Genetic diversity and geographic distribution of Bemisia tabaci and Trialeurodes vaporariorum in Costa Rica

The tobacco whitefly Bemisia tabaci (Gennadius) cryptic species complex and of the greenhouse whitefly Trialeurodes vaporariorum (Westwood) are extensively reported as destructive pests in vegetable crops worldwide. A survey was conducted in 2011 and 2012 to determine the occurrence and genetic diversity present in the populations of these whiteflies in the major vegetable production areas of Costa Rica. Insect samples were collected from sweet pepper (Capsicum annuum L.), tomato (Solanum lycopersicum L.), common bean (Phaseolus vulgaris L.) and weeds present in commercial crops either in open field or greenhouse conditions. PCR‐RFLP analysis of mitochondrial cytochrome c oxidase subunit 1 gene (mtCOI) sequences of 621 whitefly individuals confirmed the presence of the Mediterranean (MED) type of the B. tabaci and of T. vaporariorum in most sampled regions. Also, individuals of the Middle East‐Asia Minor 1 (MEAM1) type of the B. tabaci were observed in low numbers. Contingency analyses based on type of crop, geographical region, whitefly species, year of collection and production system confirmed that T. vaporariorum was the most frequent species in vegetable production areas in Costa Rica, both in greenhouses and in open fields. B. tabaci MED is likely spreading to new areas of the country, whereas B. tabaci MEAM1 was mostly absent or rarely found. Comparisons of mtCOI sequences from B. tabaci individuals revealed the presence of four B. tabaci sequence haplotypes (named MED‐i, MED‐ii, MEAM1‐i, MEAM1‐xviii) in Costa Rica, three of them identical to B. tabaci haplotypes previously reported in the Western Hemisphere and other parts of the world. Analysis of sequences of T. vaporariorum individuals revealed a more complex population with the presence of 11 haplotypes, two of which were identical to T. vaporariorum sequences reported from other countries.     

Multiplex loop‐mediated isothermal amplification assay for the identification of three major whitefly species in the greenhouse

A multiplex loop‐mediated isothermal amplification (mLAMP) assay was developed for the identification of three species of whitefly, Trialeurodes vaporariorum, Bemisia tabaci Middle East‐Asia Minor 1 (MEAM1) and Mediterranean (MED), major pests in the greenhouse. Each of the specific LAMP primer sets was designed based on the mitochondrial cytochrome oxidase I (mtCOI) gene sequence. The mLAMP reactions using primer mixtures labelled with fluorescent dye were performed at 63°C for 60 min and centrifuged with polyethyleneimine. Thus, T. vaporariorum, MEAM1 and MED were clearly identified by the colour precipitates under UV light. The mLAMP procedure described in this study is cost‐effective and can be performed in the field not only in the laboratory, because this method is a single analysis and does not need a special gene amplification device.     

Genetic groups and endosymbiotic microbiota of the Bemisia tabaci species complex in Japanese agricultural sites

The whitefly Bemisia tabaci is a cryptic species complex of at least 24 genetically distinct species. Thus far, one obligate and seven facultative symbiotic bacteria have been reported from the B. tabaci species complex. Both genetic groups and infected symbionts are extremely important to estimate the pest status of B. tabaci. In this study, we collected 340 whiteflies from 39 agricultural sites, covering an entire region of the B. tabaci habitat in Japan, and examined the genotypes and symbiont community composition at subspecies level. Use of the cleaved amplified polymorphic sequence technique and mitochondrial cytochrome oxidase subunit I gene sequencing detected five genetic groups: indigenous species JpL and Asia II 6, invasive species Middle East‐Asia Minor 1 (MEAM1) and Mediterranean Subclade Q1 (MED Q1), and a genetic group previously undetected in Asia, Mediterranean Subclade Q2 (MED Q2). The genetic groups exhibited characteristic infection statuses with regard to their facultative symbionts, as observed in other countries. The endosymbiotic microbiota of the Japanese MED Q1 was different from that in neighbouring countries, but similar to that in the French or Uruguayan MED Q1. These results may indicate that Japanese MED Q1 species have not invaded from neighbouring countries, but from distant countries by international transportation. All Japanese MED Q2 species were infected with Rickettsia, some of which are regarded as conferring a female‐biased sex ratio and fitness benefit on B. tabaci. The results suggest that MED Q2 may be prevalent in Japan and neighbouring countries.     

A shift of vector specificity acquired by a begomovirus through natural homologous recombination

Recombination is common in plant viruses such as geminiviruses, but the ecological and pathogenic consequences have been explored only in a few cases. Here, we found that a new begomovirus, tomato yellow leaf curl Shuangbai virus (TYLCSbV), probably originated from the recombination of Ageratum yellow vein China virus (AYVCNV) and tobacco curl shoot virus (TbCSV). Agrobacterium-mediated inoculation showed that TYLCSbV and AYVCNV have similar levels of infectivity on tomato and tobacco plants. However, the two viruses exhibit contrasting specificities for vector transmission, that is, TYLCSbV was efficiently transmitted by the whitefly Bemisia tabaci Mediterranean (MED) rather than by the whitefly B. tabaci Middle East-Asia Minor 1 (MEAM1), whereas AYVCNV was more efficiently transmitted by MEAM1. We also showed that the transmission efficiencies of TYLCSbV and AYVCNV are positively correlated with the accumulation of the viruses in whitefly whole bodies and organs/tissues. The key coat protein amino acids that determine their accumulation are between positions 147 and 256. Moreover, field surveys suggest that MED has displaced MEAM1 in some regions where TYLCSbV was collected. Viral competition assays indicated that TYLCSbV outcompeted AYVCNV when transmitted by MED, while the outcome was the opposite when transmitted by MEAM1. Our findings suggest that recombination has resulted in a shift of vector specificity that could provide TYLCSbV with a potential selective transmission advantage, and the population shift of whitefly cryptic species could have influenced virus evolution towards an extended trajectory of transmission.     

Pantothenate mediates the coordination of whitefly and symbiont fitness

Intracellular symbionts in insects often have reduced genomes. Host acquisition of genes from bacteria is an important adaptation that supports symbionts. However, the function of horizontally transferred genes in insect symbiosis remains largely unclear. The primary symbiont Portiera housed in bacteriocytes lacks pantothenate synthesis genes: panB and panC, which is presumably complemented by a fused gene panB-panC (hereafter panBC) horizontally transferred from bacteria in Bemisia tabaci MEAM1. We found panBC in many laboratory cultures, and species of B. tabaci shares a common evolutionary origin. We demonstrated that complementation with whitefly panBC rescued E. coli pantothenate gene knockout mutants. Portiera elimination decreased the pantothenate level and PanBC abundance in bacteriocytes, and reduced whitefly survival and fecundity. Silencing PanBC decreased the Portiera titer, reduced the pantothenate level, and decreased whitefly survival and fecundity. Supplementation with pantothenate restored the symbiont titer, PanBC level, and fitness of RNAi whiteflies. These data suggest that pantothenate synthesis requires cooperation and coordination of whitefly PanBC expression and Portiera. This host–symbiont co-regulation was mediated by the pantothenate level. Our findings demonstrated that pantothenate production, by the cooperation of a horizontally acquired, fused bacteria gene and Portiera, facilitates the coordination of whitefly and symbiont fitness. Thus, this study extends our understanding on the basis of complex host–symbiont interactions.Subject terms: Applied microbiology, Functional genomics     

Chromosome‐level genome assembly of the greenhouse whitefly (Trialeurodes vaporariorum Westwood)

The greenhouse whitefly, Trialeurodes vaporariorum Westwood, is an agricultural pest of global importance. Here we report a 787‐Mb high‐quality draft genome sequence of T. vaporariorum assembled from PacBio long reads and Hi‐C chromatin interaction maps, which has scaffold and contig N50 lengths of 70 Mb and 500 kb, respectively, and contains 18,275 protein‐coding genes. About 98.8% of the assembled contigs were placed onto the 11 T. vaporariorum chromosomes. Comparative genomic analysis reveals significantly expanded gene families such as aspartyl proteases in T. vaporariorum compared to Bemisia tabaci Mediterranean (MED) and Middle East‐Asia Minor 1 (MEAM1). Furthermore, the cytochrome CYP6 subfamily shows significant expansion in T. vaporariorum and several genes in this subfamily display developmental stage‐specific expression patterns. The high‐quality T. vaporariorum genome provides a valuable resource for research in a broad range of areas such as fundamental molecular ecology, insect–plant/insect–microorganism or virus interactions and pest resistance management.     

Co-infection and localization of secondary symbionts in two whitefly species

Background  

Whiteflies are cosmopolitan phloem-feeding pests that cause serious damage to many crops worldwide due to direct feeding and vectoring of many plant viruses. The sweetpotato whitefly Bemisia tabaci (Gennadius) and the greenhouse whitefly Trialeurodes vaporariorum (Westwood) are two of the most widespread and damaging whitefly species. To complete their unbalanced diet, whiteflies harbor the obligatory bacterium Portiera aleyrodidarum. B. tabaci further harbors a diverse array of secondary symbionts, including Hamiltonella, Arsenophonus, Cardinium, Wolbachia, Rickettsia and Fritschea. T. vaporariorum is only known to harbor P. aleyrodidarum and Arsenophonus. We conducted a study to survey the distribution of whitefly species in Croatia, their infection status by secondary symbionts, and the spatial distribution of these symbionts in the developmental stages of the two whitefly species.     

Cover Caption

The whitefly Bemisia tabaci contains many big bacteriocytes, which house the primary symbiont “Candidatus Portiera aleyrodidarum” and a variety of secondary symbionts (see pages 194–206). The primary symbiont provides essential amino acids to hosts and the secondary symbionts can affect the life parameters of B. tabaci including fecundity, development time and sex‐ratio. In addition, the secondary symbionts of B. tabaci have been reported to confer resistance to natural enemies, heat stress and insecticides. Photo in cover shows a nymph of the whitefly and the two kidney‐like organs are the assemblage of bacteriocytes. Image by Xiao‐Li Bing.     

Cover Caption

The whitefly vector of viruses Bemisia tabaci is one of the major threats on cassava and vegetable crops in Africa. More than 28 species have been described in the complex of B. tabaci cryptic species; among them, two are invasive pests worldwide (MEAM1 and MED), bearing a large and species specific endosymbiont community. To date, this is the first time that MEAM1and MED were described in Senegal together with their prevalence and associated endosymbiont community on vegetable crops (see pages 386–398). Photo by Antoine Franck, CIRAD, UMR PVBMT.