Population variability of Bemisia tabaci (Genn.) in different hosts.

The silverleaf whitefly, Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae), is a cryptic species complex that contains some of the most damaging pests in tropical and subtropical regions. Recent studies have indicated that this complex is composed of at least 24 distinct and morphologically indistinguishable species that mainly differ in their ability to transmit phytoviruses, adapt to hosts, and induce physiological changes in certain hosts. The importance of this species has been increasing worldwide, because it serves as a phytovirus vector, particularly for geminiviruses, in economically important crops. Here, we aimed to examine the population variability of B. tabaci populations inhabiting 6 agricultural crops grown in 5 regions of Brazil and 1 region of the USA; BRrep [Brasília (DF, Brazil) - cabbage], ILsoj [Urbana (IL/USA) - soybean], BJabo [Bom Jesus da Lapa (BA, Brazil) - pumpkin], CPsoj [Campinas (SP, Brazil) - soybean], UBman [Ubatuba (SP, Brazil) - cassava], and PEmel [Petrolina (PE, Brazil) - melon]. Thirteen polymorphic loci with 50 alleles were observed, with an average of 2.37 (range: 2.00-2.91) alleles per population. The UBman and PEmel B. tabaci populations were the most differentiated, which was probably caused by insect adaptation to the host plant and the use of insecticides. A 33.87% inter-population variation was observed, indicating that microsatellites may be used to measure differentiation among these B. tabaci populations. Based on the comparison of microsatellites in the current study, only the Middle East-Asia Minor 1 population of B. tabaci was found in the six populations.

Low polymorphism revealed in new microsatellite markers for Bemisia tabaci (Hemiptera: Aleyrodidae).

The silverleaf whitefly (Bemisia tabaci) is actually a complex of morphologically indistinct species that vary in their capacity to transmit plant viruses and to induce physiological disorders in plants of economic importance. The worldwide impact of this whitefly has increased greatly, as it is a vector of various types of phytovirus, especially geminiviruses, in plants of economic importance. The adaptability of B. tabaci to many regions of the world has fostered the appearance of various biotypes that attack a broad spectrum of host plants. We developed microsatellite markers to study genetic variability and population structure of this whitefly in Brazil. Thirteen polymorphic microsatellite markers were isolated and characterized in 20 individuals from a natural population that were collected in soybean in Campinas (SP). The number of alleles per locus ranged from one to two, and the expected heterozygosity ranged from 0.000 to 0.505. These microsatellite markers will be useful for studies and management of B. tabaci. The low polymorphism found in these molecular markers is probably associated with homology of genes expressed in these markers.

MtDNA variability in whitefly (Bemisia tabaci) populations in Brazil.

Bemisia tabaci (Hemiptera: Aleyrodidae) consists of a complex of morphologically indistinct biotypes that vary mainly in their capacity to transmit plant viruses and to induce physiological disorders in plants of economic importance. The adaptability of B. tabaci to many regions of the world has fostered the appearance of various biotypes and has resulted in a broad spectrum of host plants. Our goal was to identify which biotypes were present in four B. tabaci populations in Brazil. We quantified genetic variability between and within populations. Three individuals were collected from three host plant species: two populations on soybean (Campinas and Rondonópolis), one on pumpkin (Barreiras) and one on tomato (Cruz das Almas) in three States of Brazil (São Paulo, Mato Grosso, and Bahia). We chose one sequence of the B biotype, obtained from GenBank; the Campinas population, which had been previously characterized as biotype B, was used as a control for this biotype. We also included one sequence of the Q biotype, obtained from GenBank, as an outgroup. The COI region of the mtDNA gene was partially amplified with the CI-J-2195 and L2-N-3014 pair of primers, and the reaction products were sequenced. Based on distance-based algorithm analyses, we found that all haplotypes belong to biotype B, which was confirmed by the haplotype network. Genetic structure analyses showed that the host plant species does not influence population structuring of this pest; only the geographic location mattered.

[Population genetic structure of Bemisia tabaci (Hemiptera: Aleyrodidae) utilizing microsatellite markers]. / Estrutura genética populacional de Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) utilizando marcadores microssatélites.

We aimed to characterize the population genetic structure within and among five Bemisia tabaci (Gennadius) populations collected from different host plants and geographic regions by using microssatelites as a molecular marker. Each population was represented by 19 specimens. The host plants and geographic origins of these populations were described as follows: Pop 1: Squash Barreiras (BA); Pop 2: Cotton Barreiras (BA); Pop 3: Soybean Campinas (SP); Pop 4: Tomato Cruz das Almas (BA); and Pop 5: Soybean Rondonópolis (MT). Six polymorphic loci were observed, which discriminated 31 different alleles in the studied populations, with a mean number of alleles per population of 3.30 (2.67 - 4.00). Using Fisher's Exact test, it was observed that at least three populations were in Hardy-Weinberg equilibrium for most of the studied loci (six). The dendrogram (UPGMA) separated populations into groups mainly related to the geographic origin of the samples. Only population 5 differed from the others at a 0.15 distance (74.5% group consistency). The most similar populations were 1 and 2, with a 0.01 distance (65.3%). This is in agreement with their geographic origins and it was not consistent with host specificity. The results suggest considerable gene flow (7.3%) among all whitefly populations and indicate that a better understanding of the gene flow in populations of B. tabaci associated with different hosts is required for the management of this insect.