What is insecticide resistance

“A heritable change in the sensitivity of a pest population that is reflected in the repeated failure of a product to achieve the expected level of control when used according to the label recommendation for that pest species”.
(Insecticide Resistance Action Committee)

Management of Resistance

IGR Resistance Development

The Australian blowfly, Lucilia cuprina, has proven over time it can develop widespread resistance to chemicals that are used to control it1. Resistance can either develop through spontaneous mutations (changes) in the parasite’s genetic material or can develop as a result of repeated exposure to the same active, or class of active. Resistance development may be accelerated by the inappropriate use of an active(s) such as underdosing or poor application.

Avenge Fly Strike

Blowfly resistance to actives within the Insect Growth Regulator (IGR) group of chemicals is now well documented.

  • Cyromazine resistance and dicyclanil cross-resistance was first reported in the 2010/2011 fly season.2
  • Additional cases of concurrent dicyclanil and cyromazine resistance have been reported since, predominantly in NSW.1,3
  • All larvae samples (n=55) submitted by sheep farmers from NSW in the AWI & NSW DPI research 2018 – 2020 were found to have concurrent cyromazine and dicyclanil resistance.3

  • With resistance increasingly being reported in key sheep areas, it is timely to consider the appropriate use of actives to prolong the efficacy of all actives currently on the market.

How to Reduce Reliance on Insecticides

Breed Sheep which are resistant to flystrike.

Shear or crutch at times that provide 6 weeks protection against flystrike.

Dock tails to the correct length to maintain a cleaner breech

Manage scouring by effective and strategic drenching.

Use breech modification if required, until sheep are genetically resistant to flystrike.

Overall, drench, crutch and shear strategically as part of an integrated plan

Best Practice

Know which insecticide group your treatment belongs to not just the product name.

Rotate insecticide groups when you treat where practical.

Plan to minimise the number of treatments applied in a season. Rotate to a different group.

Always consider the treatments used for worms and lice too. Some actives are also for blowfly.

Apply insecticides carefully and strictly according to the label. Don’t over or under dose.

Monitor for flystrike frequently. Every 2nd day in the peak flystrike season.

When cleaning up strikes always collect and kill the maggots as these form the next wave of flies.

Reduce reliance on insecticides which will slow down the development of resistance.

1.Heath, ACG and Levot, GW, 2015, ‘Parasiticide resistance in flies, lice & ticks in New Zealand and Australia: mechanisms, prevalence & prevention’, NZ Veterinary Journal 63(4):199-210.
2.Levot, GW, 2012, ‘Cyromazine resistance detected in Australian sheep blowfly’, Aust Veterinary Journal, 90(11):433-437.
3.Sales, N, Suann, M, Koeford, K, 2020, ‘Dicyclanil resistance in the Australian sheep blowfly, Lucilia cuprina, substantially reduces flystrike protection by dicyclanil and cyromazine based products’, IJP: Drugs and Drug Resistance 14:118-125.