Wasps to Fight Thai Cassava Plague

BANGKOK — Entomologists deployed the first wave of an army of 250,000 tiny wasps over the weekend in a campaign to eradicate a plague of mealybugs that threatens to devastate Thailand’s $1.5 billion cassava crop.

The wasps, each smaller than a pinhead, home in on the mealybugs, piercing and laying their eggs inside them. The larvae devour the mealybugs from within, emerging in a few days from their mummified shells to seek new hosts.

It is the latest battle in a competition between farmers and predators for the crops that sustain them both, with this species of mealybugs feeding exclusively on cassava and the wasps feeding exclusively on the cassava-eating mealybugs.

“In that sense, it’s the perfect biological control,” said Rod Lefroy, regional research coordinator in Asia for the International Center for Tropical Agriculture, a nonprofit group that has coordinated the release.

The use of wasps, which has been effective in Africa, is expected to also succeed in Thailand, the world’s leading exporter of cassava, which is also known as manioc, tapioca and yucca.

In Africa, where the use of wasps to kill mealybugs was pioneered, a new plague is already threatening vast cassava plantations: a disease known as brown streak, for which no cure has yet been found.

“It’s going to be an international game of cat and mouse,” said Tony Bellotti, an entomologist at the International Center for Tropical Agriculture in Colombia who is a specialist in wasps and mealybugs. “As the cassava mealybug finds its way to new countries, we can send in the wasps.”

Early signs of mealybug infestation have been reported in Cambodia, Laos and Myanmar, Thailand’s neighbors. “Cassava production in Southeast Asia has enjoyed an extended honeymoon, relatively free of major pest and disease outbreaks,” Dr. Bellotti said.

Thailand, the third largest producer of cassava, after Nigeria and Brazil, accounts for 60 percent of worldwide exports of the root, which is used in foods like noodles, the flavor-enhancer monosodium glutamate and products including toothpaste.

Much larger areas are cultivated in Africa, but Dr. Lefroy said that about 50 percent of production there was consumed locally as food.

Most of Thailand’s exports go to China, which produces 40 percent of its own huge demand for the plant. China’s consumption is expected to double in the next few years, making cassava an increasingly lucrative crop.

The mealybugs, with a life cycle of about a month, can spread quickly, with each insect laying an average of 440 eggs and producing 10 generations in a year. The bugs feed on the tips of cassava plants, stunting their growth with a toxic saliva.

The threat to Thailand’s industry emerged in force last year, when 20 to 25 percent of the crop was destroyed, frightening farmers and driving up prices.

Hundreds of farmers attended the ceremonial first release Saturday in Khon Kaen, some of them gathering up handfuls of wasps for themselves, Dr. Lefroy said.

The tiny wasps neither buzz nor sting, he said. “You’ve got to be an entomologist to even think of them as wasps.”

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