Waterways, weeds and weevils

Introduction Water hyacinth Situation in Papua New Guinea Action Results Introduction  Papua New Guinea (PNG) is one of Australia's closest neighbours. It is a tropical country with many contrasting environments; high bush covered mountains and low-lying wetlands, tropical rainforests and grass covered plains. Huge rivers flow through the country and, with their surrounding wetlands, play an important part in the lives of the people who live along their banks. Dense vegetation and sparse population means there is a limited road network and the river systems provide: links between villages routes to gardens, markets, schools and hospitals food - fish, waterbirds and swamp plants such as sago, a staple food of the river people of PNG. Like roads, waterways need to be kept free flowing and clear for boat traffic and food gathering. However during the 1980s and early 1990s, many of PNG's rivers and wetlands were being taken over by an outside invader - water hyacinth. Water hyacinth The water hyacinth was introduced into PNG because of its attractive flower. © CSIRO Entomology A native of South America, water hyacinth is a flowering, floating, freshwater plant. It has beautiful, large, pale blue flowers with purple and yellow spots on the petals and shiny round green leaves. Away from its natural enemies, it became a vigorous growing aquatic weed that damaged water quality by blocking sunlight and oxygen and slowing river flows in many tropical and subtropical regions of Asia, Africa, America and the Pacific. Situation in Papua New Guinea The Sepik River in Papua New Guinea was especially affected and, in the ten years after it was first introduced, water hyacinth had spread so much that in places: waterways were too clogged for boats to get through water plants and animals died because sunlight could not reach them drinking, cooking and washing water quality was reduced people lost income as they could not get to their gardens and markets and tourists could not visit villages. In some villages people even died because of water hyacinth: Snake bite victims could not get to hospital in time People starved because they could not get to their gardens or to markets Contaminated water caused diseases and provided breeding grounds for malaria carrying mosquitoes Clogged waterways prevent people travelling to school, hospital and markets in Tambali Lagoon. © CSIRO Entomology The problem became too big for manual clearing (mechanical control), and herbicides (chemical control) would have been ecologically disastrous and uneconomical and have only a short-term effect, so a different solution was needed. Action   neochetina bruchi (Chevroned Waterhyacinth Weevil) The weevil introduced to attack the water hyacinth after trialling to ensure it would not cause other environmental problems. © CSIRO Entomology In nature, every plant and animal has natural enemies which help to keep the environment in balance. Using these natural enemies to attack weeds and pests is called 'biological control'. Scientists found that a particular weevil was the natural enemy of water hyacinths in South America, and that it would eat only water hyacinth and not harm any other plants. The weevils feed on the leaves, while the larvae tunnel into the leaf stalk and crown, destroying the growing points. This causes the plants to rot and die and eventually sink. Once the weevils become established on water hyacinth, the impact is rapid, visible and long lasting. The Papua New Guinea Government, with the assistance of the Australian Government, worked on a project to locate, breed and release the weevils into the worst affected areas. Field workers kept records of the numbers of insects released and their impact on water hyacinth. The project also taught communities about identifying the water hyacinth as a weed. They were asked to report any water hyacinth that they saw growing. The partnership of government, scientists and community was able to clear the waterways. This meant that people could use the lagoons again and fish stocks returned. Results Tambali Lagoon three years after the introduction of the weevil. © CSIRO Entomology The project, using the weevil for control of water hyacinth and involving the community in the program, has also been applied to clearing huge infestation of water hyacinth in Lake Victoria (Kenya, Uganda and Tanzania), Benin (West Africa), South Africa and Thailand.