Diversity of secondary endosymbionts among different putative species of the whitefly Bemisia tabaci

Endosymbionts are important components of arthropod biology. The white- fly Bemisia tabaci （Gennadius） （Hemiptera： Aleyrodidae） is a cryptic species complex composed of 〉28 putative species. In addition to the primary endosymbiont Portiera aley- rodidarum, six secondary endosymbionts （S-endosymbionts）, Hamiltonella, Rickettsia, Wolbachia, Cardinium, Arsenophonus and Fritschea, have been identified in B. tabaci thus far. Here, we tested five of the six S-endosymbiont lineages （excluding Fritschea） from 340 whitely individuals representing six putative species from China. Harniltonella was detected only in the two exotic invaders, Middle East-Asia Minor 1 （MEAM 1） and Mediter- ranean （MED）. Rickettsia was absent in Asia II 1 and MED, scarce in Asia II 3 （13%）, but abundant in Asia II 7 （63.2%）, China 1 （84.7%） and MEAM1 （100%）. Wolbachia, Cardinium and Arsenophonus were absent in the invasive MEAM1 and MED but mostly abundant in the native putative species. Furthermore, phylogenetic analyses revealed that some S-endosymbionts have several clades and different B. tabaci putative species can harbor different clades of a given S-endosymbiont, demonstrating further the complexity of S-endosymbionts in B. tabaci. All together, our results demonstrate the variation and diversity of S-endosymbionts in different putative species ofB. tabaci, especially between invasive and native whiteflies.

Crossing experiments and behavioral observations reveal reproductive incompatibility among three putative species of the whitefly Bemisia tabaci

The whitefly Bemisia tabaci has a global distribution and extensive genetic diversity. Recent phylogenetic analyses as well as crossing experiments suggest that B. tabaci is a complex composed of 〉 20 cryptic species, but more crossing studies are required to examine the reproductive compatibility among the putative species and thus further clarify the systematics of this species complex. We conducted crossing experiments and behavioral observations to investigate the reproductive compatibility between the Mediterranean, Asia II 3, and Asia II 1 putative species ofB. tabaci collected from Zhejiang, China. Female progeny were never produced in inter-species crosses, demonstrating a lack of egg fertilization; while 55%-75% females were produced in all the intra-species treatments. Continuous behavioral observations showed that frequent courtship events occurred in both intra-species treatments and inter-putative species crosses. However, copulation events occurred only in the three intra-species treatments with one exception： that one copulation event occurred between Asia II 3 and Mediterranean in the crosses where two cohorts of females and males of different putative species were enclosed together in a small arena but were not allowed access to their intra-specific mates for a long period of time. These data demonstrated complete reproductive isolation between the Mediterranean, Asia II 3, and Asia II 1 putative species, and further showed that the isolation is due to lack of copulation. Demonstration of reproductive isolation between the Mediterranean and two indigenous putative species from China provides further evidence for the existence of cryptic species within the B. tabaci complex.

Gene expression profiling of the whitefly （Bemisia tabaci） Middle East- Asia Minor 1 feeding on healthy and Tomato yellow leaf curl China virus-infected tobacco

Begomoviruses are exclusively transmitted by whitefly （Bemisia tabaci） in a circulative, non-propagative manner. The influences of begomoviruses on whitefly vector are complex with both direct and indirect effects. However, the molecular mechanisms underlying these effects are poorly understood and the transcriptional profiles of whitefly on healthy and virus-infected plants have not yet been studied. Using suppression subtractive hybridization, we investigated the differentially expressed genes in whitefly Middle East - Asia Minor 1 feeding on healthy and Tomato yellow leaf curl China virus （TYLCCNV） infected tobacco. From the forward cDNA library, 124 differentially expressed expression sequence tags （ESTs） were obtained which represent up-regulated genes in the whiteflies feeding on the infected tobacco. From the reverse library, 112 ESTs were isolated which represent down-regulated genes. Among the up-regulated genes, we identified several genes that are probably involved in direct interaction between whitefly and TYLCCN~, including a 26/29-kDa proteinase that appears to participate in the elimination of foreign proteins, heparan sulfate proteoglycan which mediates the entry of several viruses into host cells and two genes of Rickettsia-a secondary endosymbiotic bacterium of whitefly. In addition, we identified a number of genes involved in metabolism, transcription and translation which might be the result of indirect effects of TYLCCNV on the whitefly via host plants. Collectively, our results suggest that TYLCCNV-infected tobacco changes the gene expression profiles of whitefly via both direct and indirect interactions. This study revealed a number of genes involved in whitefly-TYLCCNV-tobacco interactions and provided useful information for future study on this complex system.