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PubMed1996

Existence of two acetylcholinesterases in the mosquito Culex pipiens (Diptera:Culicidae).

Two acetylcholinesterases (AChEs), AChE1 and AChE2, differing in substrate specificity and in some aspects of inhibitor sensitivity, have been characterized in the mosquito Culex pipiens. The results of ultracentrifugation in sucrose gradients and nondenaturing gel electrophoresis of AChE activity peak fractions show that each AChE is present as two molecular forms: one amphiphilic dimer possessing a glycolipid anchor and one hydrophilic dimer that does not interact with nondenaturing detergents. Treatment by phosphatidylinositol-specific phospholipase C converts each type of amphiphilic dimer into the corresponding hydrophilic dimer. Molecular forms of AChE1 have a lower electrophoretic mobility than those of AChE2. However, amphiphilic dimers and hydrophilic dimers have similar sedimentation coefficients (5.5S and 6.5S, respectively). AChE1 and AChE2 dimers, amphiphilic or hydrophilic, resist dithiothreitol reduction under conditions that allow reduction of Drosophila AChE dimers. In the insecticide-susceptible strain S-LAB, AChE1 is inhibited by 5 x 10(-4) M propoxur (a carbamate insecticide), whereas AChE2 is resistant. All animals are killed by this concentration of propoxur, indicating that only AChE1 fulfills the physiological function of neurotransmitter hydrolysis at synapses. In the insecticide-resistant strain, MSE, there is no mortality after exposure to 5 x 10(-4) M propoxur: AChE2 sensitivity to propoxur is unchanged, whereas AChE1 is now resistant to 5 x 10(-4) M propoxur. The possibility that AChE1 and AChE2 are products of tissue-specific posttranslational modifications of a single gene is discussed, but we suggest, based on recent results obtained at the molecular level in mosquitoes, that they are encoded by two different genes.

Acetylcholinesterase↗
PubMed2003

Contemporary-use pesticides in personal air samples during pregnancy and blood samples at delivery among urban minority mothers and newborns.

We have measured 29 pesticides in plasma samples collected at birth between 1998 and 2001 from 230 mother and newborn pairs enrolled in the Columbia Center for Children's Environmental Health prospective cohort study. Our prior research has shown widespread pesticide use during pregnancy among this urban minority cohort from New York City. We also measured eight pesticides in 48-hr personal air samples collected from the mothers during pregnancy. The following seven pesticides were detected in 48-83% of plasma samples (range, 1-270 pg/g): the organophosphates chlorpyrifos and diazinon, the carbamates bendiocarb and 2-isopropoxyphenol (metabolite of propoxur), and the fungicides dicloran, phthalimide (metabolite of folpet and captan), and tetrahydrophthalimide (metabolite of captan and captafol). Maternal and cord plasma levels were similar and, except for phthalimide, were highly correlated (p < 0.001). Chlorpyrifos, diazinon, and propoxur were detected in 100% of personal air samples (range, 0.7-6,010 ng/m(3)). Diazinon and propoxur levels were significantly higher in the personal air of women reporting use of an exterminator, can sprays, and/or pest bombs during pregnancy compared with women reporting no pesticide use or use of lower toxicity methods only. A significant correlation was seen between personal air level of chlorpyrifos, diazinon, and propoxur and levels of these insecticides or their metabolites in plasma samples (maternal and/or cord, p < 0.05). The fungicide ortho-phenylphenol was also detected in 100% of air samples but was not measured in plasma. The remaining 22 pesticides were detected in 0-45% of air or plasma samples. Chlorpyrifos, diazinon, propoxur, and bendiocarb levels in air and/or plasma decreased significantly between 1998 and 2001. Findings indicate that pesticide exposures are frequent but decreasing and that the pesticides are readily transferred to the developing fetus during pregnancy.

Adult↗
PubMed1992

Susceptibility status of five species of Japanese encephalitis vectors to insecticides from Kolar district, Karnataka.

Susceptibility tests were conducted on the adults of five species of mosquito vectors of Japanese encephalitis (JE) viz., Culex tritaeniorhynchus, C. vishnui, C. pseudovishnui, C. gelidus and C. fuscocephala from Kolar district, Karnataka during 1990-91 against organo chloride compounds (DDT 4%, dieldrin 4%), organo phosphate compounds (malathion 5%, fenitrothion 1.0%), carbamate (propoxur 0.1%) and pyrethroid (deltamethrin--OMS 0.025%). All the five species were found susceptible to malathion. C. tritaeniorhynchus was resistant to DDT, dieldrin and fenitrothion; C. vishnui was also susceptible to fenitrothion and propoxur; C. pseudovishnui was resistant to dieldrin but it was susceptible to fenitrothion and propoxur. C. gelidus and C. fuscocephala were susceptible to dieldrin, fenitrothion and propoxur. Deltamethrin did not exhibit a good adulticidal effect except for C. pseudovishnui and C. fuscocephala. However, verifications are required to determine the susceptibility status of C. vishnui, C. pseudovishnui, C. gelidus and C. fuscocephala against DDT, C. tritaeniorhynchus against propoxur and C. vishnui against dieldrin.

Animals↗
PubMed1993

The susceptibility of the Egyptian Phlebotomus papatasi to five insecticides.

Phlebotomus papatasi is the main vector of zoonotic cutaneous Leishmaniasis caused by L. major in nearly all the East Mediterranean Region. Generally speaking, control of any arthropod-borne disease should be directed against both the parasite and the vector. The present study was undertaken to establish a base line susceptibility levels of the Egyptian P. papatasi to five insecticides. These insecticides were: B H C and D D T (chlorinated hydrocarbon), permethrin (synthetic pyrethroides), malathion (Organophosphorus) and propoxur (carbamate). The results obtained revealed that the laboratory bred P. papatasi were more susceptible to the five insecticides than the wild caught ones. The insecticidal efficiency of the five insecticides based on LC50 was in the following descending order: propoxur, permethrin, BHC, DDT and malathion for laboratory bred flies and propoxur, permethrin, BHC, malathion then DDT for wild caught flies. The least LC50 was when using propoxur for both the wild caught flies (0.0014%) and laboratory bred ones (0.00043%). The least LT50 was when using propoxur for both the wild caught flies (4.8 seconds) and the laboratory bred flies (2.2 seconds).

Animals↗
PubMed2004

Efficacy of insecticide mixtures against larvae of Culex quinquefasciatus (Say) (Diptera: Culicidae) resistant to pyrethroids and carbamates.

The efficacy of insecticide mixtures of permethrin (pyrethroid) and propoxur (carbamate) was tested by larval bioassays on two strains of Culex quinquefasciatus (Say), one resistant to pyrethroids and the other resistant to carbamates. The method consisted in combining one insecticide at the highest concentration causing no mortality (LC0) with increasing concentrations of the second one. The concentration-mortality regression lines were determined for permethrin and propoxur alone and in combination, and synergism ratios (SR) were calculated in order to determine the magnitude of an increase or decrease in efficacy with use of the mixtures. With the pyrethroid-resistant strain (BK-PER), the results showed that propoxur at LC0 significantly enhanced the insecticidal activity of permethrin (SR50 = 1.54), especially on the upper range of the concentration-mortality regression. Conversely, when permethrin at LC0 was tested with propoxur against the carbamate resistant strain (R-LAB), an antagonistic effect was observed (SR50 = 0.67). With the BK-PER strain, an increased oxidative detoxification (MFO) appeared to be the main mechanism responsible for the synergistic interaction. Nevertheless, antagonism in the R-LAB strain is probably due to a physiological perturbation implying different target sites for pyrethroid (ie sodium channel) and carbamate insecticides [ie acetylcholinesterase (EC 3.3.3.7) and choline acetyltransferase (EC 2.3.1.6)].

Animals↗
PubMed2006

Interactions of skin thickness and physicochemical properties of test compounds in percutaneous penetration studies.

OBJECTIVES: To determine the effect of skin thickness on the percutaneous penetration and distribution of test compounds with varying physicochemical properties using in vitro systems. Studies were carried out in accordance with OECD guidelines on skin absorption tests. METHODS: Percutaneous penetration of caffeine (log P -0.01), testosterone (log P 3.32), propoxur (log P 1.52) (finite dose in ethanol to water vehicle ratio) and butoxyethanol (log P 0.83) (undiluted finite dose or as an infinite dose 50% [v/v] aqueous solution) through skin of varying thicknesses under occluded conditions was measured using flow through cells for 8-24 h. Saline (adjusted to pH 7.4) was used as receptor fluid, with BSA added for studies with testosterone and propoxur. Following exposure, the remaining surface dose was removed by swabbing and the skin digested prior to scintillation counting. RESULTS: The maximum flux of caffeine was increased with decreasing skin thickness, although these differences were found to be non-significant. The presence of caffeine in the skin membrane was not altered by skin thickness. Maximum flux and cumulative dose absorbed of testosterone and butoxyethanol (in both finite and infinite doses) were markedly reduced with full thickness (about 1 mm thick) skin compared with split thickness skin (about 0.5 mm). Maximum flux of propoxur (dissolved in 60% ethanol) was clearly higher through skin of 0.71 mm than through skin of 1.36 mm, but no difference was found between 0.56 and 0.71 mm. The proportion of propoxur present in the membrane after 24 h increased significantly over the complete range of thicknesses tested (0.56-1.36 mm). CONCLUSIONS: A complex relationship exists between skin thickness, lipophilicity and percutaneous penetration and distribution. This has implications for risk assessment studies and for the validation of models with data from different sources.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1985

Effects of insecticidal carbamates on brain acetylcholine content, acetylcholinesterase activity and behavior in mice.

Mice showed no toxic signs after a single injection of o-sec-butylphenyl methylcarbamate (BPMC, 10 mg/kg) or 2-isopropoxyphenyl-N-methylcarbamate (propoxur, 2 mg/kg). Each dose of BPMC or propoxur caused an increase in acetylcholine content and a decrease in acetylcholinesterase activity in the forebrain of mice at 10 min, followed by an almost complete recovery in the content at 60 min. Spontaneous motor activity was depressed 10 min after and recovered 60 min after, injection of BPMC or propoxur. Neither rotarod performance nor rectal temperature showed any change after injection of BPMC or propoxur. Spontaneous motor activity may therefore be a simple method for assessing small changes in the cholinergic system.

Acetylcholine↗
PubMed1999

Comparative insecticide susceptibility and detoxification enzyme activities among pestiferous blattodea.

Topical bioassays using propoxur, chlorpyrifos, and lambda-cyhalothrin were conducted on eight cockroach species. Based on lethal dose values, the relative toxicities of the insecticide classes were generally pyrethroid > carbamate > organophosphorous. Lambda-Cyhalothrin and propoxur were more toxic toward the Blattidae as compared with the Blattellidae. The order of lambda-cyhalothrin toxicity was Periplaneta americana > Periplaneta brunnea = Periplaneta australasiae = Periplaneta fuliginosa = Blatta orientalis > Blattella asahinai = Blattella germanica > Blattella vaga. The order of propoxur toxicity was B. orientalis > P. americana > P. brunnea = P. australasiae > B. asahinai > P. fuliginosa = B. germanica > B. vaga. The order of chlorpyrifos toxicity was P. americana > B. asahinai = B. vaga > B. orientalis = P. australasiae = P. brunnea > B. germanica = P. fuliginosa. Detoxification enzyme activities for each species also were measured and compared with insecticide toxicity. Propoxur LD50 was significantly (P = 0.01; r = 0.81) correlated with glutathione S-transferase activity. Lambda-Cyhalothrin LD50 correlated with methoxyresorufin O-demethylase activity (P = 0.01; r = 0.81), carboxylesterase activity (P = 0.03; r = - 0.75), general esterase activity (P = 0.02; r = - 0.79), and cockroach weight (P = 0.01; r = -0.95).

Animals↗
PubMed2000

Fiber optic monitoring of carbamate pesticides using porous glass with covalently bound chlorophenol red.

An optical fiber biosensor for the determination of the pesticides propoxur (Baygon) and carbaryl, two of the most commonly used carbamate insecticides in vegetable crops, is described. A pH indicator, chlorophenol red, is used as optical transducer of the inhibition of the enzyme acetylcholinesterase by the analytes. The biorecognition element is covalently immobilized onto controlled pore glass beads (CPG) and packed in a thermostatized bioreactor connected to a flow-through cell that contains CPG-immobilized chlorophenol red placed at the common end of a bifurcated fiber optic bundle. In the presence of a constant acetylcholine concentration, the colour of the pH sensitive layer changes and the measured reflectance signal can be related to the carbamate concentration in the sample solution. The performance of the biosensor has been optimized using a flow injection system. The linear dynamic range for the determination of carbaryl and propoxur spans from 0.8 to 3.0 mg l(-1) and from 0.03 to 0.50 mg l(-1), respectively. The detection limit (3 s) of the biosensor for propoxur (0.4 ng) is lower than that measured for carbaryl (25 ng). Reproducibility, stability and interference studies of the optical device are reported. The biosensor has been applied to the determination of propoxur in spiked vegetables (onion and lettuce) using ultrasound extraction, achieving recovery values between 93 and 95% for onion samples at the different concentration levels assayed.

Acetylcholine↗
PubMed2000

Insecticide resistance spectra and resistance mechanisms in populations of Japanese encephalitis vector mosquitoes, Culex tritaeniorhynchus and Cx. gelidus, in Sri Lanka.

Culex tritaeniorhynchus Giles and Cx. gelidus Theobald (Diptera: Culicidae), both vectors of Japanese encephalitis, were collected in 1984 and 1998 from two disease endemic localities in Sri Lanka: Anaradhapura and Kandy. Using wild-caught adult mosquitoes from light traps, log dosage-probit mortality curves for insecticide bioassays were obtained for three insecticides: malathion (organophosphate), propoxur (carbamate) and permethrin (pyrethroid). LD50 values showed that, in 1998, Cx. tritaeniorhynchus was -100-fold more resistant to malathion and 10-fold more resistant to propoxur than was Cx. gelidus. This difference was attributed to Cx. tritaeniorhynchus breeding mostly in irrigated rice paddy fields, where it would have been exposed to pesticide selection pressure, whereas Cx. gelidus breeds in other types of aquatic habitats less prone to pesticide applications. Resistance in Cx. tritaeniorhynchus increased between 1984 and 1998, whereas Cx. gelidus remained predominantly susceptible. Propoxur inhibition of acetylcholinesterase (AChE) activity (the target site of organophosphates and carbamates) indicated that in 1998, frequencies of insensitive AChE-based resistance were 9% in Cx. gelidus and 2-23% in Cx. tritaeniorhynchus, whereas in 1984 this resistance mechanism was detected only in 2% of the latter species from Anaradhapura. The AChE inhibition coefficient (ki) with propoxur was 1.86+/-0.24 x 10(5) M(-)1 min(-1) for Cx. tritaeniorhynchus from Anaradhapura in 1998. Both species were tested for activity levels of detoxifying glutathione S-transferases (GSTs) and malathion-specific as well as general carboxylesterases. High activities of GSTs and carboxylesterases were detected in Cx. tritaeniorhynchus but not Cx. gelidus. Malathion-specific carboxylesterase was absent from both species. Native polyacrylamide gel electrophoresis resolved two elevated general carboxylesterases, CtrEstbeta1 and CtrEstalpha1, from Cx. tritaeniorhynchus and none from Cx. gelidus. CtrEstbeta1 was the most intensely staining band. Gel inhibition experiments showed that both elevated esterases were inhibited by organophosphates and carbamates but not by pyrethroids. The major elevated esterase CtrEstbeta1 was partially purified (15-fold) by sequential Q-Sepharose and phenyl Sepharose column chromatography. The bimolecular rate constant (ka) and the deacylation rate constant (k3) for the malaoxon/enzyme interaction were 9.9+/-1.1 x 10(3) M(-1) min(-1) and 3.5+/-0.05 x 10(-4) M(-1) min(-1), respectively, demonstrating that the role of this enzyme in organophosphorus insecticide resistance is sequestration.

Animals↗
PubMed1990

Testing Anopheles albimanus for genetic linkage of insecticide resistance genes by combining insecticide bioassay and biochemical methods.

A microtitre-plate assay which distinguishes propoxur-resistant from susceptibles Anopheles albimanus Weidemann was used to test for linkage between the genes for propoxur- and dieldrin-resistance. The adult progeny of a backcross between a doubly-resistant colony and a fully susceptible colony were exposed in conventional test kits to the standard discriminating dose of dieldrin, and kept in the insectary overnight. Both live and dead insects were then assayed individually for propoxur-resistance. The results showed that heterozygotes for propoxur-resistance could be reliably distinguished from susceptibles whether or not they had been killed up to 24 h previously by dieldrin treatment. In this way all the backcross progeny could be scored at both resistance loci, and all four genotypic classes identified. Resistant and susceptible alleles at the two loci were inherited independently, demonstrating the absence of linkage. The usual method of testing for linkage between resistance genes is inefficient and open to bias, because insects have to be exposed to each insecticide in turn, and only half of them can be scored at both loci. The method shown here avoids these drawbacks.

Alleles↗
PubMed1999

Role of individual susceptibility in risk assessment of pesticides.

OBJECTIVES: This study presents criteria for assessing the individual pesticide burden of workers in the chemical industry. METHODS: A group of 1003 workers exposed to methylparathion or ethylparathion (alkyl phosphates), propoxur (carbamate), or cyfluthrin (pyrethroid) was investigated. After exposure to methylparathion or ethylparathion the methylparathion or ethylparathion and methylparaoxon or ethylparaoxon concentrations in plasma, the p-nitrophenol concentration in urine, and the activities of cholinesterase and acetylcholinesterase were measured. For exposure to propoxur the propoxur concentration in plasma, the 2-isopropoxyphenol concentration in urine, and the cholinesterase and acetylcholinesterase activities were measured. For exposure to cyfluthrin the cyfluthrin concentration in plasma was measured. RESULTS: At the same propoxur concentration only workers with a low individual acetylcholinesterase activity reported symptoms. Workers who metabolised cyfluthrin rapidly reported less symptoms than workers with a lower rate of metabolism. This tendency was also evident in cases of mixed exposure (cyfluthrin and methylparathion). CONCLUSIONS: In the assessment of exposure to pesticides susceptibility of the individual person has to be considered.

Acetylcholinesterase↗
PubMed1999

Insecticide cross-resistance spectra and underlying resistance mechanisms of Sri Lankan anopheline vectors of malaria.

Present status of insecticide resistance was investigated in two major vectors of malaria; An. culicifacies and An. subpictus, collected from a high malaria transmission area in Sri Lanka during 1996/1998. Adult and larval bioassays were carried out to obtain log-probit mortality lines for malathion, propoxur, permethrin and chlorpyrifos. Respective LD50 values were 4.45%, 0.002%, 0.16% and 0.001% for An. culicifacies and 0.66%, 0.004%, 0.004% and 0.04% for An. subpictus. Adults were also tested for WHO standard discriminating dosages of malathion, propoxur, permethrin, DDT, cypermethrin, deltamethlin and lambda cyhalothrin. Both populations were highly resistant to DDT. An. culicifacies was more resistant to malathion and An. subpictus was more resistant to chlorpyrifos. About 25% of both populations were resistant to permethrin. An. culicifacies was susceptible to propoxur, deltamethrin and lambda cyhalothrin and An. subpictus to cypermethrin and lambda cyhalothrin. Adult mosquitos were individually tested for their insecticide detoxifying enzyme activities and altered target-site, acetylcholinesterase. High general esterase activity indicated the presence of amplified esterase genes in both populations. Native gel electrophoresis resolved one elevated esterase isoenzyme, with high affinity to organophosphates, from each species. Malathion carboxylesterase mechanism was present in both populations. Higher glutathione-S-transferase activity was marked in An. subpictus. Synergistic studies showed the possible involvement of monooxygenases in resistance in both species. Acetylcholinesterase activity of approximately 80% of both populations was not inhibited by a standard dosage of propoxur. Low resistance to carbamates shows that the impact of agricultural pesticides is not significant in the development of resistance especially in An. culicifaies. Pyrethroids, other than permethrin, can be successfully used in vector control programs. Carbamates will be an alternative.

Acetylcholinesterase↗
PubMed2006

Selection of insensitive acetylcholinesterase as a resistance mechanism in Aedes aegypti (Diptera: Culicidae) from Santiago de Cuba.

A sample of Aedes aegypti (L.) (Diptera: Culicidae) from Santiago de Cuba, Cuba, with a high level of propoxur resistance compared with the reference susceptible Rockefeller strain (12.60 x at the 50% lethal concentration [LC50] and 18.08 at the 90% lethal concentration [LC90]), with a 4.3% frequency of insensitive acetylcholinesterase (AChE) frequency, was subjected to propoxur selection for 13 successive generations to increase the frequency of this resistance mechanism in Ae. aegypti. High resistance to propoxur was developed during this selection (41.73-fold), and the frequency of insensitive AChE mechanism was increased 13.25-fold. Other mechanisms (overproduced esterases, glutathione transferases, or monooxygenases) were not detected in the propoxur-selected strain. The selection of an insensitive AChE resistance mechanism in Ae. aegypti has important implications and will be a valuable resource for genetic studies and molecular characterization of the ace gene mutation(s) associated with insecticide resistance in Ae. aegypti.

Acetylcholinesterase↗
PubMed2006

Differential responses of eight cyanobacterial and green algal species, to carbamate insecticides.

In this study, five carbamate insecticides were subjected to 96 h acute toxicity tests to examine their effects on three cyanobacteria, Anabaena flos-aquae, Microcystis flos-aquae, and Mirocystis aeruginosa, and five green algae, Selenastrum capricornutun, Scenedesmus quadricauda, Scenedesmus obliquus, Chlorella vulgaris, and Chlorella pyrenoidosa. The average acute toxicity of the carbamate insecticides to the cyanobacteria and the green algae was in descending order carbaryl>carbofuran, propoxur, metolcarb > carbosulfan. Wide variations in response to the tested carbamate insecticides occurred among the eight individual species of cyanobacteria and green algae. The sensitivity of various species of algae exposed to carbofuran, propoxur, metolcarb, and carbaryl varied over one order of magnitude, and that of algae exposed to carbosulfan varied over two orders of magnitude. With regard to the diffrential sensitivity of cyanobacteria and green algae, the cyanobacteria were less sensitive than green algae to carbosulfan and propoxur. The pollutants may initiate a shift of algal group structure; especially, a shift from dominance by green algae to dominance by cyanobacteria, and may sustain cyanobacterial blooms at particular times. Therefore, the descending order of the ecosystem risk was carbosulfan > propoxur > carbofuran > carbaryl, metolcarb. There was a strong variance between toxicity and ecosystem risk; i.e., "low toxicity" does not imply "low ecosystem risk."

Carbamates↗
PubMed2006

Brain regional acetylcholinesterase activity and muscarinic acetylcholine receptors in rats after repeated administration of cholinesterase inhibitors and its withdrawal.

Activity of acetylcholinesterase (AChE) and specific binding of [(3)H]quinuclidinyl benzilate (QNB), [(3)H]pirenzepine (PZP) and [(3)H]AF-DX 384 to muscarinic acetylcholine receptor (mAChR) preparations in the striatum, hippocampus and cortex of rats were determined 1, 6 and 11 days after the last treatment with an organophosphate DDVP, a carbamate propoxur or a muscarinic agonist oxotremorine as a reference for 7 and 14 days. AChE activity was markedly decreased in the three regions 1 day after the treatment with DDVP for 7 and 14 days with a gradual recovery 6 to 11 days, and much less decreased 1, 6 and 11 days after the treatment with propoxur for 7 days but not for 14 days in the hippocampus and cortex. The binding of [(3)H]-QNB, PZP and AF-DX 384 in the three regions was generally decreased by the treatment with DDVP for 7 and 14 days. Such down-regulations were generally restored 6 or 11 days after the treatment for 7 but not for 14 days. The down-regulation or up-regulation as measured by [(3)H]-QNB, PZP and AF-DX 384 was observed 1, 6 or 11 days after treatment with propoxur for 7 days and/or 14 days. Repeated treatment with oxotremorine produced similar effects except AChE activity to DDVP. These results suggest that repeated inhibition of AChE activity may usually cause down-regulation of mAChRs with some exception in the hippocampus when a reversible antiChE propoxur is injected.

Acetylcholinesterase↗
PubMed1991

Effects of several insecticide formulations on oothecal drop and hatchability in German cockroaches (Dictyoptera: Blattellidae).

Formulations used for control of German cockroaches, Blattella germanica (L.), were investigated. The insecticides tested on gravid females were bendiocarb, chlorpyrifos, cyfluthrin, cypermethrin, fenvalerate, hydramethylnon, malathion, propetamphos, propoxur, and pyrethrins. Exposure to each insecticide increased the frequency of oothecal drop and reduced the percentage oothecal hatch. The percentage of oothecae that were dropped increased as a curvilinear function of insecticide concentration. An LD50 of propoxur to female German cockroaches resulted in the greatest oothecal drop (83.50%); fenvalerate caused the least drop (22.60%). LD50's of cypermethrin, propetamphos, and propoxur resulted in 29.60, 31.807, and 37.30% hatch from dropped oothecae, respectively. The smallest percentage hatch from retained oothecae was caused by LD50's of propoxur (1.5%) and cyfluthrin (7.70%). Retained oothecae from females treated with an LD50 of fenvalerate (68.70%) or pyrethrins (68.70%) had the greatest percentage hatch. Total percentage hatch (dropped and retained oothecae) declined exponentially as the insecticide concentration increased. An LD50 of cypermethrin limited total oothecal hatch to 24.50%, whereas LD50's of fenvalerate, malathion, and pyrethrins resulted in 53.60, 52.20, and 58.90% hatch, respectively. Mean time to oothecal hatch increased linearly with increasing insecticide concentration for all insecticides tested.

Animals↗
PubMedDate not supplied

[Seasonal variability in the insecticide resistance and irritability of Anopheles superpictus].

The resistance and irritability to malathion, fenitrothion, propoxur and DDT (WHO insecticide impregnated papers) in Anopheles superpictus from Dangara District were determined three times in season. Complete susceptibility to malathion, fenitrothion and DDT and low resistance to propoxur probably based on knockdown mechanism were noticed. DDT and malathion irritability levels were high, and those for fenitrothion and propoxur were lower. During the season irritability to malathion and fenitrothion (organophosphorous compounds) was slightly decreasing, and in contrast was increasing to propoxur (carbamate). Irritability to DDT (organochloride) considerably fell down in August and achieved the initial level in September again. None of the tested insecticides can be recommended for residual spraying in Dangara District because of high irritability levels in mosquitos or danger of its rapid increase after onset of spraying.

Animals↗