Species and endosymbiont diversity of Bemisia tabaci (Homoptera: Aleyrodidae) on vegetable crops in Senegal

Bemisia tabaci‐transmitted geminiviruses are one of the major threats on cassava and vegetable crops in Africa. However, to date, few studies are available on the diversity of B. tabaci and their associated endosymbionts in Africa. More than 28 species have been described in the complex of B. tabaci cryptic species; among them, 2 are invasive pests worldwide: MED and MEAM1. In order to assess the species diversity of B. tabaci in vegetable crops in Senegal, several samplings in different localities, hosts and seasons were collected and analyzed with nuclear (microsatellite) and mitochondrial (COI) markers. The bacterial endosymbiont community was also studied for each sample. Two species were detected: MED Q1 and MEAM1 B. Patterns of MED Q1 (dominance on most of the samples and sites, highest nuclear and mitochondrial diversity and broader secondary endosymbiont community: Hamiltonella, Cardinium, Wolbachia and Rickettsia), point toward a predominant resident begomovirus vector group for MED Q1 on market gardening crops. Furthermore, the lower prevalence of the second species MEAM1 B, its lower nuclear and mitochondrial diversity and a narrower secondary endosymbiont community (Hamiltonella/Rickettsia), indicate that this genetic group is exotic and results from a recent invasion in this area.     

Population structure of Spodoptera frugiperda maize and rice host forms in South America: are they host strains?

Determining which factors contribute to the formation and maintenance of genetic divergence to evaluate their relative importance as a cause of biological differentiation is among the major challenges in evolutionary biology. In Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) two host strains have been recognized in the 1980s: the corn‐strain prefers maize, sorghum, and cotton, whereas the rice‐strain prefers rice and wild grasses. However, it is not clear to what extent these so‐called ‘strains’, which have also been called ‘host races’ or even ‘sibling species’, are really associated with host plants. Due to the indeterminate evolutionary status, we will use the term ‘host forms’ (sensu Funk). Here, we characterized populations collected from maize, rice, and wild grasses from three countries in South America. Using two mitochondrial cytochrome oxidase I (mtCOI) markers and 10 polymorphisms in the triose phosphate isomerase (Tpi) gene, we found various patterns of host association. Two hundred twenty‐seven nuclear amplified fragment length polymorphisms (AFLPs) markers revealed significant genetic differentiation among populations, which was generally correlated to the host from which the larvae were collected. Using a multivariate discriminant analysis and a Bayesian clustering approach, we found that individuals could be grouped into 2–5 genetically distinct clusters, depending on the method. Together, our results indicate that although host‐associated differentiation is present in this species, it does not account for all observable genetic variation and other factors must be maintaining genetic differentiation between these forms. Therefore, the term ‘host strains’ should be abandoned and ‘host forms’ should be used instead for S. frugiperda.     

mtCOI PCR-RFLP技术鉴别中国入侵型和土著型烟粉虱种群的有效性分析

烟粉虱Bemisia tabaci (Gennadius)是世界范围内最重要的入侵生物之一,准确地鉴别烟粉虱入侵生物型和土著生物型具有十分重要的现实意义。mtCOI PCR-RFLP技术具有快速、高效的特点,是当前应用最广泛的烟粉虱生物型鉴定技术,但是,不同限制性内切酶为基础的mtCOI PCR-RFLP技术在鉴定我国烟粉虱种群中的有效性仍不明了。本文比较了已报导的5种mtCOI PCR-RFLP技术在鉴别中国烟粉虱种群入侵生物型和土著生物型(B型、Q型,ZHJ1型、ZHJ2型、ZHJ3型)的有效性。结果表明,内切酶AluI不能区分B型和ZHJ2型烟粉虱;内切酶TaqI不能准确区分ZHJ3型和Q型烟粉虱个体;而内切酶VspI不仅不能准确区分ZHJ1型和Q型烟粉虱个体,也不能准确区分B型和ZHJ2型烟粉虱;内切酶MseI和Tru9I则不能有效鉴别上述5种烟粉虱生物型,因此不适宜推广使用。     

Genetic diversity and geographic distribution of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) genotypes associated with cassava in East Africa

The genetic variability of whitefly (Bemisia tabaci) species, the vectors of cassava mosaic begomoviruses (CMBs) in cassava growing areas of Kenya, Tanzania, and Uganda, was investigated through comparison of partial sequences of the mitochondria cytochrome oxidase I (mtCOI) DNA in 2010/11. Two distinct species were obtained including sub‐Saharan Africa 1 (SSA1), comprising of two sub‐clades (I and II), and a South West Indian Ocean Islands (SWIO) species. Among the SSA1, sub‐clade I sequences shared a similarity of 97.8–99.7% with the published Uganda 1 genotypes, and diverged by 0.3–2.2%. A pairwise comparison of SSA1 sub‐clade II sequences revealed a similarity of 97.2–99.5% with reference southern Africa genotypes, and diverged by 0.5–2.8%. The SSA1 sub‐clade I whiteflies were widely distributed in East Africa (EA). In comparison, the SSA1 sub‐clade II whiteflies were detected for the first time in the EA region, and occurred predominantly in the coast regions of Kenya, southern and coast Tanzania. They occurred in low abundance in the Lake Victoria Basin of Tanzania and were widespread in all four regions in Uganda. The SWIO species had a sequence similarity of 97.2–97.7% with the published Reunion sequence and diverged by 2.3–2.8%. The SWIO whiteflies occurred in coast Kenya only. The sub‐Saharan Africa 2 whitefly species (Ug2) that was associated with the severe CMD pandemic in Uganda was not detected in our study.     

Incomplete cryptic speciation between intertidal and subtidal morphs of Acrocnida brachiata (Echinodermata: Ophiuroidea) in the Northeast Atlantic

The brittle-star Acrocnida brachiata (Montagu) lives in sandy-bottom habitat of both intertidal and subtidal zones along the coasts of the northwestern Europe. An allozyme frequency-based survey (five enzyme loci) was combined with a mitochondrial (mt) COI haplotype analysis (598-bp sequences) on 17 populations to trace back past colonization pathways from the actual population structure of the species. Both genetic markers display a sharp genetic break between intertidal (clade I) and subtidal populations (clade S). This break corresponds to an allele frequency inversion at three enzyme loci (Hk, Pgm and Pgi) and a deep divergence of about 20% in mtCOI sequences between most of the intertidal populations and other samples. The geographic distribution of clade I seems to be more restricted than clade S as it is absent from the intertidal of the eastern English Channel and North Sea and may be replaced by clade S in south Brittany. Applying previously published rates of mutation, divergence between the two clades is estimated to pre-date 5 million years ago and may be due to allopatric speciation processes at the Mio-Pliocene transition. The occurrence of putative hybrids in a few localities, however, suggests incomplete cryptic speciation with secondary contact zones. The relative importance of colonization history vs. habitat specialization are discussed in the light of neutral evolution as tested from mtCOI gene sequences. While differential selection seems to have contributed little to the separation of the lineages, it may have played a role in the emergence of adaptive polymorphisms in the hybrid zone. Furthermore, congruent spatial patterns of differentiation were observed in both clades suggesting a recent increase in population size. These findings are in agreement with a recent expansion of the populations during or after the formation of the English Channel, from a southern refuge for the subtidal clade whereas the intertidal clade may have persisted further north. As previously suspected for a species with a very short pelagic larval phase, contemporary gene flow between distant or adjacent populations appears to be extremely reduced or even absent.     

利用mtCOI PCR-RFLP技术鉴定中国境内九个烟粉虱隐种

烟粉虱Bemisia tabaci (Gennadius)是一个物种复合体, 包括31个以上形态上无法区分的隐种, 其中少数隐种是世界性入侵害虫。目前, 在中国境内分布有2个入侵隐种和13个土著隐种。快速、 高效的鉴别方法对掌握烟粉虱田间发生规律及制定相关防控策略具有重要意义。然而到目前为止, 除了mtCOI基因测序比对外, 尚未有一种简便的方法可以有效地区分多个烟粉虱隐种。本研究采用mtCOI PCR-RFLP技术, 单独或组合使用TaqI, VspI, Van91I, NcoI和FokI这5种限制性内切酶, 酶切烟粉虱mtCOI的PCR扩增片段, 鉴别分布在中国境内的9个烟粉虱隐种。结果表明, 单独使用TaqI酶切, 可鉴别出MEAM1和China 1两个隐种, 使用TaqI+NcoI分步酶切可鉴定出MED和Asia 1两个隐种, 使用TaqI+Van91I分步酶切可鉴定出Asia II 3和Asia II 9两个隐种, 使用TaqI+VspI+FokI分步酶切可鉴定出Asia II 1, Asia II 6和Asia II 7 3个隐种。本研究为高效鉴别中国境内的多个烟粉虱隐种提供了方法。     

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.     

Comparative phylogeography of two coastal polychaete tubeworms in the Northeast Atlantic supports shared history and vicariant events

The historic processes which have led to the present-day patterns of genetic structure in the marine coastal fauna of the Northeast Atlantic are still poorly understood. While tectonic uplifts and changes in sea level may have caused large-scale vicariance, warmer conditions during glacial maxima may have allowed pockets of diversity to persist to a much wider extent than in the Northwestern Atlantic. The large-scale geographic distribution of deeply divergent lineages of the coastal polychaete tubeworms Pectinaria koreni (two clades) and Owenia fusiformis (three clades) were compared using a fragment of the mitochondrial cytochrome oxidase I gene (mtCOI). All lineages were present along the biogeographic transition zone on the north coast of Brittany (France) and we found evidence pointing towards congruence in the timing of cladogenic events between Pectinaria sp. (P. auricoma/P. belgica and P. koreni) and Owenia sp., suggesting a shared history of vicariant events. More conserved 16SrRNA sequences obtained from four species of Pectinariidae together with mtCOI sequences of P. koreni seem consistent with an initial establishment of pectinariids in the north, and a southward colonization of the Northeast Atlantic. Phylogeographic patterns in O. fusiformis were also consistent with a north/south pattern of lineage splitting and congruent levels of divergence were detected between lineages of both species. We observed signatures of both persistence in small northern glacial refugia, and of northwards range expansion from regions situated closer to the Mediterranean. However, whether the recolonization of the Northeast Atlantic by both species actually reflects separate interglacial periods is unclear with regards to the lack of molecular clock calibration in coastal polychaete species.     

Utility of MtCOI polymerase chain reaction-restriction fragment length polymorphism in differentiating between Q and B whitefly Bemisia tabaci biotypes

The invasive, insecticide-resistant, Q whitefly biotype, has gradually spread to other countries including the US via human-mediated movement of plant materials. We assessed the utility of the VspI -based mtCOI (mitochondrion cytochrome oxidase I) polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique as a rapid, cost-effective, and reliable alternative for differentiating the Q from the dominant B biotype in Arizona. Using the standard mtCOI gene sequencing and mtCOI PCR-RFLP techniques, we biotyped eight whitefly strains of five individuals each collected from poinsettia and cotton at different locations in Arizona. Complete concordance was observed between the two methods, with three strains being identified as the Q biotype and five samples as the B biotype. We also scanned the mtCOI gene sequences for VspI polymorphisms in the B and Q biotype whiteflies currently available in the GenBank database. This global screening revealed the existence of three and four VspI polymorphic types for the Q and B biotypes, respectively. Nevertheless, all three VspI polymorphic Q biotype whiteflies shared a common and unique VspI site that can be used to differentiate Q biotype from the four VspI polymorphic B biotype whiteflies identified. These results demonstrate that the VspI -based mtCOI gene PCR-RFLP provides a reliable diagnostic tool for differentiating the Q and B biotype whiteflies in the US and elsewhere.