The Ultimate Pest-buster?

If asked to name New Zealand’s public enemy number one, the first thing that springs to my mind is our most reviled Australian immigrant – the possum.

European immigrants to NZ tried to introduce these critters not once, but twice (in 1837 & 1858) to establish a fur industry – and then voila, their population exploded.  Now, New Zealand is home to over 70 million possums. In Australia, they’re a protected species.


Each year, pests like possums, rats, stoats and ferrets eat through acres of our native forests & under the cover of darkness perform night raids on our most imperilled species, such as our kokako & kaka.

The bill to save our native species, protect our forests and prevent the spread of bovine TB sits at around 100 million dollars a year.

Probably our most fecund pest- the stoat. Female stoats are pregnant for most of their lives, and can have litters of up to 12 young.

Probably our most fecund pest- the stoat. Female stoats are pregnant for most of their lives, and can have litters of up to 12 young.

The success of these species lies partly in the fact that they sire millions of new offspring each year.

The stoat – our most fecund pest – is a case in point. Males are known to impregnate young stoats at 3-5 weeks of age, at a time when their eyes have yet to open. Before they even leave their nest, young females are often carrying the next generation of stoats (up to twelve in a litter) and will remain pregnant for much of their lives.

Compare this to our critically endangered kakapo: they generally only breed in years when their food supply (rimu) is in abundance, the males don’t reach sexual maturity till 5 years of age and their females only produce broods of three chicks. No wonder kakapo scientists are freezing their sperm.

In order to halt the rampant population growth of our pests, teams of fertility scientists have been studying our pests’ reproductive cycles for the past 20 years, in an attempt to quell their breeding success.

Genetically modified vector hosts, immuno-contraceptive vaccines & injections of hormone-disrupting chemicals are just a handful of the techniques are currently being tested & trialled.

And one such project looks like it has legs  – a menopause-inducing pill is currently being trialled in Indonesia to affect the fertility of rice-paddy dwelling rats.

Currently NZ scientists are in the process of looking into modifying the pill with the American team that developed it so that it works on possums, stoats and ferrets. If successful, it will then be tested on non-target species such as birds, to ensure that it will not affect their reproductive cycle.

The beauty of this particular pill however is its easy distribution. There’s no need to drop the contraceptive repeatedly each year – it could be a one-hit wonder.

And unlike any of the genetic modification techniques trialled, this project will not have to undergo the scrutiny of the anti-GE lobby, so potentially it could be rolled out in a quick smart fashion (read:  a decade).

Of course, there will be the naysayers who say that we’re meddling with nature, but given the rapid developments in fertility treatments in recent years – frozen embryos, pregnant men – feeding our pests with trialled, tested & targeted contraceptives may not seem like such an outlandish idea.

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7 Comments

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  1. July 17, 2009 10:55 am
    Anne says

    Do you have any idea how the vectors are administered? Is it by way of feeding them with laced goodies? Or by releasing surgically-modified (or injected) hosts into the population to breed with the innocent/ignorant wild ones?

  2. July 20, 2009 2:32 pm
    Mandy says

    I don’t know much about vectors, but I imagine they can be introduced in a range of ways.

    A few years back they did a field trial in Kahurangi National Park of a gut worm that was introduced into the possum population down there. The trial was very successful, and the gut worm spread rapidly throughout the population. What scientists would need to do next though, is genetically modify the gut worm so that it is fatal to possums. A hard task given the public opposition to genetic modification

  3. July 21, 2009 3:27 pm
    Sue says

    How things stay the same! I wrote on this subject over 20 years ago in The Veterinarian. My conclusion then was that with budget limitations, the very real risk of vectors undergoing genetic drift over decades that the safest and cheapest way to limit possum breeding would be to install possum-sized condom vending machines in the bush. That though was configured into a cartoon and displayed in DoC offices for a few years.

    Mind you, removal of other mammal species by accidentally sterilising everything would help reduce environmental threats from human overpopulation.

  4. July 22, 2009 1:18 pm
    Mandy says

    Here’s a link to a video that explains how modified worms can be used to affect the fertility of possums –

    http://tiny.cc/31OrG

  5. December 9, 2011 6:23 am
    Pasha says

    What ever specises are almost important part of our natur,so we should protect them ok.

  6. November 2, 2012 10:54 am
    Bill says

    Getting rid of pests in New Zealand is such a huge issue because we have such diverse fauna and flora that we need to take care of.

  7. November 9, 2012 3:31 pm
    Human says

    Have they tested what effects these chemicals have on the animals that prey on these creatures? What would happen to the ” immuno-contraceptive vaccines & injections of hormone-disrupting chemicals” after the animal died and decays?

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