ERADICATION by sterilisation would be the ultimate silver bullet solution to the Australian sheep blowfly pest problem, according to a NSW entomologist.
While sterilisation by radiation of the male Lucilia cuprina, more commonly known as the Australian sheep blowfly, has been mooted in the past, Charles Sturt University entomology and biology lecturer Dr Paul Weston said this could become a reality now it's identified other fly species could utilise the same radiation process.
"The Australian sheep blowfly has the right characteristics for sterile insect release, but the problem was the cost of a room in a radiation facility was found to be prohibitive when a cost analysis was conducted, for it to be possible it would have to be government-funded," Dr Weston said.
Dr Weston said the sterile release technique was currently being investigated for the Queensland fruit fly - which also has suitable characteristics for producing sterile males.
"If the same radiation facility were to be used for Australian sheep blowfly and Queensland fruit fly it could become a feasible option," he said.
Dr Weston said the screw-worm fly - which impacted cattle in a similar way to flystrike in Australian sheep - was successfully eradicated in Central America and Mexico by releasing sterile males.
It was reported recently that researchers in the United States had developed a technique to control populations of the Australian sheep blowfly by making female flies dependent upon a common antibiotic to survive.
North Carolina State University entomology professor Dr Max Scott and his research team genetically modified lines of female Australian sheep blowflies so they required doses of tetracycline in order to live.
Female blowflies which did not receive the antibiotic died in the late larval or pupal stages, before reaching adulthood.
Dr Weston this was an interesting approach, but would in fact involve a lot more work to be useful.
"This could form the basis for a sterile release program, but radiation would still have to be relied on to sterilise males as there would still be male larvae laid by male flies in sheep ," he said.
"The US female fly research has some appeal as the flies they have modified die before adulthood, so when the males mate with wild flies the females will die out and gradually the population would be eradicated as the female population decreases."
Dr Weston said ultimately the "silver bullet" would be to have a radiation facility, as it would remedy the damage being caused to a number of major commodities being affected by several pests - not just the Australian sheep blowfly.
Australian Wool Innovation (AWI) program manager productivity and animal welfare, Geoff Lindon, said the research out of the US was significant as it achieved mortality rates in female Australian sheep blowfly -however, their male counterparts could still cause flystrike.
"It's a step another step in the chain, and any work on Lucilia cuprina was an advantage to growers and a spin-off of many years of work conducted in Australia," he said.
"It does show what is now possible in the genomic world and builds on a whole range of work AWI is conducting."
Baylor University in the United States last year sequenced a large percentage of the Australian sheep blowfly genome. This followed on from work done by AWI in 2006 and 2007 when about half the fly genome was sequenced.
The genome sequence is now at the University of Melbourne where the sequence will be completed over a three-year period, funded by AWI.
"They are currently cataloguing the gene sequence and isolating the genes which are specific to Lucilia cuprina and aren't found in any fruit fly species," Mr Lindon said.
"These then become a point of interest as we can hone in on those genes and investigate what those are doing to the fly as to why it will lay eggs down on sheep and why other fly species don't."
"If we can find the gene that leads the blowfly to strike sheep that other flies don't have, we will be able to knock that gene out and it may stop the blowfly striking sheep, just as other flies don't strike sheep."
Furthermore, Mr Lindon said AWI was also funding a study of gene frequencies associated with highly resistant and highly susceptible sheep to flystrike from 700k SNP tests that had been done on 960 sheep at CSIRO at Armidale.
The sheep used in the study are from the flystrike susceptible and flystrike resistant susceptible flock bred at Mt Barker, Western Australia.
Mr Lindon said they are also genotyping the bacteria in that flock to identify the exact species of the bacteria and the variation between the flystrike resistant and susceptible sheep.
"What we have found is that some of these bacteria are responsible for the odours that either repel or attract flies," he said.
"While we know the most highly wrinkled and daggy sheep are susceptible to flies, we still do have some sheep with low wrinkle and low day that get struck, so we know there is something attracting the flies and we suspect it is the odour being created by the different bacteria."