Thursday, July 12, 2007
Lake Victoria: weevils defeat water hyacinths
Lake Victorious: weevils defeat water hyacinths
11 July 2007
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 — 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.
Before - Port Bell as it was, only mechanical harvesters offered a temporary solution.
After - Port Bell dramatically changed once the beetles were established on the hyacinth weed.
THE BEETLE THAT SAVED LAKE VICTORIA
By Brad Collis
This time last year fishing villages had been abandoned and millions of people were facing dislocation and hunger because the world’s second largest fresh water lake had become so choked by water hyacinth, a weed invader from South America, that fishing dhows could no longer reach open water.
Australian scientists, with a little help from a small South American beetle, are being credited with saving the livelihoods of 30 million people through their use of biological control to remove a devastating weed from Africa’s Lake Victoria.
Lake Victoria, legendary source of the Nile and cradle of early human evolution was finally losing its capacity to support human life.
In 1998 several multi-million dollar harvesting machines were sent to the lake as a European answer to the crisis. Various chemical companies also set up office in Kampala, Uganda, hoping to secure contracts to attack the weed with herbicides. The World Bank had allocated US$9.3 million to solving the water hyacinth problem, as part of a larger Lake Victoria Environmental Management Project (LVEMP), so there was money to be made by the politically savvy.
But by late 1999 the weed, covering more than 12,000 hectares along the shores of Kenya and Uganda, was suddenly dying.
To the chagrin of chemicals and machinery salesmen, and local officials hoping for commissions, the weed was already beaten … without fuss and for a comparatively small cost.
Salvation for the 30 million people who rely on the lake for their basic sustenance had come instead from an unexpected partnership – Australian expertise in the biological control of aquatic weeds, small teams of researchers in the three lake countries Kenya, Uganda and Tanzania, and two small South American weevils of the Neochetina family which have insatiable and exclusive appetites for water hyacinth.
The defeat of water hyacinth on Lake Victoria is now emerging as one of the world’s great biological control successes and a rare humanitarian triumph.
To understand how impenetrable and wide-spread the weed had become, rail-ferry links were often broken for weeks at a time because ships couldn’t dock at their wharves, and numerous fishing villages were being abandoned; many people believing their communities had been afflicted by a calamity beyond all help.
The culprit - Water hyacinth
The problem: water hyacinth which choked the fishing ports of lake Victoria.
Thus the weed’s dramatic disappearance over the past eight months has been a salvation in every sense of the word. It has saved millions of people from social and economic dislocation and possible starvation.
Yet when biological control was mooted by scientists just four years ago, the notion was ridiculed by many officials, even some international scientists.
At that time, however, Australia, through the Commonwealth Scientific and Industrial Research Organisation’s (CSIRO) Division of Entomology, was using the Neochetina weevils to control water hyacinth in lagoons on the Sepik River in Papua New Guinea.
As in bays around Lake Victoria, the PNG lagoons had become so choked that there too, whole villages had been abandoned.
When in 1996 the scientists heard of plans to tackle water hyacinth on Lake Victoria with herbicides and machines, they urged the African governments to consider biological control.
Dr Mic Julien, the CSIRO biologist who was leading the assault on the Sepik River, took before-and-after photographs from PNG to show African authorities what could be achieved. He also argued that bio-control offered the only long-term, sustainable answer.
"But everyone was mesmerised by the notion of a quick fix … chemicals and big shiny harvesters. All we were offering were tiny weevils."
Fortunately for Dr Julien and his team the scepticism levelled at their proposal was matched by delays and arguments that were also thwarting the proponents of herbicides and harvesters. The main opponents of herbicides were politically-influential Nile Perch exporters, who feared for their profitable export trade to Europe if chemicals started being sprayed over the lake.
The argument opened a window of opportunity for the biologists. Ugandan and Kenyan scientists travelled to Australia for training in biological control techniques while Dr Julien and a colleague, Dr Tony Wright ran a course in Kenya to teach local communities how to raise the Neochetina weevils in drums and tanks.
The Neochetina beetle - a saviour to the communities living off Lake Victoria
The solution: Neochetina - the key to the biological control of hyacinth.
But there was strong political opposition. The then Uganda Minister for Agriculture visited the main research station and ridiculed the whole idea.
"It took a lot of courage for the local researchers to continue because there was real pressure coming down on them," said Dr Julien.
"There were significant gains for people backing the chemicals and machines, but there was no profit in biological control, except for the community at large."
The first weevils were released onto water hyacinth on Lake Victoria off Uganda and Kenya in 1997 while official attention was still fixed on the continuing debate over herbicides and harvesters.
About the same time as the weevils were released, the first harvesters arrived at Port Bell where some of the worst weed banks had stopped ships from docking. Working flat out the machines cleared about 300 hectares, but had no overall impact because of the weed’s rapid regrowth.
A matter of time
Meanwhile, discussions dragged on about the pros and cons of using herbicides.
"This proved to be the key for us … time for the insects to become established while committees wrangled over their preferred ‘quick-fix’ options," said Dr Julien.
"The irony was that we knew we had the answer but weren’t prepared to tout it as a ‘quick-fix’ because the weevils needed a few years. But once they were established on the weed we knew the impact would be rapid, visible and importantly, long-lasting."
The weevils kill the plant by feeding on the leaves. When the population is high this alone can destroy the leaves. But more importantly, larvae tunnel in the petioles (leaf stalks) and into the crown of the plant, destroying the growing points. When severe, the damage allows water to enter the plant and secondary rotting occurs. The combined damage reduces the plant’s ability to flower, set seed, send out off-shoots and replace damaged leaves. Under heavy attack the plants rot and become water logged and eventually sink.
In November 1999 Julien returned to the lake to assess the weevils’ progress and even from a distance as his flight descended into the lakeside town of Kisumu in Kenya, the weed was visibly diminished.
He was euphoric: "It was a wonderful feeling. There were probably only half a dozen people in the world who understood at that moment what it meant."
Sadly, given the cost and the poverty of surrounding communities, the Kenyan Government had just succumbed to the urge to use machinery and had contracted machines costing $1.5 million from USA. These were delivered but by late 1999 were sitting on the lake with little water hyacinth to work on.
It was the end of a 10-year drama textured by political maneuverings, human courage and fascinating science.
It has given hope that other environmental ills facing the lake and its people may also be cured or controlled.
Lake Victoria is said to have experienced the greatest mass extinction of vertebrates in modern times. Thirty years ago the lake boasted about 500 fish species. More than half are now extinct, including the ngege (Oreochromis esculentus) which used to be the main fish caught for food.
Restoring the lake’s health is now an international mission with the World Bank allocating US$77 million to a range of programs aimed at re-establishing a sustainable fishing industry, and solving the nutrient and siltation problems.
Posted by lmurx at 7:44 PM