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Weed Munching Weevel Saves Okavango

Three decades after the first reports of the arrival in Botswana of Salvinia molesta–a pestilential free-floating, mat-forming water fern native to Brazil–scientists from the southern African country’s Department of Water Affairs say they are at last prevailing in the struggle against the weed.

Salvinia had come too close to threatening the entire Okavango, Africa’s largest wetlands and a UNESCO World Heritage site — and sanctuary for some of the world’s most endangered species.

Their most potent weapon was not an aerial bombardment of Roundup. Instead, the scientists called on a titanic force of nature: a minuscule weevil with an outsize appetite.

A research article by Dr. C. N. Kurugundla and others, published recently in The Open Plant Science Journal, describes how teams of scientists and labourers from the Department of Water Affairs undertook the decades-long challenge  to combat salvinia and other invasive weeds in the Okavango Delta, and also the wetlands off the Kwando-Linyanti-Chobe River and the Limpopo River that borders South Africa and Zimbabwe.

“Continuous monthly surveys and monitoring of rivers, lagoons and other wetlands resulted in success and shall serve as inspiration in aquatic weeds management,” Bentham Science Publishing (publisher of the journal) declared in a news statement about the research.

The review paper, Alien Invasive Aquatic Plant Species in Botswana: Historical Perspective and Management , describes the species biology, distribution, historical spread, negative impacts, and control achieved right from the discovery of the weeds in Botswana.

The review presents success stories of control of salvinia, Salvinia molesta, by its biocontrol weevil, Cyrtobagous salviniae.

The tiny salvinia weevil, as it is commonly called, is a prolific breeder with a voracious appetite for Salvinia

molesta. It has been known to eat its way through as much as 90% of a salvinia infestation.

No fresh releases of the weevil, which is also a native of South America, were undertaken after mass releases in 1999 and 2000, which established the insect within three years of their introduction, the authors say.

The review also presents the successful eradication of water lettuce, Pistia stratiotes, in the transboundary Kwando River wetlands by 2005. Management of the growth of water hyacinth, Eichhornia crassipes, from 2012 in the transboundary Limpopo River jointly with neighboring South Africa is also discussed.

The researchers further look at legislation regarding aquatic weeds. The Government of Botswana “regulates the movement and importation of boats and aquatic apparatus to prevent the importation and spread of aquatic weeds” by the strict implementation of “Aquatic Weed (Control) Act -1986,” they say.


Benefits for Tourism,

Water Resource and Wildlife

“The efforts made by the department have benefited tourism, water resource use, and wildlife. Partly due to the achievement of aquatic weeds control, the tourism sector is now very stable and contributes [about] 25% to the country’s GDP,” the news released adds.

“The authors…suggest that integrating biological and physical control with public awareness campaigns while working with conservation groups and NGOs would provide sustainable development of wetlands for ecological integrity and livelihoods,” the statement concludes.




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