DNA Barcoding of Bemisia tabaci Complex (Hemiptera: Aleyrodidae) Reveals Southerly Expansion of the Dominant Whitefly Species on Cotton in Pakistan

Abstract

BackgroundAlthough whiteflies (Bemisia tabaci complex) are an important pest of cotton in Pakistan, its taxonomic diversity is poorly understood. As DNA barcoding is an effective tool for resolving species complexes and analyzing species distributions, we used this approach to analyze genetic diversity in the B. tabaci complex and map the distribution of B. tabaci lineages in cotton growing areas of Pakistan.Methods/Principal FindingsSequence diversity in the DNA barcode region (mtCOI-5′) was examined in 593 whiteflies from Pakistan to determine the number of whitefly species and their distributions in the cotton-growing areas of Punjab and Sindh provinces. These new records were integrated with another 173 barcode sequences for B. tabaci, most from India, to better understand regional whitefly diversity. The Barcode Index Number (BIN) System assigned the 766 sequences to 15 BINs, including nine from Pakistan. Representative specimens of each Pakistan BIN were analyzed for mtCOI-3′ to allow their assignment to one of the putative species in the B. tabaci complex recognized on the basis of sequence variation in this gene region. This analysis revealed the presence of Asia II 1, Middle East-Asia Minor 1, Asia 1, Asia II 5, Asia II 7, and a new lineage “Pakistan”. The first two taxa were found in both Punjab and Sindh, but Asia 1 was only detected in Sindh, while Asia II 5, Asia II 7 and “Pakistan” were only present in Punjab. The haplotype networks showed that most haplotypes of Asia II 1, a species implicated in transmission of the cotton leaf curl virus, occurred in both India and Pakistan.ConclusionsDNA barcodes successfully discriminated cryptic species in B. tabaci complex. The dominant haplotypes in the B. tabaci complex were shared by India and Pakistan. Asia II 1 was previously restricted to Punjab, but is now the dominant lineage in southern Sindh; its southward spread may have serious implications for cotton plantations in this region.

Genetic variability, community structure, and horizontal transfer of endosymbionts among three Asia II‐Bemisia tabaci mitotypes in Pakistan

“…This may be further explained by the minimal to no use of pesticides in the urban areas, which leaves the natural enemies relatively undisturbed, compared to agricultural areas where pesticide use during the cotton‐growing season is frequent to control the whitefly vector, with the caveat that its frequent use often leads to increases in whitefly population sizes (Anthony, Brown, Markham, & Ffrenchconstant, ; Bedford et al, ; Denholm, Cahill, Dennehy, & Horowitz, ; Horowitz & Ishaaya, ). This hypothesis is consistent with the observed small available sample sizes of the Asia II‐5 ( n = 3) and II‐7 ( n = 23) mitotypes (herein) and the results of previous studies reporting similarly low frequencies within Pakistan agroecosystems (Ahmed et al, ; Ashfaq et al, ; Masood et al, ; Paredes‐Montero et al, ).…”

“…Environment‐associated niche adaptation of B. tabaci can be influenced by endosymbiont community composition, which in turn can alter the distribution of different vector mitotype–virus combinations. In Pakistan and India, studies have shown that B. tabaci mitotypes native to Asia that transmit cotton leaf curl disease‐begomoviruses (CLCuD; Bedford et al, ) have undergone geographic expansion and/or contraction, while at the same time the composition of the cotton leaf curl disease complex has been in flux, potentially corresponding to mitotype fluctuations (Ahmed et al, ; Ashfaq et al, ; Paredes‐Montero et al, ). Although many studies have characterized a number of different begomoviral species and strains associated with CLCuD, only a few have considered whitefly vector–endosymbiont relationships and their dynamics in an ecological context.…”

DNA barcodes for bio-surveillance: regulated and economically important arthropod plant pests

“…The use of barcode data to identify species (Rakauskas and Basilova 2013) as opposed to BINs requires the species in question be represented in the barcode reference library (Ekrem et al 2007). Because the barcode reference library now includes records for many agricultural and forestry pests (Ashfaq et al 2014;Foottit et al 2014;Raupach et al 2014), newly encountered specimens of these species can be identified through barcode analysis. As well, the extension of DNA barcoding protocols onto next-generation sequencing (NGS) platforms (Shokralla et al 2014) is enabling metabarcoding studies that permit large-scale assessments of species composition (Taberlet et al 2012), an approach of high importance in monitoring plant pests.…”

“…Such discrepancies complicate the identification of their component taxa with implications for pest regulation and management. For example, the whitefly, Bemisia tabaci, is now known to be a complex of at least 34 species ) that differ in their invasiveness (De Barro and Ahmed 2011), their capacity to transmit plant pathogens (Chowda-Reddy et al 2012), and their regional pest status (Ashfaq et al 2014). Likewise, two pest thrips, Scirtothrips dorsalis and Thrips tabaci, are species complexes whose members vary in their invasiveness and viral-transmission ability (Jacobson et al 2013;Dickey et al 2015).…”

RNAi-mediated mortality of the whitefly through transgenic expression of double-stranded RNA homologous to acetylcholinesterase and ecdysone receptor in tobacco plants

“…Previous studies have identified B. tabaci haplotypes and biotypes23 from Pakistan, including the exotic, invasive MEAM I haplotype (also known as the B biotype) that groups in the North Africa-Mediterranean-Middle East (NA-MED-ME) clade (also, Middle East Asia Minor 1) that was present in only Sindh Province, and two endemic cryptic species that group in the Asia 1 and Asia II 1 clades. The Asia 1 cryptic species was identified in Punjab and Sindh Province, whereas, Asia II 1 was present only in Punjab Province242526. In a recent study that analyzed 593 whitefly collections from 255 locations of Pakistan, the presence of the aforementioned two cryptic species, was confirmed, including Asia II-5 from cotton and Asia II-7 from cotton and non-cotton hosts, and an additional previously uncharacterized species was reported from cotton plants, referred to as ‘Pakistan’25.…”