Fighting Asia’s alien invasions

4 June, 2015 by (comments)
Institut Pertanian Bogor IPB or Bogor Agricultural University, Indonesia. Researchers led by Prof. Aunu Rauf are mass rearing the parasitic wasp Anagyrus lopezi.

Bogor Agricultural University, Indonesia, where researchers are mass rearing parasitic wasps. Credit: G.Smith/CIAT

Our global resource base is fragile. As demand for food, animal feed and fuel is on the rise, together with growing global populations, farmers need to produce more food on less land. The earth is struggling to keep up, as soil fertility and environmental health are degrading.

Our environment can fight for itself. For thousands of years, complex ecosystems have evolved, with built-in resilience to fight pests and diseases. Yet the intensity of change, combined with climatic shifts, means sometimes nature needs a hand.

Action now to stop spread and build resilience, researchers warn

Dr. Tin Maung Aye explains: “Crop health is closely linked to soil health and proper fertilization of plants. When crops grow in healthy soil, with access to micro- and macro-nutrients, they will be stronger and ultimately more able to fight off native and invasive pests.”

But increasing pressure on fewer land resources is leading to soil exhaustion and nutrient depletion. When pest invaders arrive in such degraded environments, with climate-change often fuelling their spread, the impact can be grave.

Credit: I.Graziosi/ CIAT

Credit: I.Graziosi/ CIAT

This scenario is currently unfolding in Asia, where pests and diseases are invading and attacking cassava – regionally the third most important source of carbohydrates, a vital income-generator for millions of smallholder families and key food security crop.

For years, researchers at CIAT have warned about pest and disease treats in Asia. Take, for example, the rapid spread of the “pink mealybug,” or Phenacoccus manihoti. In 2008, pink mealybug was reported in Thailand and has since aggressively spread.

One of the most destructive cassava pests in the world, it can now be found throughout Cambodia, Laos, Myanmar, Thailand, Vietnam, China, and most recently, Indonesia – some of Southeast Asia’s key cassava-growing areas.

In Indonesia – where the invader has munched its way through half of the country’s cassava fields, taking a large bite out of the cassava industry’s feed-stock, farmer’s meals and incomes – there is an ideal climate for mealybug.

Since cassava originated in South America, few natural enemies are on its side in Indonesia to fight pests. “Mealybug is in the lap of luxury, with insufficient indigenous predators and parasitoids to keep populations down,” said CIAT entomologist Dr. Kris Wyckhuys.

Unleashing the enemy…

To help ecosystems fight back, researchers have investigated environmentally-sound integrated pest management solutions, involving biological control programs as an alternative to sweeping fields with pesticides, which could have disastrous environmental impacts.

The miniature South American wasp Anagyrus lopezi, which pose no threat to humans, animals or other insects – feeding only on cassava mealybug as its natural predator – gruesomely lays its eggs inside the pink mealybug slowly mummifying and killing them.

Last year, around 3,000 tiny parasitic wasps were released into a confined cage in Indonesia, in the first phase to stamp out the pest. These efforts are part of wider research investigating cassava threats and diseases in the region.

A curse on cassava farmers in Cambodia

And pests are not the only problem for cassava farmers. Spurred on by more intense agricultural production on smaller pieces of land, together with climatic changes, new and mysterious cassava diseases are emerging.

Like cassava witches’ broom disease. In key cassava growing areas of Cambodia, virtually all fields are infected, with in-field incidence at worryingly high levels, say researchers. The situation is so serious that many farmers are struggling to find disease-free cassava to plant.

The disease can wipe out whole fields and reducing crop yields by 30-35%, slashing starch content – disastrous for farmers who sell cassava to starch processors and a threat to industry, with cassava products traded from Cambodia estimated at over US$250 million.

Cassava infected by cassava witches' broom disease. Credit: G.Smith/CIAT

Cassava infected by cassava witches’ broom disease. Credit: G.Smith/CIAT

Active prevention can keep the disease at bay, but currently, once the disease has struck, farmers are doomed. With no curative solutions, there is little they can do to control the disease and save their crop.

What’s worse, farmers are often oblivious to the symptoms and only become aware when they harvest – when it’s too late. And, the disease itself moves throughout the plant at different stages, making it difficult for researchers to detect and diagnose.

Fighting back

Southeast Asian researchers are joining hands to fight the disease. Through an EC-funded, IFAD-managed initiative, Vietnamese and Thai scientists are using state-of-the-art technology to pin-point the cause of the spread and develop pregnancy-test-like diagnostic kits, which change color when the disease is present.

There is still some way to go to find a “cure,” and the rapid arrival of pest and disease invaders bolsters the likelihood that others are on the way. In the meantime, CIAT, together with national and international partners in Asia, continues to investigate resilient cassava varieties, and hammer out solutions and action plans to help the environment fight back.

Cassava witches' broom disease. Credit: G.Smith/CIAT.

Cassava witches’ broom disease. Credit: G.Smith/CIAT.

This post was originally posted on World Environment Day (WED) – a United Nations’ declared day for encouraging worldwide awareness and action for the environment – to provide an insight into what CIAT is doing to help build the environment’s resilience, to fight back against pests and diseases impacting food security.

Useful resource materials: 

Cartoon guide: Defeating cassava witches’ broom

Video: managing cassava mealybugs in Asia (available in English, Burmese, Indonesian, Khmer, Lao, Thai and Vietnamese)

Books: Farmers’ Guide: Sustainable management of cassava: from research to practice 

Reference manual: Sustainable cassava management in Asia: a reference manual 

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