The effects of cropping systems on cassava whiteflies in Columbia: implications for control of African cassava mosaic virus disease

The cassava whiteflies Aleurotrachelus socialis and Trialeurodes variabilis are outbreak pests which cause high yield losses in the Departments of Tolima and Cauca, Colombia. Studies were undertaken to examine the effects of intercopping and cassava varietal mixtures on whitefly population dynamics and related crop growth. Cassava intercropped with cowpea supported 46% fewer whiteflies per leaf and 70% fewer per plant than cassava monocultures. Reductions in whitefly numbers occurred 6 weeks after planting and persisted for 28 weeks after the cowpea crop was harvested. The lower herbivore load in the cassava/cowpea system resulted in a 13% yield loss compared with 58% loss in the monoculture, and intercropped cassava out yielded monoculture. Decreases in whiteflies resulting from intercropping cassava with maize were less substantial and led to no reduction in yield loss. Cassava varietal mixtures, consisting of alternate rows of whitefly-susceptible and partially resistant varieties, resulted in reduced T. variabilis densities on the susceptible cultivar. Implications of these results for the control of African cassava mosaic virus disease are discussed