Manipulating natural enemy behavior to improve biological control: attractants and repellents of a weaver ant.
Farmers may not want certain natural enemies of insect pests to be present in their fields all year round, due to the detrimental effects they might have on themselves or on their crop. We explored the potential for manipulating the behavior of the African weaver ant, Oecophylla longinoda, which may bite humans while being a major natural enemy against the invasive fruit fly, Bactrocera dorsalis, in Africa. Our aim was to find repellents that might help to protect farmers when working in the fields, while also coming up with ways of increasing weaver ant populations, by finding carbohydrate sources from local cultivated plants (attractant). To that end, we carried out behavioral experiments in the laboratory which revealed (i) that oily repellents were the most efficient of all those tested, (ii) that the extra floral nectar of a legume crop, such as cowpea, was consumed by weaver ants, but in quite small amounts and also differently depending on the varieties. This approach, tackling these two aspects at the same time, was based on and shaped by the reality faced by farmers. The results are key to breaking down obstacles to using weaver ants in Africa and are discussed in this respect.