1In Africa, the larvae of certain butterflies bore into the stalk of cereals such as maize or sorghum, causing average yield losses of 20% to 40%. To deal with this problem, farmers learned how to eliminate surrounding uncultivated land which, according to agronomists, formed a reservoir for these pests. This idea was refuted by other scientists as part of a programme deployed in the early 2000s in East Africa, primarily in Kenya, Uganda and Tanzania.

Larva of Busseola fusca insect, a maize and sorghum pest.

2As larvae seemed to differentiate themselves through a variety of cycles and behaviours, researchers examined them more closely and found dozens of species behind the few pests identified for close to a century. This finding, confirmed by genetic studies, raised questions about what drives only some species to become insect pests. Research revealed that most larvae are in fact highly specialised. Among the numerous species found in uncultivated land, only a few generalist species or species feeding on grasses related to cereals are capable of raiding crops.

3This uncultivated land is also home to many natural enemies of larvae, in particular wasps. Therefore, proximity to uncultivated land, far from being a problem, seems to be a solution to limit the impact of pest larvae by strengthening biological control.

4A recent biological control assessment carried out in Kenya, Mozambique and Zambia showed that it helped limit yield losses while lifting nearly 140,000 farmers out of poverty. Another promising solution to strengthen biological control would be the simultaneous cultivation of several types of cereal, to limit the proliferation of specialist insects.