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.     

Distribution and molecular characterization of distinct Asian populations of Bemisia tabaci (Hemiptera: Aleyrodidae) in Japan

Bemisia tabaci (Gennadius) is considered to be the most economically important pest insect worldwide. The invasive variant, the Q biotype of B. tabaci was first identified in 2004, and has caused significant crop yield losses in Japan. The distribution and molecular characterization of the different biotypes of B. tabaci in Japan have been little investigated. In this study, B. tabaci populations were sampled from the Japanese Archipelago, the Amami Archipelago and the Ryukyu Islands between 2004 and 2008, and the nucleotide sequences of their mitochondrial cytochrome oxidase I genes were determined. Bayesian phylogenetic relationship analysis provided the first molecular evidence that the indigenous Japanese populations could be separated into four distinct genetic groups. One major native population from the Japanese Archipelago, given the genetic group name Lonicera japonica, was separated into an independent group, distinct from the other genetic groups. The second major population, the Nauru biotype in the Asia II genetic group, was identified in the Amami Archipelago and the Ryukyu Islands. Two distinct minor genetic groups, the Asia I and the China, were also identified. One invasive B‐related population belonging to the Mediterranean/Asia Minor/Africa genetic group has been identified in Honshu. All lineages generated by the phylogenetic analyses were supported by high posterior probabilities. These distinct indigenous B. tabaci populations developed in Japan under geographical and/or biological isolation, prior to recent invasions of the B and Q biotypes.     

Digestive, salivary, and reproductive organs of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) B type

A microscopic analysis of the morphology and ultrastructure of the digestive, salivary, and reproductive systems of adult Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) B type was conducted using light, scanning, and transmission electron microscopy. The internal anatomy of B. tabaci was found to be similar to that reported for Trialeurodes vaporariorum. In a microscopic analysis of the salivary glands, we have shown that each primary salivary gland is composed of at least 13 cells varying in morphology and staining differentially, while the accessory salivary glands are composed of four morphologically similar cells. We analyzed the course of the alimentary canal in B. tabaci, demonstrated the internal morphology of the organs, and clarified the location of the filter chamber relative to other organs in the whitefly. Our observations confirm that the pair of structures extending from the connecting chamber are caeca that may aid in fluid movement through the midgut and are not Malpighian tubules, as previously suggested. We confirm an earlier finding that the whitefly lacks Malpighian tubules, having instead specialized Malpighian-like cells within the filter chamber at the juncture with the internal ileum. Finally, we provide the first scanning electron microscopic analysis showing the reproductive organs of B. tabaci. Our investigation provides clarified terminology for several components of the digestive and excretory system. We also provide drawings and micrographs that will aid future researchers in localizing the internal organs of B. tabaci. We expect our analysis to provide a valuable tool for studying B. tabaci / plant virus interactions and physiological and biological aspects of this insect.     

Efficiency of some herbal pesticides on reproductive parameters of silverleaf whitefly,Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae)

The silverleaf whitefly is one of the most important pests found commonly in Iran and in the world. The development of alternative methods instead of chemical applications is necessary in pest management for human health and environment protection. The objective of this research was to assess the effects of extracts of two medicinal plant species: Calotropis procera and Allium sativum, and a formulation containing azadirachtin on fecundity and fertility of the silverleaf whitefly, grown on greenhouse tomato plants. The effects were compared to that of pymetrozine, a synthetic insecticide. According to the results, there was a significant difference among treatments for all reproductive parameters. Gross fecundity rates for pesticides control, herbal extract control, C. procera extract, A. sativum extract, azadirachtin and pymetrozine were 184.75, 146.72, 80.11, 82.18, 63.06 and 55.96 eggs, respectively. These herbal extracts were effective against this pest and they can be the suitable choices for replacing these chemical insecticides.     

New insights into the mitochondrial phylogeny of the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) in the Mediterranean Basin

The whitefly Bemisia tabaci is vector of plant infecting viruses and it is considered as one of the most important agricultural pests around the Mediterranean basin. At present, five biotypes of B. tabaci have been reported in the Mediterranean Basin: B, Q, S, T and M. To establish the phylogeographic relationship of these Mediterranean biotypes with others, 54 samples collected in Europe and Africa were analysed by sequencing the mitochondrial cytochrome oxidase I gene (mtCOI). The phylogeny showed that Spanish samples corresponding to the biotype S were related to the haplotype Uganda 2 of the African clade, associated with recent epidemic upsurges of cassava mosaic virus (CMD) in that country. This phylogeographic relationship gave support to a distinct subgroup revealed within the African clade. Bemisia tabaci collected from Euphorbia plants in Italy (biotype T) formed one of the three distinct subgroups existing within the Southeast/Far East Asian clade, while samples from Turkey (biotype M) clustered together with reference mitochondrial sequences from whiteflies from Pakistan and Thailand. Recent reports indicate that Bemisia populations corresponding to the biotypes S and T are distributed in areas larger than those initially delimited. Other results indicated that samples collected in Sudan grouped within the Mediterranean–North Africa clade together with reference sequences of the biotype Q corresponding to insects collected in Spain and Morocco. Mitochondrial haplotypes of B. tabaci samples collected on sweet potato in Ghana clustered with reference sequences of samples from Cameroon corresponding to one of the five Sub-Saharan subgroups already described in the African clade. These data extends the phylogenetic information of the B. tabaci species complex and present new questions to be investigated.     

Colonization of non-cassava plant species by cassava whiteflies (Bemisia tabaci) in Uganda

Bemisia tabaci (Genn.) (Homoptera: Aleyrodidae) is the vector of cassava mosaic geminiviruses (CMGs), which are the main production constraint to cassava [Manihot esculenta Crantz (Euphorbiaceae)], both in Uganda and elsewhere in Africa. Two B. tabaci genotype clusters, Ug1 and Ug2, differentiated at 8% nucleotide (nt) divergence within the mitochondrial cytochrome oxidase I (mtCOI) gene, have been shown to occur on cassava in Uganda. However, the role of alternative hosts in the ecology of cassava B. tabaci genotypes and their possible involvement in the epidemiology of cassava mosaic disease (CMD) in Uganda remain unknown. In this study, we investigated the restriction of cassava B. tabaci genotypes to cassava and the colonization of alternative host species in select cassava‐growing areas of the country in 2003 and 2004. Bemisia tabaci adults and 4th instar nymphs were collected from cassava and 11 other cultivated and uncultivated species occurring adjacent to the sampled cassava fields. Phylogenetic analysis of mtCOI sequences revealed that only a single genotype cluster, Ug1, was present on both cassava and non‐cassava plant species sampled in this study. The Ug1 genotypes (n = 49) shared 97–99% nt identity with the previously described cassava‐associated B. tabaci populations in southern Africa, and were ～8% and ～13% divergent from Ug2 and the ‘Ivory Coast cassava’ genotypes in Uganda and Ivory Coast, respectively. The Ug1 genotypes occurred (as adults) on all 12 source‐plant species sampled. However, based on the presence of B. tabaci 4th instar nymphs, the Ug1 genotypes (n = 13) colonized cassava and five other non‐cassava plant species: Manihot glaziovii, Jatropha gossypifolia, Euphorbia heterophylla, Aspilia africana, and Abelmoschus esculentus, suggesting that cassava B. tabaci (Ug1 genotypes) are not restricted to cassava in Uganda. No Ug2‐like genotypes were detected on any of the plant species sampled, including cassava, in this study. The identification of additional hosts for at least one genotype cluster, Ug1, known also to colonize cassava, and which was hitherto thought to be ‘cassava‐restricted’ may have important epidemiological significance for the spread of CMGs in Uganda.     

Genetic diversity of Iberian populations of Bemisia tabaci (Hemiptera: Aleyrodidae) based on random amplified polymorphic DNA-polymerase chain reaction

The genetic structure of six Iberian populations of the whitefly Bemisia tabaci, two of them biotype Q, one biotype B, and the other three a mixture of both, has been studied using random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). A total of 336 individuals was completely discriminated by means of 234 scored bands. Separate analyses of molecular variance of haploid males and diploid females using the pairwise number of differences between haplotypes showed that biotypes contribute significantly more to the observed variability than populations within biotypes. On average, gene flow between two biotypes of the same population is lower than between populations of identical biotypes. On the basis of these results and the nondetection under natural conditions of a single hybrid, we consider that both biotypes are genetically isolated under the ecological conditions prevailing in the south Iberian Peninsula. All populations of biotype Q presented similar values of intrapopulational diversity, which were higher than the values shown by populations of biotype B.     

Biotype and status of insecticide resistance of whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) in Alhassa oasis,Eastern Province of Saudi Arabia.

The tobacco whitefly, Bemisia tabaci, is one of the major insects infesting vegetable plants. This pest is well known in Alhassa oasis, Saudi Arabia; which is historically agricultural land cultivated with date palm trees and different vegetables. A molecular key based on the sequence of the mitochondrial cytochrome oxidase gene CO1 was used for the identification of strains of the tobacco whitefly Bemisia tabaci collected from farms located in four areas of the Alhassa oasis; Northern, Southern, Eastern and Western. Only one biotype (B‐biotype) of B. tabaci was reported in the oasis. Resistance of B. tabaci was tested against eight insecticides, the results showed moderate to low levels of resistance to the tested insecticides. However, the resistance to neonicotinoid insecticides was low and established at 1.3 fold to both Imidacloprid and Acetamiprid. In addition, medium levels of resistance were detected to the insect growth regulator Pyriproxyfen (30 fold), and the pyrethroid Deltamethrin (30 fold), Bifenthrin (24 fold) and Cypermethrin (13 fold). A medium level of resistance was also detected to the carbamate insecticide Carbosulfan and was 40 fold of the laboratory strains. A low level of resistance to the organophosphorus insecticide was detected to Phenthoate (11 fold). However, these results reflect that the farmers were less dependent on the use of insecticides to control B. tabaci in the oasis and they may be implementing other environmentally sound techniques to keep the pest below the damage threshold.     

Establishment of a silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) population in western Sydney

A field survey in western Sydney found populations of Bemisia tabaci biotype B (silverleaf whitefly) that have the potential to damage greenhouse vegetable crops prevalent in the region. Adult whiteflies were collected from five farms at 2-week intervals and the proportion of silverleaf whitefly in the overall whitefly population was determined using polyacrylamide gel electrophoresis. High levels of silverleaf whitefly were detected at most sampling dates on two of the farms surveyed and a third farm exhibited lower but relatively continuous silverleaf whitefly abundance. The presence of permanent silverleaf whitefly populations must be considered by the greenhouse industry when formulating whitefly management plans for western Sydney.     

Genetic differentiation of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype Q based on mitochondrial DNA markers

In the present study, genetic differentiation of Bemisia tabaci (Gennadius) biotype Q was analyzed based on mitochondrial cytochrome oxidase I (mt COI) gene sequence. The results showed that B. tabaci biotype Q could be separated into two subclades, which were labeled as subclades Q1 and Q2. Subclade Q1 was probably indigenous to the regions around the Mediterranean area and subclade Q2 to Israel or Cyprus. It was because B. tabaci was composed of several genetically distinct groups with a strong geographical association between more closely related biotypes. Not all of the B. tabaci biotype Q in the non‐Mediterranean countries come from the same regions. Until now, all B. tabaci biotype Q in China were grouped into subclade Q1. The B. tabaci biotype Q introduced into the US included both subclades Q1 and Q2. The genetic structure analysis showed higher genetic variation of subclade Q1 than that of subclade Q2.     

施用噻虫嗪可降低B型烟粉虱群体的遗传多样性

用4个具有多态性的微卫星位点（BEM15、BEM25、BEM31和BT-b53）分析了施用化学农药噻虫嗪 （thiamethoxam）对B型烟粉虱Bemisia tabaci（Gennadius）群体遗传结构的影响。结果表明：噻虫嗪汰选18代的B型烟粉虱处理种群（抗性种群）抗药性上升到对照种群（敏感种群）的19.08倍,同时其微卫星位点不同等位基因频率分布发生了变化,等位基因数（N_a）平均值由2.750降到2.250,杂合度（h）平均值由0.459降到0.299（降低了34.8%）,多态信息含量（PIC）平均值由0.393降到0.250,有效等位基因数（N_e）平均值由2.051降到1.488;抗性种群与敏感种群的标准遗传距离为0.15。结果提示,化学农药的施用可能是B型烟粉虱群体遗传结构的重要影响因素之一。     

Occurrence of three genotypic clusters of Bemisia tabaci and the rapid spread of the B biotype in south India

The whitefly, Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), is generally considered to have originated from the Indian subcontinent, although little information has so far been collected on the molecular diversity of populations present in this region. The genetic diversity of B. tabaci populations from Karnataka State, south India was analysed using the random amplified polymorphic DNA‐polymerase chain reaction (RAPD‐PCR) technique and partial mitochondrial cytochrome oxidase I (mtCOI) gene sequences (689 bases) of 22 selected samples. A total of 108 whitefly samples analysed by RAPD‐PCR produced 89 polymorphic bands, and cluster analyses grouped them according to their geographic origin into ‘north’ and ‘south’ Karnataka. Phylogenetic analysis of mtCOI gene sequences with reference B. tabaci sequences from other Asian countries divided them into three genotypic clusters. Each cluster was supported with high bootstrap values (82–100%) and the individuals belonging to each cluster shared high nucleotide identities (up to 100%). This indicated at least three distinct genotypes, apparently indigenous to India, which are also present in China, Malaysia, Nepal, Pakistan, and Thailand. These coexist with the B biotype, which was first reported in India in 1999, and has since spread rapidly to other states in south India. The B biotype was more common than the indigenous B. tabaci, in locations where it had been present for more than 2 years. This is reminiscent of the situation in the Americas during the early 1990s, where the B biotype replaced existing biotypes and caused unprecedented losses to agriculture.     

Biology and non-preference for oviposition by Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae) on cotton cultivars

The purposes of this work were to evaluate some biological aspects of Bemisia tabaci (Gennadius) biotype B at egg and nymphal stages and to evaluate the non-preference for oviposition and its correlation with the number and type of trichomes on the cotton cultivars BRS Ipê, BRS 186-Precoce 3, BRS Acala, BRS Verde, BRS-200 Marrom, BRS Cedro, BRS Ita 90-2 and BRS Aroeira. The experiments were conducted in climatic chambers at 28 +/- 2 degrees C, 70% RH and photophase of 14h, and in greenhouse. Egg fertility was not affected by the cotton cultivars but survival in egg-adult period was influenced by the host plant. There was no influence of cultivars neither on the duration of egg stage, nymphs at 2nd, 3rd and 4th instars nor on the duration from egg to adult, but nymphs reared on the cultivar BRS Ipê had their 1st instar extended. Low number of eggs was detected on the cultivars BRS Aroeira, BRS Verde and BRS Ita 90-2 in both experiments with and without oviposition choice, indicating a possible mechanism of resistance, but no correlation could be established between trichome densisty and oviposition non-preference.     

Baseline susceptibility of Bemisia tabaci B biotype (Hemiptera: Aleyrodidae) populations from California and Arizona to spiromesifen

Susceptibility to spiromesifen, a tetronic acid derivative, was determined for three imidacloprid-resistant strains and 12 geographically discrete natural populations of Bemisia tabaci (Gennadius) (=Bemisia argentifolii Bellows & Perring) (Hemiptera: Aleyrodidae) from California and Arizona by laboratory bioassays. Newly emerged first instars were sprayed with aqueous serial dilutions of spiromesifen and evaluated for toxicity to establish baseline susceptibility data. Interpopulation variability in susceptibility to spiromesifen was observed among the natural populations of whiteflies up to 29-fold; however, there was only 30-fold difference in susceptibility among natural and resistant populations tested. In general, spiromesifen was quite toxic to first instars across most of their geographic range, with LC50 values ranging from 0.210 to 6.08 microg (AI)/ml. The magnitude of variation was smaller among the three-resistant strains. These results suggest that the observed variability reflect natural variation in spiromesifen susceptibility among all the test populations, possibly due to previous exposure to insecticides at each location. The effectiveness of spiromesifen also was evaluated against all immature stages of whiteflies from three field and two resistant strains. Spiromesifen was significantly more active against early instars of whiteflies based on lower LC50 values recorded compared with the fourth instars. Spiromesifen was effective against the resistant strains including a Q-biotype of B. tabaci from Spain, which is highly resistant to neonicotinoids. Results of this study indicate absence of cross-resistance between spiromesifen and more commonly used neonicotinoids. Our findings suggest that spiromesifen should be considered an ideal candidate for whitefly resistance management programs in rotation with other effective chemistries.     

Multiple generation effects of high temperature on the development and fecundity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B

Insects are ectotherms and their ability to resist temperature stress is limited. The immediate effects of sub‐lethal heat stress on insects are well documented, but longer‐term effects of such stresses are rarely reported. In this study, survival, development and reproduction of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, were compared over five consecutive generations at 27, 31 and 35 °C and for one generation at 37 °C. Both temperature and generation significantly affected the fitness of the whitefly. These impacts were more dramatic with increasing generations and temperatures. Among the experimental temperatures, the most favorable for development and reproduction were 27 °C and 31 °C. At 27 °C, survival, development and fecundity were all stable over these five generations. At 31 °C, immature survival rate was the highest in the fifth generation, but female fecundities decreased in the fourth and fifth generations. At 35 °C, egg hatching rate, immature survival rate and female fecundity decreased significantly in the fourth and fifth generations. At 37 °C, survival of B. tabaci was not adversely affected, but female fecundity at 37 °C was less than 10% of that at 27 °C or 31 °C. These results demonstrate that the lethal high temperature for B. tabaci is over 37 °C, and the whitefly population continued expanding in the five generations at 35 °C. The ability of B. tabaci biotype B to survive high temperature stress will play an important role in its population extension under global warming.     

Isolation and characterization of microsatellite loci in Bemisia tabaci (Hemiptera: Aleyrodidae)

Microsatellite‐enriched genomic libraries were obtained from the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) using a magnetic/biotin capture of repetitive sequences. Ten dinucleotide markers were successfully isolated and characterized from these libraries. Variability was assessed in six populations of B. tabaci collected from different localities of the island of Crete, Greece. The number of alleles per locus in approximately 105 individuals screened across populations ranged from two to 13. Averaged observed heterozygosity over the six populations ranged from 0.001 to 0.58.     

B型烟粉虱与浙江非B型烟粉虱的竞争

为了了解近年来入侵中国的B型烟粉虱(Bemisiatabaci)取代本地非B型烟粉虱的潜能,在室内将一个B型与一个浙江非B型烟粉虱种群混合饲养在不同寄主植物上,跟踪观察混合种群中两个生物型个体数量相对比例的变化。结果表明,当两种生物型在棉花(Gossypiumhirsutum)上以相同初始数量共存竞争时,经过6代,非B型完全被B型替代;而在西葫芦(Cucurbitapepo)上以相同初始数量共存竞争时,只经过2代,非B型即完全被B型替代。在棉花上,即使以非B型占87%、B型占13%开始共存竞争,经过225d后,非B型也完全被B型替代。这说明B型烟粉虱具有在短期内竞争取代浙江非B型烟粉虱的能力。经分析,B型除了寄主范围比非B型的宽这一点对其竞争有利外,较强的内在竞争潜能也是其能成功入侵并替代本地非B型烟粉虱的一个重要原因。     

四种粉虱种群超微形态特征多样性研究

运用扫描电子显微镜对烟粉虱Bemisia tabaci、非洲伯粉虱Bemisia afer、温室粉虱Trialeurodes vaporariorum和柑桔粉虱Dialeurodes citri4种粉虱4龄若虫的超微形态特征进行了初步研究。结果表明,扫描电子显微镜下的超微结构特征可很好地将4种粉虱区分开来,如烟粉虱圆锥状的舌状突,非洲伯粉虱尾沟两侧隆起上形成的横脊,温室粉虱形态典型的乳突和泌蜡孔,柑桔粉虱近圆形的皿状孔及其尾沟内的卵石状乳突等特异特征。并根据种间的超微结构特异特征,编制了不同种的简明检索表。超微形态特征为粉虱种群鉴定提供了可靠的理论参考。     

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.