Thailand imported a 1mm wasp from South America to end the cassava mealybug crisis

Cassava reached Southeast Asia from South America and grew without pesticides until the cassava mealybug arrived in 2008. Yields fell 60-80%, farmers cleared forest for extra land, and the price of cassava starch in Thailand, the top exporter, tripled as substitutes like corn and potato rose too.

The remedy was the mealybug's natural enemy in South America, a 1mm parasitic wasp, Anagyrus lopezi, which is very selective in using the mealybug as a host for its larvae. It was introduced to Thai cropland by late 2009. By mid-2010, researcher Kris Wyckhuys says, wasps were reared by the millions and mass-released throughout Thailand, including by airplane.

The same wasp had worked in West Africa in the early 1980s, cutting mealybug numbers from over 100 per cassava tip to under 10-20, and spreading over 200,000 square kilometres in southwestern Nigeria in under three years.

Find the pest's natural enemy at home and mass-release it, so a 1mm wasp does what pesticides couldn't.

The wasp attacks only the cassava mealybug, so it should not harm other species.

The pest had arrived without any natural enemy to hold it back.

Mass rearing and aerial release covered large areas fast.

The same fix had a track record in West Africa.

Classical biological control works when the enemy is host-specific and the pest arrived without its predator.

Wyckhuys told the BBC in 2020 that he calculated the benefit to farmers in 26 Asia-Pacific countries at $14.6bn to $19.5bn per year, and said no detailed data exist on how fast mealybug populations fell in Thailand. The same article stresses that biological control can go wrong, as with Australia's cane toads, introduced in 1935 against scientific advice.