Biological Weapons To Control Cane Toad Invasion In Australia

Professor Rick Shine from the University of Sydney has been studying the biology of cane toads, and will reveal his new research May 7 at the Academy of Science's peak annual event Science at the Shine Dome.

He says that controlling toads has been difficult as things that kill them will often kill frogs. Professor Shine and his team studied cane toads in Queensland that lagged behind the invasion front and found they were infected with a lungworm parasite which slows down adults and, in laboratory tests, kills around 30% of baby toads.

It was originally thought cane toads left their parasites behind when they came to Australia and that the lungworm parasite came from Australian frogs. This ruled out using the parasite for toad control due to potential frog impacts. However, DNA sequencing by Professor Shine's team has shown the parasite species came from the Amazon and is genetically different to those found in Australian frogs.

'The toads have brought with them a parasite that kills them and that doesn't attack Australian frogs, so this is a phenomenal opportunity for biological control' he said.

Professor Shine's team have also discovered pheromones used to communicate danger between toad tadpoles that have significant impacts on their size and survival. The 'alarm pheromones' are released into a pond when a tadpole is frightened or injured and warns other toad tadpoles to flee the area.

The signal stresses the toad tadpoles so much that in field trials around half of them died before they became adult toads, and those that become adults were half the size they should've been. The pheromones were also found to be different to those of Australian frogs and didn't affect them.

Using the lungworm parasite and the alarm pheromone together would be particularly powerful as the pheromone either kills or produces smaller 'toadlets', and the parasite is more effective at killing these smaller sized toads.

'...the combination of those two things start to suggest, I think, a pretty straightforward, pretty low risk, but probably pretty effective way to start controlling toads.'

Attractant pheromones have also been found by his team which can be used to lure toad tadpoles for catching and removal.

Professor Shine hopes to involve community groups in the use of these new control methods. He says that although there has been a huge effort to slow the toad front by communities in Western Australia and the Northern Territory, the toad front is progressing as fast as ever.

'We've got the toads moving across Australia faster and faster. They're widely seen as a major problem. In community surveys they're identified by many people as the worst invasive species we have.'

Previous methods for controlling cane toad numbers have included traps and fences but have mainly involved physically removing them from the environment, often by putting them in a plastic bag in the freezer.

'People have spent certainly well over $15 million on cane toads in Australia on research and control. Very little of that has actually been devoted to try to understand what toads are doing. Now that we've done that, it does seem that there are really encouraging avenues.

'By doing the detailed ecology and actually finding out about communication systems and where the parasite came from and things like this, we've got new ways to attack toads that haven't been thought of before'.

He says the main impact of the toad invasion has been on large predators such as goannas, quolls, king brown snakes and death adders. 'We've had, for example, probably 90% mortality of the big goannas and the big lizards in our study site. Its dramatic, and that has all sorts of flow on effects. You take out 90% of the big predators and that really changes the system.'

Professor Shine will present his work as winner of the Academy's Macfarlane Burnet Medal and Lecture at 9:30am Wednesday 9 May. Of the win he says: 'Its fantastic. Its one of these accolades from your peers that come along very rarely in any career and I'm just as excited as hell to be have been the fortunate recipient.'

Science at the Shine Dome is the Academy's annual celebration of science and runs from 7–9 May 2008 at the Shine Dome in Canberra.