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Australian Wool Innovation Limited
Emily King
Manager, Woolgrower Education & Capacity Building
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Cyromazine (eg Vetrazin) Resistant Flies - Bring out your Maggots!

Posted by Bestprac on Oct 01 2012


Early in 2011 a sample of blowfly larvae collected from struck ewe lambs on a Nimmitabel property were submitted to NSW DPI (Elizabeth Macarthur Agricultural Institute) as a possible cyromazine1 breakdown. Wether lambs on the same property that had been treated with dicyclanil2 were not affected. The property had a long history of cyromazine and dicyclanil use but it was deduced that the ewe lambs had been under-dosed with a cyromazine spray-on product.

Subsequent laboratory testing revealed that approximately 4% of maggots in the Nimmitabel sample were capable of surviving a concentration of cyromazine known to be lethal to ‘susceptible’ larvae. Resistance to cyromazine was low (3x) with low-level (2x) cross-resistance to dicyclanil also evident.

When we returned to Nimmitabel property in spring 2011 we trapped blowflies and collected maggots from the first sheep to be struck in spring. We tested these samples and found that the resistant types were still present. They had survived the harsh Monaro winter. We also tested blowfly larvae from several properties located within 5 km of the original property and found resistant larvae on four of those properties too. Over the past 30 years we have tested hundreds of blowfly populations for cyromazine resistance and until 2011 had not seen results like those from the Nimmitabel district.

Currently, the implications of these results for affected wool producers are unknown although there have been no further flystrike problems at Nimmitabel in lambs treated with cyromazine or dicyclanil.

Given that the Nimmitabel experience is unlike any other from the past 30 years, the prudent course of action is to conduct a broad survey of Australian sheep blowfly populations to determine whether cyromazine or dicyclanil resistant larvae exist elsewhere and, if so, to determine the practical significance of the resistance.

Australian Wool Innovation and NSW Department of Primary Industries are funding a project with the following aims:

  1. To sample and test field populations of sheep blowfly for cyromazine and dicyclanil resistance to determine whether the resistant population from the NSW Monaro is an isolated case or just one representative of a new resistant phenotype.
  2. To determine the level and practical significance of the resistance in laboratory and whole animal trials.
  3. To measure the susceptibility of field blowfly populations to ivermectin (an alternative registered insecticide capable of providing long-term flystrike protection).

Testing PacksWe need assistance to obtain blowfly maggot samples for resistance testing. We have produced sampling kits that contain a vial of vermiculite to hold the maggots, an instruction sheet and a submission form that tells us a bit about the sample such as where it came from, who sent it, what chemicals (if any) had been applied to the sheep and where the strike was located on the sheep. These items are contained in a pre-addressed, pre-paid Australia Post satchel.

If you will send us a sample of blowfly maggots from your property please see the instructions below.

NOTE: Collect blowfly maggots AFTER clipping/crutching but BEFORE applying chemical to the affected site.

1. Cyromazine is the active ingredient in several flystrike preventative products (eg. Vetrazin®, ProGuard®, Cyrazin®, Venus®, Virbazine®, Cy-Guard®, Cyro-Fly®, Exi-fly®, Lucifly® etc.).

2. Dicyclanil is the active ingredient in several flystrike preventative products (eg. Clik®).

 To be sent a blowfly maggot sampling kit please contact:

Garry Levot at NSW Department of Primary Industries
Elizabeth Macarthur Agricultural Institute
Menangle NSW 2568

Tel: 02 4640 6376

Last changed: Oct 02 2012



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