The Salvinia Weevil has a fascinating history and is a credit to the ingenuity of Australian scientists. In the 1970s and 80s, Salvinia had developed into a terrible weed both in Australia and internationally. It was responsible for several human deaths where people fell into waterways and could not swim through the thick Salvinia to safety. It had ruined fish stocks, and communities dependent on subsistence fishing were facing starvation and were forced to relocate. The mining industry around Mt Isa was crippled due to Salvinia infestations as they prevented the use of water for industrial cooling and cleaning. Something had to be done.

The distinctive roots and leaves of Salvinia.

The distinctive roots and leaves of Salvinia.

The weed we now know as Salvinia molesta, was initially confused with Salvina auriculata a closely related plant, also native to Brazil. In the 1970s, British scientists working on the Salvinia problem had collected three possible biocontrol agents: a grasshopper, a weevil (Cyrtobagous singularis) and a moth, from Salvinia auriculata. These agents were released into Salvinia infestations in Africa and other locations. When Australian entomologist (and now Land for Wildlife member at Brookfield) Dr Don Sands visited Africa in the early 80s, he saw that this weevil (C. singularis) was causing some leaf damage to Salvinia, but the weed still grew strongly.

Also in the early 1980s, CSIRO scientist, Dr Wendy Forno, travelled to Brazil and was the first scientist to find a wild population of Salvinia molesta growing in its natural habitat. She collected specimens, including potential biocontrol agents, and sent these back for study into quarantine in Australia. When Don returned to Australia, he studied these specimens sent back by Wendy and discovered that there were actually two species of weevil, not just one. The two weevil species had minute morphological differences, but quite important behavioural differences. The new weevil was named Cyrtobagous salviniae by Dr Andrew Calder and Dr Don Sands. This weevil burrowed into the plant tissue of Salvinia and killed the plant, rather than just nibbling the leaf and rhizome edges, as did C. singularis.

These new weevils (C. salviniae) were released by CSIRO at various locations in Australia and internationally, and within several months they appeared to work magic, decimating the Salvinia, causing it to die and sink to the bottom of the waterways. The before and after photos of Lake Moondarra near Mt Isa made the front page of Nature journal (April 1986, 320: 6063). For the discovery, release and success of the Salvinia Weevil, Dr Forno, Dr Sands and a team of CSIRO scientists were awarded the 1985 UNESCO Science Prize.

Article by Deborah Metters based on an interview with Dr Don Sands, CSIRO Honorary Research Fellow

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