Wading through Paraguayan wetlands last year, the CSIRO scientist Raghu Sathyamurthy was on the lookout for an aquatic plant called cabomba. Or more specifically, for the eggs and larvae of a tiny weevil known to feast on this underwater weed.

Cabomba isn’t particularly conspicuous in the wetlands around Asunción, but back in Australia, it’s choking waterways along the east coast and is one of 32 weeds classed as nationally significant.

It has spread around the globe, thanks mainly to the aquarium industry, and causes big problems wherever it takes hold – clogging watercourses and invading reservoirs. “It forms an underwater carpet so nothing else can grow and it blocks the light that should be getting to other species,” says Sathyamurthy.

Today he is back in the labs and rooftop greenhouses in CSIRO’s Ecosciences precinct in Brisbane. Here, a weevil colony is being maintained behind two-centimetre thick glass inside a double-air locked quarantine laboratory. Inside, scientists are testing the tiny weevil as a possible “biocontrol agent” that could be released into waterways to keep cabomba in check.

They are also testing the weevil’s impact on related native Australian plants. “If the weevil feeds on other Australian plants, then we’d stop right there, because it would present a risk,” says Sathyamurthy.

It is one of the latest examples of a continuing CSIRO strategy to manage invasive species using foreign bugs.

One of the earliest biocontrol success stories – and one that has taken on legendary status – is that of the invasive prickly pear cactus. By 1920, it had infested 24m hectares, mostly in Queensland. Bulldozing, burning, crushing and the use of a highly toxic chemical did little to halt its rapid spread.

The invasive species cabomba is being grown in tanks at CSIRO in Brisbane. Photograph: CSIRO

But a joint program between the commonwealth and the Queensland and New South Wales governments marked a turn of fortunes. Between 1927 and 1931, more than 2bn cactoblastis moth eggs were released. By 1932, the cactus was in retreat, enabling almost 7m hectares of previously infested land to go to settlers.

These days, identifying foreign bugs for biocontrol and then carrying out the testing can take several years, sometimes a decade or more, says Sathyamurthy. More than a dozen invasive weeds are being worked on at the CSIRO facility.

It is also collaborating with US government scientists on native Australian plants that have become pests across the Pacific, such as the earleaf acacia that is causing problems in Florida’s Everglades.

A bright green native Australian beetle with a distinctive red stripe on its back is being tested as a possible agent for release in Florida, where the fast-growing acacia is managing to outcompete native species in southern areas.

In another greenhouse, Sathyamurthy is surrounded by another “weed of national significance” called Parkinsonia – a prickly bush that is well-established in Queensland, the Northern Territory and parts of Western Australia, and that gets in the way of livestock accessing water and outcompetes native species.

After four years of testing and then government approvals, CSIRO released millions of larvae of the Eueupithecia moth – known at CSIRO as UU – two years ago at affected sites. While it’s too early to be sure of the success, Sathyamurthy says the moths are surviving and will now be stripping the leaves off the weeds, holding back their progress.

A common response when the public hears about biocontrol programs, says Sathyamurthy, is to point to one introduction that went badly wrong – the cane toad.

Cane toads were deliberately introduced in Queensland in 1935 by the state government’s Bureau of Sugar Experiment Stations – a group set up to support the industry and part-financed by a levy paid by growers – to help the industry deal with cane beetles attacking sugar cane roots.

No tests were carried out beforehand to find out what impact the toad might have on the environment, or even if it would actually eat the beetles. The release was enthusiastically supported by the industry, despite some early warnings.

Sathyamurthy says: “It’s always a relevant question, but if cane toads had gone through this process then it would have been cut off at the first hurdle. The sugar cane industry just went ahead.

“We’re incredibly cognisant of the risks of getting this wrong. We want a safe fix and we’re incredibly mindful of what we do.”

One review of all 512 known global releases of biocontrol agents found that only four had significant adverse impacts on species away from their targets.

Two major impacts from releases in 1969 and 1974 came, the study said, when biosafety standards were lower than today.

While biocontrol agents can never totally wipe out invasive weeds, Sathyamurthy believes they can offer a long-lasting remedy to stop them from becoming a problem. He claims that for every $1 invested in biocontrol, “we think we get about $23 back in productivity gains”.

Other control methods, such as burning, chemical spraying or simple bulldozing, can be costly, and in some cases, seeds of invasives can survive in the soil for decades. In and around Brisbane, the regional water authority Seqwater spends about $170,000 a year on commercial divers who manually remove cabomba.

“In rangelands, you can go and just bulldoze a huge patch of weeds, and that does happen. For other weeds, you can spray them or put fire through them - and all those control tactics have costs and benefits,” Sathyamurthy says.

“If you find a safe biocontrol agent, then it becomes a part of the natural environment and remains a pest for the weed, and then natives can compete with them.”