Water Hyacinth – biological solutions

water hyacinth image from http://biology.missouristate.edu/Water Hyacinth (Eichhornia crassipes) infestations around the world have caused environmental chaos and changed natural and human communities beyond recognition. Water Hyacinth has found uses, but in general, has proven to be a highly invasive species with few cost-effective management solutions.

Global Education reports on the use of biological control of water hyacinth in Papua New Guinea, noting that within ten years of introduction into the Sepik River, water hyacinth had invaded to the extent that some village people died – snake bite victims could not get to hospital in time, other people starved because they could not get to their gardens or to markets, and contaminated water caused diseases and provided breeding grounds for malaria carrying mosquitoes. Mechanical clearing and herbicides proved to be uneconomic and ineffective.

Weevil image from www.abc.net.auAustralian scientists from the CSIRO Entomology found that the South American Chevroned Water Hyacinth Weevil (Neochetina bruchi) fed on the leaves of water hyacinths, while their larvae tunnel into the leaf stalk and crown, destroying the growing points. The plants rot and die quickly in the warm temperatures favoured by the hyacinths. Once established, the impact of the weevils is rapid, visible and long lasting.

According to Science Daily, the CSIRO scientists released some 450,000 weevils (Neochetina bruchi and Neochetina eichhorniae) in the Sepik River wetlands. Hyacinth infestations were reduced from 27 square kilometres to just seven in five years.

Salvinia image from www.nature.orgIn the Status of biodiversity in Papua New Guinea, by Miller, S.; Hyslop, E.; Kula, G., and Burrows, I., reported that another aquatic weed, Salvinia molesta is now widespread in Papua New Guinea. First recorded in 1977 at Wau, and on the Sepik River in 1971-72; by 1979, salvinia covered 80 square kilometres and the physical impact of the weed was reflected in the decline in fish catches, crocodile hunting, and sago gathering, and also in the disruption to the lives of Sepik villagers. People in a number of villages were unable to reach markets to sell produce and children were prevented from attending school. Biological control using the South American weevil Cyrtobagous salviniae was extremely successful. By June 1985, self-sustaining populations of the weevil had destroyed an estimated two million tonnes of weed which had covered 250 square kilometres. The local people have now resumed their former lifestyles.

The techniques learned in Papua New Guinea are now being applied in other countries. The ABC report on the developments in Lake Victoria, where the use of the weevils has again begun to have an impact on the infestation. Dr Mic Julien, the CSIRO biologist who had lead the project the Sepik River has demonstrated to African authorities what can be achieved – bio-control offers a long-term, sustainable answer.

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