Cane toad: a case study
©CSIRO Australia
Cane toads were deliberately released at Gordonvale in Queensland in 1935 in an attempt to control French's cane beetle and the greyback cane beetle in sugarcane fields.
The cane toad was unsuccessful in controlling the cane beetles; instead, it flourished in Queensland's warm environment, spreading rapidly south and west. By 2001, it had reached the wetlands of Kakadu National Park. By 2005, they had spread across the Northern Territory and into southern New South Wales. Scientists predict that in the future, they will reach around the coast of Western Austrlaia and down into Victoria and South Australia.
lthough not officially recognised as a pest by all Australian states, evidence suggests that cane toads have adverse environmental impacts, and they are considered a threat to biodiversity for a number of reasons:
- They exude and can squirt deadly poison from the parotoid glands on their shoulders when threatened or handled. Freshwater crocodiles, goannas, tiger snakes, dingos, northern quolls and pet dogs have all died after eating cane toads.
- They may 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.
- They occupy holes and hollows used by native animals for nesting or hiding from predators.
- They can carry diseases that could be transmitted to native frogs and fish.
©CSIRO Australia
Conventional control methods concentrate on vehicle quarantine checks, public involvement in 'toad hunts' and education. But these have not been effective in stopping the spread of cane toads.
For many years, scientists have looked for different ways to control the cane toad.Naturally occurring, cane-toad specific biological control agents have not been found.
CSIRO researchers are using gene technology to try and find an effective biocontrol method that stops tadpoles developing (metamorphosing) into adults.
If they can identify a cane toad gene critical to metamorphosis, and use it to ‘immunise' toads at the tadpole stage, the tadpole would see the protein as foreign and mount an immune response to it. This would interrupt development and prevent the tadpoles growing into adults.
Scientists are also researching viruses to deliver the gene to the cane toad population. They are looking at a toad-specific combination of virus and gene to make sure 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 by the virus itself.
The researchers have established a cane toad breeding colony, which provides all the life stages necessary for the work. Several cane toad genes are being tested for their ability to interfere with the metamorphic process.
As with all research, possible risks 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 cane toad research at: http://www.csiro.au/science/CaneToadResearch.html