Australia's rabbits face a major blow with confirmation from CSIRO scientists that at least ten species of insects are now capable of spreading the Rabbit Calicivirus (RCV) among wild rabbit populations.

Rabbits are estimated to cost the national economy $600 million a year, as well as doing untold environmental damage.

Dr Brian Cooke, of CSIRO's Division of Wildlife and Ecology, says research has established there is a good suite of insects able to carry the virus: "We have found the virus on seven species of fly, two kinds of mosquitoes and most recently European rabbit fleas collected in the field."

The finding comes on the heels of a report from the national RCD Management Group which found increasing evidence that the disease is taking effect in many parts of Australia, and that large areas of native bush are on the comeback.

The report found there had been declines of more than 65 per cent in rabbit numbers at sites in arid and semi-arid regions of South Australia, Western Australia, Victoria, New South Wales and Tasmania, with no sign of recovery so far. Declines at sites high rainfall areas of NSW have been much smaller.

With insects likely to be an important factor in spreading the virus between rabbit populations, scientists anticipate an increase in the rate of spread as the weather warms up and insects become more active.

"We have noticed that the optimum conditions are around 24 degrees," Dr Cooke says. "We think that, below 15 degrees, the virus won't spread very well. This points to insects being the chief vectors. If it spread mainly rabbit-to-rabbit, then you'd expect to see it spread faster in winter when the virus survives best."

The patchy spread of RCD has a strong historical echo: more than 40 years ago when myxoma virus was released, it had limited effect for months to begin with ­ then suddenly began to spread like wildfire. Again, insects were shown to be a key factor.

However, like myxoma and other biological controls, Dr Cooke emphasises that RCD is not a "magic bullet" solution to Australia's rabbit problem. Landholders, National Parks' officers and pest control authorities will have to persist with conventional methods of control in order to reap the maximum benefits.

Meantime, the new insights into how RCD moves around will help scientists to fine-tune its management. "If we want to spread the virus effectively, we need to know the vectors, their range, their peak times and other factors that affect them. That is what this research will tell us," Dr Cooke said.

Dr Cooke will describe his research results at a meeting of the Anti-Rabbit Research Foundation of Australia in Adelaide on Tuesday, September 23, 1997.

More information
Dr Brian Cooke, CSIRO Wildlife and Ecology 02 6242 1517
Dr Tony Robinson, CSIRO Wildlife & Ecology 02 6242 1676