Diversity and distribution of sweet potato weevils (Cylas spp.) in southern Benin

Abstract

Sweet potato (SP) weevils, Cylas spp. are important pests of SP throughout the world and particularly in Africa. They cause damage to the crop as a result of their diet and reproduction. This study was undertaken to identify species of Cylas attached to SP production in southern Benin and to assess the distribution of the insects in study areas. A survey was conducted from October to December 2015 in fifteen districts of the departments of Mono, Couffo, Ouémé and Plateau in agro-ecological zones 6, 7 and 8 of Southern Benin. Weevil adults were collected alone in bulk but also along with infested vines and tuberous roots. Sweet potato vines and tuberous roots were incubated in laboratory for emergency of insect adults. Two species of Cylas were identified: C. puncticollis Boheman and C. brunneus Schoenherr. Cylas puncticollis were observed in 82.70% of total samples collected and were found in all districts prospected while C. brunneus were observed in 17.42% of the samples and were observed only in the districts of Adjohoun, Bopa, Houéyogbé, Ifangni and Klouékanmè. The highest incidence (100.00 ± 0.00%) and the lowest incidence (0.00 ± 0.00%) were recorded with C. puncticollis and C. brunneus, respectively, in the districts of Aplahoué, Comè, Sakété, Adja-Ouèrè and Toviklin. All SP farmers used only vine cuttings for planting, with 10% of them treating planting material with chemical insecticides. Eighty percent of farmers use planting materials taken in their own fields whereas 20% obtain them from neighboring fields either free of charge or purchase them. This study gave use more detailed information on the identity and distribution of sweet potato weevils in Benin and was useful for the establishment of control measures against them.