THE explosion in New Zealand’s possum populations could be reined in by
sterilising the female possums with genetically modified carrots. Scientists who
developed the carrots say they are a humane and environmentally sound
alternative to managing wildlife with poisons or viruses.
Settlers introduced possums to New Zealand for fur farming a century ago. But
there are now 60 million possums in the country. The animals have become a
formidable pest, chewing their way through 20 000 tonnes of foliage a night,
gorging themselves on birds’ eggs and spreading bovine tuberculosis.
The traditional way of controlling the animals has been to scatter carrots
laced with poison. But now scientists at the Marsupial Cooperative Research
Centre (MCRC) based in Sydney have created a genetically modified carrot
designed to sterilise females. They hope this could bring possums under
control.
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John Rodger and his colleagues engineered the carrots to contain a protein
that sabotages fertilisation by binding to a key protein in the coating on
possums’ eggs. He described the technique last week at a meeting on marsupial
control in Akaroa, New Zealand. First the team engineered a common soil
bacterium, Agrobacterium tumefaciens, to produce loops of DNA, or
plasmids, that contained the gene for the sabotage protein. Then they smuggled
the plasmids into carrot plant cells.
The transgenic carrots are growing at the Boyce Thompson Institute for Plant
Research in Ithaca, New York. Once fully grown, they will be flown to New
Zealand for testing on possums in captivity. Rodger says that tests showed the
sabotage proteins survive in possums’ digestive systems.
Experts warned that the plan should only go ahead after thorough analysis of
the carrots’ effects. “It needs to be carefully investigated in laboratories
before they release it into the wild,” says Diana Bell, who studies rabbit
populations at the University of East Anglia. The main risk is that the carrots
may sterilise other animals.
Rodger agrees, and says that they expect to have to tinker with the carrot
before they’re sure that it only targets introduced marsupials like possums.
“What we’re aiming for is something that will pose the minimum risk,” he says.
“Current poison technology uses a non-specific agent—I am confident we can
do much better.”
If the GM carrots go into widespread use, scientists would have to show they
don’t harm the environment. “New Zealand has considerable knowledge about safe
use of carrot in small pieces that do not regenerate in the wild,” says Rodger.