Scientists use new super-weevil to eat water hyacinth to death

A colony of new super-weevils released by the UK environment agency to reduce invasive water weeds has delivered near-complete success in clearing the country’s waterways, and offered new hope of a biological solution to the clogging of Lake Victoria by the invasive Water Hyacinth that is relied upon by thousands of residents of East Africa, now that donor funds have run out and the Lake’s demise progresses at speed.

In 2005, Kenya invested in an earlier generation of weevils to tackle the Lake’s destruction through water weeds, achieving a near 90 per cent success rate, but it later returned to chemical solutions that require constant repetition and considerable budget for buying the herbicides from global agrochemical producers. It has not revisited the scope for a biological solution since that time.

However, the weevils kill the plants by feeding on the leaves of the water weeds. More importantly, larvae tunnel into the leaf stalks and into the crown of the plant, destroying the growing points. Once 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.

Now the UK’s Environment Agency says the weevils it has introduced to deal with the problematic Azolla weed in Great Britain can be used to control any invasive weed affecting the world’s waterways, including Lake Victoria’s Water Hyacinth. The officials say the new weevils are of a superior quality to the traditional ones used even in Kenya due to their big teeth and taste for a specific plant.

In the UK, the Environment Agency officers cleared the water weed with herbicides in June last year, but, over the following months the ultra fast-growing plant, which can double in size every four to five days, had resurfaced spreading downstream and invading an even bigger mass. However, the new initiative with the super-weevils now looks set to provide an ongoing solution.

According to the officials at the environmental agency, the weevils’ numbers diminish as the volume of weeds reduces, and they can never be a threat to native species. They also remove the need for either chemicals or dredging in eradicating the weeds.

In Kenya, the water hyacinth, a free-floating perennial aquatic plant that moves seasonally with the waves from bay to bay, blocking water-ways and affecting aquatic life as it sucks oxygen from the water, has put in danger the livelihoods of some 28m East Africans who rely on Lake Victoria for survival through fishing and farming.

The weed weevils Neochetina bruchi and Neochetina eichhorniae introduced by the scientists in 2005 managed to eradicate at least 90 per cent of the hyacinth within 3 months. But ministers and government officials with affiliations to chemical companies aggressively campaigned for the use of the chemicals and harvesters instead to control the weed. Various chemical companies also set up office in Kampala, Uganda, hoping to secure contracts to attack the weed with herbicides.

At the time, the World Bank had allocated $9.3m to solving the water hyacinth problem, as part of a larger Lake Victoria Environmental Management Project (LVEMP), meaning that the clearing was seen as a commercial opportunity by many parties.

However, the hyacinth is now growing faster than ever, with all the funding from the donors now exhausted and nothing to show for it.

 “The biological control method was working out pretty well, and it was for the benefit of the millions of the beneficiaries of the Lake, and we knew with our counterparts in Uganda and Zambia that we just needed an year and we could sustain this, but the powers that be thwarted our efforts, and it’s such a shame, because many livelihoods no longer engage in economic activities like they used to even after being promised of an end to the hyacinth,” said Isaiah, one of the scientists who worked with the original biological control method.

Like many other invasive plants, both the Water Fern in the UK and the Water Hyacinth in Kenya were first introduced from the Americas in the 1800s. But they soon escaped from garden ponds into the wild and in the absence of any native predators, quickly invaded rivers, lakes and canals.

They form dense mats on the surface of the water, depriving other plants, fish and invertebrates below the water level of light and oxygen. As well as creating ‘death zones’ for aquatic wildlife, the mossy carpets can pose a flood risk as the weed clogs the watercourse.  They also make boating, canoeing and fishing impossible.

Written by Bob Koigi for African Laughter

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