Biological Control of the Cassava Green Mite in Africa with Brazilian Isolates of the Fungal Pathogen Neozygites tanajoae

Abstract

Cassava green mite (CGM), Mononychellus tanajoa (Acari: Tetranychidae), became one of the most important pests of cassava in Africa after its introduction from the Neotropics in the early 1970s. Exploration for potential natural enemies to be introduced in Africa began in Brazil in 1988 and soon revealed that the pathogenic fungus Neozygites tanajoae is an important natural enemy of CGM in Brazil and causes epizootics in CGM populations in a broad range of climates. During the last two decades, a series of studies was conducted to understand the biology and ecology of this pathogen in order to facilitate its use in Africa. A collection of N. tanajoae and N. floridana isolates from Brazil, Colombia and Benin was established, and N. tanajoae isolates from Brazil were selected based on efficient mortality and mummification levels. The selected isolates are specific to CGM, kill all active stages of the host with median lethal times of <5 days, and infections are initiated by even a single capilliconidium. Using living, infected mites, experimental releases of two isolates of N. tanajoae from Brazil and one isolate from Benin were carried out in the Adjohoun district, Republic of Benin, in January 1999. Post-release monitoring conducted up to 48 weeks after the releases revealed that higher infection rates were achieved only by introductions of Brazilian isolates and not where the native isolate or non-infected mites were released. Using molecular probes it was confirmed that the fungus recovered after the releases was from Brazil.