Biocontrol of invasive water hyacinth contributes to socioeconomic and health improvements in Africa

July 08, 2007

In research that will be presented at the annual meeting of the American Society of Plant Biologists (ASPB) in Chicago (July 7-11, 2007), scientists implemented a successful bioeradication program of an invasive water weed in Africa's Lake Victoria. Two insect biocontrol species, weevils in the genus Neochetina, were used, along with mechanical removal, to control the highly invasive water hyacinth, which has also plagued waterways in the southern United States. This method of water hyacinth biocontrol, originally researched and implemented in Florida in the 1970s, eliminates or drastically reduces the use of pesticides. In the Lake Victoria region, water hyacinth threatened livelihoods of local communities by reducing fish populations, fouling hydroelectric power turbines, and providing habitats for malaria and schistosomiasis vectors. Similar biocontrol programs have been successfully applied throughout the tropics and subtropics.

Water hyacinth, Eichhornia crassipes, is one of the most invasive water weeds in the world. A native of South America, it was spread throughout the tropics and subtropics in the last century, mostly by humans. While the plant can potentially be used for sewage treatment and biofuel production, it can also cause severe environmental and socioeconomic damage.

Dr. James Ogwang, a biocontrol entomologist with the Uganda National Agricultural Research Organization, and his colleagues, implemented a successful program that rid Lake Victoria of the weed. The control strategy integrated mechanical removal and use of two insects that are natural enemies of the weed--weevils in the genus Neochetina--N. bruchi and N. eichhorniae, both natives of South America.

Dr. Ogwang's work on the Lake Victoria water hyacinth eradication program was recently featured on National Geographic's television series, Strange Days on Planet Earth. He will be giving a presentation on this work at the annual meeting of the American Society of Plant Biologists in Chicago (July 8, 2007, 10:50 AM) in a major symposium on Plant Biology in Sub-Saharan Africa organized by Debby Delmer of UC Davis.

Water hyacinth was first observed around Lake Victoria in 1989 and by the late 1990s was choking out most of the shoreline. Lake Victoria, located in east central Africa and bordered by Tanzania, Uganda, and Kenya, is the second largest freshwater lake in the world in surface area. It is located in the same region as Africa's Great Rift Valley System, an area of tectonic rifting and ancient volcanic activity, which is considered to be the cradle of human evolution. The lake itself is a natural laboratory of evolutionary biology because of its diverse cichlid fish populations, and it has provided livelihoods for humans for many thousands of years.

With no natural enemies in Africa, the water hyacinth proliferated around Lake Victoria and resulted in reduced fish catches and biodiversity. It interfered with water transport and blocked hydroelectric power turbines, resulting in a severe drop in the supply of electricity. Human health was also threatened because the large weed mats created breeding habitat for the vectors of malaria and schistosomiasis. Rotting vegetation contaminated drinking water, increasing cases of gastrointestinal diseases.

Dr. Ogwang and his colleagues used the natural predators of the plant to help eradicate it--the mottled water hyacinth weevil, N. eichhorniae, and the chevroned water hyacinth weevil, N. bruchi. Both adults and larvae feed on the plants. The Neochetina larvae tunnel into the plant, allowing invasion by opportunistic bacteria and fungi. Additionally, water enters the tunnels and causes the plant mats to sink as the plants deteriorate further. Wind and wave action can accelerate the destruction of the weed started by the insects. No herbicide spraying was used in the Ugandan program, only mechanical removal and biocontrol, yet by 2000, 90% of the weed was cleared from the lake. The result of this remarkable program resulted in reduced cases of disease, increased power generation, and increased production of fish for export (mainly the Nile Perch).

Dr. Ogwang has also worked on other successful biocontrol programs to eradicate pests of citrus, cabbage, and cassava. He credits the development of his interest in biocontrol entomology to the traditional farmers in the village where he grew up. These farmers practiced conservation and use of a predatory ant, Lepisiota sp., to control cotton bollworms, a practice still used in organic cotton farming in Uganda. Similar biocontrol programs for water hyacinth have been successfully used throughout the tropics and subtropics, as well as in the U.S., in Florida, Louisiana, and Mississippi. Dr. Ted Center, Research Leader at the ARS/USDA Invasive Plant Research Laboratory in Fort Lauderdale, was involved in the original ARS/USDA research in the 1970s that initiated use of the Neochetina weevils as biocontrol agents of water hyacinth. He credits the success of the same biocontrol program at Lake Victoria to Dr. Ogwang and his team. Along with collaborators from Africa, Australia, and South America, the Florida facility continues to research new biocontrol agents to improve the stability of the control provided by existing ones.

Biological control programs can present some hazards. The risks of introducing non-native predatory species must be carefully evaluated before they are introduced. These risks include invasiveness by the control agents themselves and unintended effects on non-target species. Biocontrol agents must also be carefully monitored after introduction for any unforeseen environmental changes. However, the benefits of these programs are elimination or reduction of the use of pesticides, thereby enabling sustainable economies, and lowering the costs of farming, especially in resource-poor areas.
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ASPB, headquartered in Rockville, Maryland, was founded in 1924. This professional society has a membership of nearly 5,000 plant scientists from the United States and more than 50 other nations. ASPB publishes two of the most widely cited plant science journals in the world: The Plant Cell and Plant Physiology.

American Society of Plant Biologists

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