Six mango,Mangifera indica L., plantations around Parakou, northern Benin, were sampled at 2-wk intervals for fruit fly damage from early April to late May in 2005. Mean damage ranged from 1 to 24% with a weaver ant,Oecophylla longinoda (Latreille), being either abundant or absent. The fruit fly complex is made up ofCeratitis spp. andBactrocera invadens Drew et al., a new invasive species in West Africa. In 2006,Ceratitis spp. peaked twice in the late dry season in early April and early May, whereasB.invadens populations quickly increased at the onset of the rains, from mid-May onward. Exclusion experiments conducted in 2006 with ‘Eldon’, ‘Kent’, and ‘Gouverneur’ confirmed that at high ant abundance levels,Oecophylla significantly reduced fruit fly infestation. Although fruit fly control methods are still at an experimental stage in this part of the world, farmers who tolerated weaver ants in their orchard were rewarded by significantly better fruit quality. Conservation biological control with predatory ants such asOecophylla in high-value tree crops has great potential for African and Asian farmers. Implications for international research for development at the Consultative Group on International Agricultural Research level are discussed.