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PubMed1956

The significance of insecticide-resistant strains; with special reference to pests of medical importance.

The author discusses the meaning of insecticide resistance and the manner in which it should be detected and measured. From some recent data he gives a number of examples of measurements of resistance in mosquitos of different species in various areas. He then proceeds to a speculative discussion on the way in which insecticide resistance arises, whether it can be prevented and overcome, its importance in the past and at present, and finally its future prospects.

Animals↗

PubMed2004

Insecticide resistance and cross-resistance in Alabama and Florida strains of Culex quinquefasciatus [correction].

Insecticide resistance and cross-resistance was determined for three strains of Culex quinquefasciatus Say in the southeastern United States. HAmCq and MAmCq strains were collected in 2002 from Huntsville and Mobile, AL. The VBFmCq strain was collected in 1998 from Vero Beach, FL. VBFmCq, HAmCq, and MAmCq larvae showed resistance to permethrin with resistance ratios of 13, 100, and 940, respectively, compared with the susceptible S-Lab strain. Levels of resistance in HAmCq and MAmCq larvae were 200- and 830-fold to resmethrin and 4- and 70-fold to malathion, respectively. VBFmCq, HAmCq, and MAmCq strains all demonstrated a great ability to develop tolerance and/or cross-resistance to different insecticides, including deltamethrin (50-, 100-, and 300-fold), chlorpyrifos (150-, 33-, and 720-fold), fipronil (10-, 5-, and 15-fold), and imidacloprid (7.5-, 5- and 10-fold, respectively). Comparison of resistance ratios for pyrethroids, organophosphates, and imidacloprid at LC50 and LC90 and gradual slopes of dose-response curves indicated that VBFmCq, HAmCq, and MAmCq were heterozygous in response to these insecticides. All three strains showed high levels of susceptibility to Bacillus thuringiensis variety israelensis (Bti) and spinosad, although these mosquitoes had been extensively exposed to Bti. Thus, we conclude that Bti and spinosad may be valuable for the management of Cx. quinquefasciatus, especially in situations where local strains are highly resistant to other insecticides.

Alabama↗

PubMed1991

Horn fly (Diptera: Muscidae) insecticide resistance in Kentucky and Arkansas.

The effect of previous insecticide use patterns for horn fly control on the susceptibility spectrum of horn fly (Haematobia irritans [L.]) populations from Kentucky and Arkansas is described. Populations of horn flies from both states were tested with three pyrethroids (cyhalothrin, cypermethrin, and permethrin), three organophosphates (diazinon, pirimiphos methyl, and tetrachlorvinphos), and a chlorinated hydrocarbon (methoxychlor). Dose-mortality data indicated insecticide resistance in Arkansas and Kentucky. Two permethrin-resistant horn fly populations in Kentucky that did not have a history of exposure to methoxychlor were cross-resistant to this chlorinated hydrocarbon. Horn fly populations from both states with a history of at least three consecutive years of exposure to various pyrethroid ear tags were subsequently exposed to cattle tagged with cyhalothrin-impregnated ear tags for 15-16 wk. Such exposure resulted in a decrease in susceptibility to this pyrethroid (ranging from approximately 30 to greater than 100-fold) when compared with levels before treatment. Horn fly populations from Arkansas resistant to cyhalothrin (as a result of exposure to cyhalothrin ear tags) were cross-resistant to pirimiphos methyl. Seasonal exposure of an Arkansas and Kentucky horn fly population to cattle with ear tags impregnated with pirimiphos methyl resulted in a significant decrease in susceptibility to this organophosphate.

Animals↗

PubMed1999

Influence of permethrin, diazinon and ivermectin treatments on insecticide resistance in the horn fly (Diptera: Muscidae).

The history of insecticide resistance in the horn fly, Haematobia irritans, and the relationship between the characteristics of horn fly biology and insecticide use on resistance development is discussed. Colonies of susceptible horn flies were selected for resistance with six insecticide treatment regimens: continuous single use of permethrin, diazinon and ivermectin: permethrin-diazinon (1:2) mixture; and permethrin-diazinon and permethrin-ivermectin rotation (4-month cycle). Under laboratory conditions, resistance developed during generations 21, 31 and 30 to permethrin, diazinon and ivermectin, respectively. The magnitude of resistance ranged from < 3-fold with ivermectin to 1470-fold with permethrin. Field studies demonstrated that use of a single class of insecticidal ear tag during the horn-fly season resulted in product failure within 3-4 years for pyrethroids and organophosphates, respectively. In laboratory studies, use of alternating insecticides or a mixture of insecticides delayed the onset of resistance for up to 12 generations and reduced the magnitude of pyrethroid resistance. In field studies, yearly alternated use of pyrethroids and organophosphates did not slow or reverse pyrethroid resistance (Barros et al., unpublished data), while a 2-year alternated use with organophosphates resulted in partial reversion of pyrethroid resistance. When pyrethroid and organophosphate ear tags were used in a mosaic strategy at two different locations, efficacy of products did not change during a 3-year period.

Animals↗

PubMed1999

Mechanisms of insecticide resistance in the aphid Nasonovia ribisnigri (Mosley) (Homoptera: Aphididae) from France.

Nasonovia ribisnigri, a main pest of salad crops, has developed resistance to various insecticides in southern France, including the carbamate pirimicarb and the cyclodiene endosulfan, two insecticides widely used to control this aphid. Here we have investigated the mechanisms of resistance to these two insecticides by studying cross-resistance, synergism, activity of detoxifying enzymes, and possible modifications of the target proteins. Resistance to pirimicarb was shown to be mainly due to a decreased sensitivity of the target acetylcholinesterase; this modification conferred also, resistance to propoxur but not to methomyl and the two tested organophosphates (acephate and paraoxon). Endosulfan resistance was associated with a moderate level of resistance to dieldrin, and resistance to both insecticides was due, in part, to increased detoxification by glutathione S-transferases (GST). The endosulfan resistant strain displayed the same amino acid at position 302 of the Rdl gene (GABA receptor) as susceptible aphids (e.g. Ala), indicating that the Ala to Ser (or to Gly) mutation observed among dieldrin resistant strains of other insect species was not present.

Animals↗

PubMed2004

Combining zooprophylaxis and insecticide spraying: a malaria-control strategy limiting the development of insecticide resistance in vector mosquitoes.

Strategies to eradicate the vector-borne infectious diseases (e.g. malaria and Japanese encephalitis) are often directed at controlling vectors with insecticides. Spraying insecticide, however, opens the way for the development of insecticide resistance in vectors, which may lead to the failure of disease control. In this paper, we examine whether the combined use of insecticide spray and zooprophylaxis can limit the development of insecticide resistance in mosquitoes. Zooprophylaxis refers to the control of vector-borne diseases by attracting vectors to domestic animals in which the pathogen cannot amplify (a dead-end host). The human malaria parasite Plasmodium spp. has a closed transmission cycle between humans and mosquitoes, and hence cattle can serve as a dead-end host. Our model reveals that, by a suitable choice of insecticide spraying rate and cattle density and location, malaria can, in some situations, be controlled without mosquitoes developing insecticide resistance.

Animals↗

PubMed2000

Assessment of insecticide resistance in five insect pests attacking field and vegetable crops in Nicaragua.

Field populations of Hypothenemus hampei (Ferrari), Plutella xylostella (L.), Spodoptera exigua (Hübner), Helicoverpa zea (Boddie) and Bemisia tabaci (Gennadius) were tested for resistance to several insecticides commonly used in Nicariagua. Assays were conducted to estimate the LD50s or LC50s and the corresponding resistance ratios. A diagnostic concentration was used to discriminate between susceptible and resistant strains of H. hampei. The tests with >6,000 H. hampei adults collected from six different sites indicate the absence of resistance to endosulfan. Resistance to cypermethrin, deltamethrin, chlorfluazuron, thiocyclam, and methamidophos was documented in six field populations of P. xylostella. High levels of resistance to cypermethrin and deltamethrin, but moderate levels of resistance to chlorpyriphos and methomyl, were also documented in two field populations of S. exigua. Moderate levels of resistance to cypermethrin, deltamethrin and chlorpyriphos were also documented in three field populations of H. zea. Moderate to high levels of resistance to bifenthrin, methamidophos and endosulfan were documented in four field populations of B. tabaci. The presence of significant correlations between LD50s or LC50s suggests the occurrence of cross-resistance or simultaneous selection for resistance by different insecticides with different modes of action. Our data could not differentiate between these two possibilities. Because insecticides will continue being used in Nicaragua, a resistance management program is urgently needed. The implementation of integrated pest management tactics must be accompanied by specific regulations for pesticide registration. In the future, pesticide registration regulations in Nicaragua should include periodic resistance monitoring. The mechanisms to cover the costs of resistance monitoring and resistance management should also be established.

Animals↗

PubMed1970

[Insecticide resistance in bedbugs(Cimex lectularius) in Korea]

In the summer of 1969 from July through October, authors carried out a study of susceptibility in adult female bed bug(Cimex lectularius) in order to ascertain any development of resistance to insecticides in Korea. The test to DDT and Dieldrin was performed in laboratory by the continuous exposure of residues method, with standard impregnated paper used for adult mosqitoes. Some results so far obtained can be summarised as follows: 1. LC(50) were 2.839% in DDT and 0.167% in Dieldrin. 2. The resistance has been arisen 2.4~2.9 times in DDT and 1.6~2.4 times in Dieldrin as compared with London laboratory strain, but they were susceptible 1.4 times in DDT and 180 times in Dieldrin as compared to Israel resistance strain.

Journal Article↗

PubMed2002

Temporal and spatial dynamics of insecticide resistance in Myzus persicae (Hemiptera: Aphididae).

Advances in understanding insecticide resistance in the peach-potato aphid, Myzus persicae (Sulzer), at the genotypic, biochemical and molecular levels have led to rapid and precise methods for the detection of several resistance mechanisms (elevated carboxylesterase, modified acetylcholinesterase or MACE, and knockdown resistance or kdr) in individual insects, and for monitoring their frequencies over space and time. This paper summarises the results of two long-term surveys of resistance dynamics in M persicae in England, based on samples collected directly from field and glasshouse crops or from four 12.2-m suction traps. The study showed marked fluctuations in resistance frequencies that probably reflect the counteracting forces of selection imposed by insecticides for aphids possessing more copies of esterase resistance genes, and selection against these forms when insecticide use is relaxed. There is growing evidence that several different resistance mechanisms in M persicae have associated fitness costs. In the case of esterase and MACE, these costs are apparently strong enough to effect a decline in resistance frequency over winter, and a more prolonged decline over successive cropping seasons when aphid numbers are insufficient to trigger intensive chemical applications. Changes in the overall frequency of resistance genotypes may also be influenced by the predominance of year-round parthenogenesis in M persicae in the UK, leading to non-random associations between mechanisms and selection operating on clonal lineages rather than individual genotypes.

Acetylcholinesterase↗

PubMed1990

Characterization of amplification core and esterase B1 gene responsible for insecticide resistance in Culex.

Organophosphorus insecticide (OP) resistance in several Culex species is associated with increased esterase activity resulting from amplification of the corresponding structural gene. In Culex pipiens quinquefasciatus, high levels of OP resistance (approximately 800 times) are due to the esterase B1 gene, which is amplified at least 250-fold. This gene has now been sequenced, and the structure of the amplification unit (amplicon) encompassing the structural gene has been partially characterized. The inferred amino acid sequence of the enzyme revealed regions of strong homology with other eukaryotic serine-esterases, such as cholinesterases, which are the target of OPs. The amplicon covers at least 30 kilobases and contains a constant and highly conserved "core" of 25 kilobases. This core carries a single copy of the esterase gene (2.8 kilobases) as well as other sequences that are present as single or low number copies in the genomes of mosquitoes lacking overproduction of the esterase B1 protein. In the amplicon, the esterase gene is framed by two DNA sequences that are repeated in other parts of the genome of resistant mosquitoes and found in the genome of susceptible mosquitoes but not near the esterase B1 gene. It is suggested that these repetitive sequences may have a role in the amplification process.

Amino Acid Sequence↗

PubMed2000

Quantitative analysis of gene amplification in insecticide-resistant Culex mosquitoes.

The amplification of carboxylesterase structural genes followed by their overexpression is the most common mechanism of resistance to organophosphorus insecticides in Culex mosquitoes. Most resistant Culex quinquefasciatus mosquitoes have co-amplified estalpha2(1) and estbeta2(1) genes. Recently, Southern, DNA dot-blot analysis and phosphorimaging technology were used to quantify the est gene copy number in aphids and mosquitoes. Although more accurate than autoradiography, this method relies on probe hybridization, which can be variable. We have directly measured gene and mRNA copy number by using real-time quantitative PCRs in mosquitoes. The acquisition of fluorescence from incorporation of the double-strand-specific dye SYBR GreenI into a PCR product once per cycle is used to provide an absolute quantification of the initial template copy number. Thus it has been possible to show that estalpha2(1) and estbeta2(1) are co-amplified approx. 80-fold in the genome of the resistant PelRR strain of C. quinquefasciatus. The two genes, although co-amplified in a 1:1 ratio, are differentially transcribed: the estbeta2(1) gene from this amplicon has greater transcription than estalpha2(1) in all individual mosquito larvae tested, with an average ratio of 10:1. Purified esterases from mosquito homogenates were found in a ratio of 3:1, which, combined with the quantitative mRNA data, suggests the operation of both transcriptional and translational control mechanisms to regulate the expression of the amplified genes in C. quinquefasciatus insecticide-resistant mosquitoes.

Animals↗

PubMed2005

Does insecticide resistance alone account for the low genetic variability of asexually reproducing populations of the peach-potato aphid Myzus persicae?

The typical life cycle of aphids includes several parthenogenetic generations and a single sexual generation (cyclical parthenogenesis), but some species or populations are totally asexual (obligate parthenogenesis). Genetic variability is generally low in these asexually reproducing populations, that is, few genotypes are spread over large geographic areas. Both genetic drift and natural selection are often invoked to account for this low genetic variability. The peach-potato aphid, Myzus persicae, which encompasses both cyclical and obligate parthenogens, has developed several insecticide resistance mechanisms as a consequence of intense insecticide use since the 1950s. We collected asexually reproducing M. persicae from oilseed rape and examined genetic variability at eight microsatellite loci and three insecticide resistance genes to determine whether their genetic structure was driven by drift and/or selection. We identified only 16 multilocus microsatellite genotypes among 255 individuals. One clone, which combined two insecticide resistance mechanisms, was frequently detected in all populations whatever their location over a large geographical area (the northern half of France). These unexpected findings suggest that drift is not the unique cause of this low variability. Instead, the intensification of both insecticide treatments and oilseed rape cultivation may have favored a few genotypes. Thus, we propose that selective pressures resulting from human activities have considerably modified the genetic structure of M. persicae populations in northern France in a relatively short period of time.

Alleles↗

PubMed2001

Is attract-and-kill technology potent against insecticide-resistant Lepidoptera?

Attract-and-kill techniques, associating an attractant and a contact insecticide in a sticky formulation, are a new way of controlling Lepidopteran pests. Insecticide resistance may, however, limit the effectiveness and even the attractiveness of such formulations where resistance pleiotropic effects influence pheromone perception. We have tested this hypothesis on resistant codling moths Cydia pomonella (L) using a commercial formulation containing (E,E)-8,10-dodecadien-1-ol (codlemone), the major component of the sex pheromone, as an attractant and permethrin as toxicant. We first compared the attractiveness of codlemone in a wind tunnel and the contact toxicity of pyrethroids on males of one susceptible and of three strains selected for resistance to diflubenzuron, deltamethrin and azinphos-methyl. The dose-response relationships of males of susceptible and resistant strains to codlemone did not differ significantly. The deltamethrin-selected strain was the most resistant to pyrethroids, exhibiting 138-, 25- and 18-fold resistance ratios to deltamethrin, cypermethrin and permethrin, respectively. The efficiency of the attracticide formulation, applied successively on filter paper support, glass support and wood support, was estimated by recording the mortality delay of males after natural contact with the formulation in the wind tunnel. The deltamethrin- and diflubenzuron-resistant strains were significantly less affected than the susceptible strain by contact with the attracticide on the wooden support, exhibiting 58- and 2.3-fold greater LT50 ratios, respectively. Mortality of deltamethrin-resistant moths did not exceed 40% after 48 h. The LT50 value was significantly greater on filter paper support than on the two other supports. Surprisingly, the LT50 ratio of the deltamethrin-resistant strain was markedly higher on filter paper support (1021-fold), which was more absorbent, than on the glass support (31-fold). No sublethal effects in terms of pheromone response, mating or fecundity occurred in moths surviving contact with the attracticide. Choice of insecticides in attracticide formulations will be influenced by the resistance background of the target pests. Principles of insecticide resistance management may also be applied to attract-and-kill technology by alternating with other insecticides or control methods.

Animals↗

PubMed2003

Evaluation of alternative tactics for management of insecticide-resistant horn flies (Diptera: Muscidae).

A 3-yr study was conducted to determine the efficacy of tactics that could be used to manage populations of insecticide-resistant horn flies, Hematobia irritans irritans (L.). Insecticide spray, spot-on or pour-on formulations and two IGRs in bolus formulation, 1.3- and 3.2-ha pasture rotations on different rotation schedules, 0-50% Brahman breeding, selected fly-resistant cows, and a mechanical trap were evaluated singly and in combination. Concentration-mortality tests indicated that horn flies collected from cows used in the current study were significantly less susceptible to diazinon, coumaphos, and methoxychlor than horn flies from cows at the same locations previously used to determine baseline susceptibility. During the 3-yr study at the Southeast Research and Extension Center (SEREC), the IGR-bolus significantly reduced (P < 0.05) horn fly numbers on both the continuous and rotational graze regimens, resulting in significantly (P < 0.05) greater calf weaning weights (average of 24 kg). Horn fly numbers were significantly greater on untreated cows during the 3-yr study at the Southwest Research and Extension Center (SWREC) compared with the mean fly numbers on cows that received fly-management treatments. All tactics and tactic-combinations used at SWREC on cattle having no Brahman breeding failed to significantly reduce insecticide-resistant horn fly numbers. However, the combination of Brahman breeding with the IGR-Bolus and mechanical trap significantly reduced horn fly numbers and resulted in significant increases in calf weaning weight. In addition, mean horn fly numbers decreased significantly as the percentage Brahman breeding increased with 50% Brahman breeding reducing horn fly numbers by 140 flies per cow. No significant difference was found between the mean fly numbers on the fly-resistant purebred group and the cows that had no Brahman breeding but received the IGR-Bolus or used the mechanical trap. The use of synergized zeta-cypermethrin pour-on treatment successfully complimented the use of IGR-bolus and mechanical traps in reducing insecticide-resistant horn fly numbers. Neither 1.3- nor 3.2-ha size paddocks and stocking rates used in the rotation graze regimens at SEREC and SWREC, respectively, significantly reduced horn fly numbers when compared with continuously grazed paddocks. Data indicated the importance of using tactics that reduce horn fly numbers to approximately 150 horn flies per cow. These data demonstrated the efficacy of using tactic combinations to manage insecticide-resistant horn fly populations.

Animals↗

PubMed1998

Amplification of a serine esterase gene is involved in insecticide resistance in Sri Lankan Culex tritaeniorhynchus.

Culex tritaeniorhynchus, the major vector of Japanese encephalitis in Sri Lanka, is resistant to organophosphorus insecticides, with a 10-fold resistance ratio at the LC50 for chlorpyrifos, and a high heterogenelty factor in the insect field population. The major mechanism of resistance in this species, as in the mosquito C. quinquefasciatus, is elevation of esterase activity. Basic biochemical, immunological and molecular analysis suggests that the C. tritaeniorhynchus CtrEstbeta1 gene is orthologous to the C. quinquefasciatus amplified Estbetas. The Estbeta2(1) antiserum cross-reacts strongly with CtrEstbeta1(1). Its corresponding cDNA, over the 545 base pairs sequenced, has approximately 84% identity with the various C. quinquefasciatus Estbetas. The gene is amplified in C. tritaeniorhynchus. Amplification of the same esterase in two independent species, along with multiple amplification events involving this esterase gene in C. quinquefasciatus suggests that the location of this gene within the genome predisposes it to amplification.

Animals↗

PubMed2000

Identifying insecticide-resistant greenbugs (Homoptera: Aphididae) with diagnostic assay tests.

Laboratory bioassays were used to develop a diagnostic assay test for identifying greenburg, Schizaphis graminum (Rondani), populations that are insecticide-resistant. Petri dish assays with chlorpyrifos showed greenbug mortality should be monitored after 2 h of exposure. One-hour exposure did not kill a high percentage of susceptible greenbugs, and a 3-h exposure killed too many resistant greenbugs. Ethanol and methanol were both good solvents for mixing with chlorpyrifos in the petri dish assay. From the laboratory bioassays, four diagnostic concentrations of chlorpyrifos (3, 10, 30, and 100 ppm) were evaluated in the field by Texas A&M University agricultural research and extension entomologists across the Texas High Plains. Results from the diagnostic assay tests were compared with gel-electrophoresis resistance tests to validate resistance detection. The diagnostic assay tests gave the same greenbug resistance identification as the gel-electrophoresis analysis in 21 of 22 field bioassays in 1994 and 35 of 39 field bioassays in 1995. Diagnostic concentrations of 30 and 100 ppm chlorpyrifos killed > or = 85 and > or = 90%, respectively, of greenbugs identified by gel-electrophoresis as susceptible and < 40% and < 55%, respectively, of resistant greenbugs. The diagnostic assay technique is a quick, reliable, and inexpensive method for detecting insecticide resistance in greenbug populations.

Animals↗

PubMed1992

Genetics of insecticide resistance in mosquito vectors of disease.

Early studies on the genetics of insecticide resistance showed that single major semi-dominant genes were generally involved, and biochemical studies defined a limited number of enzymes and structural nerve proteins that were encoded by these genes. Recent advances in resistance detection now allow the measurement of genotype frequencies for some of these resistance mechanisms. Molecular studies are in progress for most of the major resistance genes, and the amplified esterase B(1) gene in Culex quinquefasciatus has been cloned. Changes in resistance gene expression occur, with increasing age of the adult insect, by way of specific mechanisms, and amplified esterase-based resistance genes that are not expressed can occur in aphids. Here Janet Hemingway assesses current knowledge of the genetics of insecticide resistance in mosquitoes.

Journal Article↗

PubMed1990

Distribution and insecticide resistance of the plague flea Xenopsylla cheopis in Maharashtra State, India.

Distributions are reported for commensal rat fleas, predominantly Xenopsylla cheopis (Rothschild), in the State of Maharashtra, India, including the city of Bombay, during 1965-80. The X.cheopis flea index was high in most parts of Maharashtra, but low in Bombay. Rattus rattus Linnaeus is the principal host of X.cheopis, but the host range includes Bandicota bengalensis Gray, Golunda ellioti Gray, Mus musculus Linnaeus, Rattus blandfordi Thomas, R. norvegicus Berkenhout, Suncus caerulaeus Lerr, S. murinus Linnaeus and Tatera indica Hardwicke. X.cheopis was found to have high degrees of resistance to DDT, malathion and fenthion, tolerance to gamma HCH (= gamma BCH) but susceptibility to dieldrin. This insecticide resistance situation may contribute to the high flea indices prevailing in the state, with consequent risks of plague outbreaks. Two other species of rat flea, X.astia Rothschild and X.brasiliensis (Baker) were found to be less common than previously recorded. Their apparent replacement by X.cheopis is tentatively attributed, at least partly, to the selective advantage of insecticide resistance in the latter species.

Animals↗