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.     

Esterase activity in whiteflies (Bemisia tabaci) in Israel in relation to insecticide resistance

A cotton-field population of the whitefly Bemisia tabaci (Genn.) was 3–5 times more resistant to an organophosphorous insecticide than two control populations. Esterase activity levels in individuals from the resistant population were considerable lower than in control individuals. The distribution of activity values of large numbers of adults from the cotton field was strongly skewed to the right, while the control populations had symmetrical distributions. This may reflect selection against individuals with high EST activity. Control populations are almost fixed for a fast esterase allozyme, which preferentially cleaves -Naphthyl Acetate. In field populations the alternative slow allozyme, which prefers the -form of the substrate, is dominant. Low EST activity may be used as a marker for resistant individuals in Israeli B. tabaci.

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Résumé La population de l'aleurode, B. tabaci Genn., d'un champ de coton s'est montrée 3 à 5 fois plus résistante aux organophosphorés que 2 populations témoins. Le niveau d'activité des estérases était considérablement plus faible chez les individus de la population résistante que chez les individus des populations témoins. La distribution des activités estérasiques de nombreux adultes du champ de conton étaient biaisée vers la droite, alors qu'elle était symétrique pour les populations témoins, ce qui révèle une sélection à l'encontre des individus ayant une forte activité estérasique. Cette hypothèse est étayée par l'affinité pour le substrat et des preuves électrophorétiques. Une faible activité estérasique peut être utilisée comme marqueur des individus résistants de B. tabaci en Israël.

     

Fitness cost in field Anopheles labranchiae populations associated with resistance to the insecticide deltamethrin

We evaluated in the present study the effect of deltamethrin resistance on the fitness cost of the filed populations of Anopheles labranchiae. A susceptible population was used as reference to do different comparisons. We selected the most resistant larvae population collected from northern Tunisia. Eggs were used for study of life history traits including developmental time, larvae mortality, fertility, hatchability and adult sex-ratio. Our results showed that deltamethrin resistance affected negatively (p < 0.05) the developmental time with the median range of 70 h, mortality with the rate of 7 folds in resistant population and hatchability which are lower than in susceptible population. Whereas, no significant differences were detected in adult sex-ratio and fertility of the two studied populations. Our results could help to determine the evolution of population dynamics of the resistant studied population in the areas where insecticide resistance is reported and resistance management is needed.     

B和Q型烟粉虱种群竞争与抗药性的关系

在室内用棉花植株饲养情况下,对采自浙江杭州的烟粉虱Bemisia tabaci(Gennadius)B型和Q型混合种群的生物型组成以及抗药性水平进行了多代的监测。在室内饲养的F0代,两种生物型比例相当;在F10代,Q型已经完全被B型所取代。与F0代相比,F10代烟粉虱种群对吡虫啉、阿维菌素和氟虫腈的抗性水平明显下降,而对α-氯氰聚酯的抗性保持稳定。该研究表明:在没有杀虫剂选择压力的室内条件下,B型比Q型更具生存优势。然而在烟碱类杀虫剂广泛使用的田间条件下,烟粉虱Q型因比B型对烟碱类杀虫剂具有更强的抗性而获得竞争优势。     

Transposition-mediated transcriptional overexpression as a mechanism of insecticide resistance

It has been proposed that amplification of genes for esterase that provide resistance to insecticides may originate from transposition events. To test this hypothesis, we have constructed a minigene coding for a soluble acetylcholinesterase under the control of a nontissue-specific promoter (hsp70). When introduced into Drosophila, the gene is expressed in all tissues and the extra acetylcholinesterase produced confers a low level of insecticide resistance (twofold). The minigene was mobilized by crossing the initial transformant with a strain providing a source of P-element transposase. After 34 generations of exposure to the organophosphate parathion, we obtained a strain with a higher resistance (fivefold). This strain had only one extra Ace gene, which overexpressed acetylcholinesterase. Thus, following transposition, resistance resulted from the overexpression of a single copy of the gene and not from gene amplification. Received: 9 August 1996 / Accepted: 27 May 1997     

Establishment success and extinction risk in autocorrelated environments

We consider establishment success (and extinction risk of small populations) in fluctuating environments, by means of an inhomogeneous branching process model. In this model it is assumed that individuals reproduce asexually during discrete reproduction periods. Within each period individuals reproduce independently and have random numbers of offspring. Expected numbers of offspring vary over reproduction periods due to random environmental changes. Previous simulation results indicated that there is a positive autocorrelation between the establishment probabilities of invaders in successive reproduction periods when environmental states are independently distributed. This result was never formally proved. In this paper we prove that this is indeed true, regardless of the form of the distribution of environmental states or the offspring distribution (under a monotonicity condition, which holds for biologically realistic models). Furthermore, we prove that it is also true for positively autocorrelated environmental states. We show by a counterexample that in environments with a strong negative autocorrelation establishment probabilities can be negatively autocorrelated. This was further examined through simulations. Our results imply that in independent, positively autocorrelated and weakly negatively autocorrelated environments the probability of success of invasion in different independently varying sites is the highest, followed by sequential invasion. For environments with a strong negative autocorrelation, sequential invasion has the highest probability of success. Effects of autocorrelation were further examined with simulations. From the results it appears that the expected length of 'runs of bad luck' is the most crucial factor for establishment success.     

Mutations in the Bemisia tabaci para sodium channel gene associated with resistance to a pyrethroid plus organophosphate mixture

The voltage-gated sodium channel is the primary target site of pyrethroid insecticides. In some insects, super knockdown resistance (super-kdr) to pyrethroids is caused by point mutations in the linker fragment between transmembrane segments 4 and 5 of the para-type sodium channel protein domain II (IIS4-5). Here, we identify two mutations in the IIS4-5 linker of the para-type sodium channel of the whitefly, Bemisia tabaci: methionine to valine at position 918 (M918V) and leucine to isoleucine at position 925 (L925I). Although each mutation was isolated independently from strains >100-fold resistant to a pyrethroid (fenpropathrin) plus organophosphate (acephate) mixture, only L925I was associated with resistance in strains derived from the field in 2000 and 2001. The L925I mutation occurred in all individuals from nine different field collections that survived exposure to a discriminating concentration of fenpropathrin plus acephate. Linkage analysis of hemizygous male progeny of unmated heterozygous F1 females (L925I×wild-type) shows that the observed resistance is tightly linked to the voltage-gated sodium channel locus. The results provide a molecular tool for better understanding, monitoring and managing pyrethroid resistance in B. tabaci.     

Genetic mutations associated with chemical resistance in the cytochrome P450 genes of invasive and native Bemisia tabaci (Hemiptera: Aleyrodidae) populations in China

Abstract  Bemisia tabaci (Gennadius) is a species complex, and its two most damaging biotypes B and Q are globally distributed pests. Despite increasing biological and economic impacts, little is known about the evolutionary mechanisms that favor their competition with native populations. Here, we investigated the genetic mutations in the P450 gene of the invasive B, Q biotypes and the native Cv population. Four mutations associated with chemical resistance, Pro-Leu, Ala-Ser, Ser-Phe and Trp-Leu, were found in the cytochrome P450 CYP6C and CYP9F genes of the B and Q biotypes. Bioassay results also revealed that both the B and Q biotypes have about 12–47 times more resistance to acephate, beta-cypermethrin, methomyl, and 5–7 times more resistance to imidacloprid insecticide than Cv population. Our results provide a molecular approach for better understanding and monitoring the pesticide resistances of invasive and native B. tabaci populations in China.     

Cis-acting mutation and duplication: History of molecular evolution in a P450 haplotype responsible for insecticide resistance in Culex quinquefasciatus

A cytochrome P450 gene, Cyp9m10, is more than 200-fold overexpressed in a pyrethroid resistant strain of Culex quinquefasciatus, JPal-per. The haplotype of this strain contains two copies of Cyp9m10 resulted from recent tandem duplication. In this study, we discovered and isolated a Cyp9m10 haplotype closely related to this duplicated Cyp9m10 haplotype from JHB, a strain used for the recent genome project for this mosquito species. The isolated haplotype (JHB-NIID-B haplotype) shared the same insertion of a transposable element upstream of the coding region with JPal-per strain but not duplicated. The JHB-NIID-B haplotype was considered to have diverged from the JPal-per lineage just before the duplication event. Cyp9m10 was moderately overexpressed in larvae with the JHB-NIID-B haplotype. The overexpressions in JHB-NIID-B and JPal-per haplotypes were developmentally regulated in similar pattern indicating both haplotypes share a common cis-acting mutation responsible for the overexpressions. The isolated moderately overexpressed haplotype conferred resistance, however, its efficacy was relatively small. We hypothesized that the first cis-acting mutation modified the consequence of the subsequent duplication in JPal-per lineage to confer stronger phenotypic effect than that if it occurred before the first cis-acting mutation.     

Genetic architecture in codling moth populations: comparison between microsatellite and insecticide resistance markers

The codling moth, Cydia pomonella, is renowned for developing resistance to insecticides and causing significant economic damage to pome fruits worldwide. In spite of its economic importance, little is known about the patterns of movement of this pest and the effects of insecticide treatment on the population genetic structure. Here, we investigated the genetic structure of the pest in 27 orchards from France, Italy, Armenia and Chile at seven microsatellite loci and two resistance markers [biochemical activity of cytochrome P450 oxidases and proportion of knockdown resistance (kdr) alleles in the sodium channel gene]. According to the microsatellite loci, we detected isolation by distance at the supranational scale but found no evidence of geographical structure among the 24 French orchards, which were mainly structured by the intensity of the insecticide treatments. Similarly, the highest levels of metabolic resistance associated with activity of the cytochrome P450 oxidases were detected in the most treated orchards. The kdr alleles were observed in southern France and Armenia where the pyrethroid insecticides were or have been intensively sprayed. The intensity of the insecticide treatments marginally affected the allelic richness in each orchard, but not the level of inbreeding. These results suggest important and high-distance gene flow among the codling moth populations, which were mainly structured according to the history of insecticide applications. Differences in mutation-migration-drift equilibrium among treated and untreated orchards also suggest that insecticide applications are the main force regulating the local dynamics of codling moth populations.     

北京和湖南烟粉虱生物型及其抗药性监测

烟粉虱是蔬菜等园艺作物上为害严重、最难以防治的害虫之一,生产上防治该虫主要还是依靠化学药剂。本研究鉴定了北京、湖南地区设施蔬菜上烟粉虱的生物型,并监测了其对6种不同杀虫剂的抗药性。结果表明,北京、湖南地区蔬菜烟粉虱生物型分别是Q型和B型。两地烟粉虱对阿维菌素尚处于敏感状态;对烯啶虫胺及其他烟碱类杀虫剂噻虫嗪和吡虫啉的抗药性达中抗到高抗水平,湖南地区抗性水平比北京地区更高,抗性倍数最高达到71.58倍;传统杀虫剂毒死蜱和联苯菊酯对湖南、北京两地烟粉虱的毒杀活性差。     

双斑恩蚜小蜂的生殖方式及其在烟粉虱体内的发育

首次对双斑恩蚜小蜂Encarsia bimaculata Heraty et Polaszek雌蜂的胚胎发育全过程进行连续观测和数码摄像,明确了双斑恩蚜小蜂的生殖方式是两性产雌,雌蜂为初寄生蜂,孤雌产雄且雄蜂为自复寄生。雌蜂在温度(25±1)℃,相对湿度70%±10%条件下,从卵到成虫的发育历期为(13.1±2.5)d,卵期(1.98±0.38)d,幼虫1龄(0.95±0.33)d,2龄(2.48±0.40)d,3龄(3.46±0.43)d,预蛹(0.95±0.20)d,蛹(4.88±0.80)d。     

Evolution of insecticide resistance in Culex pipiens populations: The Corsican paradox

Culex pipiens mosquitoes from Corsica have been subject to insecticide treatments since 1971, using temephos (an organophosphate). After 17 years, resistance has not developed beyond a 14-fold level. This relatively low resistance is due to the presence of several identified resistance genes, including the insensitive target ( Ace^R ) and overproduced esterases (A1, A4 and B4). The fact that only a low resistance has developed after 17 years of treatment and that this low resistance level is the result of a relatively large number of resistance genes constitute a paradox. To understand this situation and explain why a higher temephos resistance level has not evolved in Corsica as in other parts of the world, it is proposed that the occurrence (through mutation or migration) of efficient resistance genes was a limiting step, and that the only resistance genes available at that time through migration from the surrounding Mediterranean countries had a low cross-resistance to temephos. The local situation of Corsica is discussed in the light of recent data on the world distribution of the known organophosphate resistance genes in this species, and the relative role of mutation and migration in the evolution of insecticide resistance in natural populations.     

Variation between laboratory populations of Encarsia formosa in their parasitization behavior on the host Bemisia tabaci

We tested the hypothesis that two populations of the parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae) differed in their behavioral interactions with the whitefly host Bemisia tabaci Gennadius (Homoptera: Aleyrodidae). The two wasp populations were studied because previous work suggested large differences between the populations in performance on this host. In this study the populations differed behaviorally in both the number of hosts encountered and their reactions to hosts once encountered. The population reared for many years on Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) that previously performed more poorly on B. tabaci had a higher host encounter rate but rejected hosts more frequently. The population reared for a number of years on B. tabaci encountered fewer hosts but accepted a higher percentage of hosts for oviposition. The number of parasitized hosts did not differ between the two populations, however. These data demonstrate that there are heritable differences between these two populations of asexual wasps in host-associated behavioral traits. These behavioral differences in host acceptance do not explain performance differences seen in the earlier study, however, possibly due to different conditions between the two experiments.     

Control of insecticide resistance in a field population of houseflies,Musca domestica,by releasing susceptible flies

Susceptible houseflies, Musca domestica, were released at a waste disposal site to control insecticide resistance in a field housefly population. In the first experiment, a total of 163,000 pupae of the susceptible Takatsuki strain were released in October–November 1977. LD₅₀ values to fenitrothion and diazinon decreased to about one-sixth in April 1978, five months after the releases, of those before the releases. For the second experiment, a susceptible colony was derived by cross and backcross between a white-eyed substrain of the Takatsuki and a field colony. This susceptible colony consisted of whiteeyed flies with low activity and normal-eyed flies bearing no or one white eye gene. The results of large cage experiments suggested that the normal-eyed males of the susceptible colony had half the mating competitiveness of wild males. Approximately 31,000–46,000 susceptible pupae were used in each of five releases from October to November 1980. The population number of each sex, estimated by a mark-release-recapture method, increased from 12,000 in late September to 35,000–43,000 in middle November and then decreased to 5,000–8,000 in early December. The frequency of field-collected males bearing one white eye gene and those bearing one male determining factor, which were characteristics of the susceptible colony released, increased gradually during the period of releases. The susceptibility of the field population to fenitrothion and diazinon was examined five times in the period from September to December 1980. With time, the dosage-mortality regression gradually shifted towards that of the susceptible colony after starting the releases. LD₅₀ values to fenitrothion and diazinon decreased to about one-sixth and one-fifth, respectively, in June 1981, six months after the second series of susceptible fly releases, of those before the releases. Ratios of the wild flies to the released fiies were estimated to be between 4.7∶1 and 9.8∶1 in males and between 3.0∶1 and 3.9∶1 in females by taking the quality of the released colony and the population parameters of the field houseflies into consideration. Under several assumptions, the manner of resistant phenotype reduction was discussed, based on the dosage-mortality regressions and the ratios of released flies. These results showed that the releases of susceptible flies were successful in suppression of insecticide resistance in the field housefly population.     

The probability of extinction in a bovine respiratory syncytial virus epidemic model

Backward bifurcation is a relatively recent yet well-studied phenomenon associated with deterministic epidemic models. It allows for the presence of multiple subcritical endemic equilibria, and is generally found only in models possessing a reasonable degree of complexity. One particular aspect of backward bifurcation that appears to have been virtually overlooked in the literature is the potential influence its presence might have on the behaviour of any analogous stochastic model. Indeed, the primary aim of this paper is to investigate this possibility. Our approach is to compare the theoretical probabilities of extinction, calculated via a particular stochastic formulation of a deterministic model exhibiting backward bifurcation, with those obtained from a series of stochastic simulations. We have found some interesting links in the behaviour between the deterministic and stochastic models, and are able to offer plausible explanations for our observations.