Bemisia tabaci (Hemiptera : Aleyrodidae) trap catches in a cassava field in Côte d'Ivoire in relation to environmental factors and the distribution of African cassava mosaic disease

African cassava mosaic virus (ACMV), vectored by the whitefly, #Bemisia tabaci$ (Gennadius), is considered the most damaging pathogen of any African crop. Information about vector movement is important for understanding the epidemiology of this disease and the experiments reported here were designed to examine #B. tabaci$ flight activity both in and around a cassava crop in relation to time of day, crop growth stage, wind direction and speed, and to the resulting pattern of infected plants within the field at harvest. At wind speeds of < 1.4 m/s, adult #B. tabaci$ approached the yellow traps by flying upwind. At greater wind speeds, significantly fewer #B. tabaci$ adults approached the traps from downwind, thus reversing the directionality of the catch. When the direction of the prevailing south-west wind reversed, so did the directionality of the catch. #Bemisia tabaci$ adults were flight active throughout the day and the greatest percentage were caught above the canopy between 06.00-08.00 h, when wind speeds were lowest. Trap height and position significantly affected catch with the greatest numbers caught on the lowest traps. More than three times as many #B. tabaci$ adults were caught on traps situated downwind from the field compared to those upwind, suggesting that the field was acting as a source of whiteflies. In both years, African cassava mosaic disease (ACMD) incidence was highest and lowest, respectively, on the edges and in the middle of the trials, with the highest incidence occurring on the edges facing the prevailing wind direction. These results are discussed in relation to the epidemiology of ACMD and to potential cultural control methods such as the use of ACMD-resistant guard rows to protect a mainly susceptible crop. (Résumé d'auteur