Biocontrol: saving the environment, saving farmers’ incomes

Water hyacinth grows fast and can clog water bodies
Water hyacinth grows fast and can clog water bodies. Photo by IITA

Biological control of water hyacinth is not only restoring the balance of nature in Africa but also putting savings in the pockets of resource-poor farmers whose livelihoods depend on fishing, thanks to IITA.

Using natural enemies, scientists have been able to control the purple-flowered water weed in southern Bénin, for instance, showing that annual incomes in that region increased by US$30.5 million.

The result of the studies, which was published in the Journal of Agriculture, Ecosystems & Environment, estimated the total cost of the biocontrol program at $2.09 million.

“Assuming that the benefits are to stay constant over the next 20 years—a most conservative assumption—the accumulated present value would be $260 million, yielding a respectable benefit-cost ratio of 124:1,” say Drs Hugo de Groote and Peter Neuenschwander.

Water bodies, such as lakes, rivers, and dams are important for agriculture and as water sources for domestic needs.

However, floating aquatic weed species mostly originating from South America, such as water hyacinth (Eichhorniae crassipes), water lettuce (Pistia stratiotes), giant salvinia (Salvinia molesta), and the red water fern (Azolla filiculoides) were deliberately or accidentally introduced from their native home into these water bodies as ornamental plants or for use in the aquarium trade. Because of their rapid reproduction by vegetative means and through seeds, these plants have attained a pest status.

Obinna Ajuono explains how water hyacinth invasion was brought under control using a weevil
Obinna Ajuono explains how water hyacinth invasion was brought under control using a weevil. Photo by IITA

Obinna Ajuonu, IITA entomologist, says the damage caused by water hyacinth, for instance, on the fishing community alone was devastating.

“It accumulates a large biomass that enables the plants to block waterways,” he explains, “thus impeding fishing and transport by boat or canoe, leading to increased transport costs and loss of revenue. They can also increase the incidence of diseases, such as bilharzia, and provide refuge for reptiles, such as snakes.”

A survey by IITA in southern Republic of Bénin in 1999 revealed that at the peak of the infestation, water hyacinth had reduced the yearly income of a community of about 200,000 people by approximately $84 million. Men lost revenue mostly in fishing, while women experienced loss of income in trade, primarily in food crops and fish.

The intervention by IITA and partners through the release of three natural enemies, two weevil species and one moth that feed exclusively on water hyacinth, however, brought succor to the West African region where the devastation was most extensive.

Neochetina eichhorniae, the weevil that brought water hyacinth under control
Neochetina eichhorniae, the weevil that brought water hyacinth under control

IITA implemented the first biological control of floating weed in West Africa (Bénin) way back in 1991 with the release of the weevil Neochetina eichhorniae that ate nothing but the water hyacinth at immature and adult stages. Biological control of water lettuce, giant salvinia, and the red water fern using their specific agents, followed thereafter.

From IITA-Bénin, a starter colony of biocontrol agents against aquatic weeds and expertise in implementing weed biological control were provided to other countries, such as Burkina Faso, Côte d’Ivoire, Ghana, Kenya, Nigeria, Republic of Congo, Senegal, Tanzania, Uganda, and Zimbabwe.

Other benefits brought by IITA’s intervention included an improvement in water quality and human health. Before the biological option was used, national governments in the subregion applied herbicides and mechanical/manual removal to control water hyacinth—options that were neither environmentally friendly nor cost-effective.

Ajuonu says an additional biological control agent for the water hyacinth is being planned. “The new ideal candidate is the mite Orthogalumna terebranti,” he explains. This has been discussed in several Economic Community of West African States (ECOWAS) meetings on aquatic weed control, where IITA was represented.

He explained that IITA provided many of the ECOWAS countries with starter colonies of agents and would continue to do so by importing the mite in 2009/2010 and maintaining a laboratory culture for supply to individual countries.