Resistance management strategies for the Australian sheep blowfly (Lucilia cuprina)

Lucilia cuprina
Lucilia cuprina

Lucilia cuprina, the Australian sheep blowfly, initiates most cases of flystrike on Australian sheep. Like all insect pests, it has the potential to develop resistance to insecticide treatments. Some Australian sheep producers have reported shorter protection periods than claimed on the label of the flystrike products they have used.

On investigation, some of these cases are the result of improper application or heavy rain following insecticide application, however in a number of cases the presence of resistance has been confirmed.

This is a timely reminder for sheep producers to implement resistance management strategies to maintain flystrike protection for their flocks and slow the development of resistance within their local fly populations.

These signs indicate you might have resistance:

  • a shortening of the protection period (specified on product labels)
  • flystrike in multiple treated sheep rather than just a few.

However, there are other reasons why strike might occur earlier than expected after a treatment.
Before you conclude your flies are resistant, check that:

  • the sheep affected were actually treated
  • the chemical was applied following the manufacturer’s instructions
  • the appropriate amount of chemical was applied
  • the wool length was adequate to retain the treatment
  • wool or dags did not make penetration of the product difficult
  • there was not unusually heavy rain following treatment, resulting in chemical wash out.

Strategies to slow the development of resistance to flystrike preventative chemicals by flies

  1. Use an integrated approach to reduce reliance on insecticides.
  2. Know your chemical groups.
  3. Rotate chemical groups where practical.
  4. Minimise the number of treatments applied in a season.
  5. Consider treatments for other parasites, particularly lice treatments.
  6. Apply insecticides carefully and strictly as specified on the label.
  7. Monitor for flystrike frequently.
  8. Collect and kill all maggots from fly struck sheep.

(details of these strategies are provided in the first document linked below)

The two documents below will help you whether your chemicals still work well, or if your flies are already showing signs of resistance to one or more chemicals.

This document is particularly useful if you think flystrike preventative chemicals still work effectively on your property.



This document is particularly useful if you believe resistance has already emerged in the flies on your property.

These documents were prepared by Australian Wool Innovation and the AWI Sheep Blowfly Resistance Management Strategy Working Group:

Brian Horton (University of Tasmania), Peter James (University of Queensland), Deborah Maxwell (ParaBoss), Jane Morrison (MSD Animal Health), Bridget Peachey (Australian Wool Innovation), Nick Rolls (Elanco), Jane Morrison (Coopers Animal Health) and Narelle Sales (NSW Department of Primary Industries).