Behavioural Mechanisms Underlying The Competitive Displacement Between Two Invasive Cryptic Species Of The Whitefly Bemisia Tabaci

The so called'B biotype'and'Q biotype'of the whitefly Bemisia (abaci (Gennadius) (Hemiptera:Aleyrodidae) have invaded many parts of the world and caused severe damages to a range of crops. Recent phylogenetic analysis suggests that B. tabaci is a species complex containing at least 24 cryptic species, of which the B and Q'biotypes'belong to the Middle East-Asia Minor 1 (hereon MEAM1) and Mediterranean (hereon MED) putative species, respectively. While the phylogenetic analysis has provided a realistic structure against which the existence of biological species can be tested, more crossing experiments among the putative species are urgently required. Although various attempts have been made to examine the reproductive compatibility between MEAM1 and MED, most of the reports did not present the detailed experimental data, and few studies have tested the fertility of the F1 females, so the extent of possible gene flow between the two genetic groups remains unclear. Some previous studies have found that the competitive displacement between these two invasive species could occur either in the laboratory or in the field. However, the mechanisms underlying the displacement were poorly understood. Thus, this study was set up to examine in detail the reproductive compatibility between these two cryptic species using populations of the two cryptic species collected from Zhejiang, China. We also investigated the competitive displacement between the two species in the laboratory as well as the underlying behavioral mechanisms. Our study will provide more evidence for the systematic and phylogenetic relationships of whitefly species complex, and can contribute to our understanding of the mechanisms underlying invasion and competitive displacement of these two cryptic species.(1) Reproductive compatibility between MEAMl and MED putative species of B. tabaciCrossing experiments between the two cryptic species using either single-pair or small groups demonstrated that proportions of females in the F1 progeny were only 0-2%in the inter-species crosses compared to 58-68%in the intra-species treatments. Furthermore, all inter-species F1 females were sterile. In addition, continuous video observations showed that the adults of these two cryptic species very rarely copulated, and copulation occurred only when adults of opposite sex from different cryptic species were enclosed in dense cohorts for a relatively long period of time. All these data show that the populations of two cryptic species examined in this study are completely isolated in reproduction. The isolation was due to mainly a copulation barrier, but post-copulation barriers were also involved.(2) Competitive displacement between MEAM1 and MED putative species of B. tabaci on cotton without insecticide applicationThe mixed cohorts were initiated with 50% of MEAM1 and 50% of MED. MED was completely displaced by MEAM1 after five generations. During the process of competition and displacement, the percentage of females in MEAM1 increased from the second generation, and maintained at 67-71% on average; in contrast, the percentage of females in MED decreased gradually from approximately 60% in the first two generations to<40% by the fourth generation.(3) Mating interactions between MEAM1 and MED putative species of B. tabaciDetailed analysis of mating behaviour revealed asymmetric mating interactions between these two invasive species. When a pair of cryptic species coexisted with a male of the other species, the males of MEAM1 initiated more frequent and efficient courtships to females of the same or the other species. Moreover, compared to MED males, MEAM1 males showed higher capacity of interference when the males of the other cryptic were courting. These behavioural differences between the two species had the consequences that the frequency of copulation events between MED males and females decreased in the presence of the MEAM1 males. Meanwhile, the frequency of copulation events between MEAM1 males and females was not influenced by the presence of MED males. Therefore, we can conclude that the asymmetric changes of copulation events resulted in the increase of female progeny of MEAM1 and decrease of female offspring of MED. This asymmetric mating interaction could contribute to the competitive displacement of MED by MEAM1.