Australia's most unwelcome guest
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This is not the first time that Australia has tried to thwart the toads' spread. In the mid-1980s, the government financed an effort to search for diseases that could be introduced to control the toads, as it did for rabbits. But James Cook University's Alford notes that the money ran out before the program could bear fruit.
Now, the government is talking in terms of spending between $5 million and $7 million over 15 years to deal with cane toads, he adds. Last year, Australia established a National Cane Toad Task Force. And it has sponsored a design contest that aims to develop a trap that catches toads with less "by-catch."
At this stage, cane-toad control efforts are largely local, with individuals or groups of volunteers hunting them and killing them immediately or freezing them to death.
The Northern Territory has established an Island Ark program to save ecologically critical species such as cat-like quolls from cane toads by moving the quolls to nearby islands.
Meanwhile, researchers are exploring several other approaches to controlling the amphibious pests.
Over the long term, scientists with Australia's Commonwealth Scientific and Industrial Research Organization are looking for genetic approaches to cane-toad control. One approach might be to infect cane-toad tadpoles with designer viruses that immunize them against a protein their bodies make when they become adults. As they mature and make the protein, their immune systems kick in and attack the protein, which would kill the toads. In addition, teams are looking for diseases in other toad species that they can enlist against cane toads.
Alford's group is working on approaches that may have payoffs in the short term. The strategy is to fool a toad's nose and attract it to a trap or poison.
He notes that only within the past few years have scientists realized that frogs and toads have a sense of smell and use it to find food and, presumably, mates. Previously, they were thought to use sight alone.
Alford suggests that the right scent could bring the toads to the traps more efficiently, where they could dine on bait laced with poison or a tailored virus. The ultimate would be a dab of something "that would cause toads to drop what they are doing and shoot hundreds of meters" to the waiting trap, he says. But for now, he'll be happy with identifying the right scents to use.
The World Conservation Union has listed 100 of the world's worst invasive species. Among them:
• Crazy ants: Their native origin is unknown, but their impact has been felt from Hawaii to Zanzibar. On Christmas Island in the Indian Ocean, they've damaged the rain forest canopy, decimated a key native crab, and could drive an endangered bird from its only known home.
• Brown tree snakes: Originally from Oceania, they've bitten people, caused major power outages, and nearly exterminated the native forest birds of Guam. The snake has reached the mainland United States and Spain.
• Caulerpa seaweed: Introduced to the Mediterranean some 20 years ago, this tropical plant has smothered underwater habitats and threatens native marine flora and fauna.
• Feral pigs: Found throughout much of the world, they damage crops, dig up large areas of native vegetation, and spread weeds. They also eat turtles, seabirds, and reptiles.
