Toxicity and growth-suppression exerted by diafenthiuron in the sweetpotato whitefly,Bemisia tabaci

Diafenthiuron (CGA 106 ’630), a thiourea, was sprayed prior to a 48-h infestation by adult females of the sweetpotato whiteflyBemisia tabaci Gennadius, on cotton seedlings under greenhouse conditions; it subsequently suppressed strongly progeny formation of the whitefly, resulting in approximately 50% progeny formation relative to control at 5 mg a.i./l. When the different development stages were separately sprayed directly, the larval stage was the most susceptible, resulting in 50% and 90% mortality of 2nd instars at concentrations of 6.5 and 49.2 mg a.i./l, whereas the LC50 values of adults and pupae were 23 and 45 mg a.i./l, respectively. A mild (30–35%) reduction of egg hatch was obtained at a range of 5–125 mg a.i./l. Thus the potency of diafenthiuron against various stages was in the order larvae > adults > pupae > eggs. Diafenthiuron exhibited a low vapor phase toxicity and had no translaminar effect when tested on first instars ofB. tabaci. The high potency of diafenthiuron against whiteflies described herein, against aphids and mites, as stated in the literature, and against some lepidopterous pests, render this compound an important insect control agent for pests of cotton and other crops.     

Biotype and insecticide resistance status of the whitefly Bemisia tabaci from China

BACKGROUND: Resistance to numerous insecticide classes in Bemisia tabaci Gennadius has impaired field control efficacy in south‐eastern China. The biotype and resistance status of B. tabaci collected from these areas was investigated. RESULTS: Two different biotypes of B. tabaci (B‐biotype and Q‐biotype) were detected in south‐eastern China, and the samples collected from geographical regions showed a prevalence of the Q‐biotype and the coexistence of B‐ and Q‐biotypes in some regions. Moderate to high levels of resistance to two neonicotinoids were established in both biotypes (28–1900‐fold to imidacloprid, 29–1200‐fold to thiamethoxam). Medium to high levels of resistance to alpha‐cypermethrin (22–610‐fold) were also detected in both biotypes. Four out of 12 populations had low to medium levels of resistance to fipronil (10–25‐fold). Four out of 12 populations showed low levels of resistance to spinosad (5.7–6.4‐fold). All populations tested were susceptible to abamectin. CONCLUSION: The Q‐biotype B. tabaci is supplanting the B‐biotype which used to be ubiquitous in China. Field populations of both B‐ and Q‐biotypes of B. tabaci have developed high levels of resistance to imidacloprid and thiamethoxam. Abamectin is the most effective insecticide against adult B. tabaci from all populations. Copyright © 2010 Society of Chemical Industry     

Effect of endotoxic compounds isolated fromVerticillium lecanii on the sweetpotato whitefly,Bemisia tabaci

Toxic products extracted by methanol from intact mycelia ofVerticillium lecanii were tested for their toxicity to eggs, larvae, pupae and adults ofBemisia tabaci and additional insects. All stages ofB. tabaci were sensitive to the toxin, with larvae showing the highest, and adults the lowest, sensitivity. Using a 0.5% crude toxin preparation, the mortality rate ofB. tabaci was 88%, 53.5%, 53.2% and 37% for larvae, eggs, pupae and adults, respectively. High sensitivity of adults, which was characterized by rapid paralysis followed by death, was observed inB. tabaci, Myzus persicae, Aphis gossypii, Acyrthosiphon pisum andFrankliniella occidentalis. Other insects,viz., Heliothis peltigera, Maladera matrida, Carpophilus hemipterus andCeratitis capitata, exhibited significantly lower sensitivity. The toxin was partially purified by differential extraction with organic solvents and on silica gel H and Sephadex LH 20 columns. Based on the toxin inactivation by saponification and its mobility in a polar solvent on thin layer chromatography, it is suggested that the toxic products might be phospholipids.     

Diagnosis and characterization of insecticide-insensitive acetylcholinesterase in three populations of the sweetpotato whitefly Bemisia tabaci

A biochemical approach was used to characterize acetylcholinesterase (AChE) insecticide insensitivity in several sweetpotato whitefly (Bemisia tabaci; SPW) populations. Discriminating doses of insecticide were established to differentiate between sensitive and insensitive SPW strains and to genotype individual whitefly. This technique was then used to examine the frequency of insensitive AChE alleles in several SPW populations and to isolate a line homozygous for insensitive AChE from a heterogenous B-type population. Inheritance of putative altered AChE genotypes was consistent with the proposed haplo-diploid status of B. tabaci. This biochemical diagnostic was also employed to determine the role of insensitive AChE in the observed resistance profiles of several laboratory populations subjected to different selection regimes. In keeping with previous studies on insecticide resistance in SPW, resistance does not appear to be uniquely associated with the B-type but rather with SPW populations found in crop systems. © 1998 SCI.     

First record of the Q biotype of the sweetpotato whitefly, <Emphasis Type="Italic">Bemisia tabaci</Emphasis>, in Guatemala

Bemisia tabaci (Gennadius) adults and immatures were collected from poinsettia plants at two commercial production greenhouses in Guatemala during an invited tour to observe IPM practices within the facilities. Despite extensive scouting, only low numbers of insects were collected from vegetable, weed and wild ornamentals species located close to these facilities. Prior to molecular and biochemical analyses, whitefly immatures were initially identified as B. tabaci using morphological characters of the pupae to distinguish them from the greenhouse whitefly. The biotype status of adults and immatures was then established using esterase isozyme patterns and MTCO1 sequencing. The Q biotype was the only biotype found on commercially grown poinsettia plants. The previously recorded B biotype was observed outside the greenhouse facilities on Lactuca spp., Hibiscus spp. and Euphorbia spp. (wild poinsettia). The New World biotype was observed on wild poinsettia and field-grown beans (Phaseolus spp.). This is the first report of the Q biotype in Guatemala, and serves notice of the need for greater vigilance in the management of whiteflies on poinsettia mother stock used as a source of cuttings for export to the USA.     

The use of isozyme patterns to distinguish sweetpotato whitefly (Bemisia tabaci) biotypes

Recent collections ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) from California desert regions represent a mixture of biotypes. One biotype was identical to a culture originally obtained in 1981 and since maintained in the laboratory. The other and most prevalent biotype could not be distinguished morphologically but could be distinguished by esterase isozyme banding patterns. The banding patterns of the biotypes were not affected by culturing the whiteflies on different plant species. Different developmental stages, and adults of both sexes, had the same isozyme patterns.     

Effect of milbemectin on the sweetpotato whitefly,Bemisia tabad

Milbemectin has a chemical structure close to the group of avermectins, which are derived fromStreptomyces avermitilis, and is considered primarily an efficient miticide. Effects of milbemectin on the sweetpotato whitefly,Bemisia tabaci Gennadius, were investigated under laboratory and field conditions. In bioassays conducted under controlled chamber conditions, the compound affected 1st instars ofB. tabaci, resulting in a LC₉₀ of 0.06 mg a.i. I-1. Later stage larvae were much less affected. Milbemectin is highly photodegradable in sunlight. In laboratory assays, when treated cotton seedlings were subjected to 3 h of sunlight before being exposed toB. tabaci adults, no mortality of the whiteflies was observed. Milbemectin at a concentration of 2 mg a.i. I-1 applied in combination with 0.2% ‘Ultra Fine’ mineral oil showed a residual activity of 67% adult mortality 10 days after application, whereas milbemectin alone had no appreciable activity. The effect of milbemectin on whitefly populations in a cotton field was compared with that of cypermethrin and of untreated control. Although milbemectin was not applied with mineral oil, it was more effective than cypermethrin in controlling the whitefly populations. This insecticide/miticide seems not to affect appreciably natural enemies ofB. tabaci. Milbemectin may be considered a compound with the potential for controllingB. tabaci populations. Mineral oils enhanced the potency of milbemectin on both whitefly larvae and adults. http://www.phytoparasitica.org posting July 27, 1999. Contribution No. 501/99 from the Inst. of Plant Protection, Agricultural Research Organization.     

High-throughput allelic discrimination of B and Q biotypes of the whitefly, Bemisia tabaci, using TaqMan allele-selective PCR

BACKGROUND: B and Q biotypes of the whitefly, Bemisia tabaci (Gennadius), are generally regarded as the most significant given their global distribution and strong resistance to insecticides. Since these biotypes can coexist and differ markedly in their insecticide resistance profiles, a rapid but reliable means of discriminating between them would be a valuable complement to resistance monitoring and management programmes. Recently, PCR‐based methods have been developed to determine the biotype status of B. tabaci populations. However, these require post‐amplification procedures, which increase time and labour. RESULTS: The authors have developed an allelic discrimination real‐time PCR assay using fluorescent dye‐labelled probes to distinguish the B and Q biotypes. The assay targets a single nucleotide polymorphism (SNP) in the mitochondrial cytochrome oxidase I (mtCOI) gene. To evaluate the assay, DNA was extracted from individual whiteflies of six known biotype strains, and all scored correctly as either a B or Q biotype. As further validation, 72 individuals from field samples collected in different parts of the world were also tested by the assay. No failed reactions were observed, with all 72 samples scoring clearly as either the B or Q biotype. CONCLUSION: The development of this rapid and high‐throughput assay has important potential for routine monitoring of B and Q biotypes on ornamental plants and for the screening of B. tabaci populations in countries where these biotypes are not yet established. Copyright © 2007 Society of Chemical Industry     

Biochemical and molecular mechanisms of diafenthiuron resistance in the whitefly,Bemisia tabaci

B-biotype Bemisia tabaci has developed high levels of resistance to many insecticides. To investigate the risks and explore possible mechanisms of resistance to diafenthiuron in B. tabaci, a 32.8-fold diafenthiuron-resistant strain (R-DfWf) was established after selection for 36 generations compared with the susceptible strain (S-Lab). Biochemical assays showed that the activity of cytochrome P450 towards p-NA was significantly higher (4.37-fold higher) in the R-DfWf strain than in the S-Lab strain. Similarly, the carboxylesterase (COE) activity and glutathione S-transferase (GST) activity were also significantly higher (3.12- and 1.83-fold higher, respectively) in the R-DfWf strain than in the S-Lab strain. The expression of five of seven P450 genes was significantly higher (>3-fold) in the R-DfWf strain than in the S-Lab strain. The expression of COE2 was significantly higher (>2.5-fold) in the R-DfWf than in the S-Lab strain. The expression of GST and GST2 was significantly higher (>2.3-fold) in the R-DfWf than in the S-Lab. Thus, cytochrome P450, COE and GST may appear to be responsible for the resistance to diafenthiuron in B. tabaci. It is also valuable for usage of insecticides for resistance management and control of this species.     

Biological activity of natural phytoecdysteroids from Ajuga iva against the sweetpotato whitefly Bemisia tabaci and the persea mite Oligonychus perseae

BACKGROUND: Ecdysteroids are steroid hormones that control moulting and govern several changes during metamorphoses in arthropods. The discovery of the same molecules (phytoecdysteroids) in several plant species displayed a wide array of rather beneficial agricultural impact. Many representatives of the genus Ajuga plants contain phytoecdysteroids with a 5β‐7‐ene‐6‐one system exhibiting physiological activities in insects. RESULTS: By means of chromatographic (silica gel column, TLC) and LC‐MS, two major ecdysteroids (20‐hydroxyecdysone and cyasterone) have been isolated and identified from Israeli carpet bugle Ajuga iva (L.) Schreber (Lamiales: Lamiaceae) plants. Ajuga iva extract fractionated on the silica gel column yielded two fractions that showed high activity against the sweetpotato whitefly Bemisis tabaci and the persea mite Oligonychus perseae. A dose of 5 mg AI L^?1 of the purely identified A. iva ecdysterone significantly reduced fecundity, fertility and survival of these pests, while commercial 20‐hydroxyecdysone at the same dose had lesser effects. CONCLUSION: The results demonstrate considerable efficacy of natural phytoecdysteroids against major agricultural pests, and suggests that these materials should be considered for potential development of friendly control agents. Copyright © 2011 Society of Chemical Industry     

The importance of pH in food selection by the tobacco whitefly,Bemisia tabaci

The tobacco whitefly,Bemisia tabaci Gennadius, was found to differentiate between pH values at the leyel of 0.25. It had a clear preference for media with pH values of 6.0 to 7.25 offeredin vitro, in both choice and no-choice situations, when “resting whiteflies” or survival was measured. The whiteflies showed a clear preference for a sucrose concentration of 15%. The addition of 10% sucrose to buffers at various pH values did not change the pattern of their pH preference. Inin vivo experiments whiteflies preferred old cotton leaves (120 days) to younger leaves (60 days). The pH of old leaves was 6.8 while that of young leaves was 5.9. These results may explain the fact that whiteflies attacked cotton plants in commercial fields only late in the season, when the pH values of the cotton leaves exceeded pH 6.     

海氏桨角蚜小蜂对两种生物型烟粉虱的功能反应研究

本文报道海氏桨角蚜小蜂Eretmocerus hayati在室内对不同寄主密度下的B型和Q型烟粉虱Bemisia tabaci寄生和取食情况,并比较了该蜂对两种生物型烟粉虱功能反应的差异。结果表明,海氏桨角蚜小蜂对两种生物型烟粉虱的寄生率和致死率可分别达到60%和70%以上,平均每日最大致死量可达40头烟粉虱若虫。该蜂对两种生物型烟粉虱的功能反应曲线符合HollingII型,随寄主密度的增加对烟粉虱若虫的寄生和致死数量均增加直至达到每日最大致死数量,而寄生率和致死率则随寄主密度的增加而显著下降。该蜂对两种生物型烟粉虱的功能反应没有显著的差异。     

Gene expression in pyriproxyfen-resistant Bemisia tabaci Q biotype

Pyriproxyfen is a biorational insecticide that acts as a juvenile hormone (JH) analogue and disrupts insect development with an unknown molecular mode of action. Pyriproxyfen is one of the major insecticides used to control the whitefly Bemisia tabaci (Gennadius) and comply with integrated pest management (IPM) programmes, resulting in minimal effects on the environment, humans and beneficial organisms. During the last few years, resistance to pyriproxyfen has been observed in several locations in Israel, sometimes reaching a thousandfold or more. No information exists about the molecular basis underlying this resistance that may lead to understanding the mode of action of pyriproxyfen and developing molecular markers for rapid monitoring of resistance outbreaks. In this communication, a cDNA microarray from B. tabaci was used to monitor changes in gene expression in a resistant B. tabaci population. Based on statistical analysis, 111 expressed sequence tags (ESTs) were identified that were differentially upregulated in the resistant strain after pyriproxyfen treatment. Many of the upregulated ESTs observed in the present study belong to families usually associated with resistance and xenobiotic detoxification such as mitochondrial genes, P450s and oxidative stress, genes associated with protein, lipid and carbohydrate metabolism and others related to JH-associated processes in insects such as oocyte and egg development.     

Age-specific expression of resistance to a neonicotinoid insecticide in the whitefly Bemisia tabaci

Neonicotinoid insecticides retain a crucial role within many chemical and integrated control strategies for the tobacco whitefly, Bemisia tabaci Gennadius, in spite of the establishment of potent and widespread resistance in many areas. Metabolic resistance mechanisms mediated by overexpression of P450-dependent monooxygenases have been implicated in neonicotinoid resistance in the two most prevalent B. tabaci biotypes. Further characterisation of resistance to the neonicotinoid imidacloprid in populations of both these B- and Q-types is reported.Expression of resistance to imidacloprid was age specific in B- and Q-type strains of B. tabaci. The highest observed resistance ratio at LC(50) expressed in prepupal nymphs was 13, compared with at least 580 in their adult counterparts. For all strains, resistance expressed in immatures was not sufficiently potent to compromise recommended imidacloprid application rates.Targeting neonicotinoids towards immature life stages of B. tabaci may circumvent the protection conferred by current mechanisms of resistance, simultaneously reducing the selection pressures imposed. However, such tactics may enhance the expression of existing resistance mechanisms in immatures, or promote the establishment of novel ones expressed in all life stages.     

Insecticide resistance in Egyptian populations of the cotton whitefly,Bemisia tabaci (Hemiptera: Aleyrodidae)

Three collections of Bemisia tabaci were taken from cotton and vegetable crops at the beginning of the growing season in Egypt. These displayed marked resistance to the carbamates carbosulfan (ca 20- to 50-fold) and aldicarb (ca 40- to 80-fold) and moderate resistance to the pyrethroids cypermethrin (ca 10- to 30-fold) and lambda-cyhalothrin (ca 10- to 25-fold). They displayed no resistance to the organophosphates profenofos and pirimiphos-methyl, or to imidacloprid. Another population, collected at the end of the growing season, differed markedly in its response. In this population, resistance to carbosulfan remained high (ca 40-fold), resistance to profenofos and cypermethrin was increased (ca 20- and 50-fold respectively) and a slight resistance to imidacloprid was detected (ca 6-fold). Resistance to cypermethrin and profenofos was shown to be similar among adults and nymphs. Irrespective of collection date, none of the populations showed resistance to pyriproxyfen. These Egyptian populations were compared with two representative Israeli populations. The differences between their resistance profiles is discussed in terms of their collection date, their geographical proximity and the patterns of insecticide use at their sites of collection.     

Molecular diagnostics for detecting pyrethroid and organophosphate resistance mutations in the Q biotype of the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae)

Pyrethroid and organophosphate resistance-associated mutations have been recently reported in the whitefly Bemisia tabaci (Gennadius), a major pest of protected and outdoor crops worldwide. Here, we developed simple PCR–agarose gel visualization based assays for reliably monitoring the L925I and T929V pyrethroid resistance mutations in the B. tabaci para-type voltage gated sodium channel and the iAChE F331W organophosphate resistance mutation in the acetylcholinesterase enzyme ace1.PCR-RFLP assays were developed for detecting the L925I and the F331W resistance mutations. A highly specific PASA was developed for detecting the T929V mutation. The molecular diagnostic tools were used to monitor the frequency of the resistance mutations in a large number of field caught Q biotype B. tabaci from Crete (Greece), where both organophosphates and pyrethroids are extensively used. The F331W mutation was fixed in all field individuals examined. The pyrethroid resistance mutations were detected in high frequencies: 0.38 and 0.54 for L925I and T929V, respectively. The simple diagnostics are accurate and robust, to be used alongside classical bioassays to prevent ineffective insecticide applications, and for early identification of the spreading of resistant Q biotype populations into new regions around the globe.     

新型双向传导杀虫剂—螺虫乙酯对Q型烟粉虱的防治效果

为了筛选出防治Q型烟粉虱的有效药剂,研究了22.4%螺虫乙酯悬浮剂不同浓度、不同施药时间对烟粉虱卵、若虫的防治效果。螺虫乙酯和对照药阿维菌素均对Q型烟粉虱卵无效,螺虫乙酯对若虫具有非常高的杀虫活性,无论在卵期施药、若虫低龄期施药还是高龄期施药,防效均达95%以上,和对照药阿维菌素的防效无显著性差异。施药后20d接虫,防效大幅降低到21.6%以下,施药30d后接虫对若虫无效。根据烟粉虱的发育历期推算,表明螺虫乙酯持效期可达30d。     

北京地区蔬菜烟粉虱种群动态及其对烟碱类杀虫剂的抗药性监测

为了明确北京地区蔬菜烟粉虱的种群发展动态及对常用烟碱类杀虫剂的抗药性,为烟粉虱防治适期的确定及高效杀虫剂的选择提供基础资料及科学指导,2009年调查了北京地区春茬和秋茬蔬菜烟粉虱的种群动态,并监测了该地区2009-2011年度烟粉虱种群对3种烟碱类杀虫剂的抗药性。结果表明,春茬蔬菜烟粉虱在5月中旬种群快速上升,持续到春茬拉秧;秋茬蔬菜烟粉虱在塑料棚内9月上旬种群数量即开始上升,露地出现时间较晚,10月中旬后种群数量下降;塑料棚内种群数量明显高于露地蔬菜烟粉虱数量。烟粉虱2009年对吡虫啉和噻虫嗪的抗药性很高,2010年和2011年抗性程度显著下降,LC50处于133.94～251.16mg/L,属中等抗性水平;而对新型杀虫剂烯啶虫胺的抗药性在近3年内持续升高,抗性倍数由6.68倍升至83.62倍,即由低抗性水平升至高抗性水平。上述调查结果表明,北京地区蔬菜烟粉虱的防治应掌握春季5月中旬前、秋季9月中旬前种群处于低密度时进行。烟粉虱对新型杀虫剂烯啶虫胺的抗药性在近三年内快速上升,生产中应注意药剂的轮换使用。