Plant-Munching Weevil Helps Botswana Contain Weeds Threatening to Overwhelm the Okavango

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Click the image to download a pdf of the paper

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 to 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 laborers 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 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 percent of a salvinia infestation. (Photo above courtesy of Dr. C. N. Kurugundla)

This one-tenth-inch-long South American weevil, Cyrtobagous salviniae, is highly effective in reducing giant salvinia infestations to acceptable levels. (Image courtesy of U.S. Department of Agriculture)
This one-tenth-inch-long South
American weevil, Cyrtobagous
salviniae, is highly effective
in reducing giant salvinia
infestations to acceptable levels.
(Image and caption courtesy of USDA)

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 percent 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.

Reference: Kurugundla. C. N.; et al. (2016). Alien Invasive Aquatic Plant Species in Botswana: Historical Perspective and Management, Open Plant Sci. J., DOI: 10.2174/1874294701609010001

Post prepared from materials provided by Bentham Science Publishing.

Related research: Giant salvinia in the United States and Interagency Giant Salvinia Control Team

Screen Shot 2016-08-30 at 9.04.11 AMThe National Geographic Okavango Wilderness Project is a multiyear research and conservation effort to document and help protect the Okavango River Basin in Africa. One of the planet’s last wetland wildernesses, the Okavango is home to a wealth of critical wildlife populations. But this vast and untouched ecosystem is threatened. While the delta in Botswana is protected as a UNESCO World Heritage Site, the river basin and its water supply, which stretch from Angola through Namibia and into Botswana, remain vulnerable to human interference.

A team of local and international researchers, led by National Geographic Fellow and conservation biologist Steve Boyes, is providing evidence-based science that encourages local governments and communities to protect biodiversity; promote sustainable development; and preserve the rivers, forests, and wetlands that are key to the health of this region and the areas downstream. Over the next year, the team hopes to support the creation of one of the largest wildlife reserves in sub-Saharan Africa, protecting this critical region for generations to come.

12418031_10153900711084116_8462971761216697621_nDavid Braun is director of outreach with the digital and social media team illuminating the National Geographic Society’s explorer, science, and education programs.

He edits National Geographic Voices, hosting a global discussion on issues resonating with the Society’s mission and major initiatives. Contributors include grantees and Society partners, as well as universities, foundations, interest groups, and individuals dedicated to a sustainable world. More than 50,000 readers have participated in 10,000 conversations.

Braun also directs the Society side of the Fulbright-National Geographic Digital Storytelling Fellowship

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