Indigenous weaver ants and fruit fly control in Tanzanian smallholder mango production
2016
Kirkegaard, N. | Offenberg, J. | Msogoya, T. J. | Grout, B. W. W.
The presence of weaver ant colonies can reduce fruit fly oviposition in mango production and can be effective as a fruit fly control strategy. Patrolling ants may disturb landing flies and may also deposit repellent compounds on to the fruits. This control strategy is being applied to export-orientated African mango production and the present study examines its potential for income-limited, rural production. The investigation was based in a community of mango growers in Tanzania where weaver ants are present, but not actively managed, in the mango trees. Fruits are harvested as mature, but not ripe, and enter the local market chain. The growers, and local traders, reported an overall 10-25% infestation of fruit fly larvae in their fruits, with significant variation possible for an individual grower or season. Infestation is higher, to a limited degree, in fruits in the market place than in those freshly picked, suggesting continuing, postharvest attention from fruit flies. The consensus view was sceptica, of any benefits due to the presence of weaver ants. Postharvest storage and procedures to accelerate ripening of the harvested fruit fortuitously reduce the infestation levels by raising fruit temperatures to lethal levels for fruit fly eggs and larvae. Direct observations showed a small, but significant reduction in fly landings on fruits previously patrolled by ants, supporting the proposed role for persistent repellents. Gas chromatography/mass spectroscopy did not identify any compounds uniquely linked to the presence of weaver ants that have insect-repellent properties ascribed to them but did reveal that ripening fruits emit increasing amounts of ethyl crotonate, a known attractant for gravid fruit flies.
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