Ecological management of cereal stemborers in African smallholder agriculture through behavioural manipulation.

Abstract

1. Africa faces serious challenges in feeding its rapidly growing human population owing to the poor productivity of maize and sorghum, the most important staple crops for millions of smallholder farmers in the continent, with yields being among the lowest in the world.2. A complex of lepidopterous stemborers attack cereals in Africa. However, their effective control is difficult, largely as a result of the cryptic and nocturnal habits of moths, and protection provided by host stem for immature pest stages. Moreover, current control measures are uneconomical and impractical for resource‐poor farmers.3. An ecological approach, based on companion planting, known as ‘push–pull’, provides effective management of these pests, and involves combined use of inter‐ and trap cropping systems where stemborers are attracted and trapped on trap plants with added economic value (‘pull’), and are driven away from the cereal crop by antagonistic intercrops (‘push’).4. Novel defence strategies inducible by stemborer oviposition have recently been discovered, leading to the attraction of egg and larval parasitoids, in locally adapted maize lines but not in elite hybrids. We also established that landscape complexity did not improve the ecosystem service of biological control, but rather provided a disservice by acting as a ‘source’ of stemborer pests colonising the crop.5. Here we review and provide new data on the direct and indirect effects of the push–pull approach on stemborers and their natural enemies, including the mechanisms involved, and highlight opportunities for exploiting intrinsic plant defences and natural ecosystem services in pest management in smallholder farming systems in Africa.