Substrate Report for: lambda-Cyhalothrin

Pyrethroids are the third widespread used insecticides globally which have been extensively applied in agricultural or household environments. Due to continuous applications, pyrethroids have been detected both in living cells and environments. The permanent exposure to pyrethroids have caused substantial health risks and ecosystem concerns. In this work, a lambda-cyhalothrin (one kind of pyrethroid insecticides) degrading bacterium Bacillus velezensis sd was isolated and a carboxylesterase gene, CarCB2 was characterized. A whole cell biocatalyst was developed for lambda-cyhalothrin biodegradation by displaying CarCB2 on the surface of Escherichia coli cells. CarCB2 was successfully displayed and functionally expressed on E. coli cells with optimal pH and temperature of 7.5 and 30 degreesC, using p-NPC(4) as substrate, respectively. The whole cell biocatalyst exhibited better stability than the purified CarCB2, and approximately 120%, 60% or 50% of its original activity at 4 degreesC, 30 degreesC or 37 degreesC over a period of 35 d was retained, respectively. No enzymatic activity was detected when incubated the purified CarCB2 at 30 degreesC for 120 h, or 37 degreesC for 72 h, respectively. Additionally, 30 mg/L of lambda-cyhalothrin was degraded in citrate-phosphate buffer by 10 U of the whole cell biocatalyst in 150 min. This work reveals that the whole cell biocatalyst affords a promising approach for efficient biodegradation of lambda-cyhalothrin, and might have the potential to be applied in further environmental bioremediation of other different kinds of pyrethroid insecticides.

Role of immobilization stress (IMS), a psychological stressor and forced swim stress (FSS), a physical stressor was investigated on the neurobehavioral toxicity of lambda-cyhalothrin (LCT), a new generation type-II synthetic pyrethroid. Pre-exposure of rats to IMS (15 min/day) or FSS (3 min/day) for 28 days on LCT (3.0 mg/kg body weight, p.o.) treatment for 3 days resulted to decrease spatial learning and memory and muscle strength associated with cholinergic-muscarinic receptors in frontal cortex and hippocampus as compared to those exposed to IMS or FSS or LCT alone. Decrease in acetylcholinesterase activity, protein expression of ChAT and PKC-beta1 associated with decreased mRNA expression of CHRM2, AChE and ChAT in frontal cortex and hippocampus was also evident in rats pre-exposed to IMS or FSS on LCT treatment, compared to rats exposed to IMS or FSS or LCT alone. Interestingly, changes both in behavioral and neurochemical endpoints were marginal in rats subjected to IMS or FSS for 28 days or those exposed to LCT for 3 days alone, compared to controls. The results suggest that stress is an important contributor in LCT induced cholinergic deficits.

This study is focused on understanding the mechanism of neurobehavioral toxicity of lambda-cyhalothrin a new generation type II synthetic pyrethroid in developing rats following their exposure from post-lactational day PLD)22 to PLD49 and investigate whether neurobehavioral alterations are transient or persistent Post-lactational exposure to lambda-cyhalothrin 1.0 or 3.0 mg/kg body weight p.o affected grip strength and learning activity in rats on PLD50 and the persistent impairment of grip strength and learning was observed at 15 days after withdrawal of exposure on PLD65 A decrease in the binding of muscarinic-cholinergic receptors in frontocortical hippocampal and cerebellar membranes associated with decreased expression of choline acetyltransferase ChAT and acetylcholinesterase AChE in hippocampus was observed following exposure to lambda-cyhalothrin on PLD50 and PLD65 Exposure to lambda-cyhalothrin was also found to increase the expression of growth-associated protein-43 in hippocampus of rats on PLD50 and PLD65 as compared to controls A significant increase in lipid peroxidation and protein carbonyl levels and decreased levels of reduced glutathione and activity of superoxide dismutase catalase and glutathione peroxidase in brain regions of lambda-cyhalothrin exposed rats were distinctly observed indicating increased oxidative stress Inhibition of ChAT and AChE activity may cause down-regulation of muscarinic-cholinergic receptors consequently impairing learning activity in developing rats exposed to lambda-cyhalothrin The data further indicate that long-term exposure to lambda-cyhalothrin at low doses may be detrimental and changes in selected behavioral and neurochemical end points may persist if exposure to lambda-cyhalothrin continues.

The pervasive use of pyrethroids is seriously hazardous to the environment and even human health. Enzymatic bioremediation is potentially a rapid and environmentally friendly technology to combat the pollution of pyrethroid pesticides. The hydrolysis of ester linkages is the initial and critical enzymatic step in microbial degradation pathways. Here, the versatile and thermostable esterase Est816 was cloned and its new function, pyrethroid-hydrolysis activity, was expanded. To further improve its pyrethroid-hydrolysis ability, Est816 was modified by rational design. After two rounds of mutation, the best-performing mutant, Est816(A216V/K238N/M97V,) was obtained, which could completely degrade 1 mg/L lambda-cyhalothrin, cypermethrin, and deltamethrin within 20 min, and efficiently degrade fenvalerate, reaching over 80% conversion. Degradation activity analyses showed that three substitutions (A216V, K238 N and M97V) were beneficial for enhancing the activity of Est816. Enzymatic characterization showed that Est816(A216V/K238N/M97V) inherited broad substrate specificity and possessed excellent stability and adaptability over wide ranges of temperature and pH, which is essential for bioremediation in frequently changing conditions. Furthermore, Est816(A216V/K238N/M97V) had the best degradation effect on all four pyrethroid residues in Panax notoginseng root, with more than 87% conversion after 24 h. Pyrethroid residues in tea, cucumber, and soil were reduced by more than 76%, 80%, and 76%, respectively. Taken together, these findings highlight the great potential of Est816(A216V/K238N/M97V) in the bioremediation of pyrethroid-contaminated soil and agricultural products.

The long-term and excessive use of pyrethroid pesticides poses substantial health risks and ecosystem concerns. Several bacteria and fungi have been reported that could degrade pyrethroids. The ester-bond hydrolysis using hydrolases is the initial regulatory metabolic reaction of pyrethroids. However, the thoroughly biochemical characterization of hydrolases involved in this process is limited. Here, a novel carboxylesterase, designated as EstGS1 that could hydrolyze pyrethroid pesticides was characterized. EstGS1 showed low sequence identity (<27.03%) compared to other reported pyrethroid hydrolases and belonged to the hydroxynitrile lyase family that preferred short short-chain acyl esters (C2 to C8). EstGS1 displayed the maximal activity of 213.38 U/mg at 60 degreesC and pH 8.5 using pNPC2 as substrate, with K(m) and V(max) were 2.21 +/- 0.72 mM and 212.90 +/- 41.78 microM/min, respectively. EstGS1 is a halotolerant esterase and remains stable in 5.1 M NaCl. Based on molecular docking and mutational analysis, the catalytic triad of S(74)-D(181)-H(212) and three other substrate-binding residues I(108), S(159), and G(75) are critical for the enzymatic activity of EstGS1. Additionally, 61 and 40 mg/L of deltamethrin and lambda-cyhalothrin were hydrolyzed by 20 U of EstGS1 in 4 h. This work presents the first report on a pyrethroid pesticide hydrolase characterized from a halophilic actinobacteria.

Pyrethroids are the third widespread used insecticides globally which have been extensively applied in agricultural or household environments. Due to continuous applications, pyrethroids have been detected both in living cells and environments. The permanent exposure to pyrethroids have caused substantial health risks and ecosystem concerns. In this work, a lambda-cyhalothrin (one kind of pyrethroid insecticides) degrading bacterium Bacillus velezensis sd was isolated and a carboxylesterase gene, CarCB2 was characterized. A whole cell biocatalyst was developed for lambda-cyhalothrin biodegradation by displaying CarCB2 on the surface of Escherichia coli cells. CarCB2 was successfully displayed and functionally expressed on E. coli cells with optimal pH and temperature of 7.5 and 30 degreesC, using p-NPC(4) as substrate, respectively. The whole cell biocatalyst exhibited better stability than the purified CarCB2, and approximately 120%, 60% or 50% of its original activity at 4 degreesC, 30 degreesC or 37 degreesC over a period of 35 d was retained, respectively. No enzymatic activity was detected when incubated the purified CarCB2 at 30 degreesC for 120 h, or 37 degreesC for 72 h, respectively. Additionally, 30 mg/L of lambda-cyhalothrin was degraded in citrate-phosphate buffer by 10 U of the whole cell biocatalyst in 150 min. This work reveals that the whole cell biocatalyst affords a promising approach for efficient biodegradation of lambda-cyhalothrin, and might have the potential to be applied in further environmental bioremediation of other different kinds of pyrethroid insecticides.

Fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is the main destructive insect pest of grain crops that occurs in all maize growing regions of the Americas. It has rapidly invaded the Southern China since January 2019. However, the current status of insecticide resistance in S. frugiperda has not been reported in China. In this study, we determined the susceptibility of eight populations of FAW to eight insecticides by an artificial diet incorporation method. The results showed that among eight insecticides, emamectin benzoate, spinetoram, chlorantraniliprole, chlorfenapyr, and lufenuron showed higher toxicity to this pest, while lambda-cyhalothrin and azadirachtin exhibited lower toxicity. Susceptibility of S. frugiperda to indoxacarb was significantly different (10.0-fold for LC(50)) across the various geographic populations. To investigate the biochemical mechanism of FAW to lambda-cyhalothrin, we performed the synergism tests and the results showed that piperonyl butoxide (PBO) and triphenyl phosphate (TPP) produced a high synergism of lambda-cyhalothrin effects in the two field populations. Sequencing of the gene encoding the acetylcholinesterase (AChE) gene in the two field populations identified two amino acid mutations, all of which have been shown previously to confer resistance to organophosphates (OPs) in several arthropod species. The results of this study provided valuable information for choosing alternative insecticides and for insecticide resistance management of S. frugiperda.

Effects of the pyrethroid lambda-cyhalothrin (LCH) were investigated in matrinxa Brycon amazonicus, a non-target freshwater teleost. The fish were submitted to a single-pulse exposure (10% of LC50; 96 h, 0.65 mug L(-1)), followed by 7 days of recovery in clean water. Hematologic parameters indicated impairments in oxygen transport, which were not recovered. Plasma [Na(+)], [Cl(-)], and protein were diminished, and only [Na(+)] remained low after recovery. Gill Na(+)/K(+)ATPase activity was increased and recovered to basal values. Brain acetylcholinesterase activity was not responsive to LCH. Liver ascorbic acid concentration was not altered, and reduced glutathione levels remained augmented even after recovery. LCH inhibited hepatic superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activities, while glutathione-S-transferase (GST) and glucose-6-phosphate dehydrogenase (G6PDH) activities were steady. After recovery, SOD remained low, and GPx was augmented. Liver depicted lipid peroxidation, which was not observed after recovery. Hepatic morphology was affected by LCH and was not completely recovered. These responses, combined with the persistence of changes even after recovery span, clearly show the feasibility of these biomarkers in evaluating LCH toxic potential to non-target organisms, highlighting the importance of pyrethroids' responsible use.

Need for ecotoxicological information on local species has been recently highlighted as a priority issue in Latin America. In addition, little information has been found on concentration distances between lethal and sublethal effects, and the effect of mixtures at these two levels of analysis. Chlorpyrifos (CPF) is an organophosphate insecticide broadly used in soybean crops which has dramatically expanded in Latin America and other regions of the world. The aim of the present study was to evaluate lethal and sublethal effects of CPF, singly or in mixtures, on the inland "Pejerrey" (Odontesthes bonariensis) under laboratory conditions. Bioassays were performed using 15-30 d post hatch Pejerrey larvae. Six toxicity tests were run for estimating the average inter-assay dose-response curve of CPF and other six for assessing the effects of mixtures of CPF with endosulfan (EN) or lambda-cyhalothrin (LC), at three toxic units (TU) proportions (25:75, 50:50, 75:25). In addition, four assays were performed to describe the average inter-assay dose-response inhibition curve of acetylcholinesterase (AchE) for CPF alone and two for assessing the mixtures. The estimated 96 h-LC50 for CPF was 2.26 +/- 1.11 microg/L and the incipiency value was 0.048 +/- 0.012 microg/L, placing this Neotropical species among the 13% of worldwide fish more sensitive to CPF. In addition, the 96 h-LC50 for EN and LC were 0.30 +/- 0.012 microg/L and 0.043 +/- 0.031 microg/L, respectively. Therefore, relative toxicity of the three soybean insecticides for O. bonariensis was LC > EN > CPF. Effects of mixtures with EN and LC were variable, but in general fitted to both, independent action (IA) and concentration addition (CA) models. Slight antagonism was found when CPF TU proportions were above 50%. Therefore, from the regulatory point of view, the use of both mixture models, CA or IA, would be precautionary. Differential sensitivity to CPF was found for AchE inhibition at the head (96 h-IC50 = 0.065 +/- 0.058 microg/L) and the body (96 h-IC50 = 0.48 +/- 0.17 microg/L). In addition, whereas no significant effects induced by mixtures was observed in body AchE activity, antagonism was induced in head AchE inhibition in presence of both, EN and LC in the mixture. The lethal to sublethal ratio was close to 25.2 and 3.4 when comparing the CPF-LC50 and IC50s for head and body AchE activity, respectively. However, considerable overlapping was observed between concentration-response curves, indicating that the use of AchE as biomarker for environmental monitoring would be limited.

The lambda-cyhalothrin (CL) is a globally used pyrethroid insecticide that has been detected in different water bodies worldwide. However, studies on the effects of CL on freshwater fishes are still incipient. In this context, we evaluated the acute effects of a commercial formulation containing CL (Karate Zeon((R)) CS 50) in juveniles of the teleost Prochilodus lineatus exposed for 96h to four concentrations of the active ingredient (5, 50, 250 and 500ng.L(-1)). Biochemical, physiological, and genotoxic biomarkers were evaluated in different organs of the fish. Exposure to CL induced significant changes in the enzymatic profiles of P. lineatus, with specific alterations in biotransformation enzymes and antioxidant defence in different tissues. Lipid peroxidation was observed in fish gills and kidney. Increases in esterases were observed in the liver of fish exposed to all CL concentrations evaluated, whereas acetylcholinesterase activity decreased in the muscles of fish at all concentrations. CL also promoted osmoregulatory disorders, with decreases in calcium and magnesium gill ATPases, with consequent hypocalcaemia, in addition an increase in sodium-potassium ATPase activity was observed in the gills of fish exposed to the highest CL concentration, probably in order to compensate a reduction in plasma sodium. Besides, increases in DNA damage were observed in the erythrocytes of fish exposed to all CL concentrations. Thus, despite the low CL concentrations and the short exposure time, this pyrethroid caused hematological adjustments, oxidative stress, osmoregulatory disorders, and DNA damage in P. lineatus, showing that the species is highly sensitive to the deleterious effects of CL.

Quercetin as one of the key plant secondary metabolite flavonol is ubiquitous in terrestrial plants. In this study, the decrease in sensitivity to lambda-cyhalothrin was observed in quercetin-fed Helicoverpa armigera larvae. In order to figure out the mechanisms underlying the decreased sensitivity of H. armigera larvae to lambda-cyhalothrin by quercetin induction, the changes in carboxylesterase activity and in-vitro hydrolytic metabolic capacity to lambda-cyhalothrin were examined. The LC50 value of quercetin-fed H. armigera larvae to lambda-cyhalothrin showed 2.41-fold higher than that of the control. S, S, S-Tributyl phosphorotrithioate (DEF) treatment showed a synergism effect on lambda-cyhalothrin toxicity to quercetin-fed H. armigera. Moreover, the activity of carboxylesterase was significantly higher in quercetin-fed H. armigera larvae after fed on quercetin for 48 h. The in-vitro hydrolytic metabolic capacity to lambda-cyhalothrin in quercetin-fed H. armigera larvae midgut was 289.82 nmol 3-PBA/mg protein/min, which is significant higher than that in the control group (149.60 nmol 3-PBA/mg protein/min). The elevated CarE enzyme activity and corresponding increased hydrolytic metabolic capacity to lambda-cyhalothrin in quercetin-fed H. armigera contributed to the enhanced tolerance to lambda-cyhalothrin.

Role of immobilization stress (IMS), a psychological stressor and forced swim stress (FSS), a physical stressor was investigated on the neurobehavioral toxicity of lambda-cyhalothrin (LCT), a new generation type-II synthetic pyrethroid. Pre-exposure of rats to IMS (15 min/day) or FSS (3 min/day) for 28 days on LCT (3.0 mg/kg body weight, p.o.) treatment for 3 days resulted to decrease spatial learning and memory and muscle strength associated with cholinergic-muscarinic receptors in frontal cortex and hippocampus as compared to those exposed to IMS or FSS or LCT alone. Decrease in acetylcholinesterase activity, protein expression of ChAT and PKC-beta1 associated with decreased mRNA expression of CHRM2, AChE and ChAT in frontal cortex and hippocampus was also evident in rats pre-exposed to IMS or FSS on LCT treatment, compared to rats exposed to IMS or FSS or LCT alone. Interestingly, changes both in behavioral and neurochemical endpoints were marginal in rats subjected to IMS or FSS for 28 days or those exposed to LCT for 3 days alone, compared to controls. The results suggest that stress is an important contributor in LCT induced cholinergic deficits.

In China, the green mirid bug, Apolygus lucorum (Meyer-Dur), has caused severe economic damage to many kinds of crops, especially the cotton and jujubes. Pyrethroid insecticides have been widely used for controlling this pest in the transgenic Bt cotton field. Five populations of A. lucorum collected from cotton crops at different locations in China were evaluated for lambda-cyhalothrin resistance. The results showed that only the population collected from Shandong Province exhibited 30-fold of resistance to lambda-cyhalothrin. Neither PBO nor DEF had obvious synergism when compared the synergistic ratio between SS and RR strain which was originated from the Shandong population. Besides, there were no statistically significant differences (p>0.05) in the carboxylesterase, glutathione S-transferase, or 7-ethoxycoumarin O-deethylase activities between the Shandong population and the laboratory susceptible strain (SS). The full-length sodium channel gene named AlVSSC encoding 2028 amino acids was obtained by RT-PCR and rapid amplification of cDNA ends (RACE). One single point mutation L1015F in the AlVSSC was detected only in the Shandong population. Our results revealed that the L1015F mutation associated with pyrethroid resistance was identified in A. lucorum populations in China. These results will be useful for the rational chemical control of A. lucorum in the transgenic Bt cotton field.

The brown stink bug Euschistus heros is the most abundant species of the soybean-sucking bugs, and causes large economic losses. Applying different chemical groups of organosynthetic insecticides for its control increases the potential for resistance. Esterases are a group of enzymes that play a variety of roles in insects, and some of them are related to the metabolism of xenobiotics. The aim of this study was to analyze the esterase isoenzyme system of this species and investigate its response to Engeo Pleno (thiamethoxam and lambda-cyhalothrin), which is the most widely used pesticide in soybean crops. Two strains were analyzed: the EB strain, which had been free of insecticides for several generations; and the MA strain, which was collected in a location exposed to agrochemicals. By analyzing the polyacrylamide gel electrophoresis profile, seven different esterases in adults and nymphs of both strains were found. Eight gene loci were responsible for the synthesis of these enzymes. The differences in esterases between the two strains and enzyme changes in insects exposed to Engeo Pleno suggest that EST-2 and EST-4 are related to the metabolism of the agrochemical used and are mechanisms of resistance.

Resistance to widely used insecticide, lambda-cyhalothrin, was recently reported in the predatory lady beetle Eriopis connexa (Germar) (Coleoptera: Coccinellidae). However, to understand whether metabolic mechanisms underlie such resistance, synergism bioassays and in vitro studies were carried out by using inhibitors and model substrates for enzymatic assays, respectively. The LD50s estimated for susceptible and resistant populations etag of lambda-cyhalothrin/insect, and thus, a 22-fold difference in resistance ratio. Synergism ratios for the susceptible population with piperonyl butoxide (PBO), diethyl maleate (DEM), triphenyl phosphate (TPP), and S,S,S-tributylphosphorotrithioate (DEF) were respectively 33.8-, 0.24-, 0.35-, and 4.25-fold, while for the resistant population, they were 1463.0-, 0.79-, 0.85-, and 282.6-fold, respectively. The synergized resistance ratios were 0.50-, 2.00-, 6.75-, and 8.77-fold with PBO, DEF, DEM, and TPP, respectively, while resistance was virtually suppressed with DEF. The esterase exhibited 4.16-, 4.03-, and 5.38-fold greater activity towards formation of alpha-naphthol, beta-naphthol, and 4-nitrophenol in the resistant population of E. connexa than in the susceptible population. The activity of esterase depended on concentrations of DEF applied, either using alpha-naphthol or beta-naphthol, which completely inhibited the activity at 636etaM. The PBO inhibited the beta-naphthol formation in approximately 50%, suggesting it as inhibitor of esterases. The activities of glutathione-S-transferase were similar and corresponded to 0.36-0.47etamol(-1)min(-1)mug of protein, for S and R populations, respectively. Similarly, the activities of cytochrome P450-dependent microsomal monooxygenases were 0.04 and 0.05etamol(-1)min(-1)mug of protein. The native gel indicated that the formation of beta-naphthol was completely inhibited by methyl-paraoxon, but only partially inhibited by eserine, TPP, and PBO. Although other studies with DEF and PBO have demonstrated strong inhibition of type B carboxylesterase associated with insecticide resistance, the results reported here do not rule out metabolism by cytochrome P450-dependent microsomal monooxygenases as a factor conferring E. connexa resistance to lambda-cyhalothrin and confirmed that PBO may also act by inhibiting esterases of insects.

This study is focused on understanding the mechanism of neurobehavioral toxicity of lambda-cyhalothrin a new generation type II synthetic pyrethroid in developing rats following their exposure from post-lactational day PLD)22 to PLD49 and investigate whether neurobehavioral alterations are transient or persistent Post-lactational exposure to lambda-cyhalothrin 1.0 or 3.0 mg/kg body weight p.o affected grip strength and learning activity in rats on PLD50 and the persistent impairment of grip strength and learning was observed at 15 days after withdrawal of exposure on PLD65 A decrease in the binding of muscarinic-cholinergic receptors in frontocortical hippocampal and cerebellar membranes associated with decreased expression of choline acetyltransferase ChAT and acetylcholinesterase AChE in hippocampus was observed following exposure to lambda-cyhalothrin on PLD50 and PLD65 Exposure to lambda-cyhalothrin was also found to increase the expression of growth-associated protein-43 in hippocampus of rats on PLD50 and PLD65 as compared to controls A significant increase in lipid peroxidation and protein carbonyl levels and decreased levels of reduced glutathione and activity of superoxide dismutase catalase and glutathione peroxidase in brain regions of lambda-cyhalothrin exposed rats were distinctly observed indicating increased oxidative stress Inhibition of ChAT and AChE activity may cause down-regulation of muscarinic-cholinergic receptors consequently impairing learning activity in developing rats exposed to lambda-cyhalothrin The data further indicate that long-term exposure to lambda-cyhalothrin at low doses may be detrimental and changes in selected behavioral and neurochemical end points may persist if exposure to lambda-cyhalothrin continues.

This study evaluates the toxic effects of deltamethrin and lambda-cyhalothrin on Xenopus laevis tadpoles after 168 h of exposure. The LC(50) of deltamethrin and lambda-cyhalothrin at 168 h was calculated as the mug of active ingredient per liter (mug AI/L). According to these values, the LC(50) was 6.26 and 3.94 mug AI/L for deltamethrin and lambda-cyhalothrin, respectively. Several enzymes were studied for early signs of intoxication following exposure to the pesticides for 24 h. Glutathione-S-transferase,carboxylesterase, and lactate dehydrogenase were inhibited by lambda-cyhalothrin, and both pesticides inhibited acid phosphatase and aspartate aminotransferase. In contrast, acetylcholinesterase was activated by deltamethrin. The results suggest that X. laevis is sensitive to the pyrethroids that were tested, and the enzyme responses suggest that they are potential biomarkers for evaluating the toxic effect of pyrethroids on amphibians in environmental conditions.

In order to establish the insecticide susceptibility status for Anopheles darlingi in Colombia, and as part of the National Network on Insecticide Resistance Surveillance, five populations of insects from three Colombian states were evaluated. Standardised WHO and CDC bottle bioassays, in addition to microplate biochemical assays, were conducted. Populations with mortality rates below 80% in the bioassays were considered resistant. All field populations were susceptible to deltamethrin, permethrin, malathion and fenitrothion. Resistance to lambda-cyhalothrin and DDT was detected in the Ame-Bete population using both bioassay methods with mortality rates of 65-75%. Enzyme levels related to insecticide resistance, including mixed function oxidases (MFO), non-specific esterases (NSE), glutathione S-transferases and modified acetylcholinesterase were evaluated in all populations and compared with a susceptible natural strain. Only mosquitoes from Ame-Bete presented significantly increased levels of both MFO and NSE, consistent with the low mortalities found in this population. The continued use of lambda-cyhalothrin for An. darlingi control in this locality has resulted in a natural resistance to this insecticide. In addition, DDT resistance is still present in this population, although this insecticide has not been used in Colombia since 1992. Increased metabolism through MFO and NSE may be involved in cross-resistance between lambda-cyhalothrin and DDT, although kdr-type nerve insensitivity cannot be discarded as a possible hypothesis. Additional research, including development of a kdr specific assay for An. darlingi should be conducted in future studies. Our data demonstrates the urgent need to develop local insecticide resistance management and surveillance programs throughout Colombia.

Erythrocytes are a convenient model to understand the membrane oxidative damage induced by various xenobiotic-prooxidants. This study was designed to investigate (1) the possibility of lambda-cyhalothrin (LC), a type II pyrethroid, to induce oxidative stress response in rabbit erythrocytes in vitro and its effect on selected antioxidant enzymes and (2) the role of vitamin C (VC; 20mM) and vitamin E (VE; 2mM) in alleviating the cytotoxic effects of LC. Erythrocytes were divided into three groups. The first group, previously prepared erythrocytes was incubated for 4h at 37 degrees C with different concentrations (0, 0.1, 0.5, 1, 2.5, 5mM) of LC. The second and third groups were preincubated with VC or VE, respectively for 20 min and followed by LC incubation for 4h. Following in vitro exposure, LC caused a significant induction of oxidative damage in erythrocytes at different concentrations as evidenced by increased thiobarbituric acid reactive substances (TBARS) levels. However, a significant decrease in the content of sulfhydryl groups (SH-groups), and the activities of acetylcholinesterase (AChE), superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) were observed. The response was concentration dependent. VC or VE pretreated erythrocytes showed a significant protection against the cytotoxic effects induced by LC on the studied parameters. In conclusion, antioxidant vitamins especially VE could be able to ameliorate LC-induced oxidative stress by decreasing lipid peroxidation and altering antioxidant defense system in erythrocytes.

The impact of the pyrethroid lambda-cyhalothrin was studied in an in-stream mesocosm placed in a natural riffle of a Danish stream. Twice during summer 2002, the natural macroinvertebrate community was exposed in situ to a 30-min pulse of lambda-cyhalothrin. During exposure, nets caught macroinvertebrates in drift. Exposed and unexposed individuals of the amphipod Gammarus pulex (L) were transferred to aquaria in the laboratory and monitored for biochemical changes (ie biomarkers), pre-copulatory behaviour and mortality. Biochemical biomarkers were identified by screening extracts of exposed and unexposed G pulex using high-performance planar chromatography (HPPC). Biochemical biomarkers were detected 3 h after pulse-exposure, and one biomarker was persistent up to 7 days after exposure. Pre-copulatory behaviour (ie pair formation) was significantly impaired up to 5 days after exposure, and had not fully recovered at the end of the observation period. EC10(0.5 h) and EC50(0.5 h) values for pre-copulatory behaviour were 0.04 and 0.20 microg litre(-1), respectively. Mortality was significant at 0.35 microg litre(-1) with an LC50(0.5 h) of 5.69 microg litre(-1). There was a significant relationship between two biomarkers and mortality. The study demonstrated that pulse-exposure at expected environmental concentrations can reduce local populations of G pulex, resulting in severe impact on populations with limited possibilities of re-colonisation Twice during sum

The interactions of the synthetic pyrethroid, lambda-cyhalothrin and malathion were studied with purines, pyrimidines, caffeine and some other related nitrogenous compounds in resistant and susceptible strains of Triboliurn castaneum (Herbst.) The results were compared with those obtained with a known synergist, piperonyl butoxide (PBO) and precocene I. Adenine, cytosine, guanine, thymine and uracil synergised lambda-cyhalothrin, especially in the susceptible strain, with maximum effect at a 1:1 mass ratio, with the effect decreasing with increasing proportion of the heterocycle. The order of synergism of lambda-cyhalothrin was; precocene I > PBO > the nitrogenous compounds, in both resistant and susceptible strains. On the other hand, caffeine (lethal effect increased about twice), barbital (about twice), isobarbituric acid (less than twice) and bromacil (up to eight times) synergised malathion in malathion-resistant strains and antagonised in the susceptible strains. Total in-vivo esterases, carbox-ylesterases and cytochrome P450 of susceptible and resistant strains showed significantly increased activity or content when treated with either insecticide plus a heterocyclic compound. Exceptions were with bromacil and malathion and for the malathion-specific strain, Kano-C with malathion and the N-heterocycles.