Species Exclusion Between an Invasive and an Indigenous Whitefly on Host Plants with Differential Levels of Suitability

The whitefly Bemisia tabaci has risen to international prominence since the 1980s due to the rapid spread around the globe by the two species B and Q within this species complex. The invasion of B has often been associated with the displacement of indigenous whiteflies. As the genetic structure of B. tabaci is diverse, more case studies of the competitive relationships between B and indigenous species of the whitefly species complex will help to understand further the mechanisms underlying the invasion of B. We examined the competitive interactions between B and ZHJ2, a widely distributed indigenous whitefly in Asia, on host plants with differential levels of suitability to the two species in the laboratory, and also tested the effect of insecticide application on the competitive relationships. Three species of plants were tested including cotton, a plant showing similar levels of suitability to both species, squash, a plant showing higher suitability to B than to ZHJ2, and kidney bean, a plant showing higher suitability to ZHJ2 than to B. In the case of no insecticide application, B displaced ZHJ2 on cotton, squash, and kidney bean by the 6th, 3rd and 10th generation, respectively. With the application of imidacloprid, the displacement of ZHJ2 by B on cotton occurred by the 5th generation. As the displacement progressed, the proportion of B females increased, and the proportion of ZHJ2 females decreased on cotton and squash. In contrast, on kidney bean the proportion of B females remained unchanged while that of ZHJ2 increased. These results show the strong capacity of the invasive B to displace ZHJ2, and indicate that host plants with differential levels of suitability to the two species may affect the speed but not the trend of displacement and insecticide application may accelerate the process of displacement.