SCAR molecular markers of the B biotype and two non-B populations of the whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae)

Nuclear Orthologs Derived from Whole Genome Sequencing Indicate Cryptic Diversity in the Bemisia tabaci (Insecta: Aleyrodidae) Complex of Whiteflies

The Bemisia tabaci complex of whiteflies contains globally important pests thought to contain cryptic species corresponding to geographically structured phylogenetic clades. Although mostly morphologically indistinguishable, differences have been shown to exist among populations in behavior, plant virus vector capacity, ability to hybridize, and DNA sequence divergence. These differences allow for certain populations to become invasive and cause great economic damage in a monoculture setting. Although high mitochondrial DNA divergences have been reported between putative conspecifics of the B. tabaci species complex, there is limited data that exists across the whole genome for this group. Using data from 2184 orthologs obtained from whole genome sequencing (Illumina), a phylogenetic analysis using maximum likelihood and coalescent methodologies was completed on ten individuals of the B. tabaci complex. In addition, automatic barcode gap discovery methods were employed, and results suggest the existence of five species. Although the divergences of the mitochondrial cytochrome oxidase I gene are high among members of this complex, nuclear divergences are much lower in comparison. Single-copy orthologs from whole genome sequencing demonstrate divergent population structures among members of the B. tabaci complex and the sequences provide an important resource to aid in future genomic studies of the group.

Patterns of genetic differentiation among populations of Amrasca biguttula biguttula (Shiraki) (Cicadellidae: Hemiptera)

Cotton leafhopper, Amrasca biguttula biguttula (Shiraki), a serious sucking insect pest of cotton and vegetables is present throughout South and Southeast Asia. Genetic differentiation within A. biguttula biguttula populations collected from 16 cotton growing areas of Punjab, Pakistan, was examined by sequencing the barcode region of the mitochondrial cytochrome oxidase subunit 1 (COI) gene. The dendrogram obtained by neighbour joining analysis of COI sequences confirmed the presence of single species of cotton leafhopper. The overall average pairwise divergence was 0.01. Very little variation was found among populations from cotton growing areas of Punjab, Pakistan and these were most similar to populations from North India. South Indian populations were grouped together and were generally more divergent. Extensive migration of this pest species among cotton-growing areas in the Indian subcontinent may hinder genetic diversification of cotton leafhopper. Four Pakistani samples of cotton leafhopper tested positive for Wolbachia infection but were not clearly differentiated from non-Wolbachia infected samples, suggesting that Wolbachia did not cause reproductive incompatibilities.

Cryptic Species Identification and Composition of Bemisia tabaci (Hemiptera: Aleyrodidae) Complex in Henan Province, China

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex, causing significant crop losses in China during the last decade. Although knowledge of cryptic species composition and dynamics within B. tabaci complex is critical for developing sustainable pest management strategies, limited information is available on this pest in the Henan province of China. A systematic survey of the cryptic species composition and distribution of B. tabaci complex in different locations of Henan province was conducted in 2012. The results of RAPD-PCR and the gene for the mitochondrial cytochrome oxidase subunit-1 (mtCOI) based phylogenetic relationships established using Bayesian method indicated there were four known cryptic species MEAM1, MED, Asia II 3, Asia II 9 and a new cryptic species named China 6 in Henan province. In the survey, the invasive cryptic species MED and MEAM1 were found to be predominant with wide spread distribution across the surveyed regions. On the contrary, the indigenous B. tabaci cryptic species including Asia II 3, Asia II 9 and China 6 remained with low prevalence in some surveyed regions. Cryptic species MEAM1 and MED have not completely displaced the native B. tabaci in Henan province. This current study for the first time unifies our knowledge of the diversity and distribution of B. tabaci across Henan province of China.

Rapid genetic turnover in populations of the insect pest Bemisia tabaci Middle East: Asia Minor 1 in an agricultural landscape

Organisms differ greatly in dispersal ability, and landscapes differ in amenability to an organism's movement. Thus, landscape structure and heterogeneity can affect genetic composition of populations. While many agricultural pests are known for their ability to disperse rapidly, it is unclear how fast and over what spatial scale insect pests might respond to the temporally dynamic agricultural landscapes they inhabit. We used population genetic analyses of a severe crop pest, a member of the Bemisia tabaci (Hemiptera: Sternorrhyncha: Aleyrodoidea: Aleyrodidea) cryptic species complex known as Middle East-Asia Minor 1 (commonly known as biotype B), to estimate spatial and temporal genetic diversity over four months of the 2006-2007 summer growing season. We examined 559 individuals from eight sites, which were scored for eight microsatellite loci. Temporal genetic structure greatly exceeded spatial structure. There was significant temporal change in local genetic composition from the beginning to the end of the season accompanied by heterozygote deficits and inbreeding. This temporal structure suggests entire cohorts of pests can occupy a large and variable agricultural landscape but are rapidly replaced. These rapid genetic fluctuations reinforce the concept that agricultural landscapes are dynamic mosaics in time and space and may contribute to better decisions for pest and insecticide resistance management.

Reproductive incompatibility between the B and Q biotypes of the whitefly Bemisia tabaci in China: genetic and behavioural evidence

The B and Q 'biotypes' of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) have been invading many parts of the world and causing severe damage to a range of crops. Recent phylogenetic analyses indicate that B and Q are cryptic species within the B. tabaci species complex. Although various attempts have been made to examine the reproductive compatibility between B and Q, few studies have tested the fertility of the F1 females and so the extent of possible gene flow remains unclear. In this study, we conducted a series of crossing experiments and behavioural observations to examine in detail the reproductive compatibility between the B and Q biotypes collected from Zhejiang, China, a region recently invaded by these whiteflies. Crossing experiments between the two biotypes using either single-pairs or small groups demonstrated that proportions of females in the F1 progeny were only 0-2% in the inter-biotype crosses compared to 58-68% in the intra-biotype treatments. Furthermore, all inter-biotype F1 females were sterile. Continuous video observations showed that B and Q adults very rarely copulated, and copulation occurred only when adults of opposite sex from different biotypes were enclosed in dense cohorts for a relatively long period of time. These data show that the B and Q biotypes examined in this study are completely isolated in reproduction. The isolation was due to mainly a copulation barrier, but post-copulation barriers were also involved.

Reproductive incompatibility among genetic groups of Bemisia tabaci supports the proposition that the whitefly is a cryptic species complex

The worldwide distribution and extensive genetic diversity of the whitefly Bemisia tabaci has long been recognized. However, whether B. tabaci is a complex species or a species complex has been a subject of debate. Recent phylogenetic analyses suggest that B. tabaci is a cryptic species complex composed of at least 24 morphologically indistinguishable species. Here, we conducted crossing experiments and demonstrated reproductive incompatibility among three of the 24 putative species. Our data and those of previously reported crossing experiments among various putative species of B. tabaci were collated to reveal the pattern of reproductive isolation. The combined results provide strong support to the proposition that B. tabaci is a cryptic species complex.