Evaluating the relative impacts of plant quality and natural enemies on mortality of Bemisia tabaci in cotton

Plant quality and natural enemies are important determinants of insect herbivore dynamics. Host plant quality not only directly affects insect abundance but indirectly mediates the densities and impacts of insect natural enemies. We simultaneously manipulated plant quality and natural enemy abundance and evaluated their relative impact on the mortality of sweetpotato whitefly, Bemisia tabaci (Biotype B), in field grown cotton using in situ life tables and population census. Whitefly mortality was higher when natural enemies were left unaltered compared to when they were reduced, regardless of level of plant quality. These mortality differences were reflected in seasonal densities of B. tabaci with higher densities observed when natural enemies were reduced compared to when they were unaltered. Irreplaceable mortality was primarily associated with predation when natural enemy densities were unaltered and dislodgement when natural enemy densities were reduced. Key factor analyses revealed predation and parasitism as the main factors associated with generational mortality across all levels of plant quality. Our results show that predators are significantly impacting the performance of B. tabaci in cotton, and their impact is not mediated by the levels of plant quality. This emphasizes the importance of conservation biological control in this system.