Effect of Four Pesticides on Controlling Autumn Cowpea Greenhouse Whitefly

In order to mitigate the occurrence and damage of cowpea whitefly, reduce chemical pesticide consumption, residue and environmental pollution, the methods of forecasting, randomized block design andstatistical analysis were used in field efficacy trials, to study the control effect of cowpea anthracnose by usingchemical pesticides dinotefuran, acetamiprid, pymetrozine, and bio-pesticide avermectin. The results showed that after applying 1.85% avermectin EC 375 g, 20% dinotefuran SP 600 g, 5% acetamiprid WP 600 g, and 25% pymetrozine WP 600 g （control pesticide） per hm2 once every 5-8 days, and 3 times continuously underserious autumn occurrence of greenhouse whitefly, the control efficacy was 90.9%, 97.0%, 88.0%, 93.9%respectively on the 7th day after the pesticides application; 97.4%, 92.1%, 84.2%, 89.4% respectively on the 14th day after the pesticides application; and 95.6%, 86.7%, 82.2%, 84.5%, respectively on the 20th day afterthe pesticides application. The control effects among avermectin, acetamiprid and pymetrozine were not significantly different, while the effects of avermectin and pymetrozine were significantly higher than that of acetamiprid on the 7th day. The control effects among avermectin, dinotefuran and pymetrozine were not significantly different, while significantly higher than that of acetamiprid on the 14th day. The control effect of avermectin was significantly higher than that of dinotefuran, acetamiprid and pymetrozine on the 20th day. Meanwhile, the control effect of avermectin was slightly lower, higher and much higher than that of dinotefuran on the 7th, 14th, 20th day respectively after the treatment. These results indicated that the four pesticides,especiaLly biopesticide avermectin, were ideal pesticides, which could not only be used for controlling cowpea whitefly, but also realize modern, green, organic and ecological agricultural production.

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.

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.

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.

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.

Toxicity of selected insecticides against nymph of whitefly （Bemisia tabaci Gennadius）

Bemisia tabaci is one of serious insect pests attacking vegetables and has been difficult to control using conventional insecticides. In the past 10 years, new insecticides have been introduced that provide a diversity of novel modes of action and routes of activity to effectively control whitefly. Consequently, intensive used of insecticides in vegetable cultivation has resulted in reduced susceptibility and develops resistance in agriculture industry. In controlling B. tabaci population, insecticides are the common method used by farmers. This study aimed to determine the most effective insecticide against B tabaci by using LC5o value. This study was conducted at the Crop Protection Laboratory, Faculty of Applied Science, Universiti Teknologi MARA Malaysia with the controlled room temperature of 24.33 ± 0.14℃ with dark and light ratio of 1：1 （12 hours： 12 hours） is an ideal condition for rearing the insect. The hypothesis of the study is to test if insecticides can control the nymph of whitefly. A total of 50 two-day-old nymphs were treated with insecticides using leaf-dip bioassay procedure. This experiment was replicated three times. The survival rates of the nymphs were analyzed using analysis of variance （ANOVA）. Data on toxicity was analyzed by a special Probit Programme-Single Line Analysis based on Finney （1971）. There was a significant difference （df = 8, F = 85.84, P = 0.000） in survival rate of nymph ofB. tabaci to eight insecticides tested. Among the insecticides tested, dimethoate, chlorpyrifos ＋ cypermethrin and diafenthiuron showed significantly higher survival rate of nymph compared to other treatments. When LC50 values were compared for diafenthiuron which is less potent （LCs0 ---- 2.44）, abamectin was found to be 3.44 times more potent than diafenthiuron, followed by esfenvalerate,acetamiprid, profenofos, chlorpyrifos ＋ cypermethrin and dimethoate, and the least potent was deltamethrin. The toxicity of eight insecticides tested against nymphs was in the following orders： abamectin = esfenvalerate = acetamiprid = profenofos =- chlorpyrifos ＋ cypermethrin ≥ dimethoate ≥ deltamethrin 〉 diafenthiuron respectively. This study implies that a proper application of the insecticide is a key component to a successful control programme of insect oests.

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.

Role of aminopeptidase N-like in the acquisition of begomoviruses by Bemisia tabaci,the whitefly vector

Sri Lankan cassava mosaic virus(SLCMV)is a prominent causative agent of cassava mosaic disease in Asia and relies on the whitefly Bemisia tabaci cryptic complex for its transmission.However,the molecular mechanisms involved in SLCMV transmission by B.tabaci have yet to be understood.In this study,we identified an aminopeptidase N-like protein(BtAPN)in B.tabaci Asia II 1,an efficient vector of SLCMV,which is involved in the SLCMV transmission process.Through the use of glutathione S-transferase pull-down assay and LC-MS/MS analysis,we demonstrated the interaction between BtAPN and the coat protein(CP)of SLCMV.This interaction was further confirmed in vitro,and we observed an induction of BtAPN gene expression following SLCMV infection.By interfering with the function of BtAPN,the quantities of SLCMV were significantly reduced in various parts of B.tabaci Asia II 1,including the whole body,midgut,hemolymph,and primary salivary gland.Furthermore,we discovered that BtAPN is conserved in B.tabaci Middle East-Asia Minor 1(MEAM1)and interacts with the CP of tomato yellow leaf curl virus(TYLCV),a begomovirus known to cause severe damage to tomato production.Blocking BtAPN with antibody led to a significant reduction in the quantities of TYLCV in whitefly whole body and organs/tissues.These results demonstrate that BtAPN plays a generic role in interacting with the CP of begomoviruses and positively regulates their acquisition by the whitefly.

Catalase promotes whitefly adaptation to high temperature by eliminating reactive oxygen species

Thermal stress usually leads to excessive production of reactive oxygen species(ROS)in all aerobic organisms.Catalases(CAT)are the key antioxidant enzymes,which act as the first line of defense against ROS in the antioxidant pathway.The highly invasive and widely distributed whitefly Bemisia tabaci MED damages plants by feeding as well as by transmitting many plant viruses.Previous studies have shown that strong adaptability to high temperature helps explain the spread of MED around the world.However,the mechanism underlying high temperature adaptation of this pest is not well understood.In this study,6 CAT genes were identified from the MED genome and transcriptome dataset,among which BtCAT1,BtCAT2,and BtCAT3 were found to be highly expressed in adults.The expression of BtCAT1,BtCAT2,or BtCAT3 increased with induction temperature and induction time.The MED was exposed with mean high temperature(30℃ or 35℃)and a short-term extremely high temperature(39℃ or 41℃)after the silencing of BtCAT1,BtCAT2,or BtCAT3 to significantly increased ROS levels by at least 0.5 times and significantly decreased survival rate and fecundity of MED adults.The ROS level in the treated specimens gradually returned to a normal level after 24 h at 25℃,but the survival rate still declined significantly.Taken together,our results demonstrate that CAT could help B.tabaci adapt to long-term mean high temperatures and short-term extremely high temperatures by eliminating excessive ROS.

Effect of planting date and nitrogen fertilization on photosynthesis and soluble carbohydrate contents of cotton in relation to silverleaf whitefly （Bemisia tabaci biotype “B”） populations

The impacts of planting date and nitrogen fertilization on cotton （Gossypium hirsutum L.） photosynthesis and soluble carbohydrate contents in relation to silverleaf whitefly, Bemisia tabaci （Gennadius） biotype “B”, populations were examined in field experiments. Cotton planted in late April and early June was treated with 0, 112, 168 and 224 kg/N hectare in soil using urea fertilizer. The mean photosynthetic rate of April-planted cotton was 4%-20% higher than that of June-planted cotton early in the season, but 10%- 18% lower than that of June-planted cotton late in the season. The photosynthetic rates for both planting dates were positively correlated with levels of added nitrogen. While levels of glucose for both planting dates were positively correlated with nitrogen levels, fructose and sucrose levels were not. The mean levels of fructose were up to 40% lower, while that of sucrose were up to 59% higher, in April-planted cotton than in June-planted cotton. Levels of photosynthetic rate or stomatal conductance were not correlated with adult whitefly densities for either planting date. Levels of glucose and fructose were positively correlated with whitefly densities only for June-planted cotton late in the season.

Diversity of secondary endosymbionts among different putative species of the whitefly Bemisia tabaci

Endosymbionts are important components of arthropod biology. The white- fly Bemisia tabaci （Gennadius） （Hemiptera： Aleyrodidae） is a cryptic species complex composed of 〉28 putative species. In addition to the primary endosymbiont Portiera aley- rodidarum, six secondary endosymbionts （S-endosymbionts）, Hamiltonella, Rickettsia, Wolbachia, Cardinium, Arsenophonus and Fritschea, have been identified in B. tabaci thus far. Here, we tested five of the six S-endosymbiont lineages （excluding Fritschea） from 340 whitely individuals representing six putative species from China. Harniltonella was detected only in the two exotic invaders, Middle East-Asia Minor 1 （MEAM 1） and Mediter- ranean （MED）. Rickettsia was absent in Asia II 1 and MED, scarce in Asia II 3 （13%）, but abundant in Asia II 7 （63.2%）, China 1 （84.7%） and MEAM1 （100%）. Wolbachia, Cardinium and Arsenophonus were absent in the invasive MEAM1 and MED but mostly abundant in the native putative species. Furthermore, phylogenetic analyses revealed that some S-endosymbionts have several clades and different B. tabaci putative species can harbor different clades of a given S-endosymbiont, demonstrating further the complexity of S-endosymbionts in B. tabaci. All together, our results demonstrate the variation and diversity of S-endosymbionts in different putative species ofB. tabaci, especially between invasive and native whiteflies.

Genome-wide identification and characterization of HSP gene superfamily in whitefly (Bemisia tabacl)and expression profiling analysis under temperature stress

Heat shock proteins (HSP)are essential molecular chaperones that play important roles in the stress stimulation of insects.Bemisia tabaci,a phloem feeder and invasive species,can cause extensive crop damage through direct feeding and transmission of plant viruses.Here we employed comprehensive genomics approaches to identity HSP superfamily members in the Middle East Asia Minor 1 whitefly genome.In total,we identified 26 Hsp genes,including three Hsp90,17 Hsp70,one Hsp60 and five sHSP (small heat shock protein)genes.The HSP gene superfamily of whitefly is expanded compared with the other five insects surveyed here.The gene structures among the same families are relatively conserved.Meanwhile,the motif compositions and secondary structures of BtHsp proteins were predicted.In addition,quantitative polymerase chain reaction analysis showed that the expression patterns of BtHsp gene superfamily were diverse across different tissues of whiteflies.Most Hsp genes were induced or repressed by thermal stress (40℃)and cold treatment (4℃)in whitefly.Silencing the expression of BtHsp70-6 significantly decreased the survival rate of whitefly under 45℃.All the results showed the Hsps conferred thermo-tolerance or cold-tolerance to whiteflies that protect them from being affected by detrimental temperature conditions.Our observations highlighted the molecular evolutionary properties and the response mechanism to temperature assaults of Hsp genes in whitefly.

Gene expression profiling of the whitefly （Bemisia tabaci） Middle East- Asia Minor 1 feeding on healthy and Tomato yellow leaf curl China virus-infected tobacco

Begomoviruses are exclusively transmitted by whitefly （Bemisia tabaci） in a circulative, non-propagative manner. The influences of begomoviruses on whitefly vector are complex with both direct and indirect effects. However, the molecular mechanisms underlying these effects are poorly understood and the transcriptional profiles of whitefly on healthy and virus-infected plants have not yet been studied. Using suppression subtractive hybridization, we investigated the differentially expressed genes in whitefly Middle East - Asia Minor 1 feeding on healthy and Tomato yellow leaf curl China virus （TYLCCNV） infected tobacco. From the forward cDNA library, 124 differentially expressed expression sequence tags （ESTs） were obtained which represent up-regulated genes in the whiteflies feeding on the infected tobacco. From the reverse library, 112 ESTs were isolated which represent down-regulated genes. Among the up-regulated genes, we identified several genes that are probably involved in direct interaction between whitefly and TYLCCN~, including a 26/29-kDa proteinase that appears to participate in the elimination of foreign proteins, heparan sulfate proteoglycan which mediates the entry of several viruses into host cells and two genes of Rickettsia-a secondary endosymbiotic bacterium of whitefly. In addition, we identified a number of genes involved in metabolism, transcription and translation which might be the result of indirect effects of TYLCCNV on the whitefly via host plants. Collectively, our results suggest that TYLCCNV-infected tobacco changes the gene expression profiles of whitefly via both direct and indirect interactions. This study revealed a number of genes involved in whitefly-TYLCCNV-tobacco interactions and provided useful information for future study on this complex system.

Temporal changes of symbiont density and host fitness after rifampicin treatment in a whitefly of the Bemisia tabaci species complex

Microbial symbionts are essential or important partners to phloem-feeding insects. Antibiotics have been used to selectively eliminate symbionts from their host insects and establish host lines with or without certain symbionts for investigating functions of the symbionts. In this study, using the antibiotic rifampicin we attempted to selectively eliminate certain symbionts from a population of the Middle East-Asia Minor 1 whitefly of the Bemisia tabaci species complex, which harbors the primary symbiont ＂Candidatus Portiera aleyrodidarum＂ and two secondary symbionts ＂Candidatus Hamiltonella defensa＂ and Rickettsia. Neither the primary nor the secondary symbionts were completely depleted in the adults （F0） that fed for 48 h on a diet treated with rifampicin at concentrations of 1 100/zg/mL. However, both the primary and secondary symbionts were nearly completely depleted in the offspring （F 1） of the rifampicin-treated adults. Although the F1 adults produced some eggs （F2）, most of the eggs failed to hatch and none of them reached the second instar, and consequently the rifampicin-treated whitefly colony vanished at the F2 generation. Interestingly, quantitative polymerase chain reaction assays showed that in the rifampicin-treated whiteflies, the density of the primary symbiont was reduced at an obviously slower pace than the secondary symbionts. Mating experiments between rifampicin-treated and untreated adults demonstrated that the negative effects ofrifampicin on host fitness were expressed when the females were treated by the antibiotic, and whether males were treated or not by the antibiotic had little contribution to the negative effects. These observations indicate that with this whitefly population it is not feasible to selectively eliminate the secondary symbionts using rifampicin without affecting the primary symbiont and establish host lines for experimental studies. However, the extinction of the whitefly colony at the second generation after rifampicin treatment indicates the potential of the antibiotic as a control agent of the whitefly pest.

Whitefly feeding behavior and retention of a foregut-borne crinivirus exposed to artificial diets with different pH values

Transmission of plant viruses by phytophagous hemipteran insects encompasses complex interactions underlying a continuum of processes involved in virus acquisition, retention and inoculation combined with vector feeding behavior. Here, we investigated the effects of dietary pH on whitefly （Bemisia tabaci） feeding behavior and release of Lettuce infectious yellows virus （LIYV） virions retained in the vector＇s foregut. Electrical penetration graph analysis revealed that variables associated with whitefly probing and ingestion did not differ significantly in pH （4, 7.4, and 9） adjusted artificial diets. To investigate virus retention and release, whiteflies allowed to acquire LIYV virions in a pH 7.4 artificial diet were fed pH 4, 7.4, or 9 virion-free artificial （clearing） diets. Immunofluorescent localization analyses indicated that virions remained bound to the foreguts of approximately 20%-24% of vectors after they fed on each of the 3 pH- adjusted clearing diets. When RNA preparations from the clearing diets were analyzed by reverse transcription （RT） nested-PCR and, in some cases, real-time qPCR, successful amplification of LIYV-specific sequence was infrequent but consistently repeatable for the pH 7.4 diet but never observed for the pH 4 and 9 diets, suggesting a weak pH-dependent effect for virion release. Viruliferous vectors that fed on each of the 3 pH-adjusted clearing diets transmitted LIYV to virus-free plants. These results suggest that changes in pH values alone in artificial diet do not result in observable changes in whitefly feeding behaviors, an observation that marks a first in the feeding of artificial diet by whitefly vectors; and that there is a potential causal and contingent relationship between the pH in artificial diet and the release/inoculation of foregut bound virions.

Impact of a novel Rickettsia symbiont on the life history and virus transmission capacity of its host whitefly(Bemisia tabaci)

Rickettsia consists of some of the most prevalent symbionts of insects and often plays a significant role in the biology of its hosts.Recently,a maternally inherited Torix group Rickettsia,provisionally named as RiTBt,was recorded in a species of notorious pest whitefly,tentatively named as Asia II 1,from the Bemisia tabaci complex.The role of this Rickettsia in the biology of its host is unknown.Here we investigated the impact of RiTBt on the performance and virus transmission capacity of Asia II 1.RiTBt did not significantly affect the life history parameters of the whitefly when the host insect was reared on tobacco,tomato,and cotton,three host plants with relatively low,medium and high suitability to the whitefly.Intriguingly,RiTBt slightly enhanced whitefly transmission of cotton leaf curl Multan virus(CLCuMuV),a virus that is transmitted by the whitefly in the field and has caused extensive damage to cotton production.Specifically,compared with whiteflies without RiTBt,following a 48 h virus acquisition whiteflies with RiTBt had higher titer of virus and showed higher efficiency of virus transmission.A rickettsial secretory protein BtR242 was identified as a putative virus-binding protein,and was observed to interact with the coat protein of CLCuMuV in vitro.Viral infection of the whitefly downregulated gene transcript levels of the BtR242 gene.These observations indicate that RiTBt has limited impact on the biology of the Asia II 1 whitefly,and whether this symbiont has functions in the biology of other host whiteflies warrants future investigation.