Fourth International Bemisia Workshop International Whitefly Genomics Workshop
Mortality factors affecting populations of Bemisia tabaci on cassava in Uganda
1 International Institute of Tropical Agriculture-Uganda, Kampala, Uganda. Correspondence: p.asiimwe@iitaesarc.co.ug
2 Makerere University, Kampala, Uganda
3 Tel Aviv University, Ramat Aviv, Israel
4 International Institute of Tropical Agriculture-Tanzania, Dar es Salaam, Tanzania
5 Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent, UK
A cohort-based approach was used to determine the sources and rates of mortality of Bemisia tabaci on field-grown cassava in Uganda. Daily direct observations were used to construct partial life tables for twelve generations of egg and nymph populations which were studied over a one year period. Mortality was categorized as due to dislodgement, predation, parasitism (for nymphs only), unknown death and inviability (for eggs only). The highest mean rate of marginal mortality across all stages was attributed to parasitism, with dislodgement and predation following respectively. Across all factors, the highest mean rate of marginal mortality was observed in the fourth instar followed by the eggs, first, second and third instars respectively. Key factor analysis revealed that dislodgement was the major mortality factor contributing to generational mortality in eggs while for nymphs, parasitism in the fourth instar was the main driving force behind the observed generational mortality. Highest irreplaceable mortality in both the egg and nymph stages was attributed to dislodgement followed by parasitism, predation and least was due to unknown death. Across stages, the highest irreplaceable mortality rates were observed in the eggs and the fourth instar nymphs. The other stages had relatively low rates of irreplaceable mortality. Rain protection experiments revealed no significant differences in marginal mortality rates when compared to the open field situation.