We’ve released tiny weed-chomping weevils, smaller than a grain of rice, in Queensland. The weevils have travelled from South America to stop the spread of cabomba, a weed choking our waterways.
Cabomba weed goes wild
Cabomba (Cabomba caroliniana) is a fast-spreading freshwater weed from South America. It reduces water quality, strangles ecosystems and is harmful to aquatic plants and animals.
The weed was originally introduced to Australia as an aquarium plant sold by aquariums and nurseries. It was either deliberately released into freshwater bodies for commercial purposes, or possibly dumped there. Fortunately, all states and territories have now banned its sale and distribution.
It is highly invasive Weevil imports, quarantine and testing
We’re working with one of our country’s largest water asset managers, Seqwater. We’ve imported an army of cabomba weevils (Hydrotimetes natans) from South America to help rid our waterways of cabomba weed. The weevils feed and develop exclusively on cabomba. They spend their entire life on the weed, making these tiny insects the ideal biological control tool.
The weevils have quarantined in our labs. To confirm they won’t damage our native plants, we’ve exposed the weevils to 17 native species over a 150-day period. This is enough time to produce three generations of weevils. Significantly, the weevils showed no interest in our native plants and continued to only eat the cabomba weed.
These tests were part of extensive research undertaken in South America and Australia which showed the weevils are not a risk to other species.
Hope for our waterways
Lake Kurwongbah and a dam on a private property, north of Brisbane, were the sites for the first trial weevil releases in December 2022. Since then, there have been further releases at multiple sites in Queensland, New South Wales and most recently at Lake Benalla in Victoria.
Preliminary observations show the weevils are having a positive impact at these sites.