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.     

Resistance to selected organochlorin, organophosphate, carbamate and pyrethroid, in Spodoptera litura (Lepidoptera: Noctuidae) from Pakistan

The toxicity of the most commonly used insecticides of organochlorine, organophosphate, pyrethroid, and carbamate groups were investigated against Spodoptera litura (F.) (Lepidoptera: Noctuidae) populations collected for three consecutive years (2004-2006). For a chlorocyclodiene and pyrethroids tested, the resistance ratios compared with Lab-PK were in the range of 10- to 92-fold for endosulfan, 5- to 111-fold for cypermethrin, 2- to 98-fold for deltamethrin, and 7- to 86-fold for beta-cyfluthrin. For organophosphates and carbamates, resistance ratios were in the range of 3- to 169-fold for profenofos, 18- to 421-fold for chlorpyrifos, 3- to 160-fold for quinalphos, 6- to 126-fold for phoxim, 7- to 463-fold for triazophos, and 10- to 389-fold for methomyl and 16- to 200-fold for thiodicarb. Resistance ratios were generally low to medium for deltamethrin and beta-cyfluthrin and high to very high for endosulfan, cypermethrin, profenofos, chlorpyrifos, quinalphos, phoxim, triazophos, methomyl, or thiodicarb. Pairwise comparisons of the log LC50 values of insecticides tested for all the populations showed correlations among several insecticides, suggesting a cross-resistance mechanism. Integration of timely judgment of pest problem, delimiting growing of alternate crops such as arum, rotation of insecticides with new chemicals, and insect growth regulators in relation to integrated pest management could help in manageable control of this important pest.     

Toxicity of seventeen insecticides to Camponotus sericeus (Hymenoptera: Formicidae)

The success of chemical control depends on toxicity of insecticides against insect pests. Camponotus sericeus is an important urban pest with the ability to cause substantial damage to wooden structures, but there is a lack of information on toxicity of insecticides against C. sericeus. To determine the insecticide toxicity, workers of C. sericeus were exposed to 17 insecticides from different classes: carbamate (methomyl, bendiocarb), organophosphate (chlorpyrifos, profenofos, temephos), pyrethroid (bifenthrin, deltamethrin, permethrin), neonicotinoid (acetamiprid, imidacloprid, thiamethoxam), avermectin (abamectin, emamectin), pyrrole (chlorfenapyr), phenylpyrazole (fipronil), and spinosyn (spinosad and spinetoram), via residual bioassay method. The LC₅₀ ranged from: 0.15 to 0.20 µg/vial for carbamates, 0.09 to 0.27 µg/vial for organophosphates, 0.09 to 0.44 µg/vial for pyrethroids, 0.02 to 0.67 µg/vial for neonicotinoids, 0.54 to 0.82 µg/vial for avermectins, 0.78 µg/vial for pyrrole, 0.62 µg/vial for phenylpyrazole, and 1.96 to 2.05 µg/vial for spinosyns. Overall, acetamiprid was the most toxic one among the tested insecticides followed by permethrin, temephos, profenofos, bendiocarb and methomyl, while spinosad and spinetoram were the least toxic insecticides. Considering the potential toxicity of different insecticides against C. sericeus, future studies could investigate the practical application of these insecticides in order to design an effective management plan.     

Mutation in the ace‐1 gene of the tomato leaf miner (Tuta absoluta) associated with organophosphates resistance

The tomato leaf miner, Tuta absoluta (Lepidoptera: Gelechiidae), is a major invasive pest that has spread throughout many countries in the Mediterranean basin and parts of Asia over the last decade. The control of T. absoluta has relied heavily on the use of chemical insecticides, a strategy that has led to the evolution of resistance. In this study, biological and molecular methods were used to determine the susceptibility of five strains of T. absoluta to the organophosphate chlorpyrifos and to investigate the molecular mechanisms underlying resistance to this class of insecticides. High levels of resistance to chlorpyrifos were observed in all five strains tested. Cloning and sequencing of the gene encoding the organophosphate target site, ace‐1, of T. absoluta revealed the presence of an alanine to serine substitution at a position that has been previously linked with organophosphate resistance across a range of different insect and mite species. The presence of this mutation at high frequency in T. absoluta populations originating from various countries further supports the suggestion that the rapid expansion of this species is, in part, mediated by the resistance of this pest to chemical insecticides.     

Carbamate and organophosphate resistance in cotton pests in India, 1995 to 1999

Monitoring for organophosphate and carbamate resistance was carried out on five major insect pests of cotton collected from 22 cotton-growing districts across India. Resistance was monitored in Helicoverpa armigera (Hübner) and Pectinophora gossypiella (Saunders) for the period 1995-1999 and for Spodoptera litura (Fabricius), Earias vittella (Fabricius) and Bemisia tabaci (Gennadius) in a survey conducted during the 1997-98 cropping season. Of the 53 field strains of H. armigera, only four were found to exhibit resistance to quinalphos, the highest 15-fold, whereas all 16 field strains tested were found to be resistant to monocrotophos. Similarly, out of 40 field strains tested, only eight were found to express appreciable resistance to methomyl. Resistance in P. gossypiella to quinalphos was high in the majority of the strains tested. Of the seven strains of E. vittella tested, two strains from northern India exhibited > 70-fold resistance to monocrotophos. Of the 11 S. litura strains tested, only four were found to exhibit resistance factors of 10 to 30-fold to quinalphos and monocrotophos. All of the B. tabaci field strains exhibited resistance to methomyl and monocrotophos and susceptibility to triazophos. Practical implications for pest control resulting from the observed patterns of cross-resistance between quinalphos, monocrotophos and methomyl are discussed.     

A point mutation in the acetylcholinesterase-1 gene is associated with chlorpyrifos resistance in the plant bug Apolygus lucorum

Control of Chinese Apolygus lucorum relies heavily on organophosphate insecticides. Here we describe resistance to the organophosphate chlorpyrifos in an A. lucorum strain, BZ-R, which was developed from a field-collected strain (BZ) by selection with chlorpyrifos in the laboratory. BZ-R showed 21–58 fold resistance to chlorpyrifos compared with the laboratory reference strain LSF and another susceptible strain, BZ-S, derived from BZ. BZ-R also showed several fold resistance to two other organophosphates and a carbamate. No synergism of chlorpyrifos by metabolic enzyme inhibitors nor any increase in detoxifying enzyme activities were observed in BZ-R. No sequence differences in acetylcholinesterase-2 were found to be associated with the resistance but the frequency of an alanine to serine substitution at position 216 of acetylcholinesterase-1 was 100% in BZ-R, ∼21–23% in SLF and BZ, and 0% in BZ-S. A single generation treatment of chlorpyrifos on the BZ strain also increased its frequency of the serine substitution to 64%. Recombinantly expressed acetylcholinesterase-1 carrying the serine substitution was about five fold less sensitive to inhibition by chlorpyrifos oxon than the wild-type enzyme. Quantitative real-time PCR found no differences in ace1 or ace2 expression levels among the strains tested. Thus the chlorpyrifos resistance is strongly associated with the serine substituted acetylcholinesterase-1. An equivalent substitution has been found to confer resistance to many organophosphate and carbamate insecticides in four other insect species.     

Behavioural and insecticidal effects of organophosphate‐, carbamate‐ and pyrethroid‐treated mosquito nets against African malaria vectors

Three insecticides – the pyrethroid deltamethrin, the carbamate carbosulfan and the organophosphate chlorpyrifos‐methyl – were tested on mosquito nets in experimental huts to determine their potential for introduction as malaria control measures. Their behavioural effects and efficacy were examined in Anopheles gambiae Giles s.s. (Diptera: Culicidae) and Anopheles funestus Giles s.s. in Muheza, Tanzania, and in Anopheles arabiensis Patton and Culex quinquefasciatus Say in Moshi, Tanzania. A standardized dosage of 25 mg/m² plus high dosages of carbosulfan (50 mg/m², 100 mg/m² and 200 mg/m²) and chlorpyrifos‐methyl (100 mg/m²) were used to compare the three types of insecticide. At 25 mg/m², the rank order of the insecticides for insecticide‐induced mortality in wild An. gambiae and An. funestus was, respectively, carbosulfan (88%, 86%) > deltamethrin (79%, 78%) > chlorpyrifos‐methyl (35%, 53%). The rank order of the insecticides for blood‐feeding inhibition (reduction in the number of blood‐fed mosquitoes compared with control) in wild An. gambiae and An. funestus was deltamethrin > chlorpyrifos‐methyl > carbosulfan. Carbosulfan was particularly toxic to endophilic anophelines at 200 mg/m², killing 100% of An. gambiae and 98% of An. funestus that entered the huts. It was less effective against the more exophilic An. arabiensis (67% mortality) and carbamate‐resistant Cx quinquefasciatus (36% mortality). Carbosulfan deterred anophelines from entering huts, but did not deter carbamate‐resistant Cx quinquefasciatus. Deltamethrin reduced the proportion of insects engaged in blood‐feeding, probably as a consequence of contact irritancy, whereas carbosulfan seemed to provide personal protection through deterred entry or perhaps a spatial repellent action. Any deployment of carbosulfan as an individual treatment on nets should be carried out on a large scale to reduce the risk of diverting mosquitoes to unprotected individuals. Chlorpyrifos‐methyl was inferior to deltamethrin in terms of mortality and blood‐feeding inhibition and would be better deployed on a net in combination with a pyrethroid to control insecticide‐resistant mosquitoes.     

Detection of insecticide resistance in Plutella xylostella (L.) (Lepidoptera: Plutellidae) populations in South Australian crucifer crops

In response to reports of failures of sprays to control Plutella xylostella infestations in vegetable-growing areas around Adelaide in 1991, the extent of resistance to six insecticides in several South Australian populations of P. xylostella was determined. Populations sampled from vegetable crops in the Adelaide region were five- to 200-fold resistant to organophosphates (chlorpyrifos, methamidophos and mevinphos), eight- to 400-fold resistant to pyrethroids (esfenvalerate and permethrin) and six-fold resistant to the carbamate methomyl compared with a susceptible strain. Mevinphos and esfenvalerate were the most effective of the tested insecticides. These, together with Bacillus thuringiensis products, have continued until 1998 to be used almost exclusively for the control of P. xylostella in South Australian vegetable crops in the absence of any resistance management strategy.     

Mechanisms of organophosphate insecticide-induced airway hyperreactivity

It has been suggested that pesticide exposure may be a contributing factor underlying the increased incidence of asthma in the United States and other industrialized nations. To test this hypothesis, airway hyperreactivity was measured in guinea pigs exposed to chlorpyrifos, a widely used organophosphate pesticide. Electrical stimulation of the vagus nerves caused frequency-dependent bronchoconstriction that was significantly potentiated in animals 24 h or 7 days after a single subcutaneous injection of either 390 mg/kg or 70 mg/kg of chlorpyrifos, respectively. Mechanisms by which chlorpyrifos may cause airway hyperreactivity include inhibition of acetylcholinesterase (AChE) or dysfunction of M3 muscarinic receptors on airway smooth muscle or of autoinhibitory M2 muscarinic receptors on parasympathetic nerves in the lung. AChE activity in the lung was significantly inhibited 24 h after treatment with 390 mg/kg of chlorpyrifos, but not 7 days after injection of 70 mg/kg of chlorpyrifos. Acute exposure to eserine (250 microg/ml) also significantly inhibited lung AChE but did not potentiate vagally induced bronchoconstriction. Neuronal M2 receptor function was tested using the M2 agonist pilocarpine, which inhibits vagally induced bronchoconstriction in control animals. In chlorpyrifos-treated animals, pilocarpine dose-response curves were shifted significantly to the right, demonstrating decreased responsiveness of neuronal M2 receptors. In contrast, chlorpyrifos treatment did not alter methacholine-induced bronchoconstriction, suggesting that chlorpyrifos does not alter M3 muscarinic receptor function on airway smooth muscle. These data demonstrate that organophosphate insecticides can cause airway hyperreactivity in the absence of AChE inhibition by decreasing neuronal M2 receptor function.     

Susceptibility of the parasitoidMicroplitis croceipes [Hymenoptera: Braconidae] to field rates of selected cotton insecticides

Microplitis croceipes (Cresson), a parasitoid ofHeliothis spp., was treated topically with field rates of 5 formulated insecticides commonly used in cotton to controlHeliothis spp. Treatment with the pyrethroid fenvalerate, a mixture of the formamidine chlordimeform plus fenvalerate, and the carbamate thiodicarb resulted in nearly 100% survival at both the lowest and highest field rates recommended for these insecticides. The organophosphate acephate and the carbamate methomyl were extremely toxic to adultM. croceipes, causing 100% mortality at the lowest recommended field rates. Comparisons are made to previously reported laboratory toxicity data for some of these insecticides for adultM. croceipes. Choice of insecticides to control pyrethroid-resistantHeliothis spp., and the effects of these insecticides on adultM. croceipes survival, are discussed. This article reports the results of research only. Mention of a proprietary product does not constitute endorsement or a recommendation for its use by the U. S. Department of Agriculture.     

Biochemical basis of organophosphate and carbamate resistance in Asian citrus psyllid

The Asian citrus psyllid, Diaphorina citri Kuwayama, is a worldwide pest of citrus, which vectors the putative causal pathogen of huanglongbing. Current management practices warrant continuous monitoring of field populations for insecticide resistance. Baseline activities of acetylcholinesterase (AChE), general esterase, and glutathione S-transferase as well as sensitivity of AChE to selected organophosphate and carbamate insecticides were established for a susceptible laboratory strain (Lab) and compared with several field populations of D. citri from Florida. The specific activity of AChE in various D. citri populations ranged from 0.77 to 1.29 microM min(-1) mg of protein(-1); the Lab strain was characterized by the highest activity. Although reduced AChE sensitivity was observed in the Lab strain compared with field populations, overlap of 95% confidence intervals of I50 values (concentration required for 50% AChE activity inhibition) suggests no significant difference in AChE sensitivity among all populations tested for a given insecticide. There was no significant evidence of target site insensitivity in field populations that were exposed to the selected organophosphate and carbamate insecticides tested. The specific activity of general esterase and glutathione S-transferase was lowest in the Lab strain and was generally comparable to that of the field populations evaluated. The current data provide a mode-of-action specific baseline for future monitoring of resistance to organophosphate and carbamate insecticides in populations of D. citri.     

Mutations in acetylcholinesterase genes of Rhopalosiphum padi resistant to organophosphate and carbamate insecticides.

Apple grain aphid, Rhopalosiphum padi (Linnaeus), is an important wheat pest. In China, it has been reported that R. padi has developed high resistance to carbamate and organophosphate insecticides. Previous work cloned from this aphid 2 different genes encoding acetylcholinesterase (AChE), which is the target enzyme for carbamate and organophosphate insecticides, and its insensitive alteration has been proven to be an important mechanism for insecticide resistance in other insects. In this study, both resistant and susceptible strains of R, padi were developed, and their AChEs were compared to determine whether resistance resulted from this mechanism and whether these 2 genes both play a role in resistance. Bioassays showed that the resistant strain used was highly or moderately resistant to pirimicarb, omethoate, and monocrotophos (resistance ratio, 263.8, 53.8, and 17.5, respectively), and showed little resistance to deltamethrin or thiodicarb (resistance ratio, 5.2 and 3.4, respectively). Correspondingly, biochemistry analysis found that AChE from resistant aphids was very insensitive to the first 3 insecticides (I50 increased 43.0-, 15.2-, and 8.8-fold, respectively), but not to thiodicarb (I50 increased 1.1-fold). Enzyme kinetics tests showed that resistant and susceptible strains had different AChEs. Sequence analysis of the 2 AChE genes cloned from resistant and susceptible aphids revealed that 2 mutations in Ace2 and 1 in Ace1 were consistently associated with resistance. Mutation F368(290)L in Ace2 localized at the same position as a previously proven resistance mutation site in other insects. The other 2 mutations, S329(228)P in Ace1 and V435(356)A in Ace2, were also found to affect the enzyme structure. These findings indicate that resistance in this aphid is mainly the result of insensistive AChE alteration, that the 3 mutations found might contribute to resistance, and that the AChEs encoded by both genes could serve as targets of insecticides.     

禾谷缢管蚜和麦长管蚜玻璃管药膜法敏感毒力基线的建立

【目的】建立禾谷缢管蚜Rhopalosiphum padi（Linnaeus）和麦长管蚜Sitobion avenae（Fabricius）对常用杀虫剂的相对敏感基线。【方法】从田间采集麦蚜在实验室内饲养30代以上,利用玻璃管药膜法测定其对杀虫剂的敏感度,每条毒力基线为2次以上独立测定数据合并后的计算结果。【结果】用玻璃管药膜法建立了包括新烟碱类、吡啶类、氨基甲酸酯类、有机磷类和拟除虫菊酯类共22个药剂品种对禾谷缢管蚜和麦长管蚜3 h的敏感毒力基线。禾谷缢管蚜对新烟碱类药剂吡虫啉和啶虫脒的LC₅₀值分别为0.02和0.007 μg/cm²;对吡啶类药剂吡蚜酮的LC₅₀值为0.124 μg/cm²;对氨基甲酸酯类药剂丁硫克百威、硫双灭多威、灭多威、抗蚜威、西维因的LC₅₀值为0.0026~0.70 μg/cm²;对有机磷类药剂三唑磷、丙溴磷、氧乐果、乐果、马拉硫磷、辛硫磷、敌敌畏、毒死蜱的LC₅₀值为0.005~0.065 μg/cm²;对拟除虫菊酯类药剂三氟氯氰菊酯、高效氯氰菊酯、溴氰菊酯、联苯菊酯、氰戊菊酯、氯氰菊酯的LC₅₀值为0.033~0.240 μg/cm²。麦长管蚜对新烟碱类药剂吡虫啉和啶虫脒的LC₅₀值分别为0.15和0.12 μg/cm²;对吡啶类药剂吡蚜酮的LC₅₀值为0.41 μg/cm²;对氨基甲酸酯类药剂丁硫克百威、硫双灭多威、灭多威、抗蚜威、西维因的LC50值为0.005~0.76 μg/cm²;对有机磷类药剂三唑磷、丙溴磷、氧乐果、乐果、马拉硫磷、辛硫磷、敌敌畏、毒死蜱的LC₅₀值为0.018~0.36 μg/cm²;对拟除虫菊酯类药剂三氟氯氰菊酯、高效氯氰菊酯、溴氰菊酯、联苯菊酯、氰戊菊酯、氯氰菊酯的LC50值为0.20~2.94 μg/cm²。【结论】建立的两种麦蚜对22种杀虫药剂的相对敏感基线,包括当前所有可能用于防治麦蚜的药剂,可以用于以后麦蚜抗药性监测或其他相关研究的参照;禾谷缢管蚜对药剂的敏感度高于麦长管蚜。     

Insecticidal control of the mealybug Phenacoccus gossypiphilous (Hemiptera: Pseudococcidae), a new pest of cotton in Pakistan

The mealybug Phenacoccus gossypiphilous (Stanley) played havoc with the cotton crop in Pakistan during 2005. To control this pest, insecticides of different groups were evaluated in both the laboratory and in field conditions. In the laboratory, bifenthrin, profenofos and chlorpyrifos proved to be the best insecticides for mealybug control, based on their susceptibility with the leaf dip method for their LC₅₀. In field conditions, the recommended application rates of methomyl, profenofos and chlorpyrifos provided the best control: the lethal time studies proved their efficiency for better and timely control of this sporadic pest. The present study has shown that the insecticides tested, in particular profenofos, chlorpyrifos, methomyl and bifenthrin, provide satisfactory control of the cotton mealybug. The control of the insect pest complex throughout the cotton crop predominantly depends on wise and justified use of these chemicals, and necessitates development of an integrated pest management strategy.     

Monitoring and mechanisms of organophosphate resistance in San Jose scale,Diaspidiotus perniciosus (Hemiptera: Diaspididae)

San Jose scale, Diaspidiotus perniciosus (Comstock), is a serious pest in Chilean apple tree orchards, and a number of organophosphate insecticides were used to control them for decades. Recently, control failures with these insecticides were reported and linked to insecticide resistance development. In this study, 40 San Jose scale field populations were collected and their susceptibility to two commonly used organophosphate insecticides, that is chlorpyrifos and methidathion, was assessed. The obtained bioassay data suggest moderate levels of resistance to both insecticides when compared to a reference susceptible strain. The highest resistance ratio (RR) detected for chlorpyrifos and methidathion was 31‐fold and 11‐fold, respectively. The bioassay results suggest the occurrence of a significant cross‐resistance between both compounds. Biochemical measurements revealed a role for esterases in conferring resistance to organophosphates, but not modified acetylcholinesterase. The spatial spread and extend of insecticide resistance were also evaluated. Our result shows that no autocorrelation can be assumed, and then, insecticide resistance is caused by random factors.     

Biochemical characterization of hydrolytic and oxidative enzymes in insecticide resistant and susceptible strains of the German cockroach (Dictyoptera: Blattellidae).

We have identified resistance mechanisms in the German cockroach, Blattella germanica (L.), for propoxur and chlorpyrifos in strains of cockroaches that display multiresistance to several organophosphate and carbamate insecticides. The resistance mechanisms involve the combined effects of increased oxidative and hydrolytic metabolism and both strains are resistant to chlorpyrifos and propoxur. Experiments designed to test for similarity in metabolic enzymes suggest that, although the mechanisms involve similar processes, the enzymes responsible for insecticide detoxification are different in the two strains. Both resistant strains exhibited enhanced activity toward alpha-naphtholic esters relative to a standard susceptible strain; however, analysis of the progeny from resistant X susceptible crosses suggests that this general esterase activity is inherited differently than propoxur or chlorpyrifos resistance. Hybrids of the propoxur-resistant strain displayed the highest activity of all cockroaches tested, in contrast to hybrids of the chlorpyrifos-resistant strain, which were similar to the susceptible strain. Native gel electrophoresis of cytosolic preparations provided further evidence for differences in the pattern of hydrolytic enzymes and inheritance of resistance in the two strains. Analysis of components of the cytochrome P450-dependent monooxygenase system and activities toward model substrates indicate that the two resistance mechanisms also involve different oxidative processes. The propoxur-resistant strain displayed significantly higher levels of total cytochrome P450, but no other components were correlated with resistance. In contrast with the chlopyrifos-resistant strain, which was similar to the susceptible strain in all parameters measured, activity toward model substrates was higher in the propoxur-resistant strain than in any of the other strains and hybrids tested.(ABSTRACT TRUNCATED AT 250 WORDS)     

BIOCHEMICAL ASPECTS OF INSECTICIDE RESISTANCE IN COTTON BOLLWORM FROM HANDAN OF HEBEI PROVINCE*

Abstract The cotton bollworms, Helicoverpa armigera Hübner, collected from Handan of Hebei Province, have evolved high resistance to pyrethroid, organophosphate and carbamate insecticides, The sensitivity of acetylcholinesterase (AChEs) to paraoxon and methomyl varied with the development stages of the cotton bollworm. After the treatments with LD₅ and LD₅₀ of parathion and methomyl to the cotton bollworms, the affinity of AChE to acetylthiocholine (ATCh) and acetyl-β-bmethyl-thio choline (MeTCh) increased significantly except the treatment of parathion using LD₅₀ dosage while the sensitivity of AChEs to paraoxon significantly decreased. The sensitivity of AChEs to methomyl strongly increased in the treatment of parathion using LD₅₀ dosages while strongly decreased in other treatments. The affinity of carboxylesterase to β-naphthyl acetate (β-NA) was higher in groups of treatment with insecticides than in group of control. The glutathione-s-transferase (GST) activity significantly decreased in the induced groups using LD₅ dosages, while increased in the selection groups using LD₅₀ dosages. The effects of parathion and methomyl on the phosphatases of cotton bollworm were related to the dosages of application and the time after treatment and the effect on the alkaline phosphatase was stronger than on acid phosphatase.     

Determination of organophosphate and carbamate pesticides in spiked samples of tap water and fruit juices by a biosensor with photothermal detection.

The determination of organophosphate (paraoxon, chlorpyrifos, diazinon) and carbamate (carbaryl, carbofuran) pesticides in spiked drinking water and fruit juices was carried out using a photothermal biosensor. The biosensor consists of a cartridge containing immobilised enzyme acetylcholinesterase (AChE) placed in a flow-injection analysis (FIA) manifold and a photothermal detector based on thermal lens spectrometry. With this approach, 0.2 ng/ml of paraoxon can be detected in less than 15 min. Limits of detection for other organophosphate (chlorpyrifos, diazinon) and carbamate (carbaryl, carbofuran) pesticides varied, depending on their antiacetylcholinesterase (AntiAChE) toxicity, from 1 ng/ml to 4 microg/ml. The biosensor was used for the direct detection of pesticides in spiked tap water and fruit juices without any pretreatment steps. In these cases, the LOD3sigma of 1.5, 2.8 and 4 ng/ml paraoxon in tap water, orange juice and apple juice were obtained, respectively.