Lake Victorious: weevils defeat water hyacinths
Michael Malakata
11 July 2007
Source: SciDev.Net

Scientists have announced the success of a biological, pesticide-
free method in eradicating the highly invasive water hyacinth from
Africa's waterways.

James Ogwang, an entomologist specialising in biological control at
the Ugandan National Agriculture Research Organisation, and his
colleagues presented their work at the annual meeting of the
American Society of Plant Biologists last week (8 July) in Chicago,
United States.

The scientists' control strategy involves mechanical removal of the
plants, and harnessing two natural enemies of the water hyacinth â€"
the weed weevils Neochetina bruchi and Neochetina eichhorniae. Using
this method, the scientists successfully eradicated 90 per cent of
the water hyacinth in Africa's Lake Victoria.

The water hyacinth plants that proliferated around Lake Victoria
throughout the 1990s resulted a decrease in the lake's biodiversity,
said Ogwang in a press release. They also disrupted activities on
the lake: fishermen caught less fish, the plants interfered with
water transport and blocked hydroelectric power turbines, which
resulted in a severe drop in the supply of electricity.

The 'mats' of water hyacinth are also a threat to human health; they
provide a habitat for insects carrying malaria and schistosomiasis,
and rotting hyacinths contaminate drinking water, causing
gastrointestinal disease.

Both the adult and larval weed weevils eat water hyacinth and, by
tunnelling into the plant, allow bacteria and fungi to invade the
plant. Water also enters these tunnels, sinking the mats. Once
submerged, water and wave action continue to degrade the plant
matter.
The control strategy resulted in reduced cases of disease, increased
power generation and larger catches of fish for export. And because
pesticide was not used, the process is a cheaper and more
sustainable way of removing the weeds.

Amon Mwape, an environmental scientist from the Zambian Ministry of
Tourism, Environment and Natural Resources says water hyacinths are
invading most of Africa's rivers, and they are a big challenge.
"It is a good effort by the scientists to come up with a natural and
less expensive way of controlling the weeds," he said.
But he also warned of the dangers of introducing new, non-native
species into the environment.

"The scientists must be cautious that these insects do not cause
damage to other plant species," said Mwape.

Water hyacinth, Eichhornia crassipes, is one of the most invasive
waterweeds in the world, and was first observed in Lake Victoria in
1989.

The biological method of water hyacinth control used in Lake
Victoria was originally implemented in Florida, United States, in
the 1970s.