South American wasps to be let loose on Thailand's cassava crop

Jul 16, 2010, 11:01 GMT

Bangkok - Scientists are soon to release a quarter of a million South American wasps on Thailand's cassava crop in a sting operation against an infestation of mealybugs.

The Department of Agriculture was scheduled Saturday to release the Anagyrus lopezi wasps in Khon Kaen province, 350 kilometres north-east of Bangkok, said Rod Lefroy, regional research leader for the non-profit International Center for Tropical Agriculture (CIAT).

'In the coming months more wasps will be let loose on other areas in north-east Thailand where mealybugs have been detected, and some may even be sent across-border to Cambodia,' Lefroy said in a telephone interview.

The Anagyrus lopezi wasp, indigenous to Paraguay, is the natural enemy of the mealybug.

Thailand's cassava crop, which generates 1.5 billion dollars in revenues each year and accounts for 60 per cent of the world's cassava exports, has been hit by a mealybug infestation that affected about 200,00 hectares last year.

Cassava output during the first six months of this year fell 26 per cent because of the infestation.

Cassava, also known as manioc or tapioca, became a major export crop in the 1960s-70s. It was initially introduced to South-East Asia by Portugese traders hundreds of years ago.

For decades, the region's cassava crop eluded its natural enemy, the tiny South American mealybug, Phenacoccus manihoti.

'Cassava production in South-East Asia has enjoyed an extended honeymoon, relatively free of major pest and disease outbreaks,' said Tony Bellotti, a CIAT entomologist, who has spent 35 years investigating cassava pests. 'But now it's over.'

Scientists do not know when or how the mealybug was introduced to Thailand.

'We're almost certain someone brought a cassava plant in, either from Africa or Latin America, and unintentionally brought in the mealybug as well,' Lefroy said.

Mealybugs turned into a major infestation last year and now threaten to wipe out half this year's crop.

CIAT, in collaboration with the Department of Agriculture, imported 500 pairs of the wasp in November.

Thai scientists have increased the wasp colony to a quarter of a million and are now ready to release them.

Female wasps seek out the bug, inject their eggs into them and as the wasp larvae grow it feeds on the host and kills it.

In several controlled tests, scientists have found no alternative hosts for the South American wasps.

'The wasps will not be 100 per cent effective,' Lefroy said. 'The mealybugs won't disappear completely but their numbers will come down, bringing the wasp numbers down with them, and eventually an equilibrium is reached.'

CIAT and the Nigeria-based International Institute of Tropical Agriculture (IITA) carried out a similar wasp-led campaign in Africa in the 1980s, staving off a major food security catastrophe.

'Sending in the wasps is a proven way to kill the cassava mealybugs quickly and effectively,' Bellotti said. 'Think of them as a kind of eco-friendly SWAT team.'