Weevils, Weeds and Waterways - a matter of survival.

The Biological Control Of Water Hyacinth in Papua New Guinea.

Case Study

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Papua New Guinea (PNG) is one of Australia's closest neighbours and over many years the two countries have developed close working relationships. Experts from both countries frequently work together on projects to solve problems. The Water Hyacinth Project, based in PNG, is typical of such projects.

Water Hyacinth Flower
Adapted From an Illustration by Sainty & Jacobs 1994
Courtesy Hawkesbury Nepean Catchment Management Trust

Water hyacinth, a native of South America, is an attractive, flowering, freshwater plant. Its dramatic blue flowers and shiny green leaves make it highly prized as an ornamental plant. However its beauty is deceptive. Wherever it has been introduced, particularly into tropical climates, the plant spreads so rapidly that it is now regarded as the world's worst aquatic weed.

The introduction of water hyacinth into PNG more than thirty years ago, has had drastic results. It now grows prolifically in more than 200 locations throughout the country, clogging many of PNG's most important waterways. Its impact disrupts human activities and threatens entire ecosystems. In some areas such as the Sepik River region, its growth has had a huge impact on the health and activities of the local people. Yet people continue to collect and grow it as an ornamental plant.

The Sepik River people depend on the river's system of wetlands for their survival. The waterways provide transport and trade routes, fishing grounds, means of communication and access to gardens and cash crop areas. The waterways also transport tourists in search of highly prized Sepik artefacts. This activity forms an important part of the local economy.

The main impacts of water hyacinth on the local people and their environment are:

• clogged water surfaces
• displacement of native plants
• loss of aquatic habitats and species
• loss of water transport
• restricted access to services such as schools, markets and hospitals
• decreased food supplies
• loss of income
• interference with fishing
• reduced water quality for drinking, cooking and washing
• increased disease breeding grounds
• increased disease carriers such as mosquitoes, as the weed provides an ideal habitat for these insects

The impact of water hyacinth in the Sepik area has disrupted the lives of many thousands of people and in some cases has resulted in death. There are reports of people dying from a combination of :

• hunger because they can no longer access traditional food sources
• snakebite due to reduced speed of travel to hospital
• fatigue from trying to push canoes through the clogged waterways

By the early 1990s the problem had become so serious that the Government of Papua New Guinea requested assistance from the Australian Government to control the weed. In 1993 The Project on Biological Control of Water Hyacinth commenced. Funded by the Government of PNG (GOPNG) and AusAID, the project aims to;

• introduce control agents to eradicate water hyacinth
• monitor the spread of water hyacinth and the control agents
• locate water hyacinth infestation; and
• raise public awareness of the dangers of water hyacinth

The Water Hyacinth Project takes two main approaches:

1. To remove and destroy the weed in small isolated pockets using local human labour and;
2. To control the weed with biological control agents - using the water hyacinth's natural enemy to destroy the plant

While physical removal and burning of water hyacinth controls small pockets of the weed, these methods are not effective for larger areas. Biological controls, however, imitate nature and are considered to be the only long term, sustainable, economic and safe solution for large infestations.

The known natural enemies of water hyacinth are certain weevils and moths. They keep the weed under control by eating it. Once the plant infestation is reduced in size the insect population dies down. When the plant begins to spread again the insects naturally increase in number and the cycle continues. The aim is to keep the ecological balance between water hyacinth and insects. The insects are bred in special places and then released into infested areas.

A work base, established on the Sepik River, collects, rears and redistributes weevils which are already established in the field. Project staff closely monitor their numbers and their impact on the weed.

Public awareness campaigns also support the project. Local people learn about the dangers of water hyacinth to the environment and economy. They are also asked to report any sightings of the weed to prevent its further spread.

The second phase of the project, begun in 1996, continues the work of rearing and releasing the control agents, training field workers, monitoring, surveying and developing community awareness. In the third and final year of the project, community involvement will be very important so that insect releases can be made before the project finishes in 1998.

While water hyacinth continues to appear in new areas, control is being achieved in the worst affected areas due to the work of the project. In areas where the control agents have been released for the longest time the results are evident. On the Sepik river it is estimated that there is now 10 km2 of infestation in 40 lagoons, compared with 28 km2 in only 11 lagoons in 1994. Many lagoons which were almost entirely covered are now have less than 30% covered. People are able to use these lagoons again and fish are returning.

However, new infestations are still being reported and it will take time to see the full impact of biological controls on the water hyacinth problem throughout PNG.

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