Something old, something transgenic, or something fungal for mosquito control?

In spite of the current research emphasis on the use of transgenic mosquitoes, insecticides are still the main method for controlling malarial mosquitoes. Although pyrethroids are the compounds of choice, insecticide resistance is now threatening the effective life of these invaluable compounds. Two recent studies have re-focused interest on entomopathogenic fungi as useful alternatives to conventional insecticides, suggesting that these fungi could be used as alternative control methods, which would thus also prolong the effective lifetime of pyrethroids.     

Evolution of insecticide resistance in non-target black flies (Diptera: Simuliidae) from Argentina

Black flies, a non-target species of the insecticides used in fruit production, represent a severe medical and veterinary problem. Large increases in the level of resistance to the pyrethroids fenvalerate (more than 355-fold) and deltamethrin (162-fold) and a small increase in resistance to the organophosphate azinphos methyl (2-fold) were observed between 1996-2008 in black fly larvae under insecticide pressure. Eventually, no change or a slight variation in insecticide resistance was followed by a subsequent increase in resistance. The evolution of pesticide resistance in a field population is a complex and stepwise process that is influenced by several factors, the most significant of which is the insecticide selection pressure, such as the dose and frequency of application. The variation in insecticide susceptibility within a black fly population in the productive area may be related to changes in fruit-pest control. The frequency of individuals with esterase activities higher than the maximum value determined in the susceptible population increased consistently over the sampling period. However, the insecticide resistance was not attributed to glutathione S-transferase activity. In conclusion, esterase activity in black flies from the productive area is one mechanism underlying the high levels of resistance to pyrethroids, which have been recently used infrequently. These enzymes may be reselected by currently used pesticides and enhance the resistance to these insecticides.     

Impact of environment on mosquito response to pyrethroid insecticides: Facts,evidences and prospects

By transmitting major human diseases such as malaria, dengue fever and filariasis, mosquito species represent a serious threat worldwide in terms of public health, and pose a significant economic burden for the African continent and developing tropical regions. Most vector control programmes aiming at controlling life-threatening mosquitoes rely on the use of chemical insecticides, mainly belonging to the pyrethroid class. However, resistance of mosquito populations to pyrethroids is increasing at a dramatic rate, threatening the efficacy of control programmes throughout insecticide-treated areas, where mosquito-borne diseases are still prevalent. In the absence of new insecticides and efficient alternative vector control methods, resistance management strategies are therefore critical, but these require a deep understanding of adaptive mechanisms underlying resistance. Although insecticide resistance mechanisms are intensively studied in mosquitoes, such adaptation is often considered as the unique result of the selection pressure caused by insecticides used for vector control. Indeed, additional environmental parameters, such as insecticides/pesticides usage in agriculture, the presence of anthropogenic or natural xenobiotics, and biotic interactions between vectors and other organisms, may affect both the overall mosquito responses to pyrethroids and the selection of resistance mechanisms. In this context, the present work aims at updating current knowledge on pyrethroid resistance mechanisms in mosquitoes and compiling available data, often from different research fields, on the impact of the environment on mosquito response to pyrethroids. Key environmental factors, such as the presence of urban or agricultural pollutants and biotic interactions between mosquitoes and their microbiome are discussed, and research perspectives to fill in knowledge gaps are suggested.     

苹果蠹蛾抗药性研究进展

苹果蠹蛾是世界各国高度关注的严重危害苹果生产的外来有害生物。该虫于20世纪50年代在我国首次报道,目前是我国一类进境检疫性有害生物,正严重威胁我国苹果主产区的水果生产安全。苹果蠹蛾以幼虫钻蛀到果实内部为害,防治难度高,对其主要采用化学农药、交配干扰和苹果蠹蛾颗粒体病毒进行防治。由于农药的长期大量使用,苹果蠹蛾已对有机磷、氨基甲酸酯、拟除虫菊酯、昆虫生长调节剂、阿维菌素和苹果蠹蛾颗粒体病毒等不同类型的杀虫剂产生了抗药性。本文总结了国内外有关苹果蠹蛾抗药性现状和抗药性机理方面的研究,并分析了其对几种农药产生抗性的主要原因,同时结合国外苹果蠹蛾防治和抗药性相关研究,以及其在我国发生与防治的现状,提出该虫抗药性治理策略,即及时对我国疫区苹果蠹蛾的抗药性现状进行监测,在此基础上,注意科学地使用化学农药,并结合农业防治和生物防治等措施对该虫进行综合治理。     

Infestation by pyrethroids resistant bed bugs in the suburb of Paris,France

Bed bugs are hematophagous insects responsible for a re-emerging and challenging indoor pest in many countries. Bed bugs infestations may have health consequences including nuisance biting, cutaneous and systemic reactions. This resurgence can probably be attributed to factors such as increased international travel and development of resistance against insecticides. Resistance against pyrethroids has been reported several times from the USA and rarely in Europe. In France, very few data on bed bugs are available. The present study aimed to assess the infestation by bed bugs of a complex of two high-rise apartment buildings in the suburb of Paris and to evaluate their susceptibility to pyrethroid insecticides. We inspected for bed bugs 192 out of 198 apartments units (97%) and interviewed their residents. 76 (39.6%) apartments were infested. Among the 97 residents living in infested apartments, 53 (54.6%) reported bed bug bites. A total of 564 bed bugs were collected in the infested units. Bioassays showed that 54 out of 143 bed bugs were resistant to pyrethroids (37.8%; 95% confidence interval: 29.9-45.7%). DNA sequencing showed that all bed bugs tested (n = 124) had homozygous L925I kdr-like gene mutation. The level of pyrethroid resistance found indicates that this phenomenon was already established in the site and prompts the need to reevaluate the wide use of pyrethroids to control bed bugs.     

昆虫钠离子通道的研究进展

昆虫只有一个或两个电压门控钠离子通道α亚基基因,但两种转录后修饰(选择性剪切和RNA编辑)实现了昆虫钠离子通道的功能多样性.昆虫β辅助亚基TipE和TEH1-4在钠离子通道表达和调控中也起着重要作用.电压门控钠离子通道在动作电位的产生和传递中至关重要,是多种天然和人工合成神经毒素及杀虫剂的作用靶标,包括广泛使用的拟除虫...     

烟粉虱抗药性的研究进展

烟粉虱是一种世界性的重要害虫,目前已对有机磷、拟除虫菊酯和氨基甲酸酯等许多常规杀虫剂产生高水平抗性,在一些地区烟粉虱对昆虫生长调节剂和烟碱类杀虫剂的抗性也是十分普遍.文中综述了世界范围内烟粉虱的抗药性现状、抗药性机理、以及抗药性与生物型的关系,并介绍了美国和以色列较为成功的烟粉虱抗药性治理计划.     

The molecular biology of knockdown resistance to pyrethroid insecticides

The term "knockdown resistance" is used to describe cases of resistance to diphenylethane (e.g. DDT) and pyrethroid insecticides in insects and other arthropods that result from reduced sensitivity of the nervous system. Knockdown resistance, first identified and characterized in the house fly (Musca domestica) in the 1950's, remains a threat to the continued usefulness of pyrethroids in the control of many pest species. Research since 1990 has provided a wealth of new information on the molecular basis of knockdown resistance. This paper reviews these recent developments with emphasis on the results of genetic linkage analyses, the identification of gene mutations associated with knockdown resistance, and the functional characterization of resistance-associated mutations. Results of these studies identify voltage-sensitive sodium channel genes orthologous to the para gene of Drosophila melanogaster as the site of multiple knockdown resistance mutations and define the molecular mechanisms by which these mutations cause pyrethroid resistance. These results also provide new insight into the mechanisms by which pyrethroids modify the function of voltage-sensitive sodium channels.     

Nucleopolyhedrovirus introduction in Australia

Nucleopolyhedrovirus (NPV) has become an integral part of integrated pest management (IPM) in many Australian agricultural and horticultural crops. This is the culmination of years of work conducted by researchers at the Queensland Department of Primary Industries and Fisheries (QDPI&F) and Ag Biotech Australia Pty Ltd. In the early 1970's researchers at QDPI&F identified and isolated a virus in Helicoverpa armigera populations in the field. This NPV was extensively studied and shown to be highly specific to Helicoverpa and Heliothis species. Further work showed that when used appropriately the virus could be used effectively to manage these insects in crops such as sorghum, cotton, chickpea and sweet corn. A similar virus was first commercially produced in the USA in the 1970's. This product, Elcar(R), was introduced into Australia in the late 1970's by Shell Chemicals with limited success. A major factor contributing to the poor adoption of Elcar was the concurrent enormous success of the synthetic pyrethroids. The importance of integrated pest management was probably also not widely accepted at that time. Gradual development of insect resistance to synthetic pyrethroids and other synthetic insecticides in Australia and the increased awareness of the importance of IPM meant that researchers once again turned their attentions to environmentally friendly pest management tools such NPV and beneficial insects. In the 1990's a company called Rhone-Poulenc registered an NPV for use in Australian sorghum, chickpea and cotton. This product, Gemstar(R), was imported from the USA. In 2000 Ag Biotech Australia established an in-vivo production facility in Australia to produce commercial volumes of a product similar to the imported product. This product was branded, ViVUS(R), and was first registered and sold commercially in Australia in 2003. The initial production of ViVUS used a virus identical to the American product but replicating it in an Australian Helicoverpa species, H. armigera. Subsequent research collaboration between QDPI&F and Ag Biotech reinvigorated interest in the local virus strain. This was purified and the production system adapted to produce it on a commercial scale. This new version of ViVUS, which was branded ViVUS Gold(R), was first registered and sold commercially in 2004. Widespread insect resistance to insecticides and a greater understanding of integrated pest management is leading to increased adoption of technologies such NPV in Australian agriculture.     

Mediation of pyrethroid insecticide toxicity to honey bees (Hymenoptera: Apidae) by cytochrome P450 monooxygenases

Honey bees, Apis mellifera L., often thought to be extremely susceptible to insecticides in general, exhibit considerable variation in tolerance to pyrethroid insecticides. Although some pyrethroids, such as cyfluthrin and lambda-cyhalothrin, are highly toxic to honey bees, the toxicity of tau-fluvalinate is low enough to warrant its use to control parasitic mites inside honey bee colonies. Metabolic insecticide resistance in other insects is mediated by three major groups of detoxifying enzymes: the cytochrome P450 monooxygenases (P450s), the carboxylesterases (COEs), and the glutathione S-transferases (GSTs). To test the role of metabolic detoxification in mediating the relatively low toxicity of tau-fluvalinate compared with more toxic pyrethroid insecticides, we examined the effects of piperonyl butoxide (PBO), S,S,S-tributylphosphorotrithioate (DEF), and diethyl maleate (DEM) on the toxicity of these pyrethroids. The toxicity of the three pyrethroids to bees was greatly synergized by the P450 inhibitor PBO and synergized at low levels by the carboxylesterase inhibitor DEF. Little synergism was observed with DEM. These results suggest that metabolic detoxification, especially that mediated by P450s, contributes significantly to honey bee tolerance of pyrethroid insecticides. The potent synergism between tau-fluvalinate and PBO suggests that P450s are especially important in the detoxification of this pyrethroid and explains the ability of honey bees to tolerate its presence.     

昆虫抗药性产生机制

杀虫剂是害虫防治的有效途径之一,但随着杀虫剂长期和广泛的使用,昆虫种群对各种杀虫剂的敏感性降低,产生了抗药性,如何克服昆虫的抗药性是害虫综合治理的重要问题。近年来,借助基因组测序和遗传操作技术的发展,对昆虫抗药性的研究已经深入到细胞水平和分子水平,取得诸多重要的突破,为害虫抗性的控制奠定了理论基础。本文从常见杀虫剂的历史沿革及作用机理切入,从靶标抗性、代谢抗性和穿透抗性3个方面阐述了杀虫剂抗性产生的机制:杀虫剂作用位点的突变降低了靶标与杀虫剂的亲和力,细胞色素P450酶系和谷胱甘肽转移酶系的激活增加了杀虫剂的降解,表皮结构成分的变化和ABC转运蛋白的增加有效阻挡了杀虫剂的渗入。利用基因操作手段或抑制剂,对上述3种抗性机制的关键步骤进行调控可能成为未来杀虫剂抗性控制的新策略。     

昆虫钠离子通道基因突变及其与杀虫剂抗性关系的研究进展

昆虫电压门控钠离子通道(voltage-gated sodium channel)存在于所有可兴奋细胞的细胞膜上,在动作电位的产生和传导上起重要作用,是有机氯和拟除虫菊酯杀虫剂的靶标位点。在农业和医学害虫控制过程中,由于有机氯和拟除虫菊酯杀虫剂的广泛使用,抗药性问题日益突出。其中,由于钠离子通道基因突变,降低了钠离子通道对有机氯和拟除虫菊酯类杀虫剂的亲和性,从而产生击倒抗性(knock-down resistance, kdr),已成为抗性产生的重要机制之一。本文综述了昆虫钠离子通道的跨膜拓扑结构、功能、进化及其基因的克隆;更重要的是总结了已报道的40多种昆虫40个钠离子通道基因非同义突变,以及钠离子通道基因选择性mRNA剪接和编辑,以及它们与杀虫剂抗性的关系;也评述了钠离子通道基因突变引起蛋白质结构的改变,从而对杀虫剂抗性的影响机制。这些研究对于进一步鉴定与杀虫剂抗性相关的突变及抗性机制,开发有机氯和拟除虫菊酯类杀虫剂抗性分子监测方法具有重要意义。     

An overview of pyrethroid insecticides

Background

Pesticides are used to control various pests of agricultural crops worldwide. Despite their agricultural benefits, pesticides are often considered a serious threat to the environment because of their persistence. Pyrethroids are synthetic derivates of pyrethrins, which are natural organic insecticides procured from the flowers of Chrysanthemum cinerariaefolium and C. coccineum. Pyrethroids are classified into two groups—class I and class II—based on their toxicity and physical properties. These pyrethroids are now used in many synthetic insecticides and are highly specific against insects; they are generally used against mosquitoes. The prominent site of insecticidal action of pyrethroids is the voltage-sensitive sodium channels.

Methods and Results

Pyrethroids are found to be stable, and they persist in the environment for a long period. This article provides an overview of the different classes, structure, and insecticidal properties of pyrethroid. Furthermore, the toxicity of pyrethroids is also discussed with emphasis on bioremediation to alleviate pollution.

Conclusions

The article focuses on various microorganisms used in the degradation of pyrethroids, the molecular basis of degradation, and the role of carboxylesterase enzymes and genes in the detoxification of pyrethroid.

     

Organophosphorus insecticides synergize pyrethroids in the resistant strain of cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae) from West Africa

Helicoverpa armigera (Hübner) populations from West Africa recently developed resistance to pyrethroid insecticides through enhanced metabolism by mixed-function oxidases. The combination index method was used to study the synergism of pyrethroids by organophosphorus insecticides. Several mixtures of insecticides currently registered to control cotton pest complex in West Africa were tested, including: cypermethrin/ethion, cypermethrin/profenofos, deltamethrin/ triazophos, deltamethrin/chlorpyriphos, cyfluthrin/chlorpyriphos, and betacyfluthrin/chlorpyriphos. In the resistant strain, the organophosphorus insecticides significantly increased the toxicity of pyrethroids suppressing the resistance effect, either by additive or synergistic effects. Significant synergism was shown for the following mixtures: cypermethrin/ethion, deltamethrin/triazophos, and deltamethrin/chlorpyriphos. The use of synergism from these insecticide mixtures should prove to be an additional tool in the overall resistance management strategy because the pyrethroid resistance in H. armigera from West Africa is not yet stable, decreasing between cotton seasons and increasing with treatments. In absence of selection, the susceptibility of H. armigera to insecticides should be restored.     

The re-emergence of the bed bug as a nuisance pest: implications of resistance to the pyrethroid insecticides

A global resurgence of bed bugs (Hemiptera: Cimicidae) has led to renewed scientific interest in these insects. The current bed bug upsurge appears to have started almost synchronously in the late 1990 s in Europe, the U.S.A. and Australia. Several factors have led to this situation, with resistance to applied insecticides making a significant contribution. With a growing number of insecticides (DDT, carbamates, organophosphates etc.) being no longer available as a result of regulatory restrictions, the mainstay chemistry used for bed bug control over the past few decades has been the pyrethroid insecticides. With reports of increasing tolerance to pyrethroids leading to control failures on the rise, containing and eradicating bed bugs is proving to be a difficult task. Consequently, several recent studies have focused on determining the mode of action of pyrethroid resistance in bed bug populations sourced from different locations. Correct identification of the factor(s) responsible for the increasing resistance is critical to the development of effective management strategies, which need to be based, wherever possible, on firm scientific evidence. Here we review the literature on this topic, highlighting the mechanisms thought to be involved and the problems currently faced by pest control professionals in dealing with a developing pandemic.     

A Locomotor Deficit Induced by Sublethal Doses of Pyrethroid and Neonicotinoid Insecticides in the Honeybee Apis mellifera

The toxicity of pesticides used in agriculture towards non-targeted organisms and especially pollinators has recently drawn the attention from a broad scientific community. Increased honeybee mortality observed worldwide certainly contributes to this interest. The potential role of several neurotoxic insecticides in triggering or potentiating honeybee mortality was considered, in particular phenylpyrazoles and neonicotinoids, given that they are widely used and highly toxic for insects. Along with their ability to kill insects at lethal doses, they can compromise survival at sublethal doses by producing subtle deleterious effects. In this study, we compared the bee’s locomotor ability, which is crucial for many tasks within the hive (e.g. cleaning brood cells, feeding larvae…), before and after an acute sublethal exposure to one insecticide belonging to the two insecticide classes, fipronil and thiamethoxam. Additionally, we examined the locomotor ability after exposure to pyrethroids, an older chemical insecticide class still widely used and known to be highly toxic to bees as well. Our study focused on young bees (day 1 after emergence) since (i) few studies are available on locomotion at this stage and (ii) in recent years, pesticides have been reported to accumulate in different hive matrices, where young bees undergo their early development. At sublethal doses (SLD_48h, i.e. causing no mortality at 48h), three pyrethroids, namely cypermethrin (2.5 ng/bee), tetramethrin (70 ng/bee), tau-fluvalinate (33 ng/bee) and the neonicotinoid thiamethoxam (3.8 ng/bee) caused a locomotor deficit in honeybees. While the SLD_48h of fipronil (a phenylpyrazole, 0.5 ng/bee) had no measurable effect on locomotion, we observed high mortality several days after exposure, an effect that was not observed with the other insecticides. Although locomotor deficits observed in the sublethal range of pyrethroids and thiamethoxam would suggest deleterious effects in the field, the case of fipronil demonstrates that toxicity evaluation requires information on multiple endpoints (e.g. long term survival) to fully address pesticides risks for honeybees. Pyrethroid-induced locomotor deficits are discussed in light of recent advances regarding their mode of action on honeybee ion channels and current structure-function studies.     

Insecticidal activity of cerrado plant extracts on Rhodnius milesi Carcavallo, Rocha, Galvão & Jurberg (Hemiptera: Reduviidae), under laboratory conditions

Chagas' disease is chiefly transmitted by feces of haematophagous bugs (Triatominae) that ingested Trypanosoma cruzi from blood of infected people or animals. Pyrethroids have been the main insecticides used against these insects. However, some populations of insects have shown significant levels of resistance to several pyrethroids, indicating the need of new insecticides for the control of triatomines. Insecticidal activity of 24 Cerrado plant extracts belonging to five species of four families were assayed on fourth instar nymphs of Rhodnius milesi Carcavallo, Rocha, Galv?o & Jurberg (Hemiptera: Reduviidae), under laboratory conditions. For the extract application on triatomines, 50 microg of the extract were topically applied in duplicate on dorsal tergites of ten insects. Insects topically treated with acetone, ethanol, as well as insects with no treatment were used as controls. Triatomines were observed over a 28-day period. Hexanic and ethanolic extracts of Simarouba versicolor, Guarea kunthiana, Guarea guidonia and Talauma ovata caused mortality between 20% and 95% of R. milesi in comparison with the controls, which showed no insect mortality. These preliminary data suggest that the ethanolic extract of the root bark of S. versicolor and the hexanic extract of the root of G. guidonia, responsible for a 95% and 75% insect mortality, respectively, should be chemically investigated and monitored through biological assays in order to determine their insecticidal components, that could be used as a molecular model or as biorational compounds for use in insect control programmes.     

Bioassay and biochemical analyses of insecticide resistance in southern African Anopheles funestus (Diptera: Culicidae)

Anopheles funestus Giles has been implicated as a major malaria vector in sub-Saharan Africa where pyrethroid insecticides are widely used in agriculture and public health. Samples of this species from northern Kwazulu/Natal in South Africa and the Beluluane region of southern Mozambique showed evidence of resistance to pyrethroid insecticides. Insecticide exposure, synergist and biochemical assays conducted on A. funestus suggested that elevated levels of mixed function oxidases were responsible for the detoxification of pyrethroids in resistant mosquitoes in these areas. The data suggested that this mechanism was also conferring cross-resistance to the carbamate insecticide propoxur.