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Thailand taps IITA’s expertise as cassava mealybug invades Asia

By Godwin Atser

The Thai Department of Agriculture at Chatuchak, Bangkok, has contacted the International Institute of Tropical Agriculture (IITA) for help in the biological control of the cassava mealybug, Phenacoccus manihoti, which had recently invaded Thailand and probably also Laos and Cambodia.

The mealybug has already spread over 160,000 hectares around the East and Northeastern provinces of Thailand, where cassava is an important export crop mainly for starch production and cattle feed.

To halt the spread of the mealy bug, a stock rearing colony of Anagyrus lopezi has been imported into Thailand from the IITA laboratories in Benin by Georg Goergen, IITA Entomologist. Goergen brought the materials in September 2009.

The wasps were placed into rearing under quarantine conditions in Bangkok and released in November 2009 after release permits were issued. Further releases were made in January 2010.

It will be recalled that this same mealybug had reached Africa in the late 1970s and caused widespread devastation and even famine when it destroyed cassava, which in Africa is an important food and locally traded subsistence crop.

Respite however came when an IITA-led group of institutions initiated a campaign to find, import, rear and distribute adapted natural enemies from South America, the purported home of the foreign invader. By 1981, the encyrtid parasitoid A. lopezi (then Apoanagyrus or Epidinocarsis) was located in Paraguay, later in Brazil, shipped through quarantine, mass-reared at IITA and distributed. What followed was one of the greatest recent successes in classical biological control.

In Thailand, the cassava mealybug was not immediately recognized because another closely related mealybug species common on cassava, presumably Phenacoccus madeirensis, confused the situation, according to Peter Neuenschwander, IITA Emeritus Scientist based in IITA-Benin. He says the identification of the mealybug by a taxonomic authority cleared the path for classical biological control.

It is hoped that IITA's involvement in the mealybug control project in Asia will produce results within a much shorter time span and at much reduced costs as experts intend to leverage on past experience and techniques that made the African success story.