SYDNEY MORNING HERALD (Australia) 22 November 06 The good behind the bad and the ugly (Richard Macey)

There may be a surprise silver lining to the cane toad's relentless march across Australia.

Research suggests cane toads may be an ally in the war against another pest, the mosquito.

Rick Shine, from the University of Sydney's School of Biological Science, has studied cane toads for more than five years as they approached, then occupied, Fogg Dam, in the Northern Territory.

In 2002 his team was awarded almost $1 million by the Australian Research Council to study the invader's impact.

Professor Shine said yesterday there was evidence Australia's native wildlife was evolving, or at least learning to cope with the invader. And the toad could even offer benefits for human health.

His team found that mosquito larvae laid in water containing toad tadpoles produced insects much smaller than normal. This was important because smaller mosquitoes were thought to be less able to spread disease.

Exposure to toad tadpoles also reduced significantly the survival rates of one Sydney mosquito species. It was was not clear why. Being herbivorous, tadpoles do not eat the larvae.

Professor Shine speculated tadpoles might carry "some nasty fungus-type organism" in their droppings. Maybe their endless swimming stirred the water, causing the mosquito's food to sink beyond reach. Or the larvae could not cope with swimming tadpoles banging into them.

Water bowls, some containing cane toad tadpoles and some with no tadpoles, were placed in the open at Fogg Dam. The scientists found that mosquitoes seeking places to lay eggs steered away from the bowls with tadpoles.

Publishing their findings in the journal Biological Invasions, Professor Shine and PhD student, Mattias Hagman noted: "It is ironic that our study [the first on cane toad impacts to involve field experimentation] reveals an effect that most people would perceive as positive rather than negative."

Professor Shine said that while toads had been a disaster for quolls, goannas and death adders around Fogg Dam "no species is known to have gone extinct … We may not see a massive ecological disaster".
The good behind the bad and the ugly

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