Effects of malathion on disease susceptibility in Woodhouse's toads.

Adult male Woodhouse's toads (Bufo woodhousi) developed clinical disease, hepatomegaly, and died at a higher rate when externally exposed once to either a high or low sublethal dose (0.011 or 0.0011 mg malathion/g toad) of field grade malathion and challenged with a sublethal dose of Aeromonas hydrophila injected intraperintoneally (1.1 x 10(4) bacteria/g toad) when compared to toads not exposed to malathion but challenged with A. hydrophila (P < 0.007). Toads exposed to malathion (high or low dose) and challenged with A. hyydrophila had clinical disease, hepatomegaly, and died at a higher rate [9 (90%) of 10] than toads exposed to malathion alone (P < 0.002). Toads exposed to the high and low doses of malathion had a 22% and 17% decrease in brain cholinesterase levels, respectively, when they were compared to nonmalathion exposed toads (P < 0.025, P < 0.006). It appears that field grade malathion applied externally to adult Woodhouse's toads may cause increased disease susceptibility when challenged with a potentially pathogenic bacteria.     

Malathion-induced Oxidative Stress in Rat Brain Regions

Malathion is a pesticide with high potential for human exposure. However, it is possible that during the malathion metabolism, there is generation of reactive oxygen species (ROS) and malathion may produce oxidative stress in intoxicated rats. The present study was therefore undertaken to determine malathion-induced lipid peroxidation (LPO), protein carbonylation and to determine whether malathion intoxication alters the antioxidant system in brain rats. Malathion was administered intraperitoneally in the acute and chronic protocols in the doses of 25, 50, 100 and 150 mg malathion/kg. The results showed that LPO in brain increased in both protocols. The increased oxidative stress resulted in an increased in the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT), observed in cortex, striatum in the acute malathion protocol and hippocampus in the chronic malathion protocol. Our results demonstrated that malathion induced oxidative stress and modulated SOD and CAT activity in selective brain regions.     

Involvement of chromosomally-encoded genes in malathion utilization by Pseudomonas aeruginosa AA112

Malathion is an organophosphate insecticide that has been widely used for both domestic and commercial agricultural purposes. However, malathion has the potential to produce toxic effects in mammalian systems. In this study, Pseudomonas aeruginosa AA 112 which was isolated from soil using enrichment technique could utilize the malathion as a sole carbon source and a source of energy. Pseudomonas aeruginosa AA112 was able to grow in MSMPY medium containing 42.75 mg/ml malathion. However, the optimum concentration of malathion which supported the maximum bacterial growth was found to be 22. 8 mg/ml. Malathion was used as an initial source of energy and carbon when it was found without additional carbon sources (in MSM medium) while it was utilized as second source of energy and carbon in a nutrient-supplemented medium (in MSMPY medium). Moreover, lead acetate test indicated that malathion was first attacked at a sulphur site 1-2 hours after the start of incubation. TLC and IR analysis indicated that malathion was completely degraded into diethyl succinate, hydrogen sulphide and phosphates. Therefore a malathion degradation pathway was proporsed. The degradation of malathion is attributed to the genes located on the chromosome and at least three proteins of high molecular size might be involved in malathion utilization. Bacteria able to use malathion as a food source or metabolize its residues in the environment to inactive, less toxic, and harmless compounds, could be used in bioremediation of an environmental pollution caused by the pesticide.     

The breakdown of malathion in soil and soil components

The disappearance of the organophosphorus insecticide, malathion, from a silt loam soil and from its organic and inorganic components was examined. Half-lives and the time taken for 90% decomposition in nonsterile, sodium azide-treated, and 2.5 Mrad-irradiated soils were similar (3/4–1 1/2 days and 4–6 days, respectively) but breakdown in autoclaved soils was negligible. Decay in nonsterile sand, silt, and clay minus organic matter fractions was 3–6 times slower than that recorded in the original soil. Breakdown of malathion in the clay plus organic matter fraction (organo-mineral complex) was rapid (half-life, 1 day), as was the case in the separated organic matter (half-life, 1 3/4 days). Filter-sterilized organic matter was not as effective in catalyzing the breakdown of malathion (half-life, 4 days), and no loss occurred from any of the autoclaved components. Irradiation doses of 2.5 and 5.0 Mrad had little influence on the ability of soil to degrade malathion. Thereafter, increases up to 20 Mrad had a more drastic, though far from totally inhibitory, effect. Our results suggest that either the colloidal organic matter itself, or a fraction associated with it, is the most important single factor concerned with the rapid breakdown of malathion in the soil studied. Direct microbial metabolism is a slower process and may have a significant role in malathion disappearance in coarsetextured soils low in colloidal organic matter. The catalytic component of the organic matter is suggested to be a stable exoenzyme and is supportive of reports by other workers. The quantitative effect of organo-mineral complex (containing the active degradative ingredient) additions to sand and silt fractions on the rate of subsequent malathion decay is also described.     

Multiacreage evaluation of aerially applied adherent malathion granules for selective insect control and indirect reduction of mycotoxigenic fungi in specialty corn

Aerially applied adherent corn flour granules containing 1% malathion were more often as, or more, effective than 15% chlorpyrifos (Lorsban 15G) granules in controlling caterpillars and sap beetles in high amylose corn in 1997 than 1996. Use of malathion granules corresponding closely in size to chlorpyrifos granules in the second year of the study apparently increased relative efficacy. Significantly less corn borer damage occurred on plants (1996) or ears (1997) within 2 wk of application for both types of insecticide granules compared with untreated plots. In 1997, there were sixfold fewer milk stage ears with more than 20 kernels damaged per ear in the malathion-treated plots compared with chlorpyrifos-treated plots, and severity of caterpillar damage was also less in malathion versus chlorpyrifos-treated plots at harvest. Control of beetles (corn rootworm adults and sap beetles) for both treatments was less effective compared with caterpillars. Significant corn rootworm adult control was noted for both chlorpyrifos and malathion in 1996 and significant sap beetle control was noted for the malathion granules in 1997. Significantly fewer live lady beetles, and more dead lady beetles were present in chlorpyrifos-treated plots compared with malathion-treated or untreated plots in 1996. The incidence and severity of Fusarium mold on ears at harvest was often indirectly reduced by both malathion treatments and chlorpyrifos treatments, with the malathion treatment significantly better than the chlorpyrifos treatment in one case.     

Boll weevil (Coleoptera: Curculionidae) bait sticks: toxicity and malathion content

Assays of malathion content and toxicity to boll weevil, Anthonomus grandis grandis Bohemian, were conducted on boll weevil bait sticks, now marketed as Boll Weevil Attract and Control Tubes (BWACTs; Plato Industries, Houston, TX). In general, the longer BWACTs were in the field, the lower the mortality of weevils that were exposed to them. Bioassays of weevil mortality correlated with hexane washes of BWACT surfaces showed highly variable mortality when surface malathion fell below approximately 20 ng per 1 microl of hexane, but consistently high mortality (> or = 90%) when surface malathion was above 30 ng per 1 microl of hexane. A linear equation was calculated to predict mortality as a function of malathion on a BWACT surface. Although mortality was related to surface amounts of malathion, it was unrelated to the total amount of malathion present in BWACTs. Similarly, surface malathion was unrelated to the total amount present in BWACTs. As with mortality, amount of surface malathion declined with time, but total malathion did not decline with time. Boll weevils placed on fresh BWACTs tended to accumulate more malathion and died in greater numbers as time spent on fresh tubes increased, but not as time spent on tubes aged in the field (for 5 mo total) increased. Weevils that landed on tubes after a short flight died in approximately the same numbers as those that were placed on tubes using proper methodology. The amount of malathion expected to cause 90% mortality of boll weevils subjected to proper methodology was 47% higher than for a less stringent methodology (34.3 versus 23.4 ng), which demonstrates the importance of strictly adhering to proper methodology; nevertheless, chemical assay of malathion on the BWACT surface proved to be a more consistent measure of BWACT toxicity than bioassay, and it should replace the bioassay.     

Efficacy of ground spray application of bait sprays with malathion or spinosad on Mexican fruit fly (Diptera: Tephritidae) in Texas citrus

An important component in the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae), eradication program is bait spray application to knock down localized A. ludens infestations enhancing the sterile to wild fly ratio and increasing the effectiveness of the sterile insect release program. Efficacy tests were conducted using spray equipment that applies ultralow application rates of malathion NU-LURE or GF-120 spinosad by ground into citrus. Trapit Dome traps located in fields treated with malathion NU-LURE and GF-120 spinosad high rate caught significantly fewer flies than the control in all replications. Treatments reduced the Mexican fruit fly populations by 99.1 and 92.5% with malathion and 98.2 and 89.9% with GF-120 spinosad high rate. Traps in plots with lower rates of GF-120 reduced fly populations by 76.3 and 74.3% in winter and summer test, respectively. There was no indication of fly repulsion from either malathion or GF-120 spinosad during this test. The bait spray option using ground spray equipment to apply ultra-low rates of either malathion NU-LURE or GF-120 spinosad high rate is a viable cost effective treatment method to treat small acreages for A. ludens. For organic growers, the ground spray equipment is effective in applying GF-120 spinosad at the labeled rates.     

Malathion and pyrethroid resistance in Culex quinquefasciatus from Cuba: efficacy of pirimiphos-methyl in the presence of at least three resistance mechanisms

Use of malathion for mosquito control in Cuba for 7 years up to 1986 has selected for elevated non-specific esterase and altered acetylcholinesterase (AChE) resistance mechanisms in populations of the pest mosquito Culex quinquefasciatus Say. These mechanisms are still present in relatively high frequencies in the Havana area, despite the replacement of malathion by pyrethroid insecticides for the last 3 years in the mosquito control programme. Samples of Culex quinquefasciatus populations from within a 100 km radius of Havana had high levels of resistance to malathion and lower levels of resistance to propoxur, but there was little or no cross-resistance to the organophosphorus insecticide pirimiphos-methyl. Selection with malathion for twenty-two consecutive generations in the laboratory increased the level of malathion resistance to 1208-fold and propoxur level to 1002-fold, but the maximum level of pirimiphos-methyl resistance was only 11-fold. Pirimiphos-methyl is still operationally effective, despite the resistance mechanisms segregating, so this insecticide if used for control is unlikely to select either of the known resistance factors directly in the field population. Since 1986, pyrethroids have been used extensively, and low levels of pyrethroid resistance were detected in two of five field population samples tested. Malathion selection did not increase the level of pyrethroid resistance, which indicates that one or more distinct pyrethroid resistance factors are now being selected in the field populations of Culex quinquefasciatus.     

抗马拉硫磷淡色库蚊不同基因型的自然内禀增长率及其对抗性演化的影响

本文涉及淡色库蚊(Culex pipiens pallens)抗马拉硫磷纯合子(RR)、杂合子(RS)和敏感纯合子(SS)的自然内禀增长率及其对马拉硫磷抗性演化的影响。RR、RS和SS的内禀增长率分别为0.1118、0.1171和0.1339。RR和RS基因型在无杀虫剂时呈现出繁殖不利性,RR和RS的相对适合度分别是SS的0.65和0.68。 影响淡色库蚊对马拉硫磷进化的某些因子在计算机上进行了模拟。模拟的因子包括R等位基因的起始频率(P_o)、所用马拉硫磷的剂量和迁入率(m)。模拟结果表明(I)不用药时R等位基因衰减是由于RR和RS基因型的繁殖不利性;(2)在起始种群N_o=200,P_o=0.1,使用杀死全部SS和RS的剂量(8ppm)处理,使R等位基因为有效隐性,并且m≥0.15时可阻止马拉硫磷抗性的发生。     

Evaluation of malathion-induced cytogenetical effects and oxidative stress in plants using Allium test

The present study emphasized to explore the toxicity effect of malathion on plants using Allium test. The experiments explored the mitotic inhibition, growth and activity of antioxidant enzymes in roots of Allium cepa at different concentrations (50, 125, 250 and 375 ppm) of malathion under different exposure periods (3, 9 and 18 h). The results revealed that all concentrations of malathion were capable to decline the root growth. Malathion-induced mitotic alterations varying from reduction in mitotic index (MI), relative division rate (RDR) and phase distribution along with large number of chromosomal aberrations. These changes were of varying degree depending on the concentration and treatment period. The roots treated with malathion (375 ppm) showed significant (p ≤ 0.05) higher levels of superoxide dismutase and catalase than the control, while the activity of peroxidase was significantly (p ≤ 0.05) low. At 375 ppm malathion, malondialdehyde content was significantly high (p ≤ 0.05) that was increased with the treatment period. Findings concluded that variations in mitotic index, chromosomal aberrations, alterations in malondialdehyde content and activities of antioxidant enzyme could serve as the useful indicators for monitoring the effects of malathion exposures in the real scenario. Superoxide dismutase and catalase enzyme play vital roles in the antioxidant defence mechanisms under malathion toxicity. According to the data on the malondialdehyde content show malathion to be capable of producing superoxide radicals indirectly, and to result in membrane damage and oxidative stress.     

Use of Malathion Against Ectoparasites on Lactating Cows

The clinical effect, residues in milk and toxicological properties of a non-commercial formulation of malathion used as an ectoparasitic agent on cattle were investigated. The results show that the malathion preparation has a desired clinical effect. The maximum concentration of malathion in milk after topical application of 5 g malathion was 0.054 μg/ml 4–6 h post-treatment, and declined to 0.005 and 0.002 μg/ml 24 and 48 h post-treatment, respectively. Totally 0.006–0.03 % of the applied dose was excreted in the milk. No toxic effect, measured as inhibition of the cholinesterases in erythrocytes and plasma, could be detected after therapeutic use of malathion. The pharmacokinetic evaluation after 2.5 g intravenous administration of malathion, indicated that the kinetics could probably be described by a multicompartment model.     

The effect of gamma-irradiation on the toxicity of malathion in V79 Chinese hamster cells and Molt-4 human lymphocytes.

There is growing interest in the irradiation of food and agricultural products for insect disinfestation, sprout inhibition, delayed ripening and the reduction of microbiological loads. Extensive research has been done on this process, and irradiation to a maximum dose of 10 kGy is recognized as safe by national and international regulatory agencies. The question has been raised, however, whether irradiation of pesticide residues might produce radiation products that were more toxic or less toxic than the original pesticide. To address this question, we observed the effects of 10 kGy of gamma-radiation on malathion as measured by sister-chromatid exchange (SCE), micronuclei formation, cell survival, growth rate and polyploid formation. We found no significant differences between the effects of irradiated and unirradiated malathion on any of these end-points. Polyploid formation was the most dramatic effect of both irradiated and control malathion on V79 Chinese hamster cells. Cell survival, polyploid formation and growth rate were slightly better in cells treated with irradiated malathion. In Molt-4 human lymphocyte cells, micronuclei formation was not affected by irradiated or unirradiated malathion. Compared to malathion alone, the lack of such biological effects indicates that none of the presumed radiation-induced breakdown products increased or decreased the endpoints studied. The number of SCE was consistently, but not significantly, higher in the cells treated with irradiated malathion. There were no significant differences in cell survival or micronucleus formation in the human lymphocyte cell line Molt-4 treated with irradiated or control malathion. Thus, the irradiation of the pesticide malathion to 10 kGy, a recommended upper dose for most food irradiations, does not significantly alter its toxicity in these in vitro systems.     

Mitochondrial Respiratory Dysfunction and Oxidative Stress after Chronic Malathion Exposure

Malathion is a pesticide used on a large scale and with high potential risk for human exposure. However, it is reasonable to hypothesize that while the malathion is metabolizing reactive oxygen species (ROS) can be generated and subsequently there is onset of an oxidative stress in central nervous system (CNS) structures: hippocampus, cortex, striatum and cerebellum of intoxicated rats due to mitochondrial respiratory chain disfunctions. The present study was therefore undertaken to evaluate malathion-induced lipid peroxidation (LPO), superoxide production from sub-mitochondrial particles and the activity of complexes II and IV of the mitochondrial respiratory chain. Malathion was administered in doses of 25, 50, 100 and 150 mg malathion/kg. After malathion administration LPO increased in hippocampus and striatum. This was accompanied by an increase in the formation of superoxide in submitochondrial particles in the hippocampus. Complex IV suffered significant inhibition of its activity. We could demonstrate in this study that malathion induces oxidative stress and it could be due to inactivation of mitochondrial respiratory complexes.     

The genetic basis of malathion resistance in housefly (Musca domestica L.) strains from Turkey

Organophosphate insecticide (parathion/diazinon) resistance in housefly (Musca domestica L.) is associated with the change in carboxylesterase activity. The product of MdalphaE7 gene is probably playing a role in detoxification of xenebiotic esters. In our research, we have isolated, cloned and sequenced the MdalphaE7 gene from 5 different Turkish housefly strains. High doses of malathion (600 microg/fly) were applied in a laboratory environment for one year to Ceyhan1, Ceyhan2, Adana and Ankara strains while no insecticide treatment was performed in the laboratory to Kirazli strain. Trp251 --> Ser substitution was found in the product of MdalphaE7 gene in all malathion resistant and Kirazli stocks. In addition, we checked the malathion carboxylesterase (MCE), percent remaining activities in acetylcholinesterase (AChE), glutathion-S-transferase (GST), and general esterase activities in all 5 strains used in this study. In comparing with universal standard sensitive control WHO, a high level of MCE and GST activities were observed while lower level of general esterase activities was detected in the tested strains. In addition, a higher percent remaining activities in AChE than WHO susceptible strain were observed in all malathion resistant strains.     

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

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

N‐Acetyl‐cysteine mediated inhibition of spermatogonial cells apoptosis against malathion exposure in testicular tissue

Toxicological studies so far suggest that excessive use of malathion, an organophosphate insecticide, causes serious ill‐effects in mammalian reproductive physiology. The present study aims at assessing malathion‐induced toxicity in a dose‐ and time‐dependent manner with mitigating effects of N‐acetyl‐l ‐cysteine. The testicular germ cell viability was monitored using MTT assay, where NAC, being an antioxidant significantly reduced malathion‐induced toxicity by enhancing the frequency of cell viability. The histomorphological analysis showed that NAC successfully diminished several apoptotic features in testicular cells, induced by malathion. The differential EB/AO staining revealed a significant decline in the percentage of apoptosis after NAC supplementation. NAC also diminished the malathion‐induced DNA fragmentation along with significantly reduction in oxidative stress parameters causing decrease in lipid peroxidation and enhancement of ferric reducing antioxidant power within testicular germ cells. Thus, NAC mitigated the malathion‐induced toxicity, proving its potential in infertility treatment.     

Genetic consequences of linkage between malathion resistance and an autosomal male-determining factor in house fly (Diptera: Muscidae).

The pattern of inheritance of genes conferring resistance to malathion and genetic consequences of linkage between an autosomal male-determining factor and resistance genes on the second chromosome were investigated in a strain of house fly, Musca domestica L., selected for malathion resistance. The second and fifth chromosomes contribute significantly to malathion resistance. The presence of a male-determining factor linked with the resistance genes on the second chromosome resulted in a strong sexual dimorphism in malathion resistance. We also observed that the male-determining factor changed its linkage relationship from the third linkage group to the second linkage group during the selection experiments.     

Very high DDT-resistant population of Anopheles pharoensis Theobald (Diptera: Culicidae) from Gorgora, northern Ethiopia

Standard WHO insecticide bioassay tests were carried out in Gorgora, northern Ethiopia to evaluate the susceptibility status of Anopheles pharoensis Theobald for the insecticides DDT, malathion, permethrin and deltamethrin. The mortality and when appropriate knockdown effect of the insecticides were observed. The results indicated that this species was resistant to DDT. A high mortality was obtained after exposure to permethrin and deltamethrin but below 97 % which is the limit for susceptibility according to WHO. A prolonged knockdown time was noted for DDT and the two pyrethroids. An. phoaroensis was found to be susceptible to malathion.     

A 5000-Fold Increase in the Specificity of a Bacterial Phosphotriesterase for Malathion through Combinatorial Active Site Mutagenesis

Phosphotriesterases (PTEs) have been isolated from a range of bacterial species, including Agrobcaterium radiobacter (PTE_Ar), and are efficient enzymes with broad substrate ranges. The turnover rate of PTE_Ar for the common organophosphorous insecticide malathion is lower than expected based on its physical properties; principally the pk_a of its leaving group. In this study, we rationalise the turnover rate of PTE_Ar for malathion using computational docking of the substrate into a high resolution crystal structure of the enzyme, suggesting that malathion is too large for the PTE_Ar binding pocket. Protein engineering through combinatorial active site saturation testing (CASTing) was then used to increase the rate of malathion turnover. Variants from a CASTing library in which Ser308 and Tyr309 were mutated yielded variants with increased activity towards malathion. The most active PTE_Ar variant carried Ser308Leu and Tyr309Ala substitutions, which resulted in a ca. 5000-fold increase in k _cat/K _M for malathion. X-ray crystal structures for the PTE_Ar Ser308Leu\Tyr309Ala variant demonstrate that the access to the binding pocket was enhanced by the replacement of the bulky Tyr309 residue with the smaller alanine residue.