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Biological control of cassava green mite in Tanzania
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The cassava green mite Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) is one of the most important pests of cassava, a main staple food crop in Tanzania. The International Institute of Tropical Agriculture (ETA) in collaboration with the Tanzania National Biological Control P r o m (NBCP) launched in 1998 the biological control campaign against cassava green mite in Tanzania with the release of the neotropicd phytoseiid predator Z)phlodromallus aripo DeLeon (Acari: Phytoseiidae), which had proven to be an efficient biological control agent of the cassava green mite in West Mca. The campaign consisted of new introductions and redistributions of I: aripo from infested cassava shoot tips, follow-up surveys to determine establishment, spread, and impact, as well as extension and farmer training on pest and natural enemy recognition and means of enhancing predator efficacy. ~phlodromallusa ripo was h t fo und in March 1998 in the Tanga region, most likely invading h m the southern Kenya coast where it was released in 1996. Subsequently, the Tanzania NBCP in close collaboration with IITA has carried out numerous introductions and redistributions of the predator. Surveys conducted in the following 6 years revealed success M establishment, persistence and spread in five agro-ecological zones including the Lalce (Mars and Kagera regions, except parts of Mwanza region), Western (Kigorna region except Shinyanga region), Southern Highlands (Mbeya and Iringa region), Eastem (Tanga and Coast regions) and Southern (Lindi and Mtwara regions) zones. Up to 2005, there was still no T. arip in parts of 3 regions: Mwanza, Shinyanga and Ruvuma. Cassava green mite mean densities have declined to low levels (less than 20 actives per leaf) in all regions where 'I: a r b has been present. In on-fm impact assessment trial, 'I: aripo was capable of reducing population density of cassava green mite by 64.3% and increasing total and marketable cassava root weights by 61.2% and 71.7%, respectively. There was also a significant increase in total number of roots (25.4%), number of marketable roots (45.78%), stem weights (47.39%), and leaf weight (40.7%) where T, aripo was not eliminated. This report present evidence of the impact of biological control on cassava green mite populations and cassava yield in Tam&, and recommends the use of exotic isolates of the fungal pathogen Neozygites tanajoae, which has been established in West Africa, as a complementary alternative approach in controlling further the cassava green mite in the remaining spots of high infestations.