The relative influence of plant quality and natural enemies on population dynamics of Bemisia tabaci in cotton

Plant quality and natural enemies are influential in determining the abundance and seasonal dynamics of herbivores on plants. Field experiments examined the comparative influences of plant quality and natural enemies on the population dynamics of Bemisia tabaci in cotton. Plant quality was varied using different irrigation regimes within which natural enemy densities were either reduced using broad spectrum acephate sprays or left unaltered. Cohort-based life tables for immature whiteflies showed that regardless of irrigation regime marginal rates of immature mortality were reduced, resulting in higher adult densities following reduction of natural enemies compared with plots in which natural enemies were unaltered. Mortality was consistently highest later in the season and particularly in the 4th nymphal stadium, regardless of levels of plant quality and natural enemy manipulation. The largest sources of irreplaceable mortality were due to predation in the unaltered plots and dislodgement in plots where natural enemies had been reduced. No significant differences in marginal mortality were observed among the different levels of plant quality receiving the same natural enemy treatment. These results indicate a stronger influence of natural enemies compared to plant quality in the population dynamics of Bemisia tabaci and emphasize the continued importance of conservation biological control in integrated management of whiteflies on cotton.