Migrations ofDysdercusspp. (Hemiptera: Pyrrhocoridae) related to movements of the Inter-Tropical Convergence Zone in West Africa

Abstract

AbstractThe possibilities of migrations in the West African species ofDysdercusare discussed and a hypothesis of long-range migrations associated with the Inter-Tropioal Convergence Zone and its wind systems is proposed. Catches of adultDysdercusin four light-traps distributed from south to north of the Ivory Coast showed that the phenology of assumed migratory activity inD. voelkeriSchmidt differs with latitude and may be correlated with particular types of weather; stainer migrations taking place during the warm, wet and sunny part of the year. The whole life cycle of the insects as well as their flight activity occur under these climatic conditions, prevailing in a belt of 600–900 km width, situated immediately to the south of the Inter-Tropical Front. Colonisation of newly available habitats is thus only possible when climatic factors allow: (i), migratory flight activity and (ii), survival in the colonised area. A close examination of the timing of both migrations in the two main species,D. voelkeriandD. melanoderesKarsch, and of annual movements of the I.T.F. leads to the only logical hypothesis that the transportation of migrating insects is effected by atmospheric convergence, prevailing wind currents and air mass displacements.