Common weedkiller could make cane toads deadlier

Cane toads could become even more deadly because of their exposure to a common weedkiller.


Scientists in Hungary have found that when toad tadpoles come into contact with the widely used weedkiller Glyphogan, their bodies produce more of the toxic chemicals they use to ward off predators.


The scientists say their findings, published by ‘The Royal Society’ on Wednesday, are particularly relevant to Australia’s cane toad population which they fear could become even more toxic given they live in a wide variety of habitats that are exposed to pollutants and pesticides.

“Our results indicate that pesticide pollution might exacerbate the problem of invasive toxic species,” study author Veronika Bokony, of the Hungarian Academy of Sciences said.

“For example, in Australia, the survival of native tadpoles is reduced by poisoning from ingestion of toxic cane toad eggs, and predators suffer drastic mortality due to ingesting or mouthing cane toads.”

The scientists tested the effects of the glyphosate-based weedkiller Glyphogan on large batches of common tadpoles in a laboratory and a pond at an experiment station near Budapest.

All the tadpoles produced significantly more amounts of bufadienolides – the toxic steroids used by toads, fireflies, some snakes and plants to poison or deter predators – after being exposed to Glyphogan for between nine days and three weeks.

The scientists said that if toads become more toxic, their predators may switch to other more palatable prey, posing an even greater threat to other animals.

Cane toads store toxins containing bufadienolides in glands on their shoulders, using them to deliver a poisonous blast that can cause heart convulsions or death for predators.

The cane toads have had a huge impact on native animals since arriving from Hawaii in 1935 and spreading across most of northern Australia.

Northern quoll populations were devastated by the toad, whose poison also has been known to kill freshwater crocodiles, snakes and goannas.

Cane toad expert professor Rick Shine, of the University of Sydney, says the new research adds to a growing body of evidence showing how toads develop their defensive chemical “weapons” in reaction to their experiences.

But he says while weedkiller can increase the amount of poison in a toad, it might not necessarily mean the cane toad will have an even greater ecological impact in Australia.

“Most native predators in areas where cane toads live have already learned that toads are deadly, and don’t eat them – or can tolerate the poison, and thus are not at risk no matter how much the toad ramps up its poison content,” he said.

The Hungarian scientists have called for more studies to be done on how environmental contaminants like weedkillers affect the chemical defences in bufadienolides.