The CSIRO and Seqwater are employing a tiny defender – a weevil the size of a grain of rice – to help stop cabomba weed from spreading through Australia’s waterways.
Cabomba (Cabomba caroliniana) is a South American aquatic weed that, if not controlled, has the potential to take over many of Australia’s waterways.
According to the CSIRO, scientists have introduced the cabomba weevil (Hydrotimetes natans) into Lake Kurwongbah, a water asset administered by Seqwater north of Brisbane, after years of rigorous research in South America and Australia. This is the first time a biocontrol agent against Cabomba has been released anywhere in the world.
CSIRO scientist Dr Kumaran Nagalingam stated that cabomba was first brought to Australia in 1967 as an aquarium plant, and it has since expanded from Cairns to Melbourne along the country’s east coast.
“Cabomba grows up to 5cm a day, strangling native ecosystems, choking waterways and impacting native aquatic animal and plant populations,” Dr Nagalingam said.
Dr Nagalingam added that the researchers also know there are fewer platypus in northern Queensland’s cabomba-infested creeks than in uninfested ones.
“Our research in South America shows that the cabomba weevil spends its entire life feeding only on cabomba, and extensive research in Australian quarantine has confirmed the cabomba weevil is not a risk to native plant species,” he stated.
The cabomba weevil was tested on 17 Australian plant species closely related to cabomba as prospective feeding sources for the weevil. Three generations of weevils were fed native plant species during their whole life cycle. According to CSIRO, the weevils avoided the Australian plants and only ate cabomba.
Seqwater Senior Research Scientist Dr David Roberts recalls the long and challenging road that led to this point.
“It has been 19 years since Seqwater supported the first efforts to find a biocontrol agent for cabomba in its home country of Argentina. It is great to finally see a successful control agent that is ready for use in south-east Queensland to halt the ongoing spread of this costly weed,” Dr Roberts said.
Dr Roberts stated that cabomba grows in dense clumps, reducing light and water quality. Since the weed is so dense, according to Dr Roberts, recreational activities like swimming, fishing, and canoeing are difficult and dangerous.
“The weed also reduces the water holding capacity of dams and significantly adds to the cost of treating drinking water,” he added.
Every cabomba weevil was screened for hitchhikers in the form of parasites or pathogens before leaving quarantine, in accordance with Department of Agriculture, Fisheries, and Forestry standards. The weevils were then mass-reared in glasshouses until there were enough for a successful field release.
Seqwater, in consultation with CSIRO, has created a weevil nursery near Lake Kurwongbah. More weevils are being raised here in preparation for the discharge of this promising biocontrol agent into other South East Queensland lakes with cabomba weed infestations in the future.
Biological control is a long-term, successful, low-cost technique for controlling pests like cabomba. Mechanical treatments can be excessively expensive and only function in the short term, allowing the weed to regrow quickly. Seqwater spends roughly $170,000 annually manually removing cabomba from only three of its lakes.
Further weevil releases are planned for Lake MacDonald, near Noosa. The CSIRO is also looking into releases in central Queensland, northern New South Wales, and maybe the Northern Territory.
The following projects were led by AgriFutures Australia as part of this research: ‘Biocontrol solutions for sustainable management of weed impacts on agricultural profitability’ (2016-2020) and ‘Underpinning agricultural productivity and biosecurity by weed biological control’ (2019-2022). The Australian Government Department of Agriculture, Fisheries, and Forestry is funding this study through the Rural R&D for Profit initiative, with Seqwater contributing.
