The relationship of esterases to organophosphorus insecticide tolerance in mosquitofish

The levels of peripheral acetylcholinesterase and carboxylesterases and their organophosphate sensitivities were studied in two populations of mosquitofish (Gambusia affinis). One population, highly resistant to organochlorine insecticides, demonstrated a low tolerance to parathion and methyl parathion. The organochlorine resistant fish possessed higher levels of both peripheral acetylcholinesterase and carboxylesterases. The sensitivities of these esterases to organophosphate inhibition were the same in both populations. The esterases were more sensitive to paraoxon than to methyl paraoxon. Carboxylesterases were far more sensitive to organophosphate inhibition than was acetylcholinesterase. Carboxylesterases, by their higher affinity for the organophosphates, may serve to protect acetylcholinesterase from inhibition.     

Functional neurotoxic effects in rats acutely exposed to insecticide combinations

The aim of the present study was to analyse the alterations in the cortical and peripheral electrophysiological activity of rats acutely treated with combinations of insecticides. Young adult male Wistar rats were treated with 1/5 and 1/25 LD₅₀ of the insecticides dimethoate, propoxur, cypermethrin and amitraz, given alone or in triple or quadruple combinations. After 24 h, spontaneous cortical activity, and stimulus-evoked cortical and peripheral responses, was recorded and analysed. All treatments changed the cortical activity spectrum. The effect of the 1/5 LD₅₀ combinations indicated non-additive interactions. In the cortical-evoked responses, dimethoate and its combinations gave the strongest change in the latency, while amitraz and its combinations, in the response duration. In the tail nerve, relative refractory period was the most sensitive parameter. The frequency dependence of the cortical responses was the most strongly altered by propoxur, and the least, by amitraz. Our results indicate that simultaneous exposure by various pesticide agents, which happens possibly also in humans, deserves further investigation in, among others, neurotoxicological points of view.     

Recovery of cholinesterase activity in five avian species exposed to dicrotophos,and organophosphorus pesticide

The responses of brain and plasma cholinesterase (ChE) activities were examined in mallard ducks, bobwhite quail, barn owls, starlings, and common grackles given oral doses of dicrotophos, an organophosphorus insecticide. Up to an eightfold difference in response of brain ChE activity to dicrotophos was found among these species. Brain ChE activity recovered to within 2 SD of normal within 26 days after being depressed 55 to 64%. Recovery of brain ChE activity was similar among species and followed the model Y = a + b (log₁₀X).     

Osmoregulatory function in ducks following ingestion of the organophosphorus insecticide fenthion

Salt gland function and osmoregulation in aquatic birds drinking hyperosmotic water has been suggested to be impaired by organophosphorus insecticides. To test this hypothesis, adult black ducks (Anas rubripes) were provided various regimens of fresh or salt (1.5% NaCl) water before, during, and after ingestion of mash containing 21 ppm fenthion. Ducks were bled by jugular venipuncture after 1, 7, and 12 days of treatment, and were then killed. Brain and salt gland acetylcholinesterase activities were substantially inhibited (44–61% and 14–36%) by fenthion. However, salt gland weight and Na⁺-K⁺-ATPase activity, and plasma Na⁺, Cl^?, and osmolality, were uniformly elevated in all groups receiving salt water including those ingesting fenthion. In a second study, salt gland Na⁺-K⁺-ATPase activity in mallards (A. platyrhynchos) was not affected after in vitro incubation with either fenthion oxon at concentrations ranging from 0.04 to 400 μM, but was reduced in the presence of 40 and 400 μM DDE (positive control). These findings suggest than environmentally realistic concentrations of organophosphorus insecticides do not markedly affect osmoregulatory function in adult black ducks.     

Time trends in mortality of Conophthorus ponderosae (Hopkins) exposed to insecticide residues

The protection of the female cones of Pinus monticola (Dougl. ex D. Don) from attack by Conophthorus ponderosae (Hopkins) requires that the beetles be killed before they enter the cone. This encourages consideration of the distributions of length of time to death and how these distributions are changed with different concentrations of various candidate insecticides. In this study a three-parameter Weibull function was employed to depict the distributions for data originally collected for a probit analysis. The time to achieve 90% mortality as defined by the Weibull function was taken as a dependent variable, and a regression evaluation was used to define relationships with concentration for selected insecticides. The mode Y = b0 + b1 · X⁻1, in which Y = LT90 and × = insecticide concentration in g litre⁻1, proved useful when a sufficient range of concentrations was included in the testing.     

The role of Caenorhabditis elegans sex-determination homologs,Mi-sdc-1 and Mi-tra-1 in Meloidogyne incognita

European Journal of Plant Pathology - Sex determination is a key developmental event in all organisms. The pathway that regulates sexual fate has been well characterized at the molecular level in...     

Amelioratory effect of vitamin E on organophosphorus insecticide diazinon-induced oxidative stress in mice liver

Considering that the involvement of reactive oxygen species (ROS) has been implicated in the toxicity of organophosphate insecticides (OPIs), the aim of this study was to investigate the ameliorative properties of vitamin E (vitE) against the subchronic effect of diazinon (DZN) on oxidative damage markers such as lipid peroxidation (LPO) and the antioxidant defense system (ADS) in the liver of male MFI albino mice. The groups were intraperitoneally (i.p) administered with either vehicle or vitE (100 mg/kg body weight) or ¼ LD₅₀ of DZN (16.25 mg/kg b.w.) or ½ LD₅₀ of DZN; 32.5 mg/kg b.w) or ¼ LD₅₀-DZN + vitE or ½ LD₅₀ + vitE every consecutive day for 14 days. Hepatic damage markers analysis revealed that alanine transferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and lactate dehydrogenase (LDH) were significantly decreased in both DZN doses. Also, the significantly increased levels of biomarkers of oxidative stress as LPO and protein carbonyl (PC) and the decreased antioxidant defenses like reduced glutathione (GSH), and free radical scavenger enzymes viz., catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and glutathione reductase (GSH-Rx) were noted in DZN-treated groups as compared to control group. Distinctly lower levels of GSH and increased levels of LPO, along with alterations in endogenous antioxidant enzymes were evident in hepatic toxicity of DZN which is dose-dependent. Hepatic specific marker enzymes were restored to normalcy in mice supplemented with vitE following treatment with DZN which otherwise was decreased in the DZN-treated mice. The results show that co-treatment of vitE with DZN prevents or diminishes the oxidative stress of DZN-treated mice and may act as a putative protective agent against DZN-induced liver tissue injury.     

Nematicidal activity of anion transport blockers against Meloidogyne incognita, Caenorhabditis elegans and Heterorhabditis bacteriophora

BACKGROUND: Because methyl bromide has been phased out as a soil sterilant, new nematicides are urgently needed. Four different chemical classes of organic acids acting as anion transport (AT) blockers were tested against a free-living nematode, Caenorhabditis elegans Maupas, a plant-parasitic nematode, Meloidogyne incognita (Kofoid and White) Chitwood, and an entomopathogenic nematode, Heterorhabditis bacteriophora Poinar, in toxicity bioassays. The materials tested were DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid), 9-AC (anthracene-9-carboxylic acid), NPPB [5-nitro-2-(3-phenylpropylamino)benzoic acid] and IAA-94 (indanyloxyacetic acid). RESULTS: All the compounds showed slowly developing nematicidal activity against second-stage juveniles of M. incognita and adults of C. elegans, but not against H. bacteriophora infective-stage juveniles. The LC(50) values of these compounds were < 50 mg L(-1) after 48 and 72 h incubation, while at 168 h incubation the LC(50) values were < 10 mg L(-1) for both sensitive species. Across both species and time, the LC(50) values generally differed no more than twofold among the four compounds tested in this study. In contrast, none of the compounds (200 mg L(-1)) caused more than control mortality to H. bacteriophora, even after 168 h of incubation. CONCLUSION: These compounds are potential leads for commercial nematicides. The insensitivity to H. bacteriophora is consistent with the natural exposure of this nematode to DST (3,5-dihydroxy-4-isopropylstilbene), a stilbene produced by its symbiotic bacterium. Based on the known activity of the compounds used in this study, it is suggested that anion transporters form the probable target sites for DIDS, 9-AC, NPPB and IAA-94 in nematodes.     

Oxidative damage, biochemical and histopathological alterations in rats exposed to chlorpyrifos and the antioxidant role of zinc

The protective effects of zinc on liver and kidney injury induced by chlorpyrifos (CPF) were investigated in rats. Male and female rats were orally administered CPF at a dose of 6.75 mg kg⁻¹ body weight for 28 consecutive days. An additional CPF group received zinc (227 mg l⁻¹) in drinking water throughout the experimental duration. Two groups more served as controls. Administration of CPF resulted in a significant increase in serum lipid peroxidation (LPO) level, while induced significant decreases in the activities of plasma superoxide dismutase (SOD), glutathione-S-transferase (GST) and serum acetylcholinesterase (AChE) either in male or female rats. Similarly, a significant increase in the levels of various serum marker enzymes [e.g. aminotransferases (AST and ALT), lactate dehydrogenase (LDH) and gamma glutamyl transferase (GGT)] and increase the level of total protein, uric acid and creatinine. In contrast, co-administration of zinc to CPF-treated animals restored most of these biochemical parameters to within normal levels. In case of AChE, supplementation of zinc showed little alteration in the activity of this enzyme especially in male rats treated with CPF. CPF caused histopathological change in liver and kidneys of male and female rats. However, zinc administration to CPF-treated animals resulted in overall improvement in liver and kidneys damage, emphasizing its antioxidant role. In light of the available data, it can deduce that CPF-induced lipid peroxidation, oxidative stress, liver and kidneys damage in male and female rats, and conjunction supplementation of zinc has resulted in pronounced ameliorating effect.     

Mechanism of resistance to dichlorvos in adult houseflies

Houseflies (Musca domestica) originating from agricultural buildings in Jalasjarvi (Vaasa province of Finland) were found to be resistant to contact with a variety of organophosphorus insecticides, including dichlorvos. Tolerance to topical application of bromophos, crotoxyphos, and trichlorfon was fairly high, to dimethoate and dichlorvos it was moderate, and to tetrachlorvinphos it was very low. Much higher degrees of resistance were obtained after exposure to surface deposits.Evidence is presented to suggest that the mechanism of resistance in the Jalasjarvi flies is probably based on reduced penetration. With dichlorvos less of the absorbed chemical penetrates the central nervous system (the thoracic ganglionic complex) of the resistant fly than penetrates that of the susceptible fly. No differences were apparent between the strains in the otherwise small rates of degradation of dichlorvos.     

Designing,implementing and servicing an insecticide resistance management strategy

Drawing on the experience gained in the management of resistance in Heliothis armigera in Australia, the successive stages of designing, setting up and monitoring an insecticide resistance management (I R M) programme are discussed, along with the problems that may have to be overcome in order to achieve success. While individual strategies will inevitably differ, the Australian experience should give valuable information for the setting up of IRM programmes worldwide.     

Toxic effects of novel organophosphorus insecticide (RPR-V) on certain biochemical parameters of euryhaline fish, Oreochromis mossambicus

The euryhaline fish, Oreochromis mossambicus was exposed to sub-lethal concentration (0.017 mg L⁻¹) of a novel phosphorothionate, 2-butenoic acid-3-(diethoxy phosphinothionyl) ethyl ester (RPR-V) for 30 days and allowed to recover for 7 days. Important biomarker enzymes were assayed in plasma, brain, gill, liver, kidney, and muscle during exposure tenures of day-3, -7, -15, -30, and also at 7 days (withdrawal) after stopping treatment. Acetylcholinesterase (AChE) activities of brain, gill, and muscle were strongly inhibited by 67, 75, and 66%, respectively, on day-30. Exposure (time) dependent increases in alanine aminotransferase (ALAT), and aspartate aminotransferase (ASAT), acid phosphatase (AcP), and alkaline phosphatase (AkP), activities in plasma and kidney; AcP and AkP activities in gill were noticed. However, significant decrease in ALAT, ASAT, AcP, and AkP activities in liver was observed. The depletion of glycogen was observed in liver, brain, and gill tissues, an indication of typical stress related response of the fish with pesticide. A significant increase in lactate dehydrogenase (LDH) activity in gill and brain was observed and decreased in liver and muscle, indicating tissue damage and muscular harm. Depletion of glutathione (GSH) was observed in the above tissues, there by enhancing the lipid peroxidation resulting in cell damage. The induction in hepatic glutathione-S-transferase (GST) levels indicates the protection against the toxicity of xenobiotic-induced lipid peroxidation. There was a significant recovery in all the above biochemical parameters, in all the tissues of fish after a recovery period of 7 days. These results revealed that RPR-V affects the intermediary metabolism of O. mossambicus and the increase of biomarker enzymes in plasma, might be due to the necrosis of liver.     

The effects of salinity and temperature on the in vitro metabolism of the organophosphorus insecticide fenitrothion by the blue crab,Callinectes sapidus

The in vitro metabolism of fenitrothion [O,O-dimethyl-O-(3-methyl-4-nitrophenyl)phosphorothioate] by subcellular fractions prepared from the hepatopancrease of blue crabs, Callinectes sapidus, which had been acclimated to either 22°C, 34‰ (parts per thousand); 22°C, 17‰; or 17°C, 34‰ seawater was investigated. In the microsomal fraction, fenitrothion was metabolized to fenitrooxon and 3-methyl-4-nitrophenol. Fenitrothion was metabolized to desmethyl fenitrothion in the cytosolic fraction. The rates of formation of the detoxification products, 3-methyl-4-nitrophenol and desmethyl fenitrothion, were greater in subcellular fractions prepared from crabs which had been acclimated to the lower salinity seawater. The rate of formation of the more toxic metabolite fenitrooxon was greater in the microsomal fraction prepared from crabs which had been acclimated to higher salinity water. All three of these metabolites were formed at considerably faster rates in subcellular fractions from crabs acclimated to and incubated at 22 than at 17°C. These results suggest that enzyme activity contributes to the increased in vivo toxicity of fenitrothion to blue crabs at elevated salinities and temperatures. Also, the observed differences in the rate of formation of the oxon have a greater effect on toxicity than differences in the rate of formation of 3-methyl-4-nitrophenol and desmethyl fenitrothion.     

四种新烟碱类杀虫剂对蜜蜂的急性毒性及初级风险评估

杀虫剂增效剂是提高杀虫剂杀虫效果和降低抗药性的关键成分。本文对具有特异性增效活性的八元氧桥环结构进一步衍生,设计合成了15个新型的N-苯基八元氧桥环新烟碱化合物,并测试了目标化合物与吡虫啉联用时对苜蓿蚜Aphis craccivora 的致死率。结果表明：在1 mg/L质量浓度下,大部分目标化合物能使吡虫啉对苜蓿蚜的毒力增加,表现出增效作用,其中苯环上无取代的化合物4a和4-CF₃取代的化合物4m增效活性相当,其对吡虫啉毒力的增效倍数分别为3.44和3.58,可作为候选化合物进一步研究。

     

Neonicotinoids-from zero to hero in insecticide chemistry

In recent years, neonicotinoids have been the fastest-growing class of insecticides in modern crop protection, with widespread use against a broad spectrum of sucking and certain chewing pests. As potent agonists, they act selectively on insect nicotinic acetylcholine receptors, their molecular target site. The discovery of neonicotinoids can be considered as a milestone in insecticide research and facilitates greatly the understanding of the functional properties of insect nicotinic acetylcholine receptors. Because of the relatively low risk for non-target organisms and environment, the high target specificity of neonicotinoid insecticides and their versatility in application methods, this important class has to be maintained globally for integrated pest management strategies and insect resistance management programmes. This review comprehensively describes particularly the origin, structure and bonding as well as associated properties of neonicotinoid insecticides.     

Evaluation of inexpensive thin-layer chromatographic procedures for the estimation of some organophosphorus and carbamate insecticide residues in fruit and vegetables

Modified versions of previously published procedures for the extraction and clean-up of some organophosphorus insecticide residues in fruits and vegetables are described, and their usefulness in combination with selected thin-layer chromatographic procedures is experimentally assessed for several pesticides in apples, oranges, tomatoes, carrots and peas. A simple extraction procedure for insecticidal carbamates is similarly evaluated for carbaryl and propoxur residues in apples, carrots and peas. Semi-quantitative estimation, by visual comparison with standards, is shown to be possible in many cases at residue levels as low as 0.4 mg kg^?1, and the combined procedures should be useful in the screening of fruits or vegetables for compliance with maximum residue limits.     

Resistance of Thrips tabaci to pyrethroid and organophosphorus insecticides in Ontario, Canada

Onion thrips, Thrips tabaci Lindeman, were collected from commercial onion fields in 2001, 2002 and 2003 to assess resistance to lambda-cyhalothrin, deltamethrin and diazinon. In 2001, six of eight adult populations were resistant to lambda-cyhalothrin, with resistance ratios (RR) ranging from 2 to 13.1 and four of these were also resistant to deltamethrin, with RR ranging from 19.3 to 120. Three of four adult populations were resistant to diazinon with RR ranging from 2.5 to 165.8. In 2002, four of seven nymphal populations and three of six adult populations were resistant to deltamethrin, with RR ranging from 4.3 to 72.5 and 9.4 to 839.2, respectively. Only one of six nymphal populations and one of five adult populations were resistant to diazinon, with RR of 5.6 and 2.3, respectively. In 2003 diagnostic dose bioassays, 15 of 16 onion thrips populations were resistant to lambda-cyhalothrin and all were resistant to deltamethrin. Eight of the 16 were resistant to diazinon. These results indicate that insecticide resistance is widespread in onion thrips in commercial onion fields in Ontario.     

Effects of a fungicide, an insecticide, and a biopesticide on Tolypothrix scytonemoides

Lower concentrations of Bavistin supported good growth of Tolypothrix scytonemoides with maximum protein and pigment contents. The rates of photosynthetic oxygen evolution declined in cells grown in the pesticide-amended medium but rates of respiratory oxygen consumption were enhanced in cells grown in lower concentrations of Monocrotophos and Nimbicidin. Activities of nitrogenase and glutamine synthetase were affected in all the pesticide treatments but nitrogenase activity was enhanced in the presence of Bavistin. Release of ammonia and carbohydrates was enhanced in cells grown in pesticide-amended medium except for cells grown in medium containing Bavistin where the release of carbohydrates was reduced. New polypeptides of ∼280, 152, and 25 kDa (in 250 ppm Bavistin), ∼58 and 28 kDa (in 0.3 and 0.2-0.4 ppm Monocrotophos, respectively) and ∼31, 28, and 26 kDa (in 0.5 and 1.0 ppm Nimbicidin) were detected in the treated cells.