A plague on the pest – rabbit calicivirus disease and biological control
Key text
The accidental release of the rabbit calicivirus from Wardang Island in October 1995 is yet another development in the story of Australia's efforts to control pests.
Biological control is a form of pest control that uses one organism to control the numbers of another (Box 1: Biological control). It is most often used against introduced species that have become pests – most indigenous organisms are kept under control by parasites or predators that have evolved alongside them.
An early recorded attempt at biological control in Australia was the release in the 1890s of three hundred cats. They were released at Eyre, on the coast of the Great Australian Bight, in an attempt to stop rabbits spreading further into Western Australia. Many of the cats starved and the rabbits were hardly affected.
Since then biological control has been successfully used in Australia many times, most commonly for the control of insect pests or weeds. The best known examples are the introduction of the Cactoblastis moth to control prickly pear and the use of the myxoma virus to control rabbit numbers (Box 2: The history of myxoma virus in Australia).
The control agent must be thoroughly investigated before release
Nowadays biologists are required to carry out extensive research before a control organism is released because it is important to find out whether it will attack species other than the pest species. Once a control organism has been selected and found not to be harmful to other species, it is produced in large numbers and released from quarantine. It is then tested in the field and subjected to careful monitoring.
Biological control agents can get out of control
Past attempts at biological control, where the testing was not rigorous enough, have sometimes caused more harm than good. The most famous (or infamous!) example of this is the cane toad. Now a dreadful pest in many areas of northern Australia, the toad was deliberately brought here to control the beetles that were attacking sugar-cane plants in Queensland. It wasn't particularly effective at that job, but it was a great survivor and soon started moving out beyond the canefields, poisoning any birds, mammals or snakes that tried to eat it.
Rabbit calicivirus disease: history
Rabbit calicivirus disease was first noticed by scientists in 1984 when rabbits in China started dying in large numbers. The virus has since spread to Europe and Mexico.
In 1991, the Australian Animal Health Laboratory imported samples of the virus to test at its laboratory in Geelong, Victoria. After three years of testing in many species, there was no evidence that the virus could infect other hosts.
To test the potential effectiveness of the virus in the wild, the Australian and New Zealand Rabbit Calicivirus Disease Program began field trials at a high-security quarantined area on Wardang Island off the coast of South Australia in 1995.
At first the virus spread very slowly in the rabbit population, but when spring arrived it spread much more quickly. In October 1995 the virus escaped from the quarantine area and then spread to the mainland. It moved quickly through South Australia and on to western New South Wales, killing rabbits in its wake. Before long, infected rabbits were found in parts of Victoria, Queensland, New South Wales, the Northern Territory and Western Australia.
Further tests were required before a national release of the calicivirus was permitted in Australia
In April 1996 the Federal Minister for Primary Industries and Energy, John Anderson, announced that before a coordinated national release of rabbit calicivirus could occur, koalas, wombats and echidnas should be tested for possible susceptibility to infection and that there should be further study to confirm there is no effect on humans.
The official release of the virus began in October 1996
At the end of August 1996, the Minister for Primary Industries and Energy announced that the studies had been completed to his satisfaction and recommended a coordinated release of the virus.
By September all State and Territory governments had agreed to the release of the virus. New South Wales was the first State to act, releasing 20 infected rabbits on a property south of Wagga Wagga in October 1996.
Since the release of the virus, scientists have been monitoring the number of rabbits, native plants and animals by taking random samples from a number of areas and then estimating the size of the populations and determining population densities (Box 3: Estimating population size and density). They have seen a dramatic reduction in rabbit numbers, particularly in arid and semi-arid regions of Australia. But in cooler, more humid areas the results have been less spectacular.
This reduction in the rabbit population has allowed the regeneration of many arid-zone shrubs and an increase in the numbers of native animals. In some areas feral fox and cat numbers have also declined as their primary source of food became less abundant.
Rabbit calicivirus disease – a useful biological control
(Posted April 1998)
Boxes
1. Biological control
2. The history of myxoma virus in Australia
3. Estimating population size and density
Related Academy Material
Eureka moments - I'm gonna catch me a rabbit
Nova
Integrated pest management - the good, the bad and the genetically modified
Weeds - the real alien invaders
Is Australian wildlife fair game?
Interviews with Australian Scientists
Professor Frank Fenner (Microbiology and virology)
Dr Yvonne Aitken (Agriculture)
Dr Alec Costin (Land use ecology)
Dr Max Day (Ecology)
Dr Hugh Tyndale-Biscoe (Marsupial biologist)
Public Lectures
Fenner's Science Today and Tomorrow - Myxomatosis and rabbits: biological control and evolution
Dr Peter Kerr, 6 December 2011
Page updated December 2011.