Determination of the resistance to organophosphate, carbamate, and pyrethroid insecticides in Panamanian Anopheles albimanus (Diptera: Culicidae) mosquitoes

Introduction. The susceptibility of Anopheles albimanus to organophosphates, carbamates and pyrethroid insecticides was unknown in the Panama communities of Aguas Claras, Pintupo and Puente Bayano, located in the Amerindian Reservation of Madungandi. This region is considered a malaria transmission area, where An. albimanus is the main vector. Objective. The resistance to organophosphate insecticides, carbamates and pyrethroids was evaluated in field populations of the Anopheles albimanus in Panama. Materials and methods. Progeny of An. albimanus collected in three localities in the indigenous Madugandi region were exposed to bioassays of susceptibility to organophosphate insecticides (fenitrothion, malathion and chlorpyrifos), the carbamate (propoxur) and pyrethroids (deltamethrin, lambdacyhalothrin, cyfluthrin and cypermethrin). The protocols were in accordance with those established for adult mosquitoes by World Health Organization. Results. The three strains of the An. albimanus were resistant to the pyrethroid insecticides deltamethrin, lambdacyhalothrin, cyfluthrin and cypermethrin. Susceptibility remained for the organophosphate insecticides fenitrothion, malathion, chlorpyrifos, and the carbamate insecticide propoxur. Conclusion. The results provided important information to the vector control program, contributing to the application of new strategies on the use of insecticides, and thereby lengthening the life of the insecticide in use.     

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.     

Toxicity of several insecticide formulations against adult German cockroaches (Dictyoptera: Blattellidae)

Toxicity of bendiocarb, chlorpyrifos, cyfluthrin, cypermethrin, fenvalerate, hydramethylnon, malathion, propetamphos, propoxur, and pyrethrins against the adult German cockroaches, Blattella germanica (L.), was investigated. At LD50, cyfluthrin was the most toxic insecticide to adult males (0.53 microgram/g), adult females (1.2 micrograms/g), and gravid females (0.85 microgram/g). Malathion was the least toxic insecticide to adult males (464.83 micrograms/g), adult females (335.83 micrograms/g), and gravid females (275.90 micrograms/g). Males and gravid females were generally more sensitive than nongravid females to the insecticides that we tested. In tests with malathion, however, males were more tolerant. The order of toxicity of the insecticide classes varied among the stages of adult German cockroaches. The order of toxicity for males and nongravid females was pyrethroids greater than pyrethrins = organophosphates (except malathion) greater than carbamates = amidinohydrazone. The order of toxicity for gravid females was pyrethroids greater than pyrethrins = organophosphates (except malathion) greater than carbamates greater than amidinohydrazone. These differences in toxicity suggest that sex differences should be considered when determining insecticide toxicity for German cockroaches.     

Mechanisms of organophosphate resistance in a field population of oriental migratory locust, Locusta migratoria manilensis (Meyen)

The susceptibilities to three organophosphate (OP) insecticides (malathion, chlorpyrifos, and phoxim), responses to three metabolic synergists [triphenyl phosphate (TPP), piperonyl butoxide (PBO), and diethyl maleate (DEM)], activities of major detoxification enzymes [general esterases (ESTs), glutathione S-transferases (GSTs), and cytochrome P450 monooxygenases (P450s)], and sensitivity of the target enzyme acetylcholinesterase (AChE) were compared between a laboratory-susceptible strain (LS) and a field-resistant population (FR) of the oriental migratory locust, Locusta migratoria manilensis (Meyen). The FR was significantly resistant to malathion (57.5-fold), but marginally resistant to chlorpyrifos (5.4) and phoxim (2.9). The malathion resistance of the FR was significantly diminished by TPP (synergism ratio: 16.2) and DEM (3.3), but was unchanged by PBO. In contrast, none of these synergists significantly affected the toxicity of malathion in the LS. Biochemical studies indicated that EST and GST activities in the FR were 2.1- to 3.2-fold and 1.2- to 2.0-fold, respectively, higher than those in the LS, but there was no significant difference in P450 activity between the LS and FR. Furthermore, AChE from the FR showed 4.0-fold higher activity but was 3.2-, 2.2-, and 1.1-fold less sensitive to inhibition by malaoxon, chlorpyrifos-oxon, and phoxim, respectively, than that from the LS. All these results clearly indicated that the observed malathion resistance in the FR was conferred by multiple mechanisms, including increased detoxification by ESTs and GSTs, and increased activity and reduced sensitivity of AChE to OP inhibition.     

Evaluation of insecticide resistance and biochemical mechanisms in a population of Culex quinquefasciatus (Diptera: Culicidae) from São Paulo, Brazil

To establish an insecticidal resistance surveillance program, Culex quinquefasciatus mosquitoes from S?o Paulo, Brazil, were colonized (PIN95 strain) and analyzed for levels of resistance. The PIN95 strain showed low levels of resistance to organophosphates [malathion (3.3-fold), fenitrothion (11.2-fold)] and a carbamate [propoxur (3.0-fold)]. We also observed an increase of 7.4 and 9.9 in alpha and beta esterase activities, respectively, when compared with the reference IAL strain. An alteration in the sensitivity of acetylcholinesterase to insecticide inhibition was also found in the PIN95 mosquitoes. The resistant allele (Ace.1R), however, was found at low frequencies (0.12) and does not play an important role in the described insecticide resistance. One year later, Cx. quinquefasciatus mosquitoes were collected (PIN96 strain) at the same site and compared to the PIN95 strain. The esterase activity patterns observed for the PIN96 strain were similar to those of the PIN95 mosquitoes. However the occurrence of the Ace.1R allele was statistically higher in the PIN96 strain. The results show that esterase-based insecticide resistance was established in the PIN95 Cx. quinquefasciatus population and that an acethylcholinesterase based resistant mechanism has been selected for. A continuous monitoring of this phenomenon is fundamental for rational mosquito control and insecticide application programs.     

河北转Bt基因棉田棉铃虫对杀虫剂的抗性及相关酶活性的变化

为明确河北省推广种植植转Bt基因抗虫棉（简称Bt棉）后, 棉铃虫Helicoverpa armigera (Hübner)对常用杀虫剂的抗药性水平及其生化机理, 2011-2012年采用点滴法对保定南郊、 沧州南皮、 邢台巨鹿3个地区的田间种群以及敏感种群进行了室内毒力测定, 并采用生化分析法对4个种群相关的羧酸酯酶（carboxylesterase, CarE）、 谷胱甘肽S 转移酶(glutathione S-transferases, GSTs)和乙酰胆碱酯酶(acetylcholinesterase, AChE)的活性进行了研究。结果表明: 3个田间种群对高效氯氰菊酯和氰戊菊酯处于中至高抗水平, 抗性倍数为20.02~73.70倍; 对灭多威处于低至中抗水平, 抗性倍数为6.27~11.84倍; 对高效氯氟氰菊酯(抗性倍数: 1.07~4.20倍), 辛硫磷、 毒死蜱和马拉硫磷(抗性倍数: 1.00~2.69倍), 以及氯虫苯甲酰胺（抗性倍数: 2.00~3.67倍）均处于敏感水平。3个田间种群的CarE, GSTs和AChE活性分别是敏感种群的1.06~1.23, 1.20~1.63和1.15~1.23倍, 这可能与其对高效氯氰菊酯、 氰戊菊酯和灭多威产生的抗性有关。     

Inhibition of AChE by single and simultaneous exposure to malathion and its degradation products

In vitro inhibition of bovine erythrocytes acetylcholinesterase (AchE) by separate and simultaneous exposure to organophosphorous insecticide malathion and the transformation products, which are generally formed during the storage or natural as well as photochemical degradation pathways of malathion, was investigated. The increasing concentration of malathion, its oxidation product - malaoxon and isomerisation product - isomalathion inhibited AChE activity in a concentration-dependent manner. The half-maximum inhibitory concentrations (IC(50) values): (3.2 +/- 0.1) x 10(-5) mol/l, (4.7 +/- 0.8) x 10(-7) mol/l and (6.0 +/- 0.5) x 10(-7)mol/l were obtained from the inhibition curves induced by malathion, malaoxon and isomalathion, respectively. However, the products formed due to photoinduced degradation, phosphorodithioic O,O,S-trimethyl phosphorodithioic ester (OOS(S)) and O,O-dimethyl thiophosphate did not noticeably affect the enzyme activity at all investigated concentrations, while diethyl maleate inhibited the AChE activity at concentrations >10 mmol/l. By simultaneous exposure of the enzyme to malaoxon and isomalathion in various concentration combinations the additive effect was achieved by low concentration of inhibitors, while the antagonistic effect was obtained at high concentration (>or= 3 x 10(-7) mol/l) of inhibitors. Inhibitory power of irradiated samples of 1 +/- 10(-5) mol/l malathion can be attributed to the formation of malaoxon and isomalathion, organophosphates about 100 times more toxic than their parent compound, while the presence of non-inhibiting degradation product OOS(S) did not affect the inhibitor efficiency of inhibiting malathion by-products, malaoxon and isomalathion.     

Insecticide susceptibility status in two medically important mosquito vectors,Anopheles gambiae,and Culex quinquefasciatus to three insecticides commonly used in Niger State,Nigeria

High resistance ability on insecticides among major mosquito vectors of diseases in Nigeria is of growing concern for severe control strategies. The objective of this study was to assess the susceptibility status of females Anopheles gambiae and Culex quinquefasciatus complexes mosquitoes to permethrin (21.5 μg/bottle-pyrethroids), propoxur(12.5 μg/bottle-carbamate) and malathion (50 μg/bottle organophosphate), in Niger State, North-Central, Nigeria. Anopheline and Culecine larvae were collected from the larval habitats of the studied sites (Bosso, Katcha, Lapai, and Shiroro) larvae and pupae were identified guided by standard keys and reared to adults in troughs. Insecticide susceptibility bioassays were performed according to the CDC bottle bioassay standard operating procedures on 3 days old, sugar-fed female Anopheles and Culex mosquitoes. Post-exposure mortality after 24hr and knockdown values for KDT₅₀ were calculated. Knock-down at 1-hour insecticide exposure ranged (84–96 %) permethrin, (94–100 %) propoxur and (100 %) malathion for An. gambiae and (86–97 %) permethrin, (92–100 %) propoxur and (96–100 %) malathion for Cx. quinquefasciatus. Mortality, after 24hr post-exposure was 100 % in malathion, indicating the high effect of the insecticide. Tested samples were found potentially resistant to permethrin recorded against mosquitoes collected from all study sites, in two locations of the study sites to propoxur and one location site to malathion. All the tested mosquitoes were found to be potentially resistant to permethrin, however, mosquitoes tested in Katcha and Shiroro resist potentially to propoxur. Except, Culex quinqufasciatus from Lapai that partially resist malathion, all the tested mosquitoes were found to be susceptible to malathion, across the study sites.     

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.     

Comparisons of malathion susceptibility, target sensitivity, and detoxification enzyme activity in nine field populations of Oxya chinensis (Orthoptera: Acrididae)

The malathion susceptibility, acetylcholinesterase (AChE) sensitivity, and the activity of selected detoxification enzymes including general esterase (EST) and glutathione S-transferase (GST) were compared among field populations of the grasshopper Oxya chinensis (Thunberg) (Orthoptera: Acrididae) collected from nine regions of China. Bioassay results showed that these populations had various levels of the susceptibility to malathion with the LDo values ranging from 1.4- to 22.6-fold compared with the most susceptible population (Xiangyuan or XY). The Jinnan (JN) population seemed to be malathion resistant (22.6-fold), whereas other populations exhibited 1.4- to 6.8-fold reduced malathion susceptibility with a rank order of Changan > Baodi > Hanzhong > Xinxiang > Yinchuan > Beidagang > Jinyuan. It seemed that the observed malathion resistance in the JN population was attributed to at least two resistance mechanisms, including increased EST activity (2.2-fold) and reduced sensitivity of AChE to inhibition by malaoxon (4.6-fold) compared with those of the XY population. In contrast, differential malathion susceptibilities in other populations may be due to increased activities of certain detoxification enzymes (e.g., EST and GST), reduced sensitivity of AChE, or other factors, which were not consistent across the populations examined. Such differential susceptibilities to malathion were likely due to different population habitats (e.g., grasslands, rice [Oryza sativa L.]-producing regions) with very different insecticide application histories and pest management practices.     

Inhibition of AChE by malathion and some structurally similar compounds

Inhibition of bovine erythrocyte acetylcholinesterase (free and immobilized on controlled pore glass) by separate and simultaneous exposure to malathion and malathion transformation products which are generally formed during storage or through natural or photochemical degradation was investigated. Increasing concentrations of malathion, its oxidation product malaoxon, and its isomerisation product isomalathion inhibited free and immobilized AChE in a concentration-dependent manner. KI, the dissociation constant for the initial reversible enzyme inhibitor-complex, and k3, the first order rate constant for the conversion of the reversible complex into the irreversibly inhibited enzyme, were determined from the progressive development of inhibition produced by reaction of native AChE with malathion, malaoxon and isomalathion. KI values of 1.3 x 10(-4) M(-1), 5.6 x 10(-6) M(-1) and 7.2 x 10(-6)M(-1) were obtained for malathion, malaoxon and isomalathion, respectively. The IC50 values for free/immobilized AChE, (3.7 +/- 0.2) x 10(-4) M/(1.6 +/-0.1) x 10(-4), (2.4 +/- 0.3) x 10(-6)/(3.4 +/- 0.1) x 10(-6)M and (3.2 +/- 0.3) x 10(-6) M/(2.7 +/- 0.2) x 10(-6) M, were obtained from the inhibition curves induced by malathion, malaoxon and isomalathion, respectively. However, the products formed due to photoinduced degradation, phosphorodithioic O,O,S-trimethyl ester and O,O-dimethyl thiophosphate, did not noticeably affect enzymatic activity, while diethyl maleate inhibited AChE activity at concentrations > 10mM. Inhibition of acetylcholinesterase increased with the time of exposure to malathion and its inhibiting by-products within the interval from 0 to 5 minutes. Through simultaneous exposure of the enzyme to malaoxon and isomalathion, an additive effect was achieved for lower concentrations of the inhibitors (in the presence of malaoxon/isomalathion at concentrations 2 x 10(-7) M/2 x 10(-7) M, 2 x 10(-7) M/3 x 10(-7)M and 2 x 10(-7) M/4.5 x 109-7) M), while an antagonistic effect was obtained for all higher concentrations of inhibitors. The presence of a non-inhibitory degradation product (phosphorodithioic O,O,S-trimethyl ester) did not affect the inhibition efficiencies of the malathion by-products, malaoxon and isomalathion.     

Changes in malathion and pyrethroid resistance after cypermethrin selection of Culex quinquefasciatus field populations of Cuba

Abstract. 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.     

Comparison of chlorpyrifos resistance in Culex pipiens pipiens (Diptera: Culicidae) collected from Northern and Southern Tunisia

In this study, we investigated resistance to the organophosphates chlorpyrifos in Tunisian populations of Culex pipiens pipiens. Three field populations were collected from Northern and central Tunisia between 2003 and 2005 and used for the bioassays tests. Our results registered moderate and high levels of resistance to chlorpyrifos which ranged from 33.8 to 111. The chlorpyrifos resistant populations were highly resistant to propoxur indicated an insensitive acetylcholinesterase 1 (AChE 1). The highest frequency of AChE 1 resistant phenotypes (64%) was recorded in the most resistant population (sample # 1). Bioassays conducted in the presence of synergists showed that not esterases were involved as the resistance mechanism to chlorpyrifos. However, CYP450 was partly involved in the resistance of the most resistant sample (# 1). Starch electrophoresis showed that three esterases were present in studied samples: A2‐B2, A4‐B4 and B12. Results are discussed in relation to the selection pressure caused by insecticide treatments.     

The acetylcholinesterase gene and organophosphorus resistance in the Australian sheep blowfly, Lucilia cuprina

Acetylcholinesterase (AChE), encoded by the Ace gene, is the primary target of organophosphorous (OP) and carbamate insecticides. Ace mutations have been identified in OP resistants strains of Drosophila melanogaster. However, in the Australian sheep blowfly, Lucilia cuprina, resistance in field and laboratory generated strains is determined by point mutations in the Rop-1 gene, which encodes a carboxylesterase, E3. To investigate the apparent bias for the Rop-1/E3 mechanism in the evolution of OP resistance in L. cuprina, we have cloned the Ace gene from this species and characterized its product. Southern hybridization indicates the existence of a single Ace gene in L. cuprina. The amino acid sequence of L. cuprina AChE shares 85.3% identity with D. melanogaster and 92.4% with Musca domestica AChE. Five point mutations in Ace associated with reduced sensitivity to OP insecticides have been previously detected in resistant strains of D. melanogaster. These residues are identical in susceptible strains of D. melanogaster and L. cuprina, although different codons are used. Each of the amino acid substitutions that confer OP resistance in D. melanogaster could also occur in L. cuprina by a single non-synonymous substitution. These data suggest that the resistance mechanism used in L. cuprina is determined by factors other than codon bias. The same point mutations, singly and in combination, were introduced into the Ace gene of L. cuprina by site-directed mutagenesis and the resulting AChE enzymes expressed using a baculovirus system to characterise their kinetic properties and interactions with OP insecticides. The K(m) of wild type AChE for acetylthiocholine (ASCh) is 23.13 microM and the point mutations change the affinity to the substrate. The turnover number of Lucilia AChE for ASCh was estimated to be 1.27x10(3) min(-1), similar to Drosophila or housefly AChE. The single amino acid replacements reduce the affinities of the AChE for OPs and give up to 8.7-fold OP insensitivity, while combined mutations give up to 35-fold insensitivity. However, other published studies indicate these same mutations yield higher levels of OP insensitivity in D. melanogaster and A. aegypti. The inhibition data indicate that the wild type form of AChE of L. cuprina is 12.4-fold less sensitive to OP inhibition than the susceptible form of E3, suggesting that the carboxylesterases may have a role in the protection of AChE via a sequestration mechanism. This provides a possible explanation for the bias towards the evolution of resistance via the Rop-1/E3 mechanism in L. cuprina.     

Current Perspectives on Plague Vector Control in Madagascar: Susceptibility Status of Xenopsylla cheopis to 12 Insecticides

Plague is a rodent disease transmissible to humans by infected flea bites, and Madagascar is one of the countries with the highest plague incidence in the world. This study reports the susceptibility of the main plague vector Xenopsylla cheopis to 12 different insecticides belonging to 4 insecticide families (carbamates, organophosphates, pyrethroids and organochlorines). Eight populations from different geographical regions of Madagascar previously resistant to deltamethrin were tested with a World Health Organization standard bioassay. Insecticide susceptibility varied amongst populations, but all of them were resistant to six insecticides belonging to pyrethroid and carbamate insecticides (alphacypermethrin, lambdacyhalothrin, etofenprox, deltamethrin, bendiocarb and propoxur). Only one insecticide (dieldrin) was an efficient pulicide for all flea populations. Cross resistances were suspected. This study proposes at least three alternative insecticides (malathion, fenitrothion and cyfluthrin) to replace deltamethrin during plague epidemic responses, but the most efficient insecticide may be different for each population studied. We highlight the importance of continuous insecticide susceptibility surveillance in the areas of high plague risk in Madagascar.     

Temporal and spatial incidence of alleles conferring knockdown resistance to pyrethroids in the peach-potato aphid, Myzus persicae (Hemiptera: Aphididae), and their association with other insecticide resistance mechanisms

The peach-potato aphid, Myzus persicae (sulzer), is an important arable pest species throughout the world. Extensive use of insecticides has led to the selection of resistance to most chemical classes including organochlorines, organophosphates, carbamates and pyrethroids. Resistance to pyrethroids is often the result of mutations in the para-type sodium channel protein (knockdown resistance or kdr). In M. persicae, knockdown resistance is associated with two amino-acid substitutions, L1014F (kdr) and M918T (super-kdr). In this study, the temporal and spatial distributions of these mutations, diagnosed using an allelic discriminating polymerase chain reaction assay, were investigated alongside other resistance mechanisms (modified acetylcholinesterase (MACE) and elevated carboxylesterases). Samples were collected from the UK, mainland Europe, Zimbabwe and south-eastern Australia. The kdr mutation and elevated carboxylesterases were widely distributed and recorded from nearly every country. MACE and super-kdr were widespread in Europe but absent from Australian samples. The detection of a strongly significant heterozygote excess for both kdr and super-kdr throughout implies strong selection against individuals homozygous for these resistance mutations. The pattern of distribution found in the UK seemed to indicate strong selection against the super-kdr (but not the kdr) mutation in any genotype, in the absence of insecticide pressure. There was a significant association (linkage disequilibrium) between different resistance mechanisms, which was probably promoted by a lack of recombination due to parthenogenesis.     

Acetylcholinesterase target sites for developing environmentally friendly insecticides against Tetranychus urticae (Acari: Tetranychidae)

Experimental and Applied Acarology - The non-target toxicity and resistance problems of acetylcholinesterase (AChE) insecticides, such as organophosphates and carbamates, are of growing concern. To...     

Epidemio-entomological survey of Japanese encephalitis in Korea.

In order to determine the seasonal prevalence and population dynamics of Culex tritaeniorhynchus in relation to the epidemics of Japanese encephalitis, and ecology of these vector mosquito in Kyungpook Province, Korea, studies were conducted during the period of 7 years from 1984 to 1990. Cx. tritaeniorhynchus first collected in June between 4th and 28th, and trapped in large numbers during the period from mid-August to early September, showed a simple sharply pointed one-peaked curve. There was a gradual decrease from mid-September, with a very small number of them collected until early October in every year. The average number of Cx. tritaeniorhynchus rapidly decreased after 1985, and the number became particularly low in 1989. The highest population density, which was observed in August during the initial three years, was found to be delayed in the following years, accompanied by a decrease in the number of mosquitoes. In the trend of nocturnal activity of Cx. tritaeniorhynchus, with oncoming darkness they become very active, gradually decreasing in activity toward mid night, but slightly increasing toward dawn. The immature stages of Cx. tritaeniorhynchus were first found in rice fields contributing to peak adult densities in mid-July. The highest average densities of Cx. tritaeniorhynchus was 14,900 per m2 on mid-August 19th. The larval Cx. tritaeniorhynchus showed high resistance levels and resistance ratios against 5 organophosphorus compounds. In the adult horizontal life table characteristics of Kyungsan colonies of Cx. tritaeniorhynchus under insectary conditions, life expectancy was 28.3 days for males and 59.8 days for females. The net reproductive rate was 7.8 and generation time was 25.6 days.