Cloning of a putative extracellular Cu/Zn superoxide dismutase and functional differences of superoxide dismutases in invasive and indigenous whiteflies

Superoxide dismutases （SODs） are a group of important antioxidant defense enzymes. In this study, a putative extracellular Cu/Zn superoxide dismutase （ecCuZnSOD） complementary DNA was cloned and characterized from the whitefly, Bemisia tabaci. Quantitative polymerase chain reaction analysis showed that the expression level of BtecCuZnSOD was more than 10-fold higher in the invasive Middle East Asia Minor 1 （MEAM1） than in the native Asia II 3 species of the B. tabaci species complex. After exposure to low temperature （4 ℃）, the expression of Bt-ecCuZnSOD gene was significantly up-regulated in MEAM1 but not in Asia II 3. Furthermore, the expression level ofB. tabaci intracellular CuZnSOD （Bt-icCuZnSOD）, Bt-ecCuZnSOD and mitochondrial MnSOD （Bt-mMnSOD） was compared after transferring MEAM1 and Asia II 3 whiteflies from favorable （cotton） to unfavorable host plants （tobacco）. On cotton, both CuZnSOD genes were expressed at a higher level in MEAM1 compared with Asia II 3. Interestingly, after transferring onto tobacco, the expression of Bt-ecCuZnSOD was significantly induced in Asia II 3 but not in MEAM1. On the other hand, while Bt-mMnSOD was expressed equally in both species on cotton, Bt-mMnSOD messenger RNA was up-regulated in MEAM 1 on tobacco. Consistently, enzymatic activity assays of CuZnSOD and MnSOD demonstrated that CuZnSOD might play an important protective role against oxidative stress in Asia II 3, whereas MnSOD activation was critical for MEAM1 whiteflies during host adaptation. Taken together, our results suggest that the successful invasion ofMEAM 1 is correlated with its constitutive high activity of CuZnSOD and inducible expression of MnSOD under stress conditions.

Genomic and transcriptomic analyses reveal metabolic complementarity between whiteflies and their symbionts

Nutritional mutualism between insects and symbiotic bacteria is widespread.The various sap-feeding whitefly species within the Bemisia tabaci complex associate with the same obligate symbiont(Portiera)and multiple secondary symbionts.It is often assumed that some of the symbionts residing in the whiteflies play crucial roles in the nutritional physiology of their insect hosts.Although effort has been made to understand the functions of the whitefly symbionts,the metabolic complementarity offered by these symbionts to the hosts is not yet well understood.We examined two secondary symbionts,Arsenophonus and Wolbachia,in two species of the B.tabaci whitefly complex,provisionally named as Asia II 3 and China 1.Genomic sequence analyses revealed that Arsenophonus and Wolbachia retained genes responsible for the biosynthesis of B vitamins.We then conducted transcriptomic surveys of the bacteriomes in these two species of whiteflies together with that in another species named MED of this whitefly complex previously reported.The analyses indicated that several key genes in B vitamin syntheses from the three whitefly species were identical.Our findings suggest that,similar to another secondary symbiont Hamiltonella,Arsenophonus and Wolbachia function in the nutrient provision of host whiteflies.Although phylogenetically distant species of symbionts are associated with their respective hosts,they have evolved and retained similar functions in biosynthesis of some B vitamins.Such metabolic complementarity between whiteflies and symbionts represents an important feature of their coevolution.

Patterns of host cell inheritance in the bacterial symbiosis of whiteflies

Whiteflies possess bacterial symbionts Candidatus Portiera aleyrodidium that are housed in specialized cells called bacteriocytes and are faithfully transmitted via the ovary to insect offspring.In one whitefly species studied previously,Bemisia tabaci MEAMI,transmission is mediated by somatic inheritance of bacteriocytes,with a single bacteriocyte transferred to each oocyte and persisting through embryogenesis to the next generation.Here,we investigate the mode of bacteriocyte transmission in two whiefly species,B.tabaci MED,the sister species of MEAM1,and the phylogenetically distant species Trialeurodes vaporariorum.Microsatllite analysis supported by microscopical studies demonstrates that B.tabaci MED bacteriocytes are genetically different from other somatic cells and persist through embryogenesis,as for MEAMI,but T.vaporariorum bacteriocytes are genetically identical to other somatic cells of the insect,likely mediated by the degradation of maternal bacteriocytes in the embryo.These two alternative modes of transmission provide a first demonstration among insect symbioses that the cellular processes underlying vertical transmission of bacterial symbionts can diversify among related host species associated with a single lineage of symbiotic bacteria.

Extracts of Melia azedarach Increases Mulberry Whitefly Mortality without Affecting Silkworm Survivorship

Melia azedarach L. extracts were studied in comparison with selected synthetic in-secticides against the mulberry whiteflies Pealiusma chili and P. mori under labora-tory conditions. Morus alba (cv. “Early Spring”) leaves infested by mulberry white-flies were exposed to Melia extracts of green fruits, l-cyhalothrin (10% a.i.) and con-trol. Also, white mulberry leaves after treatment with the same insecticides were provided to silkworms for consumption. Results have shown that there were signif-icant differences in the nymphal mortality of the whiteflies among treatments. Melia extracts and l-cyhalothrin were effective in increasing whitefly mortality 24 h after application. Furthermore, Melia extracts didn’t affect silkworm survivorship, which was severely affected by l-cyhalothrin treatment, since all the silkworms fed on treated leaves were found dead. Thus, these extracts might be considered a potential alternative in management of the mulberry whiteflies.

Species Concepts as Applied to the Whitefly Bemisia tabaci Systematics:How Many Species Are There?

The worldwide distribution and extensive genetic diversity of the whitefly,Bemisia tabaci,has long been recognized.However,the levels of separation within B.tabaci and the nomenclature of the various genetic groups have been a subject of debate.Recent phylogenetic analyses indicate that B.tabaci is a complex composed of 28 morphologically indistinguishable species.In this article,we first review the debate and difficulties associated with B.tabaci＇s taxonomy and systematics,and argue for the need to apply the biological species concept in order to elucidate B.tabaci＇s systematics.We summarize the accumulated genetic and behavioural data on reproductive incompatibilities evident amongst phylogenetic mtCOI groups of B.tabaci.Crossing studies have been conducted with 14 of the 28 putative species covering 54 reciprocal inter-species pairs,and observations on mating behaviour have been conducted for seven species pairs.Data from both crossing trials and behavioural observations indicate a consistent pattern of reproductive isolation among the putative species.We then discuss the technical and conceptual complexities associated with crossing experiments and behavioural observations designed to reveal reproductive incompatibility.Finally,we elaborate on a strategy for further clarifying the pattern of reproductive isolation between B.tabaci groups and propose future research directions on the systematics of this complex.

Diversity and Genetic Differentiation of the Whitefly Bemisia tabaci Species Complex in China Based on mtCOI and cDNA-AFLP Analysis

The whitefly Bemisia tabaci are considered as a taxonomically complex that contained some destructive pests.Two of the most prevalent cryptic species are B.tabaci Middle East-Asia Minor 1（MEAM1）and Mediterranean（MED）.In an extensive field survey of the B.tabaci complex present throughout part of China from 2004 to 2007,we obtained 93 samples of B.tabaci from 22 provinces.We determined that these Chinese haplotypes included 2 invasive species（MEAM1 and MED）,and 4 indigenous cryptic species（Asia II 1,Asia II 3,China 3 and Asia II 7）by sequencing mitochondrial cytochrome oxidose one gene（mtCOI）.The diversity and genetic differentiation of a subset of 19 populations of B.tabaci were studied using cDNA amplified fragment length polymorphism（AFLP）.Prior to 2007,MEAM1 was a dominant species in many provinces in China.By 2007,MED was dominant in 11 provinces.Both invasive and indigenous species were simultaneously found in some regions.Indigenous species of B.tabaci were found in six provinces in southern China.MED and MEAM1 have broad ranges of host plants,and indigenous species appeared to have much narrower host ranges.All Asia II 3 samples were found on cotton except one on aubergine.China 3 has more host plants than Asia II 3.Twelve samples of China 3 were collected from sweet potato,Japanese hop,squash and cotton.A total of 677 reproducible bands amplified with 5 AFLP primer combinations were obtained.The highest proportion of polymorphic bands was 98.7% and the lowest was 91.9%.Unweighted pair-group method analysis indicated that the clustering was independent of the different species.MED showed the lowest degree of similarity than the other species.The data indicate that both MEAM1and MED were rapidly established in China.

Density and Seasonal Dynamics of Bemisia tabaci(Gennadius) Mediterranean on Common Crops and Weeds Around Cotton Fields in Northern China

The density seasonal dynamics of Bemisia tabaci MED were evaluated over two years in a cotton-growing area in Langfang, Hebei Province, northern China on cotton （Gossypium hirsutum L.） and six other co-occurring common plants, common ragweed （Ambrosia artemisiifolia L.）, piemarker （Abutilon theophrasti Medicus）, sunflower （Helianthus annuus L.）, sweet potato （Ipomoea batatas L.）, soybean （Glycine max L.）, and maize （Zea mays L.）. The whitefly species identity was repeatedly tested and confirmed; seasonal dynamics on the various host plants were standardized by the quartile method. B. tabaci MED appeared on weeds （the common ragweed and piemarker） about 10 days earlier than on cotton, or the other cultivated plants. The peak population densities were observed over a span of 2 to 3 weeks on cotton, starting in early （2010） or mid-August （2011）. The common ragweed growing adjacent to cotton supported the highest B. tabaci densities （no. on 100 cm2 leaf surface）, 12-22 fold higher than on cotton itself. Sunflower supported more B. tabaci than the other plants, and about 1.5-2 fold higher than cotton did, Our results indicate that weeds （esp. the common ragweed） around cotton fields could increase the population density of B. tabaci MED on cotton, while sunflower could act as a trap crop for decreasing pest pressure on cotton.

Bemisia tabaci Phylogenetic Groups in India and the Relative Transmission Efficacy of Tomato leaf curl Bangalore virus by an Indigenous and an Exotic Population

Bemisia tabaci adults from various host-plant species were collected from 31 regions across India.266 B.tabaci samples were first screened by RAPD-PCR to examine molecular variability and to select individuals with different fingerprints.Host-plant and region of collection were then used to select 25 individuals for PCR amplification and sequencing of their partial mitochondrial cytochrome oxidase subunit one（mtCOI）genes.Pairwise comparisons with mtCOI consensus sequences showed that the majority of these samples had 〈3.5% sequence divergence from groups currently termed Asia I,Asia II-5,Asia II-7,and Asia II-8.The biotype-B B.tabaci from India clustered into the Middle East-Asia Minor 1 group.A new group of B.tabaci from Coimbatore,collected from pumpkin,was related most closely to the Asia I group（6.2% sequence divergence from the consensus Asia I sequence）.To increase our understanding of the epidemiology of tomato leaf curl disease（ToLCD）and the key B.tabaci genetic groups involved in virus spread,the indigenous Asia I and the exotic biotype-B population from South India were used to carry out transmission experiments using Tomato leaf curl Bangalore virus（ToLCBV）.The acquisition access periods（AAP）,inoculation access periods（IAP）,latent periods（LP）,and ToLCBV transmission efficiencies of the two populations were compared and the biotype-B had the more efficient transmission characteristics.These results are discussed in relation to recent changes in the epidemiology of tomato leaf curl disease in South India.

Next Generation Transcriptome Sequencing and Quantitative Real-Time PCR Technologies for Characterisation of the Bemisia tabaci Asia 1 mtCOI Phylogenetic Clade

A programme of functional genomics research is underway at the University of Greenwich,UK,to develop and apply genomics technologies to characterise an economically-important but under-researched Bemisia tabaci（Hemiptera：Aleyrodidae）,the Asia 1 mtCOI phylogenetic group.A comparison of this putative species from India with other important B.tabaci populations and insect species may provide targets for the development of more effective whitefly control strategies.As a first step,next-generation sequencing（NGS）has been used to survey the transcriptome of adult female whitefly,with high quality RNA preparations being used to generate cDNA libraries for NGS using the Roche 454 Titanium DNA sequencing platform.Contig assemblies constructed from the resultant sequences（301 094 reads）using the software program CLC Genomics Workbench generated 3 821 core contigs.Comparison of a selection of these contigs with related sequences from other B.tabaci genetic groups has revealed good alignment for some genes（e.g.,HSP90）but misassemblies in other datasets（e.g.,the vitellogenin gene family）,highlighting the need for manual curation as well as collaborative international efforts to obtain accurate assemblies from the existing next generation sequence datasets.Nevertheless,data emerging from the NGS has facilitated the development of accurate and reliable methods for analysing gene expression based on quantitative real-time RT-PCR,illustrating the power of this approach to enable rapid expression analyses in an organism for which a complete genome sequence is currently lacking.

African Cassava Whitefly,Bemisia tabaci,Resistance in African and South American Cassava Genotypes

The whitefly,Bemisia tabaci,is a major pest of cassava,particularly in Africa where it is responsible both for the transmission of plant viruses and,increasingly,for direct damage due to feeding by high populations.To date,there have been no practical solutions to combat this emerging problem,due to the inability of the subsistence farmers that grow cassava to afford expensive inputs such as insecticides.A programme of research was carried out linking institutes in Africa,the UK and South America,to identify possible resistance sources in cassava to the whitefly,Bemisia tabaci.The South American genotype MEcu 72 and several Ugandan cassava landraces including Ofumba Chai,Nabwire 1 and Mercury showed good levels of resistance to B.tabaci.Field and screen-house experiments showed that all of the improved,high-yielding cassava mosaic disease（CMD）resistant cassava genotypes assessed were highly susceptible to B.tabaci and supported high populations of all life stages.These data support the hypothesis that the continuing high populations of cassava B.tabaci in Uganda are due,in part,to the widespread adoption of CMD-resistant cassava varieties during the CMD pandemic.They also show that the whitefly,Aleurotrachelus socialis,resistance present in the South American cassava genotypes could have broader applicability in the Old World.

Homopteran Vector Biomarkers for Efficient Circulative Plant Virus Transmission are Conserved in Multiple Aphid Species and the Whitefly Bemisia tabaci

Plant viruses in the families Luteoviridae and Geminiviridae are phloem restricted and are transmitted in a persistent,circulative manner by homopteran insects.Using fluorescence 2-D difference gel electrophoresis to compare the proteomes of F2 genotypes of Schizaphis graminum segregating for virus transmission ability,we recently discovered a panel of protein biomarkers that predict vector competency.Here we used aphid and whitefly nucleotide and expressed sequence tag database mining to test whether these biomarkers are conserved in other homopteran insects.S.graminum gene homologs that shared a high degree of predicted amino acid identity were discovered in two other aphid species and in the whitefly Bemisia tabaci.Selected reaction monitoring mass spectrometry was used to validate the expression of these biomarkers proteins in multiple aphid vector species.The conservation of these proteins in multiple insect taxa that transmit plant viruses along the circulative transmission pathway creates the opportunity to use these biomarkers to rapidly identify insect populations that are the most efficient vectors and allow them to be targeted for control prior to the spread of virus within a crop.

Epidemiology of Okra Yellow Vein Mosaic Virus (OYVMV) and Its Management through Tracer, Mycotal and Imidacloprid

Field trials were conducted to evaluate the epidemiological factors of okra yellow vein mosaic virus (OYVMV). Four varieties of okra were subjected to screening and evaluation of the chemicals. The variety Saloni F1 was highly resistant while Subz Pari was moderately resistant. Diksha was the tolerant variety while Lush Green was moderately susceptible. The chemical Imidacloprid was most effective to control whitefly population and okra yellow vein mosaic virus (OYVMV). Correlation of environmental factors (maximum and minimum temperature, relative humidity and rainfall) with percent plant infection of okra yellow vein mosaic virus (OYVMV) was also determined. There was a significant correlation between environment and disease severity.

Special Issue Introduction-The Whitefly Bemisia tabaci Species Complex and Begomoviruses:Research Progress and Future Prospects

The whitefly Bemisia tabaci species complex and the begomoviruses they transmit are devastating agricultural pests worldwide.With the rapid and further inva-sions by some members of the whitefly species complex into new regions,their impacts on human society are likely to increase in the years to come.

Resistance to the Whitefly Aleurotrachelus socialis(Hemiptera:Aleyrodidae) and SSR Marker Identification in Advanced Populations of the Hybrid Manihot esculenta subsp.Manihot flabellifolia

Genes resistant to Aleurotrachelus socialis were transferred to the F 1 from the interspecific hybrid wild species of Manihot flabellifolia to M.esculenta and two advanced generations of backcrosses（BC 1 and BC 2）.We characterized the resistance of A.socialis transferred to BC 2 parents（CW67-160,CW67-130,CW67-44）,MTAI-8（BC 1）,resistant（CMB9B-73） and susceptible（CMB9B-104） genotypes from contrasting pools,and resistant（MEcu-72） and susceptible（CMC-40） genotypes.Whitefly demography and biology were evaluated.SSR molecular markers associated with a phenotypic response of plant resistance were detected in segregating populations（BC 2）.Results showed that although female survival time was similar on all hosts,the lowest averages of longevity,fecundity and oviposition rate were observed in the resistant control MEcu- 72,only being significantly similar to the parent CW67-130.When the BC 1 and BC 2 populations were compared,it was found that A.socialis fecundity was eight times lower on CMB9B-73 progeny than on CW67-130,expressing the highest levels of resistance to the whitefly.Ten genotypes of CMB9A and CMB9B family had the best segregation.A total of 486 microsatellite primers were evaluated using bulked segregant analysis（BSA）,11 showed polymorphism between the contrasting pools and only one showed significant differences between resistant and susceptible individuals.In conclusion,fecundity was the parameter that impacted most on the intrinsic rate of A.socialis population growth.

Cryptic species composition and genetic diversity within Bemisia tabaci complex in soybean in India revealed by mtCOI DNA sequence

Bemisia tabaci is a cryptic species complex, causing signiifcant loss on many agricultural y important crops worldwide. Knowledge on species composition and diversity within B. tabaci complex is critical for evolving sustainable pest management strategies. Here we investigate the whitelfy species complex in soybean in major soybean growing states of India. The mitochondrial cytochrome oxidase gene subunit-1 (mtCOI) based phylogenetic relationships established using Bayesian methods indicated the existence of three cryptic species namely Asia I, Asia II 1, and Asia II 7. Al the haplotypes detected in the study could be assigned to these three cryptic species fol owing the species demarcation criteria of 3.5%divergence threshold. Of these, Asia II 1 was found to be predominant with wide spread distribution across the surveyed regions from cool temperate zones to hot and humid tropical plains. On the contrary, cryptic species Asia II 7 showed localized distribu-tion. The Asia II 1 exhibited the highest haplotype diversity and Asia I showed high level of nucleotide diversity. There was a signiifcantly high genetic differentiation among these three cryptic species. The MEAM 1, a dreadful invasive species was not detected in the specimens tested in the current study. The diversity and distribution of three cryptic species is discussed in the light of current knowledge on distribution of whitelfy species in India and yel ow mosaic disease observed during sampling survey.

Multiple Cassava Viruses’ Co-Infections and Resurgence of Pests Are Leading to Severe Symptoms and Yield Losses on Cassava in the South-Kivu Region, Democratic Republic of Congo

A survey was completed during the last five years (2014-2018) to update and assess changes in the cassava pests and diseases occurrence as well as to understand how these changes occur regarding the recent new viruses spread under a climate change context in the South-Kivu region, Democratic Republic of Congo. The eight territories of South-Kivu were surveyed during the rainy seasons from 2015 until 2017 except for Uvira and Fizi where data were recorded in 2018 regarding the prevalence of unstable agro ecological factors which may influence pest and diseases dynamic in these two territories. During the data collection, pests and disease incidence and severity were recorded as well as the sampling of cassava leaves for molecular viruses’ detection. The recorded data showed that Cassava mosaic disease (CMD) remains the most encountered disease (75% - 80%) and its vector (the whitefly Bemisia tabaci) the most important pest (10 - 18 adult whiteflies per leaf). The major changes were recorded for Cassava brown streak disease, recently reported in the region, for which a significant increase was recorded, with not reports before 2012 to 70% - 80% incidence in 2018 in the Ruzizi plain area (Uvira and Fizi). Molecular detection revealed a coexistence of both two viruses, the cassava brown streak virus (CBSV) and Ugandan cassava brown streak virus (UCBSV) in single and mixed infections. Co-infections cassava mosaic and cassava brown streak diseases were frequently recorded resulting in severe expression leaves’ symptoms and tuber yields’ losses. Common pests and diseases considered as minor have drastically become serious threat to cassava production by increasing both their incidence and severity values. The cassava bacterial blight (20%), cassava green mite (20% - 70%), cassava mealy bugs and cassava grasshoppers were recorded as a great challenge in relation with an occurrence of long dry season resulting in four consecutive dry months without rain. The high occurrence of CBSD on new CMD-resistant varieties has enforced farmers to recover local CMD-susceptible varieties which revealed a relative CBSD-tolerance and moderate yield losses. This need for virus control is really challenging cassava crop in a region where the diseases pressure is high and people consume cassava and its products seven days a week. Research gaps identified in the study are the need for breeding new varieties with tolerance/resistance to both CMD and CBSD viruses as well as the extensive use of rapid multiplex diagnostic tools to ensure early diagnostic and availability of good quality planting material at farmers’ level.

Efficacy of Less Toxic Phytochemicals to Prevent the Insect Vector of <i>Mungbean Yellow Mosaic Virus</i>(<i>MYMV</i>)

Planting material BARI mungbean-5 and two phytochemicals viz. Imitaf, active ingredient imidacloprid and ACmix, active ingredient chloropyriphos (50%) + Cypermethrin (5%) were used in this experiment. In case of Imitaf, the lowest percent disease incidence (10.12% per plant and 3.51% per plot) and severity (7.21%) were recorded in four times spray (T4) at 70 DAS. The highest percent disease incidence (36.50% per plant and 11.37% per plot) and severity (23.33%) were recorded in no spray (T0) at 70 DAS. In case of ACmix, the lowest percent disease incidence (12.21% per plant and 4.21% per plot) and severity (7.53%) were recorded in four times spray (T4) at 70 DAS. The highest percent disease incidence (36.49% per plant and 11.37% per plot) and severity (36.67%) was recorded in T0 at 70 DAS. The highest number of flower, no of pod and yield was found in four times spray (T4) that was higher in Imitaf than ACmix. The highest chlorophyll content was recorded in four times spray (T4) for Imitaf (49.62 μmol·m-2·s-1) and ACmix (56.80 μmol·m-2·s-1), and the lowest chlorophyll content was recorded in T0 for Imitaf (42.01 μmol·m-2·s-1) and ACmix (48.34 μmol·m-2·s-1). However from the results of this experiment it was revealed that Imitaf gave the better performance to control the insect vector (Whitefly) of MYMV with four times spray.

Prediction of Whitefly Population and Infestation Based on Multitrophic Analysis between Competitor Pest,Plant Traits and Natural Enemy

Interaction among arthropods(insect-acarine)was investigated at all trophic levels in agro-ecosystem and affects the population dynamic and diversification of arthropod pests and intensity of natural enemy(parasitism)as well as stimulates the plant chemical defence.In the present study of two cropping periods,nutrient concentration and early infestation of plant-sucking pests are known to trigger different degrees of interactions(plant’s parameters)which potentially alert abundance and diversity of the insect pests.Clearer interaction and magnitude of impact could be assessed(multivariate analysis of variance(MANOVA)and redundancy analysis(RDA))and observed between arthropods(insect-acarine)community and plants’parameters from the strongest to the lowest effects.The two factors could have affected the community of insect-pests with various degrees of pressure effect and interaction that occurred naturally,thus leading to the predictable abundance of insect-acarine populations under eggplant leaves in response to plant physical characteristics(e.g.,size of leaves,number of leaves and plant height)and biochemical constituents(flavonoid,phenolic,peroxidase andβ-1,3-glucanase).Based on multivariate analyses of multitrophic interaction,MANOVA and RDA have the potential to elucidate the complex interaction among plant performance,abundance of pests and activity chemical defence compounds.Both analyses interpreted similar interactions of measured parameters in different ways.Whitefly population in this study was predictable by aphids,thrips and total phenolic contents in eggplant.Eggplant has capable defence systems against insect-acarine pests after stimulation(pre-infestation).In relation to IPM strategy,early stages of plant growth are known as susceptible periods for pests attack but the plant becomes more tolerant during the fruiting stage.

Toxicity of Pyrifluquinazon against Greenhouse Whitefly on Tomato Produced in Greenhouses

The greenhouse whitefly, Trialeurodes vaporariorum (Westwood), is a major pest of tomato, Solanum lycopersicum L. Management in both the field and greenhouse is often based on foliar applications of insecticides. A lack of control along with resistance development requires development of alternatives to currently available insecticides. Pyrifluquinazon is a recently developed insecticide by Nichino/Nihon Nohyaku Co., Japan and is marketed in the US by Nichino America. The insecticide inhibits feeding by aphids, thrips, mealybugs and scale insects resulting in death. Because limited information exists on pyrifluquinazon effectiveness against whiteflies, tests were initiated to establish its toxicity against the greenhouse whitefly on greenhouse produced tomato. Data reported herein indicate that pyrifluquinazon was highly effective against adult greenhouse whiteflies. When adults were transferred to tomato shortly after the application had dried, mortality counts taken after 48 h produced LC50 and LC95 values of 0.2469 and 2.4826 μg·g-1, respectively. Although few adults were observed on tomato foliage 24 h post-exposure, little mortality was observed until the 48 h observation. When adult whiteflies were placed on tomato 3 d after pyrifluquinazon application, the LC50 value was 0.3343 μg·g-1 which did not significantly differ from the 0 h LC50 value. A significant increase in LC50 value was observed when adults were placed on tomato 5 d after pyrifluquinazon application. In a greenhouse efficacy trial, both the recommended pyrifluquinazon rate (46.8 g active ingredient [AI] ha-1) and a reduced rate (11.7 g·AI·ha-1) significantly reduced numbers of whitefly adults when compared to the non-treated control for 10 days. The 46.8 g·AI·ha-1 rate was as effective as the insecticide standard, imidacloprid. Pyrifluquinazon applied to tomato foliage in the greenhouse offers a useful alternative to currently available insecticides for control of greenhouse whitefly. Further, its unique mode of action may represent a new tool in management of insecticide resistance.

Morphology and glucosinolate profiles of chimeric Brassica and the responses of Bemisia tabaci in host selection,oviposition and development

Plant structures and chemicals, which are developed from the shoot apical meristem（SAM）, form the main barriers to insect feeding. A plant chimera containing cells of different genetic origins in the SAM will be morphologically and chemically different compared with the parents and thus may result in differential resistance to herbivores. In this study, we explore if particular elements of plant resistance are localized in one of the layers of SAM; the replacement of one cell layer in a chimera may be linked to change of a single resistance trait to herbivores. The morphology and glucosinolate profiles of two periclinal chimeras（labeled as TTC and TCC, respectively） and grafted parents tuber mustard（labeled as TTT） and red cabbage（labeled as CCC） were compared and the performance of whitefly（Bemisia tabaci） in host selection, oviposition preference and development were assessed under controlled conditions. Both chimeras possessed leaf trichomes as parent tuber mustard TTT, however, TTC had significantly more trichomes than TCC and parent TTT. Leaf wax content of both chimeras was intermediate between the two parents. Five aliphatic and two indole glucosinolates were detected in both chimeras, whereas three aliphatic glucosinolates（3-methyl-sulfinylpropyl, 4-methyl-sulfinylbutyl and 2-hydroxy-3-butenyl） were not detected in tuber mustard, and one aliphatic glucosinolate（3-butenyl） was not detected in red cabbage. Unexpectedly for a chimera, the quantities of two aliphatic glucosinolates（3-methyl-sulfinylpropyl and 4-methyl-sulfinylbutyl） in both TTC and TCC were 3-to 5-fold higher than parents. In olfactory preference assays, B. tabaci showed preference to CCC, followed by TCC, TTC and TTT, and number of eggs laid showed the same pattern： CCC〉TCC〉TTC〉TTT. Interestingly, more whiteflies landed on TTT plants than the other three types in a free choice experiment and the developmental duration from egg to adult was the shortest on TTT and increased in the order TTT