The cassava mealybug, Phenacoccus manihoti, is originally from South America. It sucks the sap out of plants causing abnormal growth, a sooty mould, wilting and discolouration. A severe attack can have devastating effects on cassava plantations.The mealybug has already spread over 160,000 hectares across the East and North-eastern provinces of Thailand, where cassava is an important export crop. The bug was not immediately recognized because another closely related mealybug species common on cassava confused the situation.
To halt the spread of the mealybug a colony of wasps, the natural enemy of the pest, has been imported into Thailand from the IITA laboratories in Benin by Georg Goergen, an IITA Entomologist.
The same mealybug caused widespread devastation and famine when it destroyed cassava in Africa in the late 1970s. IITA came to the rescue then too, when they led a group of institutions in a campaign to find, import, rear and distribute the wasps from South America. By 1981, the wasps were located in Paraguay and later in Brazil; then shipped to IITA where they were mass-reared and distributed. The campaign was one of the greatest recent successes in biological control.
Anagyrus lopezi is a parasitoid wasp that also comes from South America. It lays its eggs on the cassava mealybug so that when its larvae are fully grown they can eat the bug. Using a biological control like this wasp negates the need for harmful chemicals.
The African success story means that experts are able to deal with infestations faster and at reduced costs because of the techniques learnt then. It is hoped that IITA’s involvement in the mealybug control project in Asia will produce similar positive results.