Propoxur Resistance Research Articles

Diversity and distribution of Mdace mutations involved in propoxur resistance in the house fly (Musca domestica L.) in China.

The house fly is a public health pest due to its ability to transmit various pathogens worldwide. The suppression of house flies is frequently controlled by organophosphate and carbamate insecticides, but recurrent selection has led to the mutated target. To understand the spread and evolution of Mdace mutations in house flies, we sampled flies in eight different China provinces, sequenced, and then estimated the frequencies of mutations. The inhibition of AChE towards propoxur varied geographically and was lowest in the Heilongjiang field population, and highest in Jiangsu population. The overall frequencies of the different Mdace mutations (V260L, G342A, G342V, F407Y) varied considerably between populations. Strong positive correlations were found between acetylcholinesterase (AChE) insensitivity and the frequencies of G342V allele, 342A/V genotype and combination (260V/L-342A/V-407Y/Y) for the field populations. Eighteen combinations of Mdace at three sites (V260L, G342A/V, F407Y) were observed, with the majority of flies being categorized into the combination (260V/L-342A/V-407Y/Y), ranging in frequency from 24% (in field populations in Hubei and Hainan) to 96% (Jiangsu). Based on comparison with historical data, the mutations responsible for the extremely high resistance to the level of insecticide resistance spread widely, propoxur should be limited to use for house fly control in China. © 2024 Society of Chemical Industry.

Functional characterization of CYP6G4 from the house fly in propoxur metabolism and resistance

The house fly (Musca domestica L.) (Diptera: Muscidae) is a global vector that can transmit >250 human and animal diseases. The control of house flies has heavily relied on the application of various chemical insecticides. The carbamate insecticide propoxur has been widely used for the control of house flies, and resistance to propoxur has been documented in many house fly populations worldwide. Previous studies have identified several propoxur resistance-conferring mutations in the target protein acetylcholinesterase; however, the molecular basis for metabolic resistance to propoxur remains unknown. In this study, we investigated the involvement of CYP6G4, a cytochrome P450 overexpressed in many insecticide resistant populations of Musca domestica, in propoxur metabolism and resistance by using combined approaches of recombinant protein-based insecticide metabolism and the Drosophila GAL4/UAS transgenic system. The recombinant CYP6G4 and its redox partners (NADPH-dependent cytochrome P450 reductase and cytochrome b5) were functionally expressed in Escherichia coli. Metabolism experiments showed that CYP6G4 was able to transform propoxur with a turnover rate of around 0.79 min−1. Six metabolites were putatively identified, suggesting that CYP6G4 could metabolize propoxur via hydroxylation, O-depropylation and N-demethylation. Moreover, bioassay results showed that ectopic overexpression of CYP6G4 in fruit flies significantly increased their tolerance to propoxur. Our in vivo and in vitro data convincingly demonstrate that CYP6G4 contributes to propoxur metabolism and resistance.

Common substitution mutation F348Y of acetylcholinesterase gene contributes to organophosphate and carbamate resistance in Cimex lectularius and C. hemipterus

Bed bug control highly depends on insecticides with a limited number of modes of action, especially since the global prevalence of pyrethroid resistance. De facto insecticide options against bed bugs in Japan are acetylcholinesterase inhibitors (AChEis) that consist of organophosphates and carbamates. However, the status of AChEi resistance and the mechanisms involved have not been ascertained. An amino acid substitution mutation, F348Y (or F331Y in standard numbering), occurring at an acyl-binding site of the paralogous AChE gene (p-Ace), was identified among AChEi-resistant colonies of both common and tropical bed bugs (Cimex lectularius and C. hemipterus, respectively). This mutation was genetically associated with propoxur and fenitrothion resistance in F348Y-segregating colonies of C. hemipterus. Inhibition of heterologously expressed C. lectularius p-Ace with insecticides revealed that the sensitivities of F348Y-carrying AChE decreased by orders of 10- to more than 100-fold for diazoxon, carbaryl, fenitroxon, paraoxon, chlorpyrifos-methyl, malaoxon, azamethiphos, methyl-paraoxon, and propoxur. In contrast, the mutant AChE showed a slightly decreased degree of sensitivity for dichlorvos and almost unchanged sensitivity for metoxadiazone. Further studies are needed to ascertain whether the practical efficacies of dichlorvos and metoxadiazone are ensured against F348Y-carrying bed bugs and whether other resistance mechanisms are involved.

Dynamics of organophosphate and carbamate resistance in Anopheles gambiae s. l. populations from south and north Benin, West Africa

The current study was aimed to investigate on dynamics of propoxur resistance in Anopheles gambiae s.l. populations from N’ dali district in northern Benin (West Africa) and also to investigate on dynamics of malathion resistance in Anopheles gambiae s. l. populations from Toffo district in southern Benin. Larvae and pupae of Anopheles gambiae s. l . mosquitoes were collected from the breeding sites in Borgou and Atlantic departments in 2015 and 2019. WHO susceptibility tests were conducted on unfed female mosquitoes aged 2-5 days old. WHO bioassays were performed with impregnated papers with propoxur 0.1% and with malathion 5%. PCR techniques were used to detect species and Ace-1 mutations in 2015. Anopheles gambiae s. l. populations from N’dali were resistant to propoxur in 2015 and were still remained resistant to this product in 2019. Regarding Anopheles gambiae s. l. populations from Toffo, they were susceptible to malathion in 2015 whereas the malathion resistance status of these mosquitoes requires further investigation in 2019. PCR revealed that all specimens tested were Anopheles gambiae s. s. The presence of Ace-1R at very low frequency (0.01) was observed in Anopheles gambiae s. l. populations from both districts. This study shows that propoxur resistance detected in An. gambiae s. l. populations from N’ dali needs to be monitored for insecticide resistance in this area.

The overexpression and variant of CYP6G4 associated with propoxur resistance in the housefly, Musca domestica L.

The control of the housefly, Musca domestica, heavily relies on the application of insecticides. Propoxur, a carbamate, has been widely used for vector control. The housefly populations with high propoxur resistance display point mutations and overexpression of acetylcholinesterase. However, the roles of cytochrome P450 monoxygenases (P450s), as important detoxification enzymes, remain poorly understand in the housefly resistant to propoxur. P450s were implied to contribute to propoxur resistance based on the synergism of piperonyl butoxide (PBO) and the increase of P450 enzyme activity in the near-isogenic line propoxur resistant strain (N-PRS). Five P450 genes (CYP6G4, CYP6A25, CYP304A1, CYP6D3, and CYP6A1) by RNA-sequencing comparison were significantly up-regulated in the N-PRS strain with >1035-fold resistance to propoxur. A total of 13 non-synonymous mutations of three P450 genes (CYP6G4, CYP6D3, and CYP6D8) were found in the N-PRS strain. The amino acid substitutions of CYP6D3 and CYP6D8 were probably not resistance-associated single nucleotide polymorphisms (SNPs) because they were also found in the aabys susceptible strain. However, CYP6G4 variant in the N-PRS strain was not found in the aabys strain. The conjoint analysis of mutations and a series of genetic crosses exhibited that the housefly propoxur resistance was strongly associated with the mutations of CYP6G4 gene. Our results suggested that a combination of up-regulated transcript levels and mutations of CYP6G4 contributed to propoxur resistance in the housefly. © 2021 Society of Chemical Industry.

Propoxur resistance associated with insensitivity of acetylcholinesterase (AChE) in the housefly, Musca domestica (Diptera: Muscidae)

Two unique housefly strains, PSS and N-PRS (near-isogenic line with the PSS), were used to clarify the mechanisms associated with propoxur resistance in the housefly, Musca domestica. The propoxur-selected resistant (N-PRS) strain exhibited >1035-fold resistance to propoxur and 1.70-, 12.06-, 4.28-, 57.76-, and 57.54-fold cross-resistance to beta-cypermethrin, deltamethrin, bifenthrin, phoxim, and azamethiphos, respectively, compared to the susceptible (PSS) strain. We purified acetylcholinesterase (AChE) from the N-PRS and PSS strains using a procainamide affinity column and characterized the AChE. The sensitivity of AChE to propoxur based on the bimolecular rate constant (Ki) was approximately 100-fold higher in the PSS strain compared to the N-PRS strain. The cDNA encoding Mdace from both the N-PRS strain and the PSS strain were cloned and sequenced using RT-PCR. The cDNA was 2073 nucleotides long and encoded a protein of 691 amino acids. A total of four single nucleotide polymorphisms (SNPs), I162M, V260L, G342A, and F407Y, were present in the region of the active site of AChE from the N-PRS strain. The transcription level and DNA copy number of Mdace were significantly higher in the resistant strain than in the susceptible strain. These results indicated that mutations combined with the up-regulation of Mdace might be essential in the housefly resistance to propoxur.

Mapping insecticide resistance and characterization of resistance mechanisms in Anopheles arabiensis (Diptera: Culicidae) in Ethiopia

BackgroundThe emergence and spread of insecticide resistance in the major African malaria vectors Anopheles gambiae (s.s.) and An. arabiensis may compromise the current vector control interventions and threatens the global malaria control and elimination efforts.MethodsInsecticide resistance was monitored in several study sites in Ethiopia from 2013 to 2015 using papers impregnated with discriminating concentrations of DDT, deltamethrin, bendiocarb, propoxur, malathion, fenitrothion and pirimiphos-methyl, following the WHO insecticide susceptibility test procedure. Mosquitoes sampled from different localities for WHO bioassay were morphologically identified as An. gambiae (s.l.) using standard taxonomic keys. Samples were identified to species using species-specific polymerase chain reaction (PCR) and screened for the presence of target site mutations L1014F, L1014S and N1575Y in the voltage gated sodium channel (VGSC) gene and G119S in the acethylcholinesterase (AChE) gene using allele-specific PCR. Biochemical assays were performed to assess elevated levels of acetylcholinesterases, carboxylcholinesterases, glutathione-S-transferases (GSTs) and cytochrome P450s monooxygenases in wild populations of An. arabiensis, compared to the fully susceptible Sekoru An. arabiensis laboratory strain.ResultsPopulations of An. arabiensis were resistant to DDT and deltamethrin but were susceptible to fenitrothion in all the study sites. Reduced susceptibility to malathion, pirimiphos-methyl, propoxur and bendiocarb was observed in some of the study sites. Knockdown resistance (kdr L1014F) was detected in all mosquito populations with allele frequency ranging from 42 to 91%. Elevated levels of glutathione-S-transferases (GSTs) were detected in some of the mosquito populations. However, no elevated levels of monooxygenases and esterases were detected in any of the populations assessed.ConclusionsAnopheles arabiensis populations from all surveyed sites in Ethiopia exhibited resistance against DDT and pyrethroids. Moreover, some mosquito populations exhibited resistance to propoxur and possible resistance to bendiocarb. Target site mutation kdr L1014F was detected in all mosquito populations while elevated levels of glutathione-S-transferases (GSTs) was detected in some mosquito populations. The reduced susceptibility of An. arabiensis to propoxur and bendiocarb, which are currently used for indoor residual spraying (IRS) in Ethiopia, calls for continuous resistance monitoring, in order to plan and implement evidence based insecticide resistance management.

Evaluation of Fenitrothion against Culex pipiens (Diptera: Culicidae) Larvae in Grand Tunis Area of Tunisia

Resistance toward 2 insecticides (fenitrothion and propoxur) was analyzed in 5 samples of Culex pipiens populations collected from various localities of Grand Tunis area, Northeast Tunisia. All studied samples were resistant to fenitrothion and propoxur insecticides. The study of esterase’s activities showed the existence of five overproduced esterases: C1, A1, A2-B2, A4-B4 (and/or A5-B5) and B12. One or several esterases were detected in the studied samples. We also showed that the resistance to fenitrothion was correlated with the propoxur resistance indicating that modifications of the target, the AChE 1, can be involved in the OP resistance. These results should be considered in the current mosquitoes control programs in Tunisia.

Evaluation of Fenitrothion Resistance and Biochemical Mechanism in three Populations of Culex pipiens (Diptera: Culicidae) from Southern Tunisia

Evaluation of fenitrothion resistance was realized in three populations of Culex pipiens collected in Southern Tunisia between March 2002 and October 2005. It was not possible to considered bioassays tests to fenitrothion in sample # 3 due to their control-level mortality. The RR50 were 27.1 in sample # 1 and 179 in sample # 2. All the studied samples showed the presence of one or more esterases in their electrophoretic profiles except the sample # 3 which was sensitive to propoxur. The addition of Pb to fenitrothion bioassays indicated the involvement of CYTP450 in the recorded resistance. This result could be explained by the massive use of the permethrine in the control against these insects in southern Tunisia. We also showed that the resistance to fenitrothion was correlated with the propoxur resistance. These results indicate that modifications of the target, AChE1, can be involved in the recorded resistance.

Inheritance of Propoxur Resistance in a Near-Isogenic Line of Musca domestica (Diptera: Muscidae).

Propoxur, a carbamate insecticide, has been used worldwide for the control of house flies (Musca domestica L.) for many decades. Resistance levels to propoxur have been detected in field populations of house flies in many parts of the world, including China. In this study, a near-isogenic house fly line (N-PRR) resistant to propoxur was used to determine the mode of inheritance. Bioassay results showed no significant differences in LD50 values or in the slope of log dose-probit lines between the reciprocal F1 and F1’ progenies, and the degree of dominance (D) was more than −1 and less than 0. Chi-square analysis of the responses of self-bred (F2, F2’) and backcross progenies (BC1, BC2, BC1’, and BC2’) indicated that a single gene was responsible for resistance. Propoxur resistance in the N-PRR strain of house fly was inherited as a single, major, autosomal, and incompletely recessive factor. These results should be useful to reveal the mode of inheritance and the development trend of propoxur resistance and develop a systematic strategy for the resistance management in house flies.

Malathion and propoxur resistance in Turkish populations of the Anopheles maculipennis Meigen (Diptera: Culicidae) and relation to the insensitive acetylcholinesterase

The objective of this study was to evaluate insecticide resistance related to acetylcholinesterase (AChE) sensitivity and annual changes in An. maculipennis from six different populations. Larvae and adult samples of An. maculipennis were collected from six different localities (Birecik, Beysehir, Cankiri, Avariz, Tatarkoy, Derekoy) in Turkey. Insecticide susceptibility against malathion and propoxur was determined. AChE and insensitive AChE levels were measured individually. All Anopheles maculipennis population mortality rates were placed in the suspected resistance category for malathion and propoxur in 2007. While Thrace region populations (Avariz, Tatarkoy, Derekoy) were placed in the surveillance category in 2008, the Birecik, Beysehir, and Cankiri populations were identified in the resistance category. According to the biochemical assay, AChE inhibition rates were high in 2007 and decreased in 2008, except in Derekoy. Our results revealed that insecticide resistance against malathion and propoxur increased from 2007 to 2008. Biochemical assay results showed that the AChE insensitivity for 2 test years and insensitive AChE frequency had increased annually. Our results also showed that extensive usage of organophosphate and carbamate for pest control in agriculture is a key factor for malathion and propoxur resistance in all tested populations rather than direct usage of mosquito control.

Point mutations associated with organophosphate and carbamate resistance in Chinese strains of Culex pipiens quinquefasciatus (Diptera: Culicidae).

Acetylcholinesterase resistance has been well documented in many insects, including several mosquito species. We tested the resistance of five wild, Chinese strains of the mosquito Culex pipiens quinquefasciatus to two kinds of pesticides, dichlorvos and propoxur. An acetylcholinesterase gene (ace1) was cloned and sequenced from a pooled sample of mosquitoes from these five strains and the amino acids of five positions were found to vary (V185M, G247S, A328S, A391T, and T682A). Analysis of the correlation between mutation frequencies and resistance levels (LC50) suggests that two point mutations, G247S (r2 = 0.732, P = 0.065) and A328S (r2 = 0.891, P = 0.016), are associated with resistance to propoxur but not to dichlorvos. Although the V185M mutation was not associated with either dichlorvos or propoxur resistance, its RS genotype frequency was correlated with propoxur resistance (r2 = 0.815, P = 0.036). And the HWE test showed the A328S mutation is linked with V185M, also with G247S mutation. This suggested that these three mutations may contribute synergistically to propoxur resistance. The T682A mutation was negatively correlated with propoxur (r2 = 0.788, P = 0.045) resistance. Knowledge of these mutations may help design strategies for managing pesticide resistance in wild mosquito populations.

Bendiocarb resistance in Anopheles gambiae s.l. populations from Atacora department in Benin, West Africa: a threat for malaria vector control.

BackgroundOwing to pyrethroid resistance in An. gambiae, the carbamate and organophosphate insecticides are currently regarded as alternatives or supplements to pyrethroids for use on mosquito net treatments. Resistance monitoring is therefore essential to investigate the susceptibility of An. gambiae s.l to these alternative products.MethodsTwo to three day old adult female Anopheles mosquitoes were reared from larvae collected in the five districts (Kouandé, Natitingou, Matéri, Péhunco, Tanguiéta) of the Atacora department. Mosquitoes were then exposed to WHO impregnated papers. The four treatments consisted of: carbamates (0.1% bendiocarb, 0.1% propoxur) and organophosphates (0.25% pirimiphosmethyl, 1% fenitrothion). PCR assays were run to determine the members of the An. gambiae complex, the molecular forms (M) and (S), as well as phenotypes for insensitive acetylcholinesterase (AChE1) due to ace-1R mutation.ResultsBioassays showed bendiocarb resistance in all populations of An. gambiae s.s. tested. Propoxur resistance was observed in Matéri, Péhunco and Tanguiéta, while it was suspected in Kouandé and Natitingou. As for the organophosphates, susceptibility to pirimiphos-methyl was assessed in all populations. Fenitrothion resistance was detected in Kouandé, Péhunco and Tanguiéta, while it was suspected in Matéri and Natitingou. The S-form was predominant in tested samples (94.44%). M and S molecular forms were sympatric but no M/S hybrids were detected. The ace-1R mutation was found in both S and M molecular forms with frequency from 3.6 to 12%. Although the homozygous resistant genotype was the most prevalent genotype among survivors, the genotypes could not entirely explain the bioassay results.ConclusionEvidence of bendiocarb resistance in An. gambiae populations is a clear indication that calls for the implementation of insecticide resistance management strategies. The ace-1R mutation could not entirely explain the resistance to bendiocarb observed and is highly suggestive of involvement of other resistance mechanisms such as metabolic detoxification.

Insecticide resistance and, efficacy of space spraying and larviciding in the control of dengue vectors Aedes aegypti and Aedes albopictus in Sri Lanka

Unprecedented incidence of dengue has been recorded in Sri Lanka in recent times. Source reduction and use of insecticides in space spraying/fogging and larviciding, are the primary means of controlling the vector mosquitoes Aedes aegypti and Ae. albopictus in the island nation. A study was carried out to understand insecticide cross-resistance spectra and mechanisms of insecticide resistance of both these vectors from six administrative districts, i.e. Kandy, Kurunegala, Puttalam, Gampaha, Ratnapura and Jaffna, of Sri Lanka. Efficacy of the recommended dosages of frequently used insecticides in space spraying and larviciding in dengue vector control programmes was also tested.Insecticide bioassay results revealed that, in general, both mosquito species were highly resistant to DDT but susceptible to propoxur and malathion except Jaffna Ae. aegypti population. Moderate resistance to malathion shown by Jaffna Ae. aegypti population correlated with esterase and malathion carboxylesterase activities of the population. High levels of acetylcholinesterase (AChE) insensitivity in the absence of malathion and propoxur resistance may be due to non-synaptic forms of AChE proteins. Moderate pyrethroid resistance in the absence of high monooxygenase levels indicated the possible involvement of ‘kdr’ type resistance mechanism in Sri Lankan dengue vectors.Results of the space spraying experiments revealed that 100% mortality at a 10m distance and >50% mortality at a 50m distance can be achieved with malathion, pesguard and deltacide even in a ground with dense vegetation. Pesguard and deltacide spraying gave 100% mortality up to 50m distance in open area and areas with little vegetation. Both species gave >50% mortalities for deltacide at a distance of 75m in a dense vegetation area. Larval bioassays conducted in the laboratory showed that a 1ppm temephos solution can maintain a larval mortality rate of 100% for ten months, and the mortality rate declined to 0% in the eleventh month. In the field, where 1ppm concentration is gradually decreased with water usage, 100% mortality was observed only for the first four months, <50% mortality for the next two months, and 0% mortality was observed eight months after the application of temephos. Deltacide can be effectively used for space spraying programmes in Sri Lanka. Larval control can be successfully achieved through temephos with public participation.

Current Susceptibility Status of MalaysianCulex quinquefasciatus(Diptera: Culicidae) Against DDT, Propoxur, Malathion, and Permethrin

A nationwide investigation was carried out to determine the current susceptibility status of Culex quinquefasciatus Say populations against four active ingredients representing four major insecticide classes: DDT, propoxur, malathion, and permethrin. Across 14 study sites, both larval and adult bioassays exhibited dissimilar trends in susceptibility. A correlation between propoxur and malathion resistance and between propoxur and permethrin resistance in larval bioassays was found. The results obtained from this study provide baseline information for vector control programs conducted by local authorities. The susceptibility status of this mosquito should be monitored from time to time to ensure the effectiveness of current vector control operations in Malaysia.

Evidence of carbamate resistance in urban populations of Anopheles gambiae s.s. mosquitoes resistant to DDT and deltamethrin insecticides in Lagos, South-Western Nigeria

BackgroundResistance monitoring is essential in ensuring the success of insecticide based vector control programmes. This study was carried out to assess the susceptibility status of urban populations of Anopheles gambiae to carbamate insecticide being considered for vector control in mosquito populations previously reported to be resistant to DDT and permethrin.MethodsTwo – three day old adult female Anopheles mosquitoes reared from larval collections in 11 study sites from Local Government Areas of Lagos were exposed to test papers impregnated with DDT 4%, deltamethrin 0.05% and propoxur 0.1% insecticides. Additional tests were carried out to determine the susceptibility status of the Anopheles gambiae population to bendiocarb insecticide. Members of the A. gambiae complex, the molecular forms, were identified by PCR assays. The involvement of metabolic enzymes in carbamate resistance was assessed using Piperonyl butoxide (PBO) synergist assays. The presence of kdr-w/e and ace-1R point mutations responsible for DDT-pyrethroid and carbamate resistance mechanisms was also investigated by PCR.ResultsPropoxur resistance was found in 10 out of the 11 study sites. Resistance to three classes of insecticides was observed in five urban localities. Mortality rates in mosquitoes exposed to deltamethrin and propoxur did not show any significant difference (P > 0.05) but was significantly higher (P < 0.05) in populations exposed to DDT. All mosquitoes tested were identified as A. gambiae s.s (M form). The kdr -w point mutation at allelic frequencies between 45%-77% was identified as one of the resistant mechanisms responsible for DDT and pyrethroid resistance. Ace-1R point mutation was absent in the carbamate resistant population. However, the possible involvement of metabolic resistance was confirmed by synergistic assays conducted.ConclusionEvidence of carbamate resistance in A. gambiae populations already harbouring resistance to DDT and permethrin is a clear indication that calls for the implementation of insecticide resistance management strategies to combat the multiple resistance identified.

Insecticide resistance in the sand fly, Phlebotomus papatasi from Khartoum State, Sudan.

BackgroundPhlebotomus papatasi the vector of cutaneous leishmaniasis (CL) is the most widely spread sand fly in Sudan. No data has previously been collected on insecticide susceptibility and/or resistance of this vector, and a first study to establish a baseline data is reported here.MethodsSand flies were collected from Surogia village, (Khartoum State), Rahad Game Reserve (eastern Sudan) and White Nile area (Central Sudan) using light traps. Sand flies were reared in the Tropical Medicine Research Institute laboratory. The insecticide susceptibility status of first progeny (F1) of P. papatasi of each population was tested using WHO insecticide kits. Also, P. papatasi specimens from Surogia village and Rahad Game Reserve were assayed for activities of enzyme systems involved in insecticide resistance (acetylcholinesterase (AChE), non-specific carboxylesterases (EST), glutathione-S-transferases (GSTs) and cytochrome p450 monooxygenases (Cyt p450).ResultsPopulations of P. papatasi from White Nile and Rahad Game Reserve were sensitive to dichlorodiphenyltrichloroethane (DDT), permethrin, malathion, and propoxur. However, the P. papatasi population from Surogia village was sensitive to DDT and permethrin but highly resistant to malathion and propoxur. Furthermore, P. papatasi of Surogia village had significantly higher insecticide detoxification enzyme activity than of those of Rahad Game Reserve. The sand fly population in Surogia displayed high AChE activity and only three specimens had elevated levels for EST and GST.ConclusionsThe study provided evidence for malathion and propoxur resistance in the sand fly population of Surogia village, which probably resulted from anti-malarial control activities carried out in the area during the past 50 years.

Distribution of ace-1 R and resistance to carbamates and organophosphates in Anopheles gambiae s.s. populations from Côte d'Ivoire

BackgroundThe spread of pyrethroid resistance in Anopheles gambiae s.s. is a critical issue for malaria vector control based on the use of insecticide-treated nets. Carbamates and organophosphates insecticides are regarded as alternatives or supplements to pyrethroids used in nets treatment. It is, therefore, essential to investigate on the susceptibility of pyrethroid resistant populations of An. gambiae s.s. to these alternative products.MethodsIn September 2004, a cross sectional survey was conducted in six localities in Côte d'Ivoire: Toumbokro, Yamoussoukro, Toumodi in the Southern Guinea savannah, Tiassalé in semi-deciduous forest, then Nieky and Abidjan in evergreen forest area. An. gambiae populations from these localities were previously reported to be highly resistant to pyrethroids insecticides. Anopheline larvae were collected from the field and reared to adults. Resistance/susceptibility to carbamates (0.4% carbosulfan, 0.1% propoxur) and organophosphates (0.4% chlorpyrifos-methyl, 1% fenitrothion) was assessed using WHO bioassay test kits for adult mosquitoes. Then, PCR assays were run to determine the molecular forms (M) and (S), as well as phenotypes for insensitive acetylcholinesterase (AChE1) due to G119S mutation.ResultsBioassays showed carbamates (carbosulfan and propoxur) resistance in all tested populations of An. gambiae s.s. In addition, two out of the six tested populations (Toumodi and Tiassalé) were also resistant to organophosphates (mortality rates ranged from 29.5% to 93.3%). The M-form was predominant in tested samples (91.8%). M and S molecular forms were sympatric at two localities but no M/S hybrids were detected. The highest proportion of S-form (7.9% of An. gambiae identified) was in sample from Toumbokro, in the southern Guinea savannah. The G119S mutation was found in both M and S molecular forms with frequency from 30.9 to 35.2%.ConclusionThis study revealed a wide distribution of insensitive acetylcholinesterase due to the G119S mutation in both M and S molecular forms of the populations of An. gambiae s.s. tested. The low cross-resistance between carbamates and organophosphates highly suggests involvement of other resistance mechanisms such as metabolic detoxification or F290V mutation.

Insecticide Resistance Profiles and Synergism in Field Populations of the German Cockroach (Dictyoptera: Blattellidae) From Singapore

The resistance profiles of 22 field-collected populations of the German cockroach, Blattella germanica (L.) (Dictyoptera: Blattellidae), from various localities in Singapore were determined by topical bioassay against novel and conventional insecticides from six classes: (1) pyrethroid (beta-cyfluthrin, deltamethrin), (2) carbamate (propoxur), (3) organophosphate (chlorpyrifos), (4) phenyl pyrazole (fipronil), (5) neonicotinoid (imidacloprid), and (6) oxadiazine (indoxacarb). Compared with a laboratory susceptible strain, resistance levels ranged from 3.0 to 468.0x for the pyrethroids, from 3.9 to 21.5x for the carbamate, from 1.5 to 22.8X for the organophosphate, from 1.0 to 10.0X for phenyl pyrazole, and were absent or low for the neonicotinoid (0.8-3.8x) and the oxadiazine (1.4-5.3x). One strain demonstrated broad-spectrum resistance to most of the insecticides. Synergism studies using piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) in combination with a discriminating dose (LD99) of selected insecticides were conducted to test for possible resistance mechanisms. Resistance to pyrethroid was reduced with PBO and DEF, suggesting the involvement of P450 monooxygenase and esterases in conferring resistance. Propoxur resistance also was suppressed with PBO and DEF, and coadministration of both synergists resulted in complete negation of the resistance, indicating the involvement of both P450 monooxygenase and esterase. In six B. germanica field strains evaluated, esterases were found to play a role in chlorpyrifos resistance, whereas the P450 monoxygenase involvement was registered in three strains. Additional resistance mechanisms such as kdr-type and Rdl mutation contributing toward pyrethroid and fipronil resistance, respectively, also may be involved in some strains in which the resistance levels were not affected by the synergists. We conclude that insecticide resistance is prevalent in field German cockroach populations in Singapore.

Genetic Study of Propoxur Resistance-A Carbamate Insecticide in the Malaria Mosquito, Anopheles stephensi Liston.

Anopheles stephensi Liston (Diptera: Culicidae) is the urban vector of malaria in the Indian subcontinent and several countries of the Middle East. The genetics of propoxur resistance (pr) in An. stephensi larvae was studied to determine its mode of inheritance. A diagnostic dose of 0.01 mg/L as recommended by WHO was used to establish homozygous resistant and susceptible strains. Reciprocal crosses between the resistant and susceptible strains showed an F1 generation of incomplete dominance. The progenies of backcrosses to susceptible parents were in 1 : 1 ratio of the same phenotypes as the parents and hybrids involved. The dosage mortality (d-m) lines were constructed for each one of the crosses, and the degree of dominance was calculated. It is concluded that propoxur resistance in An. stephensi larvae is due to monofactorial inheritance with incomplete dominance and is autosomal in nature.