Sugar feeders reduce weaver ants’ drawbacks when used as biological control agents in mango orchards

Abstract

The use of predatory arthropods in biological pest control in agriculture can generate resistance by farmers when these beneficials become noxious for them or their crops. The African weaver ant, Oecophylla longinoda (Hymenoptera: Formicidae), an effective biocontrol agent of pests, particularly Bactrocera dorsalis fruit flies in mango orchards in West Africa, is a good example of such inconveniences. We here explored whether manipulating their behavior by providing sugar feeders on trees would (i) alter their mutualistic relationships with scale insects, thereby reducing the incidence of this pest, (ii) decrease nest abundance often considered by farmers to reduce foliage development, and (iii) reduce their aggressiveness. To that end, a field monitoring was launched in an organic mango orchard in Senegal wherein three treatments were compared: (1) mango trees with ants and sugar feeder, (2) mango trees with ants but no sugar feeder, and (3) mango trees with neither ants nor sugar feeder. The population dynamics of scale insects and weaver ants as well as their behavior were monitored over two years. Sugar provisioning significantly reduced scale insect infestations, nest abundance, and ant aggressiveness over time. Such manipulation of ant behavior through sugar supplementation should help breaking down obstacles that hamper their wide-scale use for the biological control of fruit flies in mango orchards.