Mortality factors affecting Bemisia tabaci populations on cotton in Turkey

Cohort-based, partial life tables were constructed to determine the sources and rates of mortality factors affecting Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on cotton in the eastern Mediterranean region of Turkey over a two year period. Mortality factors were recorded as due to predation, parasitism, dislodgement and unknown for five developmental stages. Across 10 independent cohorts, the highest median rate of marginal mortality pooled over all stages was attributed to parasitism (0.69) followed by predation (0.67). The key factor was hypothesized to be parasitism based on graphical and regression-based comparison of individual factor k-values to total generational mortality. The greatest amount of marginal immature mortality occurred during the fourth nymphal stadium (median = 0.77) and mortality during this stage was also most predictive of variation in total mortality. Pooled over all developmental stages, the highest rates of irreplaceable mortality were associated with parasitism (median: 0.112), followed by predation (0.088), dislodgement (0.020) and unknown (0.017). Although crawler mortality was not explicitly measured, sensitivity analyses indicated that mortality during this stage would have changed total mortality by only 0.45-1.21% and had no effect on identification of key factors. There was no significant effect of cotton cultivar on any mortality factor or total mortality over the two years of study. Results suggest that conservation of natural enemies, particularly parasitoids, may provide for more sustainable management of B. tabaci on cotton in Turkey.