World-first vertebrate pest biocontrol from Wardang Island, South Australia: cuts nation's rabbits by 500 million
Rabbits around a waterhole in 1938 on South Australia's Wardang Island where a CSIRO (commonwealth scientific and industrial research organisation) team developed the myxoma virus that would be released against Australia's 600 million rabbits in the 1950s. The calici virus also was tested on Wardang Island and accidentally escaped in 1995.
Images courtesy National Archives of Australia and New Scientist magazine
Wardang Island in South Australia’s Spencer Gulf was the site for developing myxoma virus – the world’s first vertebrate pest biocontrol – used against wild rabbits in the 1950s – followed by another accidental release of the effective calici virus in the 1990s.
Reports that Wardang Island “teemed with rabbits” went back to 1875 – consistent with South Australia’s European settlers actively promoting rabbits to be established in the province – until the menace of their exploding numbers became evident later in the 19th Century.
In November 1937, the CSIRO (commonwealth scientific and industrial research organisation) began to use Wardang Island to conduct its first field trials of myxomatosis and setting it up for the first successful release of the myxoma virus throughout the Australia in the early 1950s.
The myxomatosis programme killed 99.8% of infected rabbits and reduced Australia's wild rabbit population from 600 million to 100 million in only two years. It became less effective over time due to genetic resistance in the rabbits but continued to affect 40-50% of the rabbit population.
In March 1995, trials started on Wardang Island of the rabbit calicivirus causing rabbit haemorrhagic disease (RHD). Laboratory experiments at the Australian Animal Health Laboratory (AAHL) in Geelong near Melbourne found that calicivirus should not spread to domestic or native animals. But, before releasing the virus on the mainland, CSIRO scientists designed a field test on Wardang Island.
AAHL experiments had shown that rabbits should readily contract the disease from one another. At first, the virus spread very slowly on Wardang Island. All this changed in September 1995 when many rabbits suddenly became sick, including those held in pens about 60 metres from the inoculated animals. This coincided with the arrival on Wardang Island of the Australian bushfly, blown in on high-altitude winds from Queensland.
The CSIRO scientists believed the flies acted as a vector for the virus, picking it up when feeding on proteins released from the tear ducts of sick rabbits. The bushflies carried the virus from the island to the mainland. This also caused widespread mortality among the wild rabbit population without other adverse effects.
Australia’s most costly pest animal, rabbits caused $206 million in losses each year to the agricultural industry. They competed with grazing stock for food, contribute to soil erosion, damages crops and destabilised land.
Rabbits threatened the survival of more than 300 Australian native flora and fauna species. This included 24 critically endangered species such as the pygmy possum, orange-bellied parrot and ballerina orchid. Less than one rabbit per football field sized paddock was enough to stop the growth of some native species and negatively affect biodiversity.