BEMISIA-TABACI (HEMIPTERA, ALEYRODIDAE) TRAP CATCHES IN A CASSAVA FIELD IN COTE-DIVOIRE 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 A frican crop. Information about vector movement is important for unders tanding the epidemiology of this disease and the experiments reported here were designed to examine B, tabaci flight activity both in and ar ound a cassava crop in relation to time of day, crop growth stage, win d direction and speed, and to the resulting pattern of infected plants within the field at harvest. At wind speeds of <0.4 ms', adult B. tab aci approached the yellow traps by flying upwind. At greater wind spee ds, significantly fewer B, tabaci adults approached the traps from dow nwind, thus reversing the directionality of the catch. When the direct ion of the prevailing south-west wind reversed, so did the directional ity of the catch. Bemisia tabaci adults were flight active throughout the day and the greatest percentage were caught above the canopy betwe en 06.00-08.00 h, when wind speeds were lowest. Trap height and positi on significantly affected catch with the greatest numbers caught on th e lowest traps. More than three times as many B. tabaci adults were ca ught on traps situated downwind from the field compared to those upwin d, suggesting that the field was acting as a source of whiteflies. Ln both years, African cassava mosaic disease (ACMD) incidence was highes t and lowest, respectively, on the edges and in the middle of the tria ls, with the highest incidence occurring on the edges facing the preva iling wind direction. These results are discussed in relation to the e pidemiology of ACMD and to potential cultural control methods such as the use of ACMD-resistant guard rows to protect a mainly susceptible c rop.