The function of esterases in insecticide resistance in Culex quinquefasciatus mosquitoes from Sri Lanka.
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Animals↗
Biomedical subjects
J Hemingway
Publications and source records attributed to J Hemingway.
Possible mechanisms of organophosphorus and carbamate insecticide resistance in German cockroaches (Dictyoptera: Blattelidae) from different geographical areas.
The resistance status of 14 strains of Blattella germanica (L.) from four countries was determined for chlorpyrifos and propoxur compared with a standard reference susceptible strain. Thirteen strains were resistant to chlorpyrifos; 12 strains were resistant to propoxur. Resistance ratios for chlorpyrifos ranged from 8- to 462-fold at LC90; for propoxur, resistance ratios ranged from 4- to 46-fold. One cockroach strain from Denmark had negative cross-resistance to chlorpyrifos, and one strain from the United States had negative cross-resistance to propoxur. Slopes of probit regressions indicated that all resistant strains were heterogeneous for resistance to both chlorpyrifos and propoxur. Synergist studies with piperonyl butoxide indicated that multifunction mono-oxidases are probably involved in resistance to chlorpyrifos in six strains and in resistance to propoxur in seven strains. Esterase activity was elevated in 10 strains; of these strains, two had only slightly elevated esterase activity as measured with the substrates 1- and 2-naphthyl acetate. The remainder had higher levels of elevated esterase activity to both substrates. Strains with elevated esterase activity were resistant to a broad spectrum of organophosphates, pyrethroids, or both. Increased levels of glutathione S-transferase activity were found in four strains. Another two strains had a low frequency (1%) of individuals with high glutathione S-transferase activity. Elevated glutathione S-transferase activity was not correlated with the observed levels of organophosphate or carbamate resistance. One strain from Dubai had an altered acetylcholinesterase-based mechanism that conferred broad-spectrum resistance to a range of organophosphates and carbamates.
Animals↗
Changes in enzyme titres with age in four geographical strains of Aedes aegypti and their association with insecticide resistance.
The enzymes acetylcholinesterase, glutathione S-transferase (GST), glucose 6-phosphate dehydrogenase (G6PD), and general esterases were assayed in four strains of Aedes aegypti mosquitoes aged between 1 and 30 days. Microtitre plate methods were used to assay activity in the homogenates of individual mosquitoes. The levels of GST and G6PD declined with the age of the mosquitoes, while the activity for the other enzymes remained constant. Soluble protein content was also found to decline with mosquito age in all the strains. Insecticide bioassays showed that two strains (Trinidad and Virtudes) of Ae. aegypti were resistant to DDT, deltamethrin and malathion, whereas two other strains (Bangkok and Indian) were susceptible to all four classes of insecticides tested. Higher esterase activity levels in the resistant compared to the susceptible strains were assumed to be the cause of organophosphate resistance. The combination of DDT and deltamethrin resistance in two strains with normal GST and G6PD characteristics suggests that a kdr-type nerve insensitivity mechanism may be involved.
Acetylcholinesterase↗
Changes in malathion and pyrethroid resistance after cypermethrin selection of Culex quinquefasciatus field populations of Cuba.
Use of the organophosphorus insecticide malathion for mosquito control in Cuba, for 7 years up to 1986, selected elevated non-specific esterase and altered acetylcholinesterase (AChE) resistance mechanisms in Culex quinquefasciatus. In central Havana space-spraying of malathion was replaced by the pyrethroid cypermethrin in 1987: alternate cycles of malathion and cypermethrin were applied in some of the more rural areas of Havana district during 1987-91. Consequently, populations of Cx quinquefasciatus in the central area of Havana developed resistance to cypermethrin, but there is no evidence of pyrethroid resistance in the outlying areas. Malathion resistance levels declined significantly after 1986, measured both by bioassay and the frequency of the elevated esterase resistance mechanism, and then stabilized with no measurable decline during 1990 in any of the populations tested. These populations had less than 10% frequency of susceptible homozygotes for both the esterase and AChE resistance mechanisms, indicating that organophosphate resistance is still prevalent in Cuban Cx quinquefasciatus. These two mechanisms appear to be in linkage equilibrium, suggesting that current selection for double resistance is not strong. In the central Havana region, pirimiphos-methyl, an organophosphorus insecticide unaffected by the two common malathion resistance mechanisms, is now being used in a resistance management strategy designed to avoid pyrethroid resistance spreading.
Animals↗
Pyrethroid resistance in German cockroaches (Dictyoptera: Blattelidae): resistance levels and underlying mechanisms.
Thirty strains of Blattella germanica (L.) reported to be pyrethroid resistant were collected from three continents. Greater than 2-fold resistance to the pyrethroids cyfluthrin, fenvalerate, cypermethrin, and lambda cyhalothrin appeared in 15 of these strains. Twelve of these strains were also resistant to chlorpyrifos and propoxur. All the field strains tested were heterogeneous with regard to resistance. Possible resistance mechanisms detected in these populations included elevated levels of cytochrome P450, general esterase and glutathione S-transferase, and nerve insensitivity (kdr-type resistance). The elevated esterases and oxidase-based resistance were the most prevalent; 11 and 10 strains, respectively, had evidence of these mechanisms. Resistance was synergized by piperonyl butoxide in some strains. In some strains, elevated esterases, although present, were primarily correlated with organophosphate resistance. Pyrethroid insecticides may still be effective against many of these populations because of the low levels of resistance detected. However, potential exists for more serious resistance problems to develop if only pyrethroids are used. Because many of these strains are already resistant to organophosphorus and carbamate insecticides, prospects for the future chemical control of these populations must be carefully considered.
Animals↗
Purification and characterization of a carboxylesterase involved in insecticide resistance from the mosquito Culex quinquefasciatus.
A carboxylesterase (EC 3.1.1.1) involved in organophosphate insecticide resistance has been purified and characterized from the mosquito Culex quinquefasciatus. The monomeric enzyme has M(r) of 67,000 and a pI of 5.2. It hydrolysed medium-chain-length mono- and di-acylglycerols in addition to xenobiotic esters. Kinetic constants determined for four insecticides, temephos, chlorpyrifos, fenitrothion and propoxur indicate the rates of acylation and the affinities of binding of the insecticides to this carboxylesterase are important. This supports the major role of the A2 carboxylesterase is the sequestration of the insecticide with a minor role in the slow turnover of the insecticide.
Animals↗
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↗
Insecticide resistance gene frequencies in Anopheles sacharovi populations of the Cukurova plain, Adana Province, Turkey.
In Turkey, the mosquito Anopheles sacharovi has been under field selection pressure sequentially with DDT, dieldrin, malathion and pirimiphosmethyl over a period of 30 years for the purpose of malaria control. In 1984, the field population of An.sacharovi in the malarious Cukurova plain of Adana Province contained an altered acetylcholinesterase-based resistance gene giving broad spectrum resistance against organophosphorus and carbamate insecticides. The cross-resistance spectrum from this mechanism conferred resistance to malathion but not to the organophosphorus insecticide pirimiphos-methyl. Over the 6 years that pirimiphos-methyl has been applied for malaria vector control in this area, the frequency of the altered acetylcholinesterase resistance gene has declined, although in 1989 and 1990 it was still present at measurable frequencies in An.sacharovi from Cukurova. In addition to the acetylcholinesterase resistance mechanism there is evidence of an increased level of glutathione S-transferase in some of the An.sacharovi populations tested. This is known to be correlated with DDT resistance in other anophelines. In Turkish An.sacharovi, DDT resistance and elevated glutathione S-transferase occur in the same populations at similar frequencies. The continued prevalence of resistance to DDT and dieldrin, long after the 1971 cessation of DDT spraying for malaria control in Turkey, suggests that the DDT resistance gene has insufficient reduced fitness associated with it to have been lost from the field population during the past two decades. The implications of the slow decline in resistance gene frequencies in this field population are discussed in relation to mathematical models for managing resistance.
Acetylcholinesterase↗
Purification and characterisation of a mosquito carboxylesterase involved in insecticide resistance.
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Animals↗
Malathion and pyrethroid resistance in Culex quinquefasciatus from Cuba: efficacy of pirimiphos-methyl in the presence of at least three resistance mechanisms.
Use of malathion for mosquito control in Cuba for 7 years up to 1986 has selected for elevated non-specific esterase and altered acetylcholinesterase (AChE) resistance mechanisms in populations of the pest mosquito Culex quinquefasciatus Say. These mechanisms are still present in relatively high frequencies in the Havana area, despite the replacement of malathion by pyrethroid insecticides for the last 3 years in the mosquito control programme. Samples of Culex quinquefasciatus populations from within a 100 km radius of Havana had high levels of resistance to malathion and lower levels of resistance to propoxur, but there was little or no cross-resistance to the organophosphorus insecticide pirimiphos-methyl. Selection with malathion for twenty-two consecutive generations in the laboratory increased the level of malathion resistance to 1208-fold and propoxur level to 1002-fold, but the maximum level of pirimiphos-methyl resistance was only 11-fold. Pirimiphos-methyl is still operationally effective, despite the resistance mechanisms segregating, so this insecticide if used for control is unlikely to select either of the known resistance factors directly in the field population. Since 1986, pyrethroids have been used extensively, and low levels of pyrethroid resistance were detected in two of five field population samples tested. Malathion selection did not increase the level of pyrethroid resistance, which indicates that one or more distinct pyrethroid resistance factors are now being selected in the field populations of Culex quinquefasciatus.
Aerosols↗
Identification of reduced fitness associated with an insecticide resistance gene in Culex pipiens by microtitre plate tests.
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Acetylcholinesterase↗
Geographical and age-related variation in the activity of some enzymes associated with insecticide detoxification in sandflies (Diptera: Phlebotominae).
The activity of glutathione s-transferase (GST), glucose 6-phosphate dehydrogenase (G6PD), and esterases (EST1, EST2) was measured using microtitre plate assays of laboratory colonised Phlebotomus papatasi originating in Afghanistan, Cyprus, India, Iraq, Saudi Arabia, Spain and Tunisia. The mean enzyme activity of the seven populations was significantly different. Enzyme activity did not vary significantly with age in sandflies, unlike some mosquitoes. A baseline enzyme activity for susceptibility is proposed for P. papatasi.
Aging↗
Renal transplant patients' knowledge concerning cyclosporine treatment.
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Adult↗
Mechanisms of organophosphate and carbamate resistance in Culex quinquefasciatus from Saudi Arabia.
Broad spectrum organophosphate resistance in Culex quinquefasciatus Say from Saudi Arabia is inherited as a semi-dominant characteristic. The resistance has a metabolic basis and confers cross-resistance against the carbamate propoxur. Organophosphate-selected strains contain two elevated esterases with the same electrophoretic mobilities as those in resistant Cx quinquefasciatus from Sri Lanka and a range of African locations. Alteration in the sensitivity of acetylcholinesterase to insecticide inhibition does not play a major role in resistance. There was a significant increase in the amount of Cytochrome P450 in Cx quinquefasciatus lines selected with the pyrethroid permethrin or with the organophosphate pirimiphos-methyl, but no change in lines selected with five other organophosphates or propoxur, compared to the parental strain, which suggests that oxidases are involved in the P450 mediated resistance to both permethrin and pirimiphos-methyl.
Animals↗
Marketing and public relations in the emergency department.
This article outlines the elements of successful ED marketing, as well as providing definitions for terms used within the marketing process. In today's competition and rapidly changing environment, marketing and public relations are tools that every ED Medical Director may want to consider. Because the marketing process requires a great deal of time and effort, as well as a high degree of intellectual honesty, it should never be entered into without a strong commitment. However, marketing the ED can be among the most productive, stimulating, and gratifying experiences for the ED Medical Director, the emergency department physicians, and all ED service personnel.
Advertising↗
Pesticide resistance mechanisms produced by field selection pressures on Anopheles nigerrimus and A. culicifacies in Sri Lanka.
In Sri Lanka, Anopheles nigerrimus is resistant to a range of organophosphate and carbamate insecticides at both the larval and adult stages. Biochemical studies indicate that an alteration in acetylcholinesterase is the basis of resistance rather than increased metabolic breakdown of the insecticides. In contrast, A. culicifacies is resistant only to malathion and closely related compounds containing a carboxylate ester bond. Agricultural pesticides are the sole source of selection pressure for resistance in A. nigerrimus, while in A. culicifacies pressure arises predominantly from antimalarial spraying.
Animals↗
Efficacy of pirimiphos methyl as a larvicide or adulticide against insecticide resistant and susceptible mosquitoes (Diptera: Culicidae).
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Animals↗
The joint action of malathion and IBP against malathion-resistant and -susceptible strains of Anopheles stephensi.
Malathion resistance in an Anopheles stephensi strain from Pakistan is dependent on a single gene, which results in increased degradation of malathion to the monocarboxylic acid. Mixtures of malathion and the fungicide IBP (O, O-bis(1-methylethyl) S-phenylmethyl phosphorothioate) were tested against this resistant strain and a laboratory susceptible strain. The mixtures were more toxic to both the resistant and susceptible insects than either IBP or malathion alone. The high degree of synergism with the mixtures against the susceptible strain would not be expected if IBP were simply competing with malathion for a common carboxylesterase detoxification enzyme. The reason for the high degree of synergism in the susceptible strain is unknown.
Anopheles↗