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PubMed2005

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.

Animals↗
PubMed2002

High Wolbachia density in insecticide-resistant mosquitoes.

Wolbachia symbionts are responsible for various alterations in host reproduction. The effects of the host genome on endosymbiont levels have often been suggested, but rarely described. Here, we show that Wolbachia density is strongly modified by the presence of insecticide-resistant genes in the common house mosquito, Culex pipiens. The Wolbachia density was estimated using a real-time quantitative PCR assay. Strains harbouring different genes conferring resistance were more infected than a susceptible strain with the same genetic background. We show that this interaction also operates in natural populations. We propose that mosquitoes may control Wolbachia density less efficiently when they carry an insecticide-resistant gene, i.e. when they suffer from a physiological resistance cost.

Animals↗
PubMed2004

The unique mutation in ace-1 giving high insecticide resistance is easily detectable in mosquito vectors.

High insecticide resistance resulting from insensitive acetylcholinesterase (AChE) has emerged in mosquitoes. A single mutation (G119S of the ace-1 gene) explains this high resistance in Culex pipiens and in Anopheles gambiae. In order to provide better documentation of the ace-1 gene and the effect of the G119S mutation, we present a three-dimension structure model of AChE, showing that this unique substitution is localized in the oxyanion hole, explaining the insecticide insensitivity and its interference with the enzyme catalytic functions. As the G119S creates a restriction site, a simple PCR test was devised to detect its presence in both A. gambiae and C. pipiens, two mosquito species belonging to different subfamilies (Culicinae and Anophelinae). It is possibile that this mutation also explains the high resistance found in other mosquitoes, and the present results indicate that the PCR test detects the G119S mutation in the malaria vector A. albimanus. The G119S has thus occurred independently at least four times in mosquitoes and this PCR test is probably of broad applicability within the Culicidae family.

Acetylcholinesterase↗
PubMed2005

Evidence for multiple origins of identical insecticide resistance mutations in the aphid Myzus persicae.

The peach-potato aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) has developed resistance to pyrethroid insecticides as a result of a mechanism conferring reduced nervous system sensitivity, termed knockdown resistance (kdr). This reduced sensitivity is caused by two mutations, L1014F (kdr) and M918T (super-kdr), in the para-type voltage gated sodium channel. Kdr mutations in M. persicae are found in field populations world-wide. In order to investigate whether this situation is due to the mutations arising independently in different populations or by single mutation events that have spread by migration, regions flanking these mutations were sequenced from different geographical areas. The DNA sequences produced, which included a 1 kb intron, were found to be highly conserved. Several different haplotypes were identified containing kdr and super-kdr. Whilst these results could indicate either multiple independent origins of both mutations or recombination following a single origin, given the short timescale of resistance development, multiple independent origins of kdr and super-kdr are the most plausible interpretation.

Amino Acid Substitution↗
PubMed1994

The molecular and population genetics of cyclodiene insecticide resistance.

Cyclodiene resistance has accounted for over 60% of reported cases of insecticide resistance. Understanding of this resistance can therefore help us answer questions relating to the mechanism and origin of representative resistance-associated mutations, questions fundamental to the molecular and populations genetics of pesticide resistance. The cyclodiene resistance gene Rdl (resistance to dieldrin) was cloned from a mutant of the model insect Drosophila resistant to cyclodienes and picrotoxinin. Rdl codes for a subunit of a novel class of GABA gated chloride ion channels and resistance is correlated with replacement of the same amino acid residue in a wide range of species from different insect orders. This single amino acid replacement Ala302 > Ser, within the proposed lining of the chloride ion channel, also confers insensitivity to the blocking action of cyclodienes and picrotoxinin on GABA gated chloride ion channels expressed in Xenopus oocytes. The resistance mechanism involves both changes in cyclodiene binding site affinity and also a change in the rate of receptor desensitization which destabilizes the cyclodiene-favored conformation. Documentation of the resistance associated mutation has allowed for the design of a PCR based molecular monitoring technique. This technique gives more accurate estimates of resistance gene frequency from smaller sample sizes and has shown the frequency of resistance in apparently unselected populations of Drosophila to be as high as 1%. We are still uncertain as to why resistance persists in the apparent absence of selection pressure and any severe reduction in the fitness of resistant strains, besides a paralytic phenotype at high temperature, remains undocumented.

Amino Acid Sequence↗
PubMed1999

CYP6B2 Expression in Insecticide-Resistant and -Suspcitible Strains of Helicoverpa armigera.

A fragment of CYP6B2 gene was obtained from the midgut cDNA library of the fifth instar larvae of the ballworm (Helicoverpa armigera) with RT-PCR. The product of 627 bp was cloned and sequenced. The results of dot blotting analysis of mRNA proved that CYP6B2 is expressed at higher level (mRNA) in an insecticide-resistant strain than in a susceptible strain, showing that the regulation was at transcription level. The mRNA is induced by pyrethroid in susceptible, but not in the insecticide-resistant strains. We guess that mutation in the 5' upstream regulator of the insecticide-resistant strain may lead to the difference in the expression level between resistant and susceptible strains.

Journal Article↗
PubMed2000

Insecticide resistance in Brazilian Triatoma infestans and Venezuelan Rhodnius prolixus.

Resistance levels to insecticides used in control of Chagas Disease vectors were assessed in two species of bugs (Hemiptera: Reduviidae): Triatoma infestans (Klug) from Brazil and Rhodnius prolixus Stål from Venezuela. The resistance ratios, compared to susceptible laboratory strains, were determined by topical application bioassays. The T. infestans PA strain exhibited resistance ratios of 7x to deltamethrin, 3.6x to beta-cyfluthrin and 3.3x to cypermethrin, but was susceptible to beta-cypermethrin and lambda-cyhalothrin. Rhodnius prolixus CA strain showed resistance to all the pyrethroids evaluated, the resistance ratios ranging between 4.5x to lambda-cyhalothrin and 12.4x to cypermethrin. Deltamethrin resistance in both strains was decreased by piperonyl butoxide, suggesting oxidative metabolism as cause of resistance.

Administration, Topical↗
PubMed2003

The house fly aliesterase gene (MdalphaE7) is not associated with insecticide resistance or P450 expression in three strains of house fly.

It was recently proposed that a mutation (G137D) in the MdalphaE7 gene was responsible for increasing transcription of a P450 (CYP6A1) resulting in resistance to diazinon. To examine if MdalphaE7 had a role in resistance in other strains we sequenced a fragment (approximately 700 bp) of the MdalphaE7 gene from individual flies of two insecticide susceptible and three insecticide resistant (due to increased monooxygenase-mediated detoxification) strains. Five unique alleles were discovered. While all of the susceptible strains had Gly137, so did the resistant LPR and NG98 strains. Of the two alleles in the YPER strain one had the G137D substitution and the other did not. Based on the lack of correlation between the presence of the 'mutant' MdalphaE7 and resistance (or P450 levels), we conclude that the G137D mutation in MdalphaE7 is not involved in transcriptional control of the P450s involved in resistance in the LPR, NG98 or YPER strains. The relationship between MdalphaE7 alleles and insecticide resistance is discussed in light of these findings.

Amino Acid Sequence↗
PubMed1958

The insecticide-resistance problem: a review of developments in 1956 and 1957.

The author reviews the growth of the insecticide-resistance problem throughout the world during the period between July 1956 and November 1957, and the developments in research on the subject during the same period.Three new resistant species have been discovered-Anopheles subpictus, Chrysomyia putoria and Rhipicephalus sanguineus-and eight new types of resistance in already resistant species have been observed. Moreover, the geographical area covered by certain resistant insect populations has considerably increased.THE RESEARCH ACCOMPLISHMENTS DURING THE PERIOD UNDER REVIEW INCLUDE: systems of detecting resistance in the field by standard test methods; confirmation of two distinct types of resistance to chlorinated-hydrocarbon insecticides in mosquitos and bed-bugs as well as in houseflies; evidence that DDT-resistance in the housefly, Anopheles sundaicus and Aëdes aegypti is due mainly to a single genetic factor associated with the ability to dehydrochlorinate DDT, and that dieldrin-resistance of Anopheles gambiae also derives from a single factor present even in untouched populations; a fuller understanding of the physiological mechanism of BHC-resistance in the housefly; and demonstration that selection pressure from organo-phosphorus compounds induces resistance to themselves and to chlorinated-hydrocarbon insecticides.

Aedes↗
PubMed2000

Cyclodiene insecticide resistance: from molecular to population genetics.

This review follows progress in the analysis of cyclodiene insecticide resistance from the initial isolation of the mutant, through cloning of the resistance gene, to an examination of the distribution of resistance alleles in natural populations. Emphasis is given to the use of a resistant Drosophila mutant as an entry point to cloning the associated gamma-aminobutyric acid (GABA) receptor subunit gene, Resistance to dieldrin. Resistance is associated with replacements of a single amino acid (alanine302) in the chloride ion channel pore of the protein. Replacements of alanine302 not only directly affect the drug binding site but also allosterically destabilize the drug preferred conformation of the receptor. Resistance is thus conferred by a unique dual mechanism associated with alanine302, which is the only residue replaced in a wide range of different resistant insects. The underlying mutations appear either to have arisen once, or multiply, depending on the population biology of the pest insect. Although resistance frequencies decline in the absence of selection, resistance alleles can persist at relatively high frequency and may cause problems for compounds to which cross-resistance is observed, such as the novel fipronils.

Animals↗
PubMed1993

A single-amino acid substitution in a gamma-aminobutyric acid subtype A receptor locus is associated with cyclodiene insecticide resistance in Drosophila populations.

Resistance to cyclodiene insecticides, documented in at least 277 species, is perhaps the most common kind of resistance to any pesticide. By using cyclodiene resistance to localize the responsible gene, a gamma-aminobutyric acid type A receptor/chloride ion-channel gene was previously cloned and sequenced from an insecticide-susceptible Drosophila melanogaster strain. We now describe the molecular genetics of the resistance allele. A single-base-pair mutation, causing a single-amino acid substitution (Ala-->Ser) within the second membrane-spanning region of the channel, was found to be the only consistent difference between resistant and susceptible strains of D. melanogaster. Some resistant strains of Drosophila simulans show the same mutation, whereas others show an alternative single-base-pair mutation in the same codon, resulting in the substitution of a different amino acid (glycine). These constitute single-box-pair mutations in insects that confer high levels of resistance to insecticides. The presence of the resistance mutations was then tested in a much larger set of strains by the PCR and subsequent digestion with a diagnostic restriction endonuclease. Both resistance-associated mutations cause the loss of a Hae II site. This site was invariably present in 122 susceptible strains but absent in 58 resistant lines of the two species sampled from five continents. PCR/restriction endonuclease treatment was also used to examine linkage of an EcoRI polymorphism in a neighboring intron in D. melanogaster, which was found associated with resistance in all but 3 of 48 strains examined. These PCR-based techniques are widely applicable to examination of the uniqueness of different resistance alleles in widespread populations, the identification of resistance mechanisms in different species, and the determination of resistance frequencies in monitoring.

Alleles↗
PubMed1991

High paraoxon-hydrolyzing activity in organophosphorus insecticide-resistant mosquitoes.

We found a strong paraoxon-hydrolyzing activity (23.4 +/- 8.50 nmol/h/individual and 137 +/- 86.2 nmol/h/mg protein) in the crude extract from larvae of Culex tritaeniorhynchus Toyama 89, which is markedly resistant to organophosphorous insecticides. The activity was higher than those from Cx. tritaeniorhynchus re-e-ae (0.175 +/- 0.0336 and 1.83 +/- 0.651), Anopheles omorii (0.112 +/- 0.0301 and 1.86 +/- 0.746) and An. stephensi (0.0651 +/- 0.0713 and 0.789 +/- 0.910), which are susceptible to organophosphorous insecticides. These facts suggest that the high paraoxon-hydrolyzing activity plays a role in the development of organophosphorous resistance in Cx. tritaeniorhynchus. The enzyme preparation obtained from Toyama 89 showed higher activity in the alkaline pH range and its Km values to paraoxon were 0.67 mM in larvae and 0.50 mM in adults. A calcium ion was strictly required for the hydrolysis of paraoxon. Fenitroxon was also hydrolyzed, in addition to paraoxon. However, it did not degradate parathion and fenitrothion at all. Dichlorvos and phenyl acetate competitively inhibited the enzyme. The phenyl acetate-hydrolyzing activity in the preparation of Toyama 89 was significantly (p less than 0.01) lower than those in susceptible strains, and was irreversibly inhibited by paraoxon. Therefore, the paraoxon-hydrolyzing activity belongs to the class of organophosphate compound hydrolases; it must be thus distinguished from bacterial phosphotriesterase.

Animals↗
PubMed1995

The same esterase B1 haplotype is amplified in insecticide-resistant mosquitoes of the Culex pipiens complex from the Americas and China.

In Culex pipiens, overproduction of nonspecific esterases is a common mechanism of resistance to organophosphate insecticides. The esterases are attributed to closely linked loci named A and B, and overproduction of all esterases B is due to gene amplification. In order to determine if the esterase B1 identified by electrophoretic studies in Culex pipiens mosquitoes from different countries is overproduced due to the amplification of the same DNA haplotype, the amplified region encompassing the structural esterase B1 gene was characterized by restriction mapping and RFLP. The same amplified haplotype was found in mosquitoes with an esterase B1 protein, independently of their geographical origin: French Guiana, Venezuela, Puerto Rico, California and China. Large variations in amplification levels were observed. It is concluded that B1 amplification has a unique origin, either in America or in Asia, and has subsequently spread by migration. This migration is more limited than that of A2-B2 esterases, since B1 is confined to the Americas, the Caribbean and part of China, whereas the A2-B2 distribution now includes the Americas, the Caribbean, Asia, Africa, the Pacific Islands and Europe.

Americas↗
PubMed2000

Insecticide resistance in Anopheles sacharovi Favre in southern Turkey.

We report the resistance to 12 insecticides of specimens of Anopheles sacharovi, both in laboratory cultures and those collected in the malarious areas of Adana, Adiyaman, Antalya, Aydin, and Muğla in southern Turkey. Mortality was higher 24 h after exposure than immediately after exposure but was unaffected by temperature (24 degrees C or 29 degrees C) or the position of the test kit (horizontal or vertical). In Adana, Adiyaman and Antalya, A. sacharovi was susceptible only to malathion and pirimiphos-methyl. In Aydin it was susceptible to both these insecticides as well as to dieldrin, lambda-cyhalothrin, and etofenprox; and in Muğla it was susceptible to dieldrin, fenitrothion, lambda-cyhalothrin, cyfluthrin and etofenprox, as well as to malathion and pirimiphos-methyl.

Animals↗
PubMed2000

Molecular characterization of the amplified carboxylesterase gene associated with organophosphorus insecticide resistance in the brown planthopper, Nilaparvata lugens.

Widespread resistance to organophosphorus insecticides (OPs) in Nilaparvata lugens is associated with elevation of carboxylesterase activity. A cDNA encoding a carboxylesterase, Nl-EST1, has been isolated from an OP-resistant Sri Lankan strain of N. lugens. The full-length cDNA codes for a 547-amino acid protein with high homology to other esterases/lipases. Nl-EST1 has an N-terminal hydrophobic signal peptide sequence of 24 amino acids which suggests that the mature protein is secreted from cells expressing it. The nucleotide sequence of the homologue of Nl-EST1 in an OP-susceptible, low esterase Sri Lankan strain of N. lugens is identical to Nl-EST1. Southern analysis of genomic DNA from the Sri Lankan OP-resistant and susceptible strains suggests that Nl-EST1 is amplified in the resistant strain. Therefore, resistance to OPs in the Sri Lankan strain is through amplification of a gene identical to that found in the susceptible strain.

Amino Acid Sequence↗
PubMed2002

Molecular characterization of the amplified aldehyde oxidase from insecticide resistant Culex quinquefasciatus.

Primary structural information including the complete nucleotide sequence of the first insect aldehyde oxidase (AO) was obtained from the common house mosquito Culex quinquefasciatus (Say) through cloning and sequencing of both genomic DNA and cDNA. The deduced amino-acid sequence encodes a 150-kDa protein of 1266 amino-acid residues, which is consistent with the expected monomeric subunit size of AO. The Culex AO sequence contains a molybdopterin cofactor binding domain and two iron-sulfur centres. A comparison of the partial sequences of AO from insecticide resistant and susceptible strains of C. quinquefasciatus shows two distinct alleles of this enzyme, one of which is amplified in the insecticide resistant strain on a 30-kb DNA amplicon alongside two resistance-associated esterases. The amplified AO gene results in elevated AO activity in all life stages, but activity is highest in 3rd instar larvae. The elevated enzyme can be seen as a separate band on polyacrylamide gel electrophoresis. The role of AO in xenobiotic oxidation in mammals and the partial inhibition of elevated AO activity by a range of insecticides in Culex, suggest that this AO may play a role in insecticide resistance.

3' Untranslated Regions↗