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Further tests on possum contraceptive bait

Media Release - April 9, 2001

Approval granted for further tests on possum contraceptive bait

Photo: New Zealand has about 70 million hungry possums and their impact on our native flora and fauna can be devastating. Landcare Research has been given the go-ahead to progress with an important new method to reduce possum numbers.

Landcare Research has been granted an approval by the Environmental Risk Management Authority (ERMA) to import genetically modified carrots and potatoes into containment in New Zealand, for feeding trials with possums.

This is the next step towards development of baits that work as birth control for possums. It follows a successful feeding trial last year where Landcare Research and Marsupial Cooperative Research Centre scientists tested genetically modified potatoes. They confirmed that plants producing foreign proteins are a good system for delivering a fertility control vaccine for possums in a bait. The potatoes were grown by the Boyce Thompson Institute for Plant Research in the United States, a world leader in developing plant-based vaccines for humans.

The next trial, due to start in May to coincide with the possum breeding season, will involve feeding possums carrots or potatoes that contain a protein called possum ZP3, from the coating of the female possum's eggs. Scientists believe that feeding possums these plants will cause the possums' immune system to make antibodies against the eggs and prevent successful breeding. This birth control method is called immunocontraception, as possums are essentially immunised against conceiving.

The feeding trial will be carried out in containment under strict controls required by ERMA and MAF. Possums will be fed three small doses of the carrots or potatoes over a 21 day period. Their immune responses will be measured by analysis of blood samples and effects on fertility will be assessed by a breeding trial in captivity under containment conditions.

The successful development of immunocontraception should be a useful and humane addition to current possum control measures, which depend largely on poisons. "Using contraceptive baits will slow the rate at which possum populations rebuild after poisoning" says Landcare Research scientist Dr Phil Cowan, who leads the programme. "This means control will be needed less frequently, resulting in less environmental contamination, and reduced risk to non-target species".

"It is important that people appreciate that ultimately the plants will be processed into baits, so that they cannot grow or spread genetic material to other plants. Also, by using parts of the possum protein that are specific to marsupials, we believe we can reduce any risk to other animals " Dr Cowan said.

"The forthcoming feeding trial is a key one for the research programme. It will be the first time we have tested a product that we hope will reduce possum breeding, in a system that can be developed for practical use in the field."

Landcare Research's chief executive, Dr Andy Pearce, says he is delighted that the research in this area can proceed. "We need to use new methods to help reduce the large possum population, rather than relying exclusively on shooting and poisoning methods, which have not been effective enough".

The Landcare Research and Marsupial CRC research team aims to have a prototype bait for limited experimental testing in the field by 2005, and a product for more general use by 2011.


For more information, contact:

Dr Phil Cowan Programme Leader, Landcare Research Ph: (06) 350 3806 Fax: (06) 355 9230 e-mail:

Dr Janine Duckworth Possum Biocontrol Scientist Ph: (03) 325 6700 x 2279 Fax: (03) 325 2418 e-mail:

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