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PubMed2005

Mutations of acetylcholinesterase which confer insecticide resistance in insect populations.

Resistance-modified acetylcholinesterases have been described in many insect species and sequencing of their genes has allowed several point mutations to be described. Most mutations line the active site gorge. Each mutation provides a specific resistance pattern: it confers resistance to one insecticide but may increase sensitivity to another. Most mutations alter hydrolysis of the substrate by decreasing the rate of enzyme deacetylation and by diminishing the stability of the enzyme. Mutations are often found in combination in the same protein. This has several consequences: it increases the level of resistance, it enlarges the spectrum of resistance and it may restore the catalytic efficiency of the enzyme. Natural populations are heterogeneous, composed of a mixture of different alleles.

Acetylcholinesterase↗

PubMed2001

Monitoring insecticide resistance in house flies (Diptera: Muscidae) from New York dairies.

House flies were collected from dairies across New York state and the levels of resistance to seven insecticides were measured using standard laboratory assays with three to five diagnostic concentrations. The highest levels of resistance were found for tetrachlorvinphos, permethrin and cyfluthrin. Although levels of resistance to methomyl were somewhat lower, they were among the highest ever reported for field-collected house flies. Resistance to pyrethrins was limited primarily to the lowest diagnostic concentration. House flies were susceptible to fipronil at all dairies, suggesting that this material would be highly effective for fly control. The levels of resistance were similar at all the dairies, irrespective of their insecticide use, suggesting substantial movement of flies between facilities. Relative to resistance levels found at New York dairies in 1987, resistance levels had increased for permethrin, were unchanged for tetrachlorvinphos and had decreased for dimethoate. To identify a single diagnostic concentration that could be used in the laboratory assays to assess accurately resistance levels in future studies, we carried out a 'simulated' field bioassay using formulated materials. A diagnostic concentration for each insecticide is proposed on the basis of a comparison of our bioassays.

Adaptation, Physiological↗

PubMed1999

Amplification and methylation of an esterase gene associated with insecticide-resistance in greenbugs, Schizaphis graminum (Rondani) (Homoptera: Aphididae).

The greenbug aphid, Schizaphis graminum (Rondani) has developed resistance to organophosphorus insecticides by the over-production of esterases that have been classified as Type I and Type II. The first twenty N-terminal amino acids of the Type I esterase were determined and used to design an oligonucleotide, which in conjunction with an active site primer derived from conserved sequences of other insect esterases and two internal primers specific for esterases from another aphid species resulted in a 0.85 kb genomic DNA fragment from resistant greenbugs. This was extended by 5' RACE which provided approximately 1.2 kb of the 5' end of the esterase gene. The 5' DNA sequence corresponded to 19 of the 20 known amino acids of the Type I esterase, with the last needing only a one base change (probably resulting from a PCR artifact). Furthermore, the sequence showed very close similarity to the amplified E4/FE4 esterase genes of Myzus persicae (Sulzer). A comparison of sequences suggested that the S. graminum gene has introns in the same positions as the first two introns of E4/FE4, with the second intron being considerably larger in S. graminum. Probing of Southern blots with the 0.85 kb esterase fragment showed that the gene encoding the Type I esterase is amplified 4- to 8-fold in resistant S. graminum and that the amplified sequences contain 5-methylcytosine at MspI/HpaII sites, again in agreement with previous findings for M. persicae genes.

Amino Acid Sequence↗

PubMed2000

Wings and bristles: character specificity of the asymmetry phenotype in insecticide-resistant strains of Lucilia cuprina.

We investigated the hypothesis that observed higher levels of asymmetry displayed by insecticide-resistance genotypes of Lucilia cuprina are restricted to bristle characters, due to the action of resistance genes in bristle cell development, rather than through the disruption of genomic coadaptation. We compared the level of asymmetry of three bristle characters and three wing characters in non-modified and modified-resistance genotypes. Consistent with previous studies, resistance genotypes displayed greater levels of bristle asymmetry than either susceptible or modified genotypes. However, there were no differences among genotypes for any of the wing characters. To confirm that this result is attributable to the action of the resistance and modifier genes themselves, we also examined the responses of both bristle and wing characters to the more general developmental stress of extreme temperature. Sub-optimal temperature was shown to increase both bristle and wing asymmetry, suggesting that there are no underlying differences between the two character types which could, of themselves, explain the differential response observed in the resistance genotypes.

Animals↗

PubMed2002

Bioassay and field-simulator studies of the efficacy of pymetrozine against peach-potato aphids, Myzus persicae (Hemiptera: Aphididae), possessing different mechanisms of insecticide resistance.

Twenty-one clones of the peach-potato aphid, Myzus persicae (Sulzer), carrying various combinations of known mechanisms of insecticide resistance were assessed for their response to the new pyridine azomethine compound, pymetrozine, in leaf-dip bioassays. Pymetrozine was also applied as a foliar spray to populations of four different UK M persicae clones on potato plants in field-simulator chambers. Neither study showed any evidence of cross-resistance to this compound. Pymetrozine, used in conjunction with other effective aphicides, such as pirimicarb and imidacloprid, can therefore play an important role in insecticide resistance-management strategies for M persicae.

Animals↗

PubMed2000

Differential glycosylation produces heterogeneity in elevated esterases associated with insecticide resistance in the brown planthopper Nilaparvata lugens Stål.

The major insecticide resistance mechanism in the brown planthopper Nilaparvata lugens involves overproduction of esterases. Esterases purified from a resistant strain appeared as a ladder of bands on isoelectric focussing (IEF) gels from pI 4.7 to 5.0. Two-dimensional electrophoresis showed that isozymes ranged in size from 66 to 68 kDa with those of lower pI being apparently smaller. All isozymes detected by two-dimensional electrophoresis were glycosylated. N-glycosidase A reduced the number of isozymes on IEF to two, with increased pI and an increased molecular weight of 69 kDa. No O-linked glycans were detected. Deglycosylation had no effect on esterase activity, hence glycosylation is not involved in active site conformation. As N-glycosidase F completely deglycosylated the esterases, none of the glycans has an alpha1,3-bound core fucose. Reactivity with the lectins GNA, MAA and DSA, combined with differential cleavage of N-linked glycans with endoglycosidases F1 and F2, indicated that terminally linked mannose is present in high mannose and/or hybrid type glycans and that terminally linked sialic acid and galactose-beta(1-4)-N-acetylglucosamine are present in biantennary complexes. Neuraminidase treatment had the same effect on pI of isozymes as complete deglycosylation. Therefore, the majority of the heterogeneity of elevated esterases on IEF is due to differential attachment of sialic acid to glycans of the two proteins.

Animals↗

PubMed1998

Molecular cloning and heterologous expression of a glutathione S-transferase involved in insecticide resistance from the diamondback moth, Plutella xylostella.

Four glutathione S-transferase (GST, EC 2.5.1.18) isozymes have been characterized in the larvae of the diamondback moth (DBM), Plutella xylostella L., a cosmopolitan insect pest of crucifiers. This work aimed at cloning and heterologously expressing the cDNA of DBM GST-3, an isozyme involved in this insect resistance to some organophosphorus insecticides, and studying the molecular basis for its increased expression in the resistant strains. Reverse-transcription polymerase chain reaction (RT-PCR) using midgut mRNA from a methyl parathion resistant MPA strain and degenerate primers complimentary to the N-terminal and internal amino acid sequences of GST-3 generated a 128 bp DNA product. A clone of 809 bp, obtained by screening a midgut cDNA library of MPA strain using this PCR product as probe, encoded a protein of 216 amino acids (calculated Mr 24,083 and pI 8.50). This GST of DBM, PxGST3, shared the highest (46.3%) amino acid sequence identity, among insects, to MsGST1 of Manduca sexta. PxGST3 mRNA level was considerably higher in MPA than in susceptible strains, and Southern blots suggested that gene amplification was probably not involved in the increased expression of this GST isozyme. Enzymatically active PxGST3 expressed heterologously in E. coli exhibited similar biochemical and toxicological properties as GST-3 purified from DBM larvae. It is the first cloned GST with a well-defined role in insecticide resistance.

Amino Acid Sequence↗

PubMed1993

Characterization of a B-type esterase involved in insecticide resistance from the mosquito Culex quinquefasciatus.

The enzyme, esterase B2, involved in insecticide resistance has been purified and characterized from the mosquito Culex quinquefasciatus. The monomeric enzyme has an M(r) of 62000 and a pI of 5.0. This enzyme is compared with the esterase A2 previously characterized [Ketterman, Jayawardena and Hemingway (1992) Biochem. J. 287, 355-360]. The kinetic constants for interaction with several insecticides indicate, as for the esterase A2, that the B2 enzyme has a role in resistance. The rates and affinities of binding observed support the hypothesis that the role mainly is sequestration followed by the slow turnover of the insecticide. Although the B2 esterase appears to have a slightly higher rate of interaction with insecticides, the A2 has a much greater Vmax. with the xenobiotic substrates studied. The B2 esterase also appears to be present in the larvae to a lesser extent than the esterase A2.

Animals↗

PubMed1997

Pleiotropy of adaptive changes in populations: comparisons among insecticide resistance genes in Culex pipiens.

Resistance to toxicants is a convenient model for investigating whether adaptive changes are associated with pleiotropic fitness costs. Despite the voluminous literature devoted to this subject, intraspecific comparisons among toxicant resistance genes are rare. We report here results on the pleiotropic effect on adult survival of Culex pipiens mutants involved in the same adaptation: the resistance to organophosphorus insecticides. This field study was performed in southern France where four resistance genes sequentially appeared and increased in frequency in response to intense insecticide control. By repeated sampling of overwintering females through winter, we analysed the impact of each of three resistance genes on adult survival. We showed that (i) the most recent gene seems to be of no disadvantage during winter, (ii) the oldest affects survival in some environmental conditions, and (iii) the third induces a constant, severe and dominant survival cost. Such variability is discussed in relation to the physiological changes involved in resistance.

Acetylcholinesterase↗

PubMed2001

Distribution and abundance of insecticide resistant greenbugs (Homoptera: Aphididae) and validation of a bioassay to assess resistance.

Laboratory bioassays were conducted to determine the toxicity of four insecticides (ethyl parathion, chlorpyrifos, malathion, and carbofuran) to insecticide-susceptible and resistant populations of greenbug, Schizaphis graminum (Rondani). These bioassays were used to develop and validate a discriminating concentration for assessing insecticide resistance in greenbug populations in the field. Samples from wheat and sorghum in two states, Oklahoma and Kansas, indicated that insecticide resistance persists in greenbug populations over a large area at a low level.

Animals↗

PubMed1980

Insecticide resistance in field strains of Lucilia cuprina.

A survey was conducted in 1977-78 to determine the level of insecticide resistance in field strains of Lucilia cuprina from a wide area of Queensland. Discriminating dose data showed that all 19 strains tested were resistant to diazinon, dichlofenthion, fenthion-ethyl and chlorfenvinphos, but resistance factors in all strains were low, the highest being 18.9 for diazinon. Six strains showed no resistance to butacarb. A strain collected in 1967 and selected with diazinon for 117 generations, attained resistance factors of organophosphorus compounds far higher than those of the present field strains.

Animals↗

PubMed1959

Insecticide resistance in populations of Anopheles gambiae in West Africa.

A method published by Elliott in 1958 for investigation of insecticide resistance in Anopheles larvae has been applied to strains of A. gambiae from various parts of West Africa, and the results analysed to provide information as to the proportions of the three possible genotypes in the different populations.At Kano, the gene conferring resistance to dieldrin and gamma-BHC appears to be increasing in the wild population, being present in about 50% and 42% of the population in the homozygous (RR) and heterozygous (RS) states respectively. Theoretical considerations suggest that in a situation where the male heterozygote is sterile, the gene in the minority will tend to become extinct in the absence of any specific selection. In a colony maintained in captivity for six generations without intentional selection the reverse was seen to happen, the S gene increasing its representation at the expense of the R gene.In Sokoto Province, some figures of the same type were obtained; these are analysed and found to produce results compatible with those from Kano, especially as regards the LC(50) level derived for the effect of gamma-BHC on the RS fraction of the population.At Freetown, a similar analysis suggests that the factor conferring resistance to gamma-BHC has also appeared. About 66% of the sample examined appear to carry the R gene.At Ibadan, samples of the population showed some tolerance to dieldrin, but the presence of the specific type of resistance seen elsewhere was not established. The tolerance appears to be non-specific, as some relative tolerance to DDT appeared to be present also.

Africa, Western↗

PubMed2003

Phenological segregation of insecticide resistance alleles in the codling moth Cydia pomonella (Lepidoptera: Tortricidae): a case study of ecological divergences associated with adaptive changes in populations.

Intrapopulation variability in the seasonal regulation of insect lifecycles has been shown to be due partly to genetic changes. Selection for insecticide resistance in the codling moth Cydia pomonella results from allelic substitution at two to three loci in south-eastern French populations of this species. However, such an adaptive process has been associated with an increased heterogeneity in the developmental responses to climatic factors such as temperature. In this paper, we investigate whether such pleiotropic effects of resistance on development induce a significant discrepancy in seasonal regulation in this species. The seasonal changes in a susceptible and two insecticide-resistant homozygous genotypes of C. pomonella, as well as their reciprocal F1 progeny, were followed under natural conditions during the reproductive season through the emergence events of adults, within-generation developmental rates and the number of generations. A significant delay in the occurrences of homozygous resistant genotypes resulted from significantly lower pre-imaginal developmental times relative to homozygous susceptible ones. Subsequent assessment of the number of generations indicated significantly higher diapause propensities in carriers of the resistance alleles (37.0-76.2%) than in susceptible homozygotes (6-7%), which mostly pupated towards a third generation of adults. In the light of these findings, pleiotropic effects of adaptive changes might be a crucial source of divergence in seasonal regulation at the population level, involving significant life-history trade-offs. In addition to man-made selective factors during the reproductive season, such an effect on the lifecycle could be a key component in the process of selection for resistance genes in south-eastern France C. pomonella populations.

Animals↗

PubMed2004

Genetic diversity and insecticide resistance of Myzus persicae (Hemiptera: Aphididae) populations from tobacco in Chile: evidence for the existence of a single predominant clone.

The tobacco-feeding race of Myzus persicae (Sulzer), formerly known as M. nicotianae Blackman, was introduced into Chile during the last decade. In order to evaluate the genetic diversity and insecticide resistance status of Chilean tobacco aphid populations, a field survey was conducted in 35 tobacco fields covering a 300 km latitudinal survey. The populations sampled were characterized using microsatellite markers and morphometric multivariate analysis. Insecticide resistance levels were assessed through a microplate esterase assay and the mutation status of the kdr gene. All samples collected corresponded to the same anholocyclic aphid genotype, and showed morphological variation within the range expected for the tobacco-feeding race of M. persicae. Esterase activity showed the level and variability expected for an R1 clone lacking mutations in the sodium channels (susceptible kdr), thus corresponding to a type slightly resistant to organophosphate and carbamate, and susceptible to pyrethroid insecticides.

Animals↗

PubMed2001

Antibiotic and insecticide resistance modeling--is it time to start talking?

Mathematical models have played an important part in understanding both antibiotic and insecticide resistance. However, there has been little, if any, interdisciplinary work between these two areas of active research. One primary reason for this is that bacterial population genetics differ substantially from the population genetics of diploid organisms. This article examines these differences and their effect on resistance. It explores what efforts have gone into modeling resistance mathematically in both arenas, and offers suggestions on how the two groups could work together to gain a more comprehensive understanding of the resistance phenomenon

Animals↗

PubMed2000

Biochemical characterization of insecticide resistance in the German cockroach, Blattella germanica, from Malaysia.

The possible insecticide resistance mechanisms of four Malaysian field-collected strains of the German cockroach, Blattella germanica (Linnaeus) (Dictyoptera: Blattellidae), were characterized with biochemical assays and native polyacrylamide gel electrophoresis (PAGE). Elevated esterase activity (at low to moderate frequency) and altered acetylcholinesterase (low frequency) were detected in all field strains, while elevated glutathione S-transferase levels were present in only two strains. Seven esterase bands were separated by native PAGE; a greater intensity occurred in three bands in the resistant strains compared to the susceptible strain. Inhibition studies using specific inhibitors on polyacrylamide gels suggested that the slowest of these three esterases is a cholinesterase, while the other two are carboxylesterases with a preference for beta- over alpha-naphthyl acetate.

Acetylcholinesterase↗

PubMed2000

Insecticide resistance and dominance levels.

Dominance has been assessed in different ways in insecticide resistance studies, based on three phenotypic traits: the insecticide concentration required to give a particular mortality (DLC), mortality at a particular insecticide dose (DML), and fitness in treated areas (DWT). We propose a general formula for estimating dominance on a scale of 0 to 1 (0 = complete recessivity and 1 = complete dominance). DLC, DML, and DWT are not directly related and their values depend on genetic background and environmental conditions. We also show that pest management strategies can have the consequence to increase DWT via the selection of dominance modifiers. Studies on resistance to Bacillus thuringiensis toxins provide the ultimate example of the complexity of the definition of the concept of dominance. Almost all studies have focused on calculation of DLC, which provides little information about the efficiency of pest management programs. For instance, one assumption of the high dose/refuge strategy is that Bacillus thuringiensis resistance must be effectively recessive (i.e., DML must be close to zero). However, DWT, rather than DML, is relevant to the resistance management strategy. Therefore, we strongly suggest that the time has come to focus on fitness dominance levels in the presence and absence of insecticide.

Animals↗

PubMed2006

Cis-regulatory elements in the Accord retrotransposon result in tissue-specific expression of the Drosophila melanogaster insecticide resistance gene Cyp6g1.

Transposable elements are a major mutation source and powerful agents of adaptive change. Some transposable element insertions in genomes increase to a high frequency because of the selective advantage the mutant phenotype provides. Cyp6g1-mediated insecticide resistance in Drosophila melanogaster is due to the upregulation of the cytochrome P450 gene Cyp6g1, leading to the resistance to a variety of insecticide classes. The upregulation of Cyp6g1 is correlated with the presence of the long terminal repeat (LTR) of an Accord retrotransposon inserted 291bp upstream of the Cyp6g1 transcription start site. This resistant allele (DDT-R) is currently at a high frequency in D. melanogaster populations around the world. Here, we characterize the spatial expression of Cyp6g1 in insecticide-resistant and -susceptible strains. We show that the Accord LTR insertion is indeed the resistance-associated mutation and demonstrate that the Accord LTR carries regulatory sequences that increase the expression of Cyp6g1 in tissues important for detoxification, the midgut, Malpighian tubules, and the fat body. This study provides a significant example of how changes in tissue-specific gene expression caused by transposable-element insertions can contribute to adaptation.

Adaptation, Biological↗