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Curbing the spread of cassava pink mealybug in the Greater Mekong Subregion

FAO project helps countries fight cassava pink mealybug infestation.

Key facts

Thailand, Viet Nam, Cambodia and Lao PDR together have the lion's share of the global cassava export market − more than 90 percent. Viet Nam, the world's second largest exporter of cassava after Thailand, shipped 3.1 million tonnes of cassava products in 2013, worth around US$ 1.1 billion. And the industry could grow as demand for industrial cassava-based products, such as biofuel and livestock feed, increases, especially in China. So when the cassava pink mealybug, which injects a toxin into the cassava plant while feeding on its leaves and stems, causing the plants to wither and die, reappeared in the region several years ago, it was a major concern. Insect pests know no borders; an infestation in one country can spread quickly to a neighbouring one, especially through trade and the movement of cassava planting material. With this in mind, the countries in the Greater Mekong Subregion − where some three million small-scale farmers earn a living by growing cassava − turned to FAO for technical assistance through the Technical Cooperation Programme (TCP) in controlling the cassava pink mealybug. Drawing on the success that Thailand had in reducing its mealybug population, an FAO TCP project set out to help other countries in the subregion − Cambodia, China, Lao PDR and Viet Nam − do the same.

Unleashing parasitic wasps
When the invasive cassava pink mealybug first began devastating vast areas of Thailand's cassava crops in 2008, farmers reacted by dousing their fields with toxic insecticides, which posed high environmental and human risks.

Yongfan Piao, senior plant protection officer at FAO's regional office in Bangkok, said that the country had lost an estimated six million tonnes of cassava root from the forecast for the 2009/10 harvest. He explained that “the total cost of 6 million tonnes of cassava would be the equivalent of some US$600 million. The estimated losses caused by the mealybug for this period would be over US$14 million.”

The Thai government appealed to the International Institute of Tropical Agriculture in Benin for assistance, as countries in Africa had managed to reduce cassava mealybugs decades earlier. 

This entailed introducing a parasitic wasp known as Anagyrus lopezi into the infected areas. Like the cassava pink mealybug, Anagyrus lopezi is native to South America. The wasp lays its eggs in the mealybug and the growing larvae eat their way out, effectively killing the host.

Six million pairs of the parasitic wasp were produced and released in Thailand between July 2010 and August 2011 − a move that, along with the release of local predatory lacewings and training on ecological pest management, helped reduce 166,700 infested hectares in May 2009 to just 10.88 hectares by October 2013.

Sharing experiences and knowledge
Tapping into Thailand's experience, an FAO project run in collaboration with Thailand’s Departments of Agriculture and Agricultural Extension supported research on the ecology of insect pests and their natural enemies, and provided technical assistance to produce large numbers of biocontrol agents, such as the wasps.

Furthermore, the project trained farmers via season-long farmer field schools on integrated pest management strategies that had been developed and successfully applied in Thailand.

Knowing what works to control mealybugs and what doesn't is essential. Nguyen Van Tan, a Vietnamese farmer with 38 years of experience growing cassava, saw farmers in his own village spray their infested crops with pesticides "without any effect".

What pesticides do, in fact, is kill off cassava mealybug's natural enemies, something Mr. Van Tan and other farmers learned through the training. They also received wasps and instructions on how to release, conserve and monitor them in the fields. 

At the time, Mr Van Tan's four-month-old cassava crop looked as if it would be a repeat of the previous year's harvest, in which mealybugs destroyed nearly half of his crop. "Some plants looked dead," he said.

Shortly after releasing the wasps, however, he noticed fewer mealybugs and new shoots on the plants. This has given him and others in the village renewed confidence and incentive to plant even more cassava the following year.

In total, the project trained 853 farmers in Cambodia, Lao PDR and Viet Nam, 321 of them women, to use living organisms to manage pests biologically and to reduce pesticide use. It also strengthened the network of extension workers to provide farmer outreach.

The ripple effect
The success of the project has also created a ripple effect, attracting the attention of regional research and development organizations such as the International Center for Tropical Agriculture (CIAT) in Colombia and the Asian Institute of Technology (AIT) in Thailand, as well as the public and private sectors. 

The Government of Viet Nam, for example, is now scaling up successful biological control efforts in all of its provinces affected by mealybug infestations, while Thailand's private sector has invested substantially in the mass rearing of biological control agents.

The Government of China has issued various quarantine regulations aimed at preventing the spread of this invasive species. And recently, FAO and CIAT helped authorities in Indonesia, a country not covered by the project, import wasps from Thailand to deal with cassava mealybug incursions on the island of Java.

Preparedness is key
Cassava is a versatile crop. In addition to being an important food source, it can be made into pellets for animal feed or converted into industrial products, from adhesives and textiles to paper and pharmaceuticals.

Because smallholder farmers are the main growers of cassava, its rising demand means that the industry has excellent potential to create jobs and boost incomes in rural communities in the Greater Mekong Subregion.

That is why vigilance against pests is so important. In addition to encouraging countries to take precautionary measures, such as strengthening quarantine procedures and setting up surveillance systems, FAO helped raise awareness − especially in China where no incursions have yet been reported − of the risk of mealybug outbreaks.

FAO's Technical Cooperation Projects (TCP) are targeted, short-term catalytic projects that leverage FAO's technical expertise to address specific problems in agriculture, fisheries, forestry and rural livelihoods among FAO Member countries, producing tangible and immediate results in a cost-effective manner. 

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