Scientists Release Ancient Enemy To Control Invasive Weed in 'World First'

Scientists in Australia are hoping to combat an invasive water weed by releasing an army of weevils, the plant's natural enemy.

Researchers from Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO) have teamed up with one of the nation's largest water companies, Seqwater, to release the diddy defenders to keep the spread of the invasive cabomba plant in check.

"It is a world first," said Kumaran Nagalingam, senior research scientist at CSIRO, in a statement. "There is no biocontrol program [for cabomba] happening in any other parts of the world."

Cabomba weevil on plant
Photo of a cabomba weevil on the stem of a cabomba plant. Cabomba is a fast-growing weed that has become an invasive species in Australia. CSIRO

Cabomba, Cabomba caroliniana, is a fast-spreading weed that was brought over to Australia from South America in the 1960s. "Unfortunately it was such a pretty plant that it was brought into the county as an aquarium plant and somehow escaped aquariums and got into our waterways," David Roberts, a senior scientist with Seqwater, said in a statement.

Cabomba might look fetching in a fish tank, but once it gets into the wild it can cause havoc on the native plants and animals.

"It outcompetes all of our native plants that used to live in the lakes and it can affect animals as well because they don't like to live in such a dense plant material," Roberts said.

"Cabomba grows up to 5cm [nearly 2 inches] a day, strangling native ecosystems, choking waterways and impacting native aquatic animal and plant populations," added Nagalingam.

The weed also blocks inlets and piping and poses a threat to boaters and swimmers, who can get tangled up in its tendrils.

Diver covered in cabomba
Photo of a diver emerging from a cabomba infestation. The plant can pose a risk to swimmers and boaters who get tangled in its tendrils. CSIRO

For over 20 years, the research team has been searching for the plant's natural enemies in its native habitat, Argentina. "Cabomba has quite a few natural enemies associated with it, but one thing that we have to make sure is that they are specific only to cabomba—it doesn't eat or double up on other native plants," Nagalingam said.

Eventually, they settled on the cabomba weevil, a creature smaller than a grain of rice. The weevil targets the plant throughout different stages of its life cycle: the larvae tunnel deep into the plant's stems while the adults feed on the plant's leaves.

While the researchers do not expect the weevils to completely eradicate the cabomba, they will hopefully reduce the plant's thickness and size and keep its growth in check. This avoids having to use harsh chemicals and expensive manual weed removal to keep the lakes clean and healthy. Seqwater said it cost about $170,000 a year to manually remove cabomba from three lakes.

To avoid accidentally releasing any unknown diseases into the water, the imported weevils were quarantined and carefully inspected for any parasitic hitchhikers before being released.

They will be trialed in Lake Kurwongbah, near Brisbane, Queensland, before being released in other lakes around the country. Seqwater will continue to rear the tiny soldiers in a purpose-built "weevil nursery" for future potential releases.