KEY POINTS:
Infestations of rabbits on the outskirts of towns in many parts of New Zealand will be targeted with the rabbit calicivirus (RCV), which is being trialled as a new means of selective rabbit control this winter.
A consortium of the country's regional councils, led by Environment Southland, has imported the virus from an Australian laboratory.
Strict protocols for the use of RCV have been agreed between the regional councils, the Environmental Risk Management Authority and the Ministry of Agriculture last year.
The imported virus is the same as the strain circulating in the New Zealand rabbit population, after being illegally released in 1997. The virus will not be available for private use.
Environment Southland biosecurity manager Richard Bowman said the virus was not a "silver bullet" that would wipe out rabbit numbers.
Landowners would need to continue present measures to control rabbits, he said.
The idea was that rabbits would eat the infected bait and die rather than pass the virus on to other rabbits.
He said the calicivirus would be used as a biocide in areas which were close to population centres or in high public use areas, because conventional control measures such as shooting and poisoning could not be used there.
Its use would be restricted to June and July, when the number of young rabbits was at its lowest, before the spring breeding season.
This was to meet concerns at some councils, such as Otago Regional Council, that the virus should not be allowed to start uncontrolled epidemics of rabbit haemorrhagic disease in the wild, and potentially upset a cycle of natural epidemics of the "wild" virus.
Council staff would even have to collect uneaten baits to avoid the possibility of the virus breaking down in sunlight and degrading to a weakened form which would simply immunise rabbits.
"Attempts to start epidemics artificially can have the effect in stimulating immunity among the rabbit population and this reduces its effectiveness as a control tool," Bowman said.
The winter use would limit the potential to build resistance in baby rabbits - which may gain immunity if exposed to the virus in the first weeks of life - and would attract rabbits when they were short of food.
Bowman said the virus should be useful in places where conventional rabbit control measures such as shooting and poisoning were not practical, but would not be used in rural areas.
Some farmers in Central Otago, the most rabbit-prone region, have recently complained of the pest's numbers reaching "quite alarming" levels and called for a new wave of rabbit haemorrhagic disease to be spread into the wild.
But the Otago Regional Council has said there is no scientific evidence that fresh batches of the disease would kill more effectively than the entrenched strain.
- NZPA
