Cassava pest in retreat

Abstract

The battle against the cassava green mite (Mononychellus tanajoa) has turned and the pest is in retreat. After 13 years of painstaking research scientists are confident they have found the right natural enemies to control the pest. In 1971, cassava green mites were found in Uganda. Within eight years they had spread right across the continent, causing crop losses as high as 80% in some places. In 1983 national and international scientists began their search in South America for biological agents to control the pest. A predatory mite, Typhlodromalus manihoti, was released by the International Institute of Tropical Agriculture (IITA) in Ghana and Benin in 1990 and it has gradually spread out and reduced populations of the cassava green mite. Three years later a second predato mite, Typhlodromalus aripo, was released in Benin and after that in other countries of East and West Africa. Initially it spread at a rate of about 12 km/year but in subsequent years has dispersed much more rapidly. One reason for this rapid spread is that T aripo has remained on planting material as it is has been moved from one farm to another. probably unbeknown to farmers. From a release site in Benin it has quickly moved 400 km into Nigeria, and this includes moving some 350 km from the coast up to the northern limits of the cassava green mite. Once T aripo has become established it has reduced pest populations by two thirds, and scientists expect this could lead to a 30% increase in cassava yields. On the cassava plant, T aripo spends its productive life in the shoot tips but in those where cassava loses its leaves due to low temperatures or drought, the predatory mite is unable to survive. IO overcome this problem scientists are going back to South America, to areas that are climatically similar, to search for more natural enemies. In the meantime IITA is testing a fungal pathogen, Neozygites floridana. The advantage of using T aripo is that it does not require a mass breeding programme. It can be transferred to new locations on the shoot tips, established in the field for multiplication and later the shoot tips can be picked and moved to the release sites. This makes it very easy for national programmes to organize and implement. Biological Control Centre for Africa IITA BP 08-0932 Cotonou, BENINThe battle against the cassava green mite (Mononychellus tanajoa) has turned and the pest is in retreat. After 13 years ofpainstaking research scientists are confident they have found the right natural enemies to control the pest. In 1971, cassava..