Desert locust outbreaks in the Sahel: resource competition, predation and ecological effects of pest control.
The desert locust Schistocerca gregaria has been considered a major pest since ancient times, as locust swarms holding millions of insects move throughout the Sahel, northern Africa, Middle East and southern Mediterranean countries. Most research has focused on the biology of the species and the development of strategies in locust control, but little is known about the place of locust pulses within food webs in which domestic herbivores and European long-distance migratory birds are also involved. We evaluated the role of desert locust outbreaks in the food webs of the Sahelian region. We analysed the potential resource competition with domestic herbivores and the response of a generalist predator by assessing its diet and foraging behaviour in relation to the availability of locusts. Stable isotope analyses revealed that little trophic overlap exists between desert locusts that feed on trees and shrubs and nomadic livestock that feed on grasses in the Sahelian savanna grasslands. These results suggest low resource competition with the main human resources in regions with little agricultural development. In addition, during an outbreak that occurred in winter, desert locusts were consumed by resident and long-distance migrant birds. This accounted for significant changes in the diet and foraging strategies of wintering generalist predators such as the black kite Milvus migrans. Synthesis and applications. Our results raise questions about the need for spraying locust swarms in areas where economic losses are scant and wintering populations of European trans-Saharan migrant birds are high. A deeper insight into the ecological and economical role of these outbreaks is urgently needed, together with a reassessment of desert locust control in the Sahel.