Studies On The Competitive Displacement Between An Alien B Biotype And A Native Non-B Biotype Of Bemisia Tabaci (Homoptera: Aleyrodidae) In Zhejiang, China

In recent years, the B biotype of Bemisia tabaci has successfully invaded China and outbreaks of this pest have occurred in some areas. B biotype of B. tabaci has caused severe losses to crops, and there has been evidence to indicate that it has been replacing the native non-B biotypes of B. tabaci. To elucidate the competition between biotypes and the mechanisms of the displacement of native non-B biotypes by the B biotype of B. tabaci, this study compared the biological characteristics between a B biotype and a non-B biotype of B. tabaci collected from Zhejiang, China in 2003, investigated the competitive displacement between them and examined the behavioral mechanisms for the displacement. The results are summarized as follows.(1) Identification of the B biotype and non-B biotype ZHJ-1 population of B. tabaci. The whiteflies collected from cabbage in Hangzhou, Zhejiang could induce silverleaf symptoms in squash plants, whereas whiteflies collected from cotton in Xiaoshan, Zhejiang could not. The two populations showed obvious differences in pupal morphology. The width of anterior and posterior wax fringes of the former were 2.5 times and 1.8 times that of the latter respectively. RAPD molecular markers with the same random primer showed obvious difference in specific fragments amplified between them. The mitochondrial cytochrome oxidase I (CO I) sequences of the two biotypes showed 85.3% identity. Phylogenetic analyses indicated that the population collected from cabbage was an alien B biotype of B. tabaci, and the population collected from cotton was a native non-B biotype from Asia. The CO I gene sequence of the non-B biotype from Zhejiang (AJ867556) has the highest similarity to that of a non-B biotype from India (AF321928) in the GenBank, but their CO I sequences show only 85.3% identity. There results suggest that the Xiaoshan population from Zhejiang is a new record of a native biotype from Asia, and this biotype is named non-B biotype ZHJ-1 population.(2) Comparison of performance on different host plants between the B biotype and non-B biotype ZHJ-1 population. In the six plant species tested, cotton was a suitable host plant for both biotypes. Squash was also a suitable host plant forthe two biotypes, but the performance of the B biotype on this plant was significantly better than that of the non-B biotype. B biotype completed its development from egg to adult on cabbage, tobacco and kidney bean, but was unable to do so on pepper. On the contrary, some individuals of the non-B biotype could complete development from egg to adult on pepper, but was unable to do so on cabbage, tobacco and kidney bean. These results indicate a broader host range for the B biotype compared to that of the non-B biotype, but host plants suitable for the non-B biotype are not always suitable for the B biotype.(3) Competitive displacement between B biotype and non-B biotype ZHJ-1 population. On squash, when the two biotypes began competition in equal numbers, the non-B biotype was completely displaced by the B biotype after only 2 generations. On cotton, when the two biotypes began competition in equal numbers, the non-B biotype was completely displaced by the B biotype after 6 generations. Even when the competition started with 87% of non-B biotype and 13% of B biotype in numbers, the non-B biotype was completely displaced after 8-9 generations. These results showed that the invasive B biotype has the capacity to displace the non-B biotype in a short period of time. Under specific conditions, the relative suitability of host plants to the biotypes determines the speed of the displacement of the native non-B biotype by the B biotype.(4) Reproductive competition and behavioral mechanisms. When males and females of the two biotypes were placed together in various inter-biotype crosses, they exhibited courtship behavior, but no copulation occurred, and all the offspring were males produced parthenogenetically. The average numbers of copulation events in the first 72 h after emergence for males and females within the B biotype and t...