

Neonicotinoid: imidacloprid - like nicotine binds to receptors which over stimulates the insect nerves causing paralysis.


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