Cane toad: a case study
©CSIRO Australia
Another animal introduced to Australia is the cane toad. It was deliberately released at Gordonvale in Queensland in 1935 in an attempt to control French’s Cane Beetle and the Greyback Cane Beetle in sugarcane.
It was unsuccessful in controlling the cane beetles. Instead, it flourished in Queensland’s warm environment, spreading rapidly south and west. By March 2001 it had reached the wetlands of Kakadu National Park, and one isolated community was recently discovered as far south as Port Macquarie in New South Wales.
Although not officially recognised as a pest by all Australian states, there is evidence to suggest that there are environmental impacts of cane toads in the areas they inhabit and they are considered a threat to biodiversity for a number of reasons:
- Cane toads exude and can squirt poison from the parotoid glands on their shoulders when threatened or handled. This toxin contains a cocktail of chemicals that can kill animals that eat it. Freshwater crocodiles, goannas, tiger snakes, dingos and northern quolls have all died after eating cane toads, as have pet dogs.
- Cane toads are likely to compete with native animals for food. Cane toads eat mainly insects, including honey bees, but will eat any small creature that fits in their mouth.
- Cane toads occupy holes and hollows used by native animals for nesting or hiding from predators.
- Cane toads are capable of carrying diseases that could be transmitted to native frogs and fishes.
©CSIRO Australia
Current conventional control methods against cane toads concentrate mainly on quarantine checks of vehicles, public involvement in 'toad hunts' and education. But these have not been effective in stopping the cane toad spreading.
For many years, scientists have looked for different ways to control the cane toad, but have been unsuccessful to date. Naturally occurring, cane-toad specific biological control agents have not been found. Current research conducted by CSIRO is using gene technology to try and find a biocontrol method.
Researchers are now looking at how to stop tadpoles developing (metamorphosing) into adults meaning they cannot mature and cannot reproduce.
They are hoping to identify a cane toad gene critical to toad metamorphosis. If that gene product is used to immunise can toads at the tadpole stage, the tadpole would see the protein as foreign and mount an immune response to it. This would interrupt toad development.
Scientists are also looking at viruses to deliver the gene to the cane toad population. They are looking at a combination of virus and gene to be specific to cane toads so it does not affect native frogs and toads. They also want to make sure the toad is responding to the gene or protein produced by the gene rather than the virus itself.
As with all research, there are possible risks which need to be determined and managed before any biological control agents are released into the environment. Even if all research goes to plan, it could still take up to ten years before a product is available to control the march of cane toads.
Read about CSIRO’s can toad research at: http://www.csiro.au/index.asp?type=faq&id=CaneToadControl and their virus control program at: http://www.csiro.au/index.asp?type=featureArticle&id=CaneToadMarch
Meanwhile, traditional methods are still being encouraged. The Northern Territory Government, for example, has contributed to controlling cane toad populations by running The Great Cane Toad Trap Competition.
Read more about the competition: http://www.ipe.nt.gov.au/haveyoursay/canetoadtrap/