Susceptibility to insecticides in the Q biotype of Bemisia tabaci is correlated with bacterial symbiont densities

BACKGROUND: The presence of symbiotic microorganisms may influence an insect's ability to tolerate natural and artificial stress agents such as insecticides. The authors have previously shown that Rickettsia in the B biotype of the whitefly Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) increases this insect's susceptibility to several insecticidal compounds. This communication reports a comparison of the susceptibilities of three isofemale strains of the Q biotype of B. tabaci harbouring different bacterial complements to major insecticides from different chemical groups: one strain harboured only Arsenophonus, one harboured Rickettsia and Arsenophonus and one harboured Arsenophonus and Wolbachia. RESULTS: The presence of different symbiont combinations in the three strains had a significant influence on their susceptibility to most of the insecticides tested. Thiamethoxam, imidacloprid, pyriproxyfen and spiromesifen had a significant influence on strains that had the double infections Rickettsia–Arsenophonus and Wolbachia–Arsenophonus, which also carried higher amounts of symbionts as assessed by quantitative real‐time PCR. No significant differences in mortality rates were observed when the tested strains were treated with diafenthiuron. CONCLUSION: The results suggest a correlation between the presence of high bacterial densities in B. tabaci and the insect's ability to detoxify toxic compounds such as insecticides. Copyright © 2009 Society of Chemical Industry     

宁夏地区烟粉虱对5种常用杀虫剂的抗药性

采用浸叶法分别测定了宁夏8个地区烟粉虱成虫田间种群对4类5种杀虫剂的抗性.结果 表明,供试烟粉虱种群对高效氯氰菊酯已产生了中等至极高水平抗性,抗性倍数为33.31～227.98倍;对烯啶虫胺产生了中等至高水平抗性,抗性倍数为12.14～69.33倍;对毒死蜱和吡虫啉产生了低至中等水平抗性,抗性倍数分别为7.63～38....     

Insecticide resistance in Bemisia tabaci (Homoptera: Aleyrodidae) populations from Crete

The resistance levels to alpha-cypermethrin, bifenthrin, pirimiphos-methyl, endosulfan and imidacloprid were determined in Bemisia tabaci (Gennadius) from Crete. Five B tabaci populations collected from greenhouse and outdoor crops were bioassayed and compared with a reference susceptible strain. Bemisia tabaci collected in a floriculture greenhouse exhibited the highest resistance against all insecticides: at LC50, resistance factors were 23-fold for bifenthrin, 80-fold for alpha-cypermethrin, 18-fold for pirimiphos-methyl, 58-fold for endosulfan and 730-fold for imidacloprid. A population collected on outdoor melons was more susceptible than the reference strain against all insecticides tested, suggesting the occurrence of local highly susceptible B tabaci populations in 'refugia'. In pairwise comparisons of resistance levels, correlation was observed between the LC50 values of the pyrethroid insecticides bifenthrin and alpha-cypermethrin.     

Insecticide resistance in field populations of Bemisia tabaci (Hemiptera: Aleyrodidae) in West Africa

BACKGROUND: The tobacco whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), has developed a high degree of resistance to several chemical classes of insecticides throughout the world. To evaluate the resistance status in West Africa, eight insecticides from different chemical families were tested using the leaf‐dip method on four field populations collected from cotton in Benin, Togo and Burkina Faso. RESULTS: Some field populations showed a significant loss of susceptibility to pyrethroids such as deltamethrin [resistance ratio (RR) 3–5] and bifenthrin (RR 4–36), to organophosphates (OPs) such as dimethoate (RR 8–15) and chlorpyrifos (RR 5–7) and to neonicotinoids such as acetamiprid (RR 7–8) and thiamethoxam (RR 3–7). Bemisia tabaci was also resistant to pymetrozine (RR 3–18) and to endosulfan (RR 14–30). CONCLUSION: The resistance of B. tabaci to pyrethroids and OPs is certainly due to their systematic use in cotton treatments for more than 30 years. Acetamiprid has been recently introduced for the control of whiteflies. Unfortunately, B. tabaci populations from Burkina Faso seem to be already resistant. Because cross‐resistance between these compounds has never been observed elsewhere, resistance to neonicotinoids could be due to the presence of an invasive B. tabaci biotype recently detected in the region. Copyright © 2010 Society of Chemical Industry     

Cotton whitefly (Bemisia tabaci) resistance to organophosphate and pyrethroid insecticides in Pakistan

Resistance to three organophosphate and four pyrethroid insecticides was monitored from 1992 to 2000 in field populations of adult whiteflies, Bemisia tabaci, from Pakistan using a leaf-dip method. There was generally a very high resistance to dimethoate and deltamethrin, and a moderate resistance to monocrotophos during 1992 to 1996. From 1997 to 2000, resistance to these insecticides dropped to low levels because of less reliance on them for whitefly control, and introduction of new chemistries with novel modes of action that had no cross-resistance to conventional insecticides. Concurrently, whitefly resistance to acephate, fenpropathrin, lambda-cyhalothrin and bifenthrin mostly remained low. An insecticide resistance management strategy is recommended that particularly emphasizes the rotation of still-effective insecticides from different chemical classes along with the use of novel chemicals and other tactics of integrated pest management.     

Resistance of Bemisia tabaci (Homoptera: Aleyrodidae) to insecticides in southern Spain with special reference to neonicotinoids

The tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) which occurs in various parts of the world, has developed a high degree of resistance against several chemical classes of insecticide, including organophosphates, carbamates, pyrethroids, insect growth regulators and chlorinated hydrocarbons. The present studies were done in order to monitor the susceptibility of whitefly populations in southern Spain to insecticides commonly used there. Systemic bioassays using Spanish field populations of B tabaci collected in 1994, 1996 and 1998 indicated an increase, albeit a slow one, in resistance to imidacloprid over this period. Comparative studies of other neonicotinoids using the same bioassay revealed a high degree of cross‐resistance to acetamiprid and thiamethoxam. Leaf‐dip bioassays with adult females from these populations revealed a high level of resistance to cyfluthrin, endosulfan, monocrotophos, methamidophos, and pymetrozine, each at 200 mg litre⁻¹. Buprofezin and pyriproxyfen were tested against second‐instar nymphs and eggs, respectively. Buprofezin also showed a lower efficacy against ESP‐98, a strain of B tabaci received from Almeria in 1998, but pyriproxyfen resistance was not obvious when tested against eggs of strain ESP‐98. Field trials in 1998 revealed good efficacy of imidacloprid in one farm in the Almeria region and two greenhouses in Murcia and Sevilla, but a loss of activity by imidacloprid in another farm in the Almeria region. Cross‐resistance between imidacloprid and thiamethoxam was also confirmed under field conditions. © 2000 Society of Chemical Industry     

Reversal of resistance to pyriproxyfen in the Q biotype of Bemisia tabaci (Hemiptera: Aleyrodidae)

Pyriproxyfen, a juvenile hormone (JH) mimic, is a biorational insecticide that disrupts insect development. It is one of the principal insecticides being used to control Bemisia tabaci (Gennadius) on cotton, and has many environmentally positive attributes that make it compatible with integrated pest management (IPM) programs. In Israel, a high level of resistance to pyriproxyfen has been observed in several isolated regions. Here, tests were conducted to establish whether temporal refuges from exposure to pyriproxyfen could be useful for restoring the effectiveness of the compound. Resistance was found to decrease by a factor of 8 when exposure to pyriproxyfen was ceased for 13 generations. Reversal of resistance was accompanied with increased biotic fitness of the revertant colony. By incorporating experimental estimates of nymph survival, sex ratio, fecundity, egg hatching rate and developmental time, the seasonal cost per generation for resistant insects was estimated to be 25%. A genetic simulation model, optimized by empirical data from bioassays, predicted fitness cost per generation of 19% for resistant homozygous (RR) females and hemizygous (R) males, and produced rates of reversal similar to the experimental results. The model also predicted that, even after 5 years ( approximately 55 generations) without pyriproxyfen treatments, the frequency of the resistance allele (R) will still remain high (0.02). It is therefore concluded, on the basis of experimental and modeling results, that the effectiveness of temporal refuges for reversing development of resistance to pyriproxyfen in B. tabaci may be limited.     

The role of B‐type esterases in conferring insecticide resistance in the tobacco whitefly,Bemisia tabaci (Genn)

Separation of non‐specific esterases on electrophoretic gels has played a key role in distinguishing between races or biotypes of the tobacco whitefly, Bemisia tabaci. One intensively staining esterase in particular (termed E_0.14) has assumed significance as a diagnostic of B‐type whiteflies (aka Bemisia argentifolii), despite any knowledge of its biological function. In this study, a whitefly strain (B‐Null) homozygous for a null allele at the E_0.14 locus that had been isolated from a B‐type population was used to demonstrate a significant role for E_0.14 in resistance of B‐type populations to pyrethroids but not to organophosphates (OPs). Bioassays with pyrethroids, following pre‐treatment with sub‐lethal doses of the OP profenofos (to inhibit esterase activity), coupled with metabolism studies with radiolabelled permethrin, supported the conclusion that pyrethroid resistance in a range of B‐type strains expressing E_0.14 was primarily due to increased ester hydrolysis. In the same strains, OP resistance appeared to be predominantly conferred by a modification to the target‐site enzyme acetylcholinesterase. © 2000 Society of Chemical Industry     

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。     

Toxicity of spiromesifen to the developmental stages of Bemisia tabaci biotype B

BACKGROUND: Spiromesifen is a novel insecticidal/acaricidal compound derived from spirocyclic tetronic acids that acts effectively against whiteflies and mites via inhibition of acetyl‐CoA‐carboxylase, a lipid metabolism enzyme. The effects of spiromesifen on the developmental stages of the whitefly Bemisia tabaci (Gennadius) were studied under laboratory conditions to generate baseline action thresholds for field evaluations of the compound. RESULTS: Adult B. tabaci mortality rate after spiromesifen treatment (5 mg L^?1) was 40%. Treatment with 0.5 mg L^?1 reduced fecundity per female by more than 80%, and fertility was almost nil. LC₅₀ for eggs was 2.6 mg L^?1, and for first instar 0.5 mg L^?1. Scanning electron microscopy revealed that eggs laid by treated adult females had an abnormally perforated chorion, and females were unable to complete oviposition. Light and fluorescent microscopy showed significantly smaller eggs following treatment, and smaller, abnormally formed and improperly localized bacteriomes in eggs and nymphs. The number of ovarioles counted in females treated with 5 mg L^?1 was significantly reduced. Spiromesifen showed no cross‐resistance with other commonly used insecticides from different chemical groups, and resistance monitoring in Israel showed no development of field resistance to this insecticide after 1 year of use. CONCLUSION: The strong effect on juvenile stages of B. tabaci with a unique mode of action and the absence of cross‐resistance with major commonly used insecticides from different chemical groups suggest the use of spiromesifen in pest and resistance management programmes. Copyright © 2008 Society of Chemical Industry     

不同温度下吡虫啉对B型烟粉虱毒杀活性的研究

分别采用浸卵法、浸渍法和浸叶法测定了22、25、28、31和34℃下吡虫啉对B型烟粉虱Bemisia tabaci B-biotype不同虫态的控制效果。结果表明,随着温度的升高,吡虫啉对B型烟粉虱不同虫态的控制效果也逐渐上升,当温度上升至34℃时,60mg/L浓度药液处理下卵、低龄若虫、高龄若虫及成虫死亡率分别较22℃时升高了20.89%、33.52%、33.37%及17.86%。因此,温度提高对吡虫啉防治B型烟粉虱起到了正面效应。     

Effectiveness of thiamethoxam and imidacloprid seed treatments against Bemisia tabaci (Hemiptera: Aleyrodidae) on cotton

BACKGROUND: Bemisia tabaci (Gennadius) biotype B is one of the most important pests on cotton around the world. Laboratory, greenhouse and field experiments were conducted to determine the efficacy of thiamethoxam and imidacloprid seed treatments against B. tabaci on cotton. RESULTS: Under laboratory conditions, the two treatments caused whitefly adult mortality, reduced oviposition and increased mortality of nymphs at 10, 20, 30 and 40 days after germination (DAG). The longer the adults fed on plants from treated seeds, the higher the mortality. The two treatments did not have any effect on eggs. The efficacy of the treated seeds against B. tabaci gradually decreased from 10 to 40 DAG, being the lowest at 40 DAG. In laboratory experiments, the efficacies between the two treatments were similar. In greenhouse experiments, the two treatments were equally effective with lower numbers of whiteflies than untreated controls. With both treatments the concentrations of the active ingredient were gradually reduced with aging of the plants and from the bottom to the top leaves of the plants. Numbers of live whiteflies were well correlated with the dosage of active ingredients. Under field conditions, the seeds treated with both insecticides exhibited similar efficacy against B. tabaci for up to ～2 months. CONCLUSION: Cotton seeds treated with imidacloprid and thiamethoxam were effective against B. tabaci for up to 45 days under laboratory and greenhouse conditions, and up to ～2 months under field conditions. Use of imidacloprid‐ and thiamethoxam‐treated seeds can be an important alternative for management of whiteflies on cotton. Copyright © 2010 Society of Chemical Industry     

The response of pyriproxyfen-resistant and susceptible Bemisia tabaci Genn (Homoptera: Aleyrodidae) to pyriproxyfen and fenoxycarb alone and in combination with piperonyl butoxide

Pyriproxyfen was effective against susceptible Bemisia tabaci eggs at a LC₅₀ of 0.003 mg litre⁻¹ and against nymphs at 0.02 mg litre⁻¹. In comparison, eggs of a laboratory selected, pyriproxyfen-resistant B tabaci strain, originating in an Israeli greenhouse, exhibited 6500-fold resistance and nymphs exhibited 1100-fold resistance. Eggs and nymphs of a strain from an Israeli sunflower field exhibited 450 and 210-fold resistance in comparison to the susceptible standard. Fenoxycarb was generally less effective than pyriproxyfen against B tabaci eggs and nymphs but was unaffected by pyriproxyfen resistance. Piperonyl butoxide (PB) was antagonistic to pyriproxyfen, and this increased with increasing pyriproxyfen resistance. PB had no effect on the toxicity of fenoxycarb. Collectively, these data imply that the modes of action of pyriproxyfen and fenoxycarb are distinct, despite the structural similarities of these molecules. Possible reasons for the antagonism of PB against pyriproxyfen are discussed. © 1999 Society of Chemical Industry     

Susceptibility of field populations of adult Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) and Eretmocerus sp (Hymenoptera: Aphelinidae) to cotton insecticides in Burkina Faso (West Africa)

Research was conducted in 14 cotton fields (3-10 ha) selected in seven localities (two fields per locality) in Burkina Faso, with the objectives of: (1) estimating Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) population abundance, (2) assessing the levels of parasitism by Encarsia spp and Eretmocerus spp (Hymenoptera: Aphelinidae) and (3) estimating the susceptibilities of the pest and of an Eretmocerus sp to the insecticides currently sprayed on cotton. Yellow sticky cards and a leaf-turning technique were used to estimate adult B. tabaci population densities. Yellow sticky cards were also used to estimate the densities of adult Eretmocerus sp and the susceptibilities of B. tabaci to insecticides. Leaf disk techniques were used to estimate B. tabaci red eye nymph populations and parasitism by Encarsia spp and Eretmoceus spp was evaluated using stereo-microscopy. A leaf cage technique was used to estimate the susceptibilities of Eretmocerus sp to insecticides. A mean of 6.5-27.4 adult B. tabaci were trapped per yellow sticky card and 5.5 to > 34.9 were counted per leaf using the leaf turning technique. There were 0.14-13 Eretmocerus sp trapped per yellow sticky card. The levels of parasitism varied between 36 and 87% by the end of the season and parasitism by Eretmocerus sp predominated in most of the fields. The susceptibilities of B. tabaci and Eretmocerus sp varied from field to field and with the insecticide tested.     

6种杀虫剂对Q型烟粉虱的田间防治效果及抗性测定

本文测试了6种常用杀虫剂对黄瓜上Q型烟粉虱的田间防治效果,并进行室内毒力测定,以确定Q型烟粉虱对不同药剂的抗性。结果表明,施药后第3天,阿维菌素防治效果达78.8%,其次为苦参&;#8226;内酯,防效达65.1%,其他药剂防效低于45%;施药7d后,6种供试杀虫剂防效均下降到45%以下,且药剂间的差异不显著。毒力测定显示,Q型烟粉虱对6种常用杀虫剂均产生不同程度的抗性,且抗性水平高于B型。其中,Q型对高效氯氰菊酯抗性（抗性倍数47.69）显著高于B型（抗性倍数7.19）;对阿维菌素抗性则相对较低,抗性指数仅为4.40;对苦参碱、啶虫脒和吡虫啉的抗性居中（抗性倍数4.57~9.44）。     

印楝素亚致死浓度对烟粉虱实验种群的生物活性

在室内条件下,以2个亚致死浓度（0.15和0.30mg/L）喷雾处理烟粉虱1、5日龄卵,明确了印楝素亚致死浓度对烟粉虱实验种群发育、存活、繁殖均具有显著的抑制作用。其中,印楝素处理1日和5日龄卵分别使幼期（卵至成虫羽化）发育历期延长0.92至2.84d,幼期存活率降低了56.3%至89.6%,若虫虫体长宽减小,雌成虫寿命降低29.8%至48.6%,平均单雌产卵量降低49.8%至72.5%。清水对照、0.15mg/L和0.30mg/L印楝素溶液处理1日龄卵,烟粉虱实验种群的内禀增长率分别为0.227、0.0742和0.060,净增殖率依次为36.40、7.29和5.33;处理5日龄卵时两者分别为0.126、0.114和0.059与39.192、3.59和4.93。     

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     

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.     

7种杀虫剂对北京地区烟粉虱成虫毒力的比较研究

本试验比较测定了7种杀虫剂对北京地区烟粉虱成虫的毒力,以期为北京地区高毒农药淘汰提供参考。结果表明:氟虫腈对烟粉虱成虫的毒力最强,其LC50值为2.98(g/mL;新烟碱类杀虫剂啶虫脒、吡虫啉对烟粉虱成虫的生物活性较好,LC50值分别为8.04(g/mL、7.49(g/mL,噻虫嗪对烟粉虱成虫毒力相对较差,LC50值仅为95.03(g/mL;烟粉虱成虫对马拉硫磷、异丙威和噻嗪酮3种杀虫剂不敏感。在北京地区,采用噻虫嗪、马拉硫磷、异丙威和噻嗪酮等杀虫剂,不能有效防治烟粉虱的成虫;氟虫腈、吡虫啉和啶虫脒可以用来防治烟粉虱成虫。