Natural Born Enemies
Copying nature to manage a weed.
Case Study
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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 with surrounding wetlands flow throughout the country and play an important part in the lives of the people who live along their banks. These river systems act as roads providing;
- links between villages
- routes to markets, schools and hospitals
- access to gardens.
The rivers and wetlands also provide food; fish, waterbirds and swamp plants such as sago, a staple food of the people of PNG.
Just as roads, the waterways need to be kept free flowing and clear for boat traffic and food gathering. However many of PNG's water bodies including some important rivers and wetlands are being taken over by an outside invader - the water hyacinth.
Water Hyacinth Flower
Adapted From an Illustration by Sainty & Jacobs 1994
Courtesy Hawkesbury Nepean Catchment Management Trust
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. Because of its beauty it has been widely spread throughout the tropics. Unfortunately it grows and spreads so quickly in warmer climates that it is now known as the world's worst water weed.
This aquatic (water) weed was first reported in PNG in 1962. It is now present in over 120 places in all 19 provinces and has led to big problems for some river systems. The Sepik River is especially affected and, in the ten years since it was first introduced, water hyacinth has spread so much that in places;
- waterways are too clogged for boats to get through
- sunlight cannot reach other water plants and animals
- local plants and animals have lost their habitat
- drinking, cooking and washing water quality is reduced
In some villages people have died because of water hyacinth. People have been reported as dying from:
- snake bites because victims could not get to hospital in time
- starvation because they could not reach food sources
- diseases bred in bad water
- fatigue from pushing canoes through clogged waterways
Unless water hyacinth is stopped from spreading it will mean disaster for a large part of PNG.
Small areas of water hyacinth may be cleared by using human labour but large areas need a different solution. It is believed that the only long term, safe way to control the weed is to copy nature.
In nature, every plant and animal has natural enemies which help to keep the environment in balance. When scientists copy nature in this way it is called 'biological control'. In the case of water hyacinth, scientists are sending in the plant's natural enemies (weevils and moths) to attack the problem. The insects eat the plant and reduce the area it covers. The insects then die off until the plant begins to spread again. The cycle is repeated and the water hyacinth is kept under control.
In the early 1990s the Papua New Guinea Government asked the Australian Government to help them solve the water hyacinth problem. Since 1993 the two countries have been working together on a project to locate, breed and release water hyacinth's natural enemies into the worst affected areas. In each of these places field workers keep records of the numbers of insects released and their impact on water hyacinth.
Another part of the project is to teach communities about water hyacinth. People learn how to identify the weed and to understand that it is a problem. They are asked to report any water hyacinth that they see growing. By working with the community as well as with science, the government hopes to stop the weed from spreading any further.
The project has now been running for 5 years and in some places there are clear signs that the water hyacinth's 'natural enemies' are winning the battle. Although water hyacinth continues to appear in new places, mainly planted for its pretty flowers, control is being achieved. As a result, many lagoons which were almost entirely covered in the weed have less than one third covered. This means that people can use the lagoons again and fish stocks are gradually returning.
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