Bemisia Tabaci Complex Research Articles

The presence of six cryptic species of the whitefly Bemisia tabaci complex in China as revealed by crossing experiments

Abstract Recent phylogenetic analysis using mitochondrial cytochrome oxidase I (mtCOI) sequences of Bemisia tabaci worldwide indicates that the whitefly comprises at least 24 morphologically indistinguishable but genetically distinct cryptic species. While evidence of reproductive isolation has been reported for some of the putative species, more extensive crossing experiments are required to clarify the systematics of this species complex. In this study, we established laboratory cultures for six putative species of B. tabaci collected in China. We conducted 22 inter-species crosses among the six putative species. The data and those reported previously were collated, and the combined dataset covered all the 30 possible inter-species crosses among the six putative species. Intra-species controls always produced female and male progeny and the proportions of females in the first generation (F1) ranged from 56% to 70%. However, in inter-species crosses female progeny were rarely produced, and the few F1 females produced in four of the 30 inter-species crosses were either sterile or significantly weaker in viability. These results demonstrate a pattern of complete reproductive isolation among the six putative species and show that they are six cryptic species in the B. tabaci complex.

Survey of Reproductive Host Plants ofBemisia tabaci(Hemiptera: Aleyrodidae) in Egypt, Including New Host Records

ABSTRACT: A field survey was conducted on the reproductive host plant species of the Bemisia tabaci (Gennadius) complex throughout Egypt. Infested plants were collected during each month of the year. Bemisia tabaci completed its development on 118 species of plants in 79 genera belonging to 28 families. The family Asteraceae (= Compositae) included 23 host plant species (20% of the total) belonging to 16 genera, while the family Fabaceae (= Leguminosae) included 17 host plant species belonging to 13 genera. The study revealed six new reproductive host plants consisting of five species and one subspecies in the families Asteraceae, Fabaceae, Piperaceae, Plantaginaceae and Portulacaceae. About 70% of the host plants are new host records for Egypt. Several recent studies have mistakenly cited a previous list of B. tabaci hosts in Egypt by erroneously referring to an early world host list as being a list of hosts in Egypt. The results of this study have implications on whitefly ecology and management.

The endosymbiont community as taxonomic character: a novel approach to resolving the Bemisia tabaci complex.

In this issue of Molecular Ecology, Gueguen et al. (2010) describe their novel approach to resolving cryptic genetic diversity in the Bemisia tabaci complex (Hemiptera: Aleyrodidae.) Complexes of cryptic species present a challenge to both morphological and molecular taxonomy – the former presumed, as shared morphology normally defines species as cryptic, but the latter also problematic when host DNA sequence data is either inconclusive or unaccompanied by independent evidence. Endosymbiont associations with insect hosts have, historically, complicated efforts to develop a robust molecular taxonomy, but the approach of Gueguen et al. takes advantage of endosymbiont community composition to help rather than hinder the task of resolving taxonomic distinctions within the B. tabaci complex.

Genetic variation and mtCOI phylogeny for Bemisia tabaci (Hemiptera, Aleyrodidae) indicate that the ‘B’ biotype predominates in Iran

Despite a large number of investigations on the molecular genetics and population structure of the whitefly Bemisia tabaci (Gennadius) complex, no such study had been conducted in Iran. The genetic variation of B. tabaci was examined using polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) for 18 field collections from cucumber, eggplant, and tomato in four provinces of Iran. PCR amplification and restriction digestion with two enzymes detected 388 RFLP fragments, of which 16 fragments showed polymorphisms. Cluster analysis of these data placed all B. tabaci individuals within a single group, and there was no evidence for between- or within-population genetic variation. Phylogenetic (Clustal W) analysis of 42 B. tabaci mtCOI sequences (n = 21 field collections) from Iran, and a comparison with well-studied haplotype or biotype reference sequences available in public sequence databases, revealed that the Iranian B. tabaci populations were most closely related to the B biotype at 0–1.2% nucleotide identity. The B biotype is a well-known member of a sister clade from the Middle East–North African region of the world, owing to its nearly worldwide distribution and invasive characteristics. This report indicates that a single major haplotype of B biotype is prevalent in Iran and that its closest relative is the B biotype. Also, given the extent of known variation in the Middle East and African continent, data indicate somewhat surprisingly that the B. tabaci collections sampled in Iran had limited genetic variation and population substructure. Knowledge that the B biotype of B. tabaci predominates in Iran is important for designing effective pest management strategies given that biotypes of B. tabaci are known to differ greatly with respect to insecticide resistance, host range, virus–vector interactions, and other key biological characteristics.

Diversity analysis of Bemisia tabaci biotypes: RAPD, PCR-RFLP and sequencing of the ITS1 rDNA region

The Bemisia tabaci complex is formed by approximately 41 biotypes, two of which (B and BR) occur in Brazil. In this work we aimed at obtaining genetic markers to assess the genetic diversity of the different biotypes. In order to do that we analyzed Bemisia tabaci biotypes B, BR, Q and Cassava using molecular techniques including RAPD, PCR-RFLP and sequencing of the ITS1 rDNA region. The analyses revealed a high similarity between the individuals of the B and Q biotypes, which could be distinguished from the BR individuals. A phylogenetic tree based on ITS1 rDNA sequence was constructed. This is the first report of the ITS1 rDNA sequence of Bemisia tuberculata and of the BR biotype of B. tabaci.

Genetic Differentiation of Different Geographical Populations of Bemisia tabaci (Gennadius) Complex

Abstract Bemisia tabaci (Gennadius) is a species complex, which includes different geographical populations with genetic differentiation. The recent progress on the genetic differentiation of various geographical populations of B. tabaci complex was introduced. The genetic differentiation was further analyzed on the basis of the sequences of mtDNA COI and rDNA ITS1 recorded in the world's GenBank. Five groups are defined on the basis of mtDNA COI and rDNA ITS1, including the Asia group, America group, Africa group, Australia group, and Biotype B/Mediterranean/Middle East/Northern Africa/Biotype Ms group. There are several ungrouped geographical classifications, such as the Uganda population, Ivory Coast population, and Taiwan population. Geographical isolation may be the most important factor that contributed to the genetic differentiation of various geographical populations of B. tabaci. Many populations with biological advantages invaded new regions and caused severe economic losses within human activity. It is necessary to strengthen the research of B. tabaci biotype to prevent the spread of invaded populations and the invasion of potentially dangerous populations.

Molecular Evidence for Five Distinct <I>Bemisia tabaci</I> (Homoptera: Aleyrodidae) Geographic Haplotypes Associated with Cassava Plants in Sub-Saharan Africa

The Bemisia tabaci (Gennadius) complex contains the only known whitefly vector of plant-infecting begomoviruses, which are the causal agents of mosaic diseases of cassava in Africa and India. Widespread phenotypic variability, together with the absence of definitive morphological taxonomic characters for this whitefly complex, has confounded both the systematics and the study of its virus vector biology. Substantial genetic variability and phylogeographical relationships have been shown for phenotypic, but morphologically identical, variants of B. tabaci based on the mitochondrial (mt) cytochrome oxidase I (COI) sequence, leading to the suggestion that they represent a species complex. Here, phylogenetic relationships were explored, using the mtCOI sequence (780 bp) as a molecular marker, for B. tabaci collected from cassava plants in southern and western Africa, including Cameroon, Zambia, Mozambique, Zimbabwe, Swaziland, and South Africa. Maximum likelihood analyses of mtCOI sequences revealed that most B. tabaci examined were placed into one of three subgroups within the major sub-Saharan African clade, which also contains previously reported populations indigenous to Malawi and Uganda, and collectively shared on overall nucleotide (nt) identity at 88.9–99.7%. Two other reference populations, the monophagous Benin haplotype from Asystasia spp. and a B. tabaci from cassava in the Ivory Coast (IC), were the most divergent outliers of the sub-Saharan clade, each representing the only member of their respective clade (I and V), at the present time. Members of the sub-Saharan clade associated with cassava had as their closest relatives haplotypes I and II of the Mediterranean-Northern Africa clade, with which they shared a collective 84.2–92.9% nt identity (not including the IC cassava reference haplotype). In contrast, the sub-Saharan African clade diverged from the Americas and Southeast Asia/Far East clades at 79.7–85.1 and 77.5–84.9%, respectively. Within the sub-Saharan clade, subclade II contained B. tabaci from Zambia, Mozambique, South Africa, and Swaziland at 95–99% identity. The sub-Saharan subcluster III contained haplotypes from southern and western Africa. Counter to the otherwise phylogeographical relationships observed for cassava-associated B. tabaci from southern Africa, one and two populations from Cameroon (okra) and Zimbabwe (cassava), respectively, grouped with the major Mediterranean-North Africa clade, together with their closest relative associated with okra from IC, are included here as a reference sequence for the first time, with which they collectively formed a new, third subclade. Thus, phylogenetic analysis of B. tabaci mtCOI haplotypes examined thus far from the African continent has revealed five major cassava-associated haplotypes, which grouped primarily based on extant geography, with the exception of one and two collections from Cameroon and Zimbabwe, respectively. Hypotheses explaining the potential distributions of haplotypes are discussed.

Geographical distribution and species composition of parasitoids (Hymenoptera: Chalcidoidea) of Trialeurodes vaporariorum and Bemisia tabaci-complex (Homoptera: Aleyrodidae) in Japan.

To determine the geographical distribution and composition of parasitoid species from Trialeurodes vaporariorum and the Bemisia tabaci-complex (B. tabaci and B. argentifolii), parasitized whiteflies were collected at different sites in Japan and parasitoids were reared for adult emergence. Amitus sp., Encarsia citri, E. formosa, E. japonica, E. lutea, E. transvena, Encarsia sp., Eretmocerus sp. and Syrphophagus sp. were reared from Trialeurodes vaporariorum sampled at 125 sites from 1977 to 1998. Amitus sp., E. azimi, E. citri, E. formosa, E. japonica, E. lutea, E. transvena and Eretmocerus sp. were reared from a B. tabaci-complex sampled at 36 sites from 1990 to 1998. The indigenous species E. japonica and E. transvena are widely distributed in Japan and are predominant parasitoids of T. vaporariorum and the B. tabaci-complex. The introduced parasitoid E. formosa has recently been found at many sites near greenhouses in which it has been used commercially by seasonal inoculative release to control T. vaporariorum and B. argentifolii. This is because some E. formosa leave the greenhouses to parasitize whiteflies in the field. Single species composition per site was dominant for T. vaporariorum and not numerous for the B. tabaci-complex. At the sites containing two or three parasitoid species, E. formosa was attacked frequently by E. japonica and E. transvena which are facultative heteronomous hyperparasitoids. In addition, male Syrphophagus sp. was also a hyperparasitoid of E. formosa.

NATURAL GENOMIC AND ANTIGENIC VARIATION IN WHITEFLY-TRANSMITTED GEMINIVIRUSES (BEGOMOVIRUSES).

Begomoviruses have circular single-stranded DNA genomes, cause many diseases of dicotyledons in areas with warm climates and are transmitted by whiteflies of the Bemisia tabaci complex. Their genomic and antigenic variation represents geography-related lineages that have little relation to host range. Genomic variation resulting from mutation is amplified by acquisition of extra DNA components, pseudo-recombination and recombination, both intraspecific and interspecific. Recombination, especially interspecific recombination, seems the key mechanism for generating novel virus forms, for enhancing biological fitness of pseudo-recombinants derived from closely related species and for maintaining the flow of genetic material among different geminiviruses occurring in the same geographical region. Recent begomovirus epidemics reflect favorable conjunctions of plant, vector, and viral (e.g. emergence of a novel recombinant virus) factors. Such epidemics typically result in co-infection of plants with different begomoviruses, leading to the appearance of further variants, especially recombinants. In their patterns of variation and evolution, begomoviruses differ greatly from plant viruses with RNA genomes.

Additions to the Encarsia parasitoids (Hymenoptera: Aphelinidae) of the Bemisia tabaci-complex (Hemiptera: Aleyrodidae)

AbstractFour new species of Encarsia, E. lanceolatasp. n., E. paracitrellasp. n., E. pseudocitrellasp. n. and E. unicitrellasp. n. are described and illustrated. All four parasitoid species were reared from the Bemisia tabaci-complex and/or other whitefly hosts in the Neotropical region. Encarsia paracitrella, E. pseudocitrella and E. unicitrella are extremely closely related, to each other and to E. citrella (Howard). A diagnosis is therefore given for the E. citrella-complex, with a key to the four currently included species. For E. citrella (Howard) a lectotype is designated, the male is described and illustrated for the first time, and the female is redescribed and illustrated. A key and a modification to an existing key are provided to facilitate the identification of the five species treated.

A New Encarsia (Hymenoptera: Aphelinidae) Species Reared from the Bemisia tabaci Complex (Homoptera: Aleyrodidae)

Encarsia polaszeki Evans n. sp., reared from the Bemisia tabaci complex from Brazil, is described and illustrated.