The invasive B whitefly and the indigenous ZHJ2 whitefly in China of the Bemisia tabaci complex represent two previously allopatric cryptic species.Laboratory experiments have shown that the invasive B can displace the indigenous ZHJ2.Here,we observed the mating behavior and mating interactions between B and ZHJ2 to elucidate the behavioral mechanisms underlying their competition.The 2 species are able to mate with each oth-er,although at a significantly lower frequency than that between males and females within the same species.Heterospecifically-mated females produce only male progeny,indicating reproductive isolation.Heterospecific mating had only a marginal effect on reproduction of females in either species.Detailed observations on mating interactions between the 2 species showed that B had higher sexual activity than ZHJ2.B males were more like-ly to interrupt courtships initiated by rival males than ZHJ2 males.Compared with ZHJ2 males,B males were also more likely to successfully interrupt courtships initiated by rival heterospecific males than by males of the same species.In addition,B males guarded B females post-copulation,whereas ZHJ2 males did not.When the 2 species co-occurred,the behavioral differences and interactions between them resulted in an increased propor-tion of females produced in the offspring of B but reduced proportion of females in the progeny of ZHJ2.These asymmetric mating interactions might be an important mechanism underlying the displacement of ZHJ2 by B.Our study shows that reproductive interference might contribute to the competitive exclusion between closely related species during biological invasions.
The whitefly Bemisia tabaci is a species complex,of which two invasive species,called MEAM1 and MED whiteflies,have invaded many parts of the world in the past 30 years and replaced native whitefly populations in many regions of invasions including many areas in China.One of the possible reasons for the invasion is that MEAM1 and MED whiteflies are more fecund than the native species.However,factors that affect reproduction and the molecular mechanism of vitellogenesis among various 6.tabaci cryptic species are not clearly known.In this study,cDNAs of vitellogenin(Vg) genes were sequenced from native 6.tabaci Asia Ⅱ 1 and invasive 6.tabaci MED in China.The deduced amino acid sequences were2182 residues in Asia Ⅱ 1 and 2217 residues in MED.Compared to the Vg gene cDNA sequence of Asia Ⅱ 1 species,the Vg gene in MED could be cleaved at least into four subunits,with deduced molecular weight of 50,90,150 and 190 kDa,respectively.However,only two different subunits were cleaved between residues 459 and 460 in the Asia Ⅱ 1.In addition,more than two serine-rich stretches located in both the N-terminal and the C-terminal region in invasive species.More GHN domains were revealed only in the N-terminal region of 6.tabaci MED.Vg gene expression pattern was characterized using quantitative real-time(qRT)-PCR to compare the dynamic of vitellogenin gene mRNA level.Vg gene transcription reached the peak level at 13 d after eclosion in 6.tabaci Asia Ⅱ 1,3 d later than that in MED and another invasive species of the6.tabaci complex MEAM1.We assumed that the present difference of Vg gene expression pattern is due to the different regulation pattern of vitellogenesis among species of the 6.tabaci complex.These results provide useful information to reveal the mechanisms of reproduction in whitefly species complex.
The whitefly Bemisia tabaci species complex and the begomoviruses they transmit are devastating agricultural pests worldwide.With the rapid and further inva-sions by some members of the whitefly species complex into new regions,their impacts on human society are likely to increase in the years to come. This special issue of the Journal of Integrative Agriculture
The worldwide distribution and extensive genetic diversity of the whitefly,Bemisia tabaci,has long been recognized.However,the levels of separation within B.tabaci and the nomenclature of the various genetic groups have been a subject of debate.Recent phylogenetic analyses indicate that B.tabaci is a complex composed of 28 morphologically indistinguishable species.In this article,we first review the debate and difficulties associated with B.tabaci's taxonomy and systematics,and argue for the need to apply the biological species concept in order to elucidate B.tabaci's systematics.We summarize the accumulated genetic and behavioural data on reproductive incompatibilities evident amongst phylogenetic mtCOI groups of B.tabaci.Crossing studies have been conducted with 14 of the 28 putative species covering 54 reciprocal inter-species pairs,and observations on mating behaviour have been conducted for seven species pairs.Data from both crossing trials and behavioural observations indicate a consistent pattern of reproductive isolation among the putative species.We then discuss the technical and conceptual complexities associated with crossing experiments and behavioural observations designed to reveal reproductive incompatibility.Finally,we elaborate on a strategy for further clarifying the pattern of reproductive isolation between B.tabaci groups and propose future research directions on the systematics of this complex.
The sweetpotato whitefly Bemisia tabaci(Homoptera:Aleyrodidae)is a destructive pest of agriculture and horticulture worldwide.Recent phylogenetic analysis using mitochondrial cytochrome oxidase 1 sequences indicates that this whitefly is a species complex including at least 24 morphologically indistinguishable but genetically distinct cryptic species.In this study,the inter-species crosses of Middle East-Asia Minor 1(MEAM1),Mediterranean(MED)and Asia II 7 cryptic species,which were referred to as B,Q and Cv biotypes before,were conducted in two different devices,leaf cages(7 cm3)and cylinder cages(280 cm3),and at three temperatures of 22,30 and 38°C.Results indicated that no female progeny were produced in the reciprocal cross between MEAM1×Asia II 7,between MED×Asia II 7 cryptic species neither in leaf cage nor in cylinder cages,while 0.81 and 1.37% of females in the offspring were recorded in the reciprocal cross between MEAM1×MED in leaf cage experiments.Approximately 0.95-0.98% female progeny were recorded in the reciprocal cross between MEAM1×MED at 30°C,0.77% female progeny were recorded in the single cross direction between MEAM1 × MED at 22°C,and no female progeny were found in their reciprocal cross at 38°C in leaf cage.Our findings indicated that neither space dimension nor temperature have a significant effect on the hybridization of different B.tabaci cryptic species.
LI Xiao-xiLI Shao-jianXUE XiaMuhammad Z AhmedREN Shun-xiangAndrew G S CuthbertsonQIU Bao-li
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.
LUAN Jun-boXU JingLIN Ke-keMyron P ZaluckiLIU Shu-sheng
