Australia is using an imported insect to control an imported weed
What do you do if a South American weed is choking up your local Australian waterways? In the case of the cabomba plant, scientists are enlisting the help of the weed's natural South American enemy, the tiny cabomba weevil.
Cabomba (Cabomba caroliniana) originally came to Australia in 1967 as an aquarium plant, and has since spread throughout lakes and rivers along the country's east coast. It grows up to 5 cm (2 in) per day, forming clumps that displace local flora and fauna, block sunlight from reaching lower depths, add to the cost of water treatment, and make boating or other recreational activities difficult if not impossible.
Large quantities of the weed are currently removed from water bodies by mechanical means, although doing so is an expensive and laborious process, plus the plant quickly grows back to problematic levels. With these limitations in mind, scientists from the Australian national science agency CSIRO looked to the cabomba weevil (Hydrotimetes natans).
Native to several South American countries, the aquatic insect is only about the size of a grain of rice, and takes its name from the fact that it feeds on nothing but the cabomba plant.
That said, in order to be on the safe side, the CSIRO scientists raised three generations of the weevils in captivity, offering them 17 Australian aquatic plants that are closely related to cabomba. The weevils showed no interest in those other plants, choosing to feed only on cabomba throughout their whole lives.
An imported batch of the weevils were initially kept in quarantine, and individually inspected for parasites and pathogens. Having passed that inspection, they were then bred in captivity, producing a population that was recently released into the cabomba-infested Lake Kurwongbah, north of Brisbane.
Time will now tell how effective the insects are at controlling the weed. In the meantime, more of the weevils are being bred for use in other lakes.
The project is funded by water company Seqwater, and by the Australian Government Department of Agriculture, Fisheries and Forestry. Leading the research are CSIRO's Dr. Kumaran Nagalingam and Seqwater's Dr. David Roberts.