Australia's Feral Rabbit Population Surges Amid Biocontrol Challenges
Australia is currently experiencing an increase in its feral European rabbit population, estimated at 200 million individuals. This surge is attributed to consecutive years of favorable breeding conditions.
Historical Biocontrol Efforts
Rabbits, introduced to Australia in 1788, became a significant pest after Thomas Austin released 24 wild rabbits in Victoria in 1859. Their rapid spread and breeding capacity led to environmental damage and competition with native species.
Early attempts at control included releasing mongooses and trialling a chicken cholera bacterium, which proved ineffective or harmful to other species.
Successful Biocontrols and Their Limitations
The Myxoma Virus (1950)
In 1950, the myxoma virus, causing myxomatosis, was introduced. It spread via biting insects and close contact. Initially, it killed an estimated 500 million rabbits within two years.
Its effectiveness declined as rabbits developed genetic resistance and the virus evolved to be milder, a classic example of host-pathogen coevolution.
Rabbit Haemorrhagic Disease (RHD) Calicivirus (1995/1996)
By the mid-1980s, rabbit numbers had risen again. Rabbit haemorrhagic disease (RHD) calicivirus, originating in China, was explored next. Accidentally spread to the mainland from a trial site in 1995, it was intentionally released in 1996.
It killed rabbits faster and was spread by insects feeding on dead animals, favoring high virulence. However, rabbits developed population immunity, particularly in cool, wet coastal areas where benign caliciviruses provided cross-protection.
Two further calicivirus strains have been released since 1996 to counter this. A non-released calicivirus strain, originating in France in 2010, was detected in Australia in 2015 and is now the dominant strain.
The Need for New Solutions
Heidi Kleinert, national feral rabbit management coordinator, states that new biocontrol agents are ideally needed every 10 to 15 years to maintain low rabbit populations. This is especially critical in peri-urban and urban areas where traditional methods like bait and toxins are restricted.
New biocontrol agents are ideally needed every 10 to 15 years to maintain low rabbit populations, especially in peri-urban and urban areas where traditional methods like bait and toxins are restricted.
Future Biocontrol Research
Scientists are exploring new avenues for rabbit control:
- Gene Drive Technology: Investigating a gene drive that could limit rabbit fertility, potentially by making female offspring infertile or ensuring only male offspring are born.
- New Viruses: Identifying new virus candidates that must meet strict criteria:
- No adverse effects on native or other species.
- Development of vaccines for pet and farmed rabbits.
- Minimization of suffering for infected rabbits.
The development and regulatory approval process for new biocontrols is lengthy. Experts emphasize that biocontrols are suppression tools, not eradication tools, and must be combined with other management strategies like burrow destruction and resource removal to effectively keep populations low.
Experts emphasize that biocontrols are suppression tools, not eradication tools, and must be combined with other management strategies like burrow destruction and resource removal to effectively keep populations low.