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PubMed2002

Susceptibility and detoxifying enzyme activity in two spider mite species (Acari: Tetranychidae) after selection with three insecticides.

Changes in the susceptibility and detoxifying enzyme activity were measured in laboratory strains of Banks grass mite, Oligonychus pratensis (Banks), and twospotted spider mite, Tetranychus urticae Koch, that were repeatedly exposed to three insecticides. Three strains of each mite species were exposed to one of two pyrethroids, bifenthrin, and lambda-cyhalothrin, or an organophosphate, dimethoate, for 10 selection cycles at the LC60 for each insecticide. A reference or nonselected strain of each mite species was not exposed to insecticides. After 10 cycles of exposure, susceptibility to the corresponding insecticides, bifenthrin, lambda-cyhalothrin, and dimethoate, decreased 4.5-, 5.9-, and 289.2-fold, respectively, relative to the reference strain in the respective O. pratensis strains, and 14.8-, 5.7-, and 104.7-fold, respectively, relative to the reference strain in the respective T. urticae strains. In the bifenthrin-exposed O. pratensis strain, there was a 88.9-fold cross-resistance to dimethoate. In the dimethoate-exposed T. urticae strain, there was a 15.9-fold cross-resistance to bifenthrin. These results suggest that there may be cross-resistance between dimethoate and bifenthrin. The reduced susceptibility to dimethoate remained stable for three months in the absence of selection pressure in both mites. The decrease in susceptibility in the O. pratensis strains exposed to bifenthrin, lambda-cyhalothrin, and dimethoate was associated with a 4.7-, 3.0-, and 3.6-fold increase in general esterase activity, respectively. The decrease in susceptibility in the T. urticae strains exposed to bifenthrin and lambda-cyhalothrin was associated with a 1.3- and 1.1-fold increase in general esterase activity, respectively. The mean general esterase activity was significantly higher in the pyrethroid-exposed O. pratensis and T. urticae strains than in the nonselected strain. There was no significant increase in esterase activity in the dimethoate-exposed T. urticae strain. The decrease in susceptibility to insecticides was also associated with reduced glutathione S-transferase 1-chloro-2, 4-dinitrobenzene conjugation activity, but this did not appear to be related to changes in insecticide susceptibility. These results suggest that in these mites, the general esterases may play a role in conferring resistance to pyrethroids. However, some other untested mechanism, such as target site insensitivity, must be involved in conferring dimethoate resistance.

Animals↗
PubMed2000

Performance of a pyrethroid-resistant strain of the predator mite Typhlodromus pyri (Acari: Phytoseiidae) under different insecticide regimes.

An organophosphate pyrethroid-resistant strain of Typhlodromus pyri Scheuten imported from New Zealand was reared on potted apple trees in an outdoor insectary. From 1988 to 1995, the population was selected one to three times per year with a dilute solution (1.7 ppm) of the pyrethroid cypermethrin. Petri dish bioassays with cypermethrin in 1995 indicated that the insectary-reared T. pyri had an LC50 of 81 ppm versus 0.006 ppm for native T. pyri taken from a research orchard. The bioassays suggested that recommended orchard rates of cypermethrin would cause heavy mortality in native populations of T. pyri but only moderate losses in the imported New Zealand strain. Bioassays in 1996 with the organophosphate insecticide dimethoate indicated both New Zealand and native T. pyri were susceptible and that recommended orchard rates of dimethoate likely would cause high mortality of T. pyri in apple orchards. These findings from bioassays were supported by data from orchard trials. In June and July 1993, insectary-reared New Zealand T. pyri were placed on five apple trees in each of eight 38-tree plots in the research orchard. In late August 1994, New Zealand T. pyri from orchard trees that had been sprayed twice by airblast sprayer with the full recommended rate of 50 g (AI)/ha (83 ppm) cypermethrin were placed on the other 33 trees in each of six plots. In the summers of 1994-1996, plots were treated with one of the following insecticide regimes: (1) conventional integrated pest management (IPM) (registered neurotoxic insecticides considered harmless or slightly toxic to T. pyri); (2) advanced IPM (use of newer, more selective insecticides); (3) pyrethroid (at least one full-rate application of cypermethrin); (4) dimethoate; and (5) dimethoate plus pyrethroid. Densities of European red mite, Panonychus ulmi (Koch), were highest in all plots treated with dimethoate and in pyrethroid plots not yet inoculated with New Zealand T. pyri. Densities of apple rust mite, Aculus schlechtendali (Nalepa), and of the stigmaeid predator Zetzellia mali (Ewing) were highest in plots treated with dimethoate and were nearly absent in the IPM plots. Densities of T. pyri were high enough for effective biocontrol in the IPM plots and in the pyrethroid plots 1-2 yr after release of the New Zealand strain, provided pyrethroid was applied just before the resistant strain was released in the orchard. A recurring theme of this study was the generally negative association between densities of phytophagous mites and those of T. pyri, suggesting the ability of this predator to suppress their prey. In contrast, the positive association between phytophagous mites and Z. mali suggests the inability of this predator to regulate their prey at least under the conditions of this study.

Animals↗
PubMed2004

Teratogenicity study of some pesticides in chicken embryos.

The use of pesticides involves the risk of poisoning on wild animals. Teratological tests carried out on avian embryos provide useful data for environmental protection and facilitate the development of environment-friendly chemical plant protection techniques. A 30% dimethoate containing insecticide formulation (BI 58 EC) and a 20% benfluralin containing herbicide formulation (Flubalex) and a 960 g/l S-metolachlor containing herbicide formulation (Dual Gold 960 EC) were studied in chicken embryos after single administration by immersion and injection technique. Treatment was done on day 0 of incubation. Applied concentration of pesticides were 0.1% (dimethoate) and 2.05% (S-metolachlor) and 0.375% (benfluralin) corresponding to that used in plant protection practice. Test materials were injected into the air chamber in a volume of 0.1 ml/egg, or eggs were treated by the immersion technique for 30 min. at 37 degrees C. Evaluation was done on day 19 of incubation. Injection treatment: the administration of S-metolachlor and benfluralin did not result a significant decrease in the average body weight of embryos. At the same time the body weight of embryos significantly decreased because of single administration of dimethoate. The embryomortality increased markedly after the administration of test materials (S-metolachlor, benfluralin, dimethoate). Immersion treatment: the administration of S-metolachlor and benfluralin and dimethoate did not result a significant decrease in the average body weight of embryos. The rate of embryomortality was low after the administration of S-metolachlor, benfluralin and dimethoate. After the immersion and the injection treatment the incidences of developmental anomalies were sporadic. In summary it can be established that the injection treatment was more toxic than immersion technique of the test materials in our study.

Animals↗
PubMed1981

Combined hemoperfusion-hemodialysis in organophosphate poisoning.

We report on a patient treated with combined prolonged hemoperfusion (HP, Adsorba 300 C, Gambro, Sweden) and hemodialysis (HD, C-DAK 1.2, Cordis Dow, USA) for severe dimethoate poisoning. This procedure was adopted since the combination of dialysis and adsorption may improve overall drug removal. Combined HP-HD was performed during 24 h using the same charcoal column and dialyser. Adequate heparinization was obtained by monitoring the whole blood activated partial thromboplastin time. The patient (a 34-year-old female) ingested approximately 10 g of dimethoate (Teletox 10) in a suicide attempt, 30 min before admission to the hospital. On admission, serum level of dimethoate (analysed by gas chromatography) was 2340 ng ml-1. She received conventional treatment and combined HP-HD was started within 2 h after admission. At this time serum levels had risen to 3110 ng ml-1. However, they declined constantly during the epuration and after 18 h no more dimethoate could be detected in the serum. She was discharged 3 days after treatment. During the 24 h of HP-HD treatment, 110.8 mg dimethoate entered the epuration system via the plasma. 55.3 mg were extracted by the charcoal column and 25.3 mg by hemodialysis.

Adult↗
PubMed1995

Does a heterogeneous distribution of food or pesticide affect the outcome of toxicity tests with Collembola?

The reproduction of two closely related soil microarthropods, Folsomia candida Willem and Folsomia fimetaria L. (Insecta: Collembola), was tested under the influence of the insecticide dimethoate. Dimethoate had an adverse effect on the survival of adults and their reproduction in concentrations of about the recommended field dose, with F. fimetaria being more sensitive than F. candida. The experimental conditions were altered to evaluate the realism in the basic single species/single chemical reproductive test system. The importance of the spatial distribution of dimethoate was studied with food applied to the surface (original procedure), mixed homogeneously in the whole soil profile or only in the top layer, or mixed heterogeneously into the soil preserving the small granula of the yeast originally in the commercial formulation. Toxicity decreased significantly when exposure could be avoided in an uncontaminated bottom layer and even more if food was available in this soil horizon. But the results indicate that Collembola were not able to completely avoid dimethoate when they had the choice. For extrapolation purposes a simple test system may be sufficient as EC50 was changed less than one order of magnitude with the different test designs. In terms of EC50 the outcome of a toxicity test with a heterogeneous distribution of food and dimethoate was changed only slightly but the effects to suboptimally fed populations should be considered because they may be more vulnerable.

Animals↗
PubMed1997

Predator-prey relationships in a two-species toxicity test system.

In a two-species toxicity test system survival and reproduction of both the predator Hypoaspis aculeifer (Gamasida) and the prey Folsomia fimetaria (Collembola) were studied after 21 days of residual exposure to a soil contamination of the insecticide dimethoate. Additional experiments were run to analyze which species-species and compound-species relationships determine the outcome of this two-species experiment. Number of adult F. fimetaria were reduced by both predation and dimethoate exposure, whereas mites preyed less efficiently on adults than on juveniles. At 0.357 mg dimethoate/kg soil, numbers of juvenile F. fimetaria were mainly reduced by predation on adults and juveniles. At 0.7 mg/kg, an additional dimethoate effect was found, which was attributed to an effect on the reproduction of F. fimetaria, mainly due to lethality of adults. It was reasoned that lethal effects on juvenile springtails are less important. Adult H. aculeifer was not affected by dimethoate exposure, whereas numbers of juvenile H. aculeifer demonstrated a decline only at the highest concentration of 0.7 mg/kg. It is hypothesized that this latter effect is possibly due to food depletion caused by a decreased availability of prey, rather than to the lethal effects of dimethoate on juvenile mites. Such a secondary effect of a pesticide application could not have been derived from a single-species toxicity experiment and demonstrates the additional value of a two-species toxicity test system.

Animals↗
PubMedDate not supplied

Differences between organophosphorus insecticides in human self-poisoning: a prospective cohort study.

BACKGROUND: Although more than 100 organophosphorus insecticides exist, organophosphorus poisoning is usually regarded as a single entity, distinguished only by the compound's lethal dose in animals. We aimed to determine whether the three most common organophosphorus insecticides used for self-poisoning in Sri Lanka differ in the clinical features and severity of poisoning they cause. METHODS: We prospectively studied 802 patients with chlorpyrifos, dimethoate, or fenthion self-poisoning admitted to three hospitals. Blood cholinesterase activity and insecticide concentration were measured to determine the compound and the patients' response to insecticide and therapy. We recorded clinical outcomes for each patient. FINDINGS: Compared with chlorpyrifos (35 of 439, 8.0%), the proportion dying was significantly higher with dimethoate (61 of 264, 23.1%, odds ratio [OR] 3.5, 95% CI 2.2-5.4) or fenthion (16 of 99, 16.2%, OR 2.2, 1.2-4.2), as was the proportion requiring endotracheal intubation (66 of 439 for chlorpyrifos, 15.0%; 93 of 264 for dimethoate, 35.2%, OR 3.1, 2.1-4.4; 31 of 99 for fenthion, 31.3%, 2.6, 1.6-4.2). Dimethoate-poisoned patients died sooner than those ingesting other pesticides and often from hypotensive shock. Fenthion poisoning initially caused few symptoms but many patients subsequently required intubation. Acetylcholinesterase inhibited by fenthion or dimethoate responded poorly to pralidoxime treatment compared with chlorpyrifos-inhibited acetylcholinesterase. INTERPRETATION: Organophosphorus insecticide poisoning is not a single entity, with substantial variability in clinical course, response to oximes, and outcome. Animal toxicity does not predict human toxicity since, although chlorpyrifos is generally the most toxic in rats, it is least toxic in people. Each organophosphorus insecticide should be considered as an individual poison and, consequently, patients might benefit from management protocols developed for particular organophosphorus insecticides.

Acetylcholinesterase↗
PubMed1976

Linkage and dominance characteristics of genes for resistance to organophosphorus acaricides and allelic inheritance of decreased brain cholinesterase activity in three strains of the cattle tick, Boophilus microplus.

Resistance to the organophosphorus acaricides diazinon, dimethoate and formothion in the Biarra (B), Mackay (M) and Ridgelands (R) strains respectively of the cattle tick B. microplus has been shown previously to be controlled in each strain by a single incompletely dominant autosomal genetic factor. A very similar mode of inheritance of fenthion resistance in strain B has now been demonstrated with no departure in degree of dominance of resistance from the mean value of +0-57 common to these strains exposed to these chemicals. No F1 larval progeny from the following crossings were appreciably more resistant than their parents to these chemicals: R x B--bromophos ethyl and fenthion; B x M--carbaryl, chlorfenvinphos, chlorpyrifos, diazinon, dimethoate, ethion, fenthion and formothion; M x R--chlorfenvinphos, diazinon, dimethoate, ethion, formothion. The field importance of this absence of overdominance is discussed. There were no susceptible double recessive F2 larval progeny of B x M crossings of F2 or F3 larval progeny of R x M crossings when tested against dimethoate to which the three parental types were similarly resistant; 1/16 of the larval progeny would be expected to be completely susceptible if the resistance genes were unlinked. F1 adult progeny of B x M and R x M crossings exhibited the incompletely recessive mutant-type decreased brain acetylcholinesterase (AChE) activity common to strains B, M and R, thus satisfying the test for allelism. No ticks with normal levels of brain AChE were detected in F2 adult progeny of B x M or R x M crossings. This evidence was strongly suggestive of a series of closely linked genes or alleles controlling dimethoate resistance and a series of alleles controlling decreased brain AChE activity in strains B, M and R.

Acetylcholinesterase↗
PubMed2007

Organophosphate resistance in olive fruit fly, Bactrocera oleae, populations in Greece and Cyprus.

The olive fruit fly Bactrocera oleae (Gmelin) (Diptera: Tephritidae) is the most important pest of olives in countries around the Mediterranean basin. Its control has been based mostly on bait sprays with organophosphate insecticides (usually dimethoate or fenthion) for about 40 years. In the present study, the resistance status of olive fruit fly populations to dimethoate was examined in Greece and Cyprus over 2 years. Thirty-one populations from various regions of Greece, nine from Cyprus and one laboratory susceptible strain, which served as a control, were assayed by topical application of dimethoate. Considerable variation in the resistance levels to dimethoate was recorded in the populations of B. oleae, with resistance ratios ranging from 6.3 to 64.4 (ED(50) values 12.5-128.7 ng dimethoate per insect). The highest resistance ratios were found in populations from Crete, and the lowest in those from Cyprus. This variation could be attributed to different selection pressures from insecticidal applications among populations from the various regions. Migration of resistant genotypes, either autonomous or via commerce, may also be involved.

Animals↗
PubMedDate not supplied

Multiresidue determination of pesticides in drinking and related waters by gas chromatography/mass spectrometry after solid-phase extraction: interlaboratory study.

As part of a project funded by the European Commission (EC) for the development and evaluation of multiresidue methods for analysis of drinking and related waters, 15 European laboratories evaluated a method using styrene-divinylbenzene co-polymer solid-phase extraction followed by gas chromatography/mass spectrometry. The main aim of the study was to evaluate whether the method meets the requirements of EC Directive 98/83 in terms of accuracy, precision, and detection limit for 22 pesticides according to the following requirements: limit of detection, < or = 0.025 microg/L; accuracy, expressed as recovery between 75 and 125%; and precision, expressed as repeatability relative standard deviation of the method of < 12.5% and as reproducibility relative standard deviation of the method of < 25%. Analyses for unknown concentrations were performed with fortified commercial bottled and tap waters. All laboratories were able to achieve detection limits of 0.01 microg/L for all pesticides except dimethoate and desisopropylatrazine (0.02 microg/L). The criteria for repeatability were met for all compounds except trifluralin, dimethoate, and lindane in bottled water and chlorpyrifos, dimethoate, and lindane in tap water. The criteria for reproducibility were met for all compounds except trifluralin, dimethoate, and lindane in bottled water and pendimethalin, chlorpyrifos, dimethoate, terbutryn, and lindane in tap water. In terms of accuracy, the method meets the requirements for all pesticides in both matrixes, except for lindane in bottled water and lindane and chlorpyrifos in tap water.

Algorithms↗
PubMed1999

Temperature-time relationship in collembolan response to chemical exposure.

Effects of temperature on chemical toxicity to a collembolan, Folsomia candida, in relation to time were studied in this experiment. Field soil was used as a test substrate. Collembolans were incubated at three different temperatures (+13, +16, and +19 degrees C) and in two different dimethoate concentrations (1 and 3 mg/kg), clean soil serving as the control. Four destructive samplings were done at 2-week intervals. Dimethoate degradation was also analyzed. Dimethoate 1 mg/kg had a slight effect on both adult growth and reproduction, whereas 3 mg/kg was fatal to F. candida in the soil used. Toxic effects tended to last longer at low temperature than at high temperature, but the differences were not extensive. Temperature was negatively correlated with adult growth but positively correlated with reproduction. The dimethoate degradation rate was similar at all temperatures but differed with the concentration.

Animals↗
PubMed1997

Effect of soil moisture on pesticide toxicity to an enchytraeid worm, Enchytraeus sp.

The aim of the study was to find out whether soil moisture affects toxicity of organic pesticides to an enchytraeid worm. Laboratory experiments were carried out with dimethoate and benomyl, using a small Enchytraeus sp. as the test species. Substrate was natural agricultural field soil cultivated without pesticides for several years. Experimental design consisted of three soil moistures (40, 55, and 70% of water holding capacity) and five pesticide concentrations, plus controls. Measured parameters were survival, size of the parent worms and number and size of juveniles produced. Dimethoate was relatively non-toxic to this species. Dimethoate did not decrease survival, but sublethal effects on adult size and number of juveniles were observed. Adverse conditions in dry soil masked these effects; dimethoate appeared to be less toxic in dry soil than in moist soil. Benomyl caused significant mortality and the effects were very abrupt. Toxicity of benomyl decreased with increasing soil moisture content; in moist soil the worms survived at higher benomyl concentrations than in drier soils.

Animals↗
PubMed1997

Aphicide persistence on spinach and mustard greens.

Laboratory bioassays with green peach aphids, Myzus persicae (Sulzer), were conducted on samples from field grown spinach and mustard greens to determine the persistence of triazamate, dimethoate, and mevinphos. Treatment with each insecticide resulted in similar mortality initially on both crops. Mortality on samples from mevinphos treated plants declined considerably by 1 d after treatment. Dimethoate persisted for > 4 d at a level that would kill at least some aphids during the allotted time. Persistence of triazamate and dimethoate activities were similar on spinach. Triazamate, however, resulted in greater aphid mortality through time on mustard greens than did dimethoate.

Animals↗
PubMed2000

Toxicity and residual effectiveness of insecticides on insecticide-treated spheres for controlling females of Rhagoletis pomonella (Diptera: Tephritidae).

This study evaluated the toxicity of five technical-grade insecticides of four different classes to apple maggot females, Rhagoletis pomonella (Walsh), following a 10-min exposure period in insecticide-coated glass jars, with or without a feeding stimulant (sucrose) present. According to LC90 values for toxicity by ingestion and tarsal contact, imidacloprid was 1.5 times more toxic than dimethoate or abamectin, diazinon was less toxic, and phloxine B (a phototoxic dye) least toxic. Based on LC90 values for tarsal contact alone, dimethoate was 2.3, 4.0, and 18.4 times more toxic than imidacloprid, abamectin, and diazinon, respectively. Contact alone with phloxine B caused no mortality. When exposure was assessed using spheres coated with a latex paint mixture containing sucrose and formulated dimethoate (Digon 400 EC) or imidacloprid (Provado 1.6 F) at concentrations ranging from 5 to 70 g (AI)/cm2, both insecticides showed reduced effectiveness compared with toxicities from glass jar tests, with Digon two times more toxic than Provado. After exposure to artificial rainfall and retreatment with sucrose, Digon- and Provado-treated spheres exhibited greatest residual effectiveness, with diazinon-treated spheres less effective. Spheres treated with formulated abamectin (Agri-Mek 0.15 EC) at 1.0% (AI) performed only slightly better than phloxine B-treated spheres, which completely lost effectiveness after exposure to rainfall. Spheres treated with formulated imidacloprid (Merit 75 WP) at 1.5% (AI) showed equal or better residual efficacy in killing apple maggot flies (> 80% mortality, shorter lethal duration of feeding) over a 12-wk exposure period to outdoor weather than spheres treated with Digon at 1.0% (AI) after both types were retreated with sucrose. Our results indicate that imidacloprid is a promising safe substitute for dimethoate as a fly killing agent on lure-kill spheres. Imidacloprid formulated as Merit 75 WP had greater residual efficacy than imidacloprid formulated as Provado 1.6 F.

Animals↗
PubMed1976

Therapeutic properties.of haemodialysis and blood exchange transfusion in organophosphate poisoning.

Human blood was contaminated with nitrostigmine, dimethoate and demeton-S-methyl sulfoxide. It was then dialysed, concentrations of organophosphates were determined and dialysance values calculated. The influence of blood exchange transfusion on poison elimination as well as on the cholinesterase activity of blood, brain and muscle was studied in rats poisoned with nitrostigmine. Haemodialysis was found to be quite an effective method for eliminating demeton-S-methyl sulfoxide and dimethoate, dialysance values of 52.98 ml/min and 59.07 ml/min being found for demeton-S-methyl sulfoxide and dimethoate respectively. Nitrostigmine could not be removed by haemodialysis. These findings suggest that haemodialysis could be of therapeutic value in the treatment of severe demeton-S-methyl sulfoxide and dimethoate poisoning in man. By blood exchange transfusion only 0.06% of the injected dose of nitrostigmine could be removed from the body of poisoned rats. Acetylcholinesterase activity increased only briefly in the period of blood exchange transfusion and decreased gradually afterwards. The enzymatic activity of brain and muscle was unaffected. Therefore, blood exchange transfusion has, if any at all, only poor therapeutic properties in nitrostigmine intoxication.

Acetylcholinesterase↗
PubMed1996

Effect of pesticide mixtures on in vitro nervous cells: comparison with single pesticides.

The toxicity of dimethoate, azinphos-methyl, diazinon, pirimiphos methyl, organophosphorus insecticides, and benomyl (a benzimidazole fungicide) singly and in mixture was studied in a human neuroblastoma cell line, SH-SY5Y. The cells were incubated for 30 min and 4 h with pesticides at concentrations ranging from 0.4 to 100 micrograms/ml, or with the same compounds mixed as follows: (a) dimethoate-diazinon-azinphos; (b) benomyl-pirimiphos; (c) all together. Pesticides in the mixtures were at the same concentration used when tested singly. Diazinon, azinphos-methyl and pirimiphos, but not dimethoate and benomyl, inhibited acetylcholine esterase (AchE) activity, whereas all the compounds inhibited protein synthesis in the following order: benomyl > azinphos > diazinon >> pirimiphos = dimethoate. The mixtures showed a toxicity on AchE activity at a maximum equal to that of the most active compound in the mixture. On the contrary, the mixture were more toxic than the single compounds on protein synthesis, and in certain cases potentiation occurred. Therefore, we can conclude that it is not feasible to predict the toxicity of pesticide mixtures on the basis of the results of the toxicity of single components.

Acetylcholinesterase↗
PubMed2006

A comparison of the effects of single and repeated exposure to an organophosphate insecticide on acetylcholinesterase activity in mammals.

Exposure to organophosphate (OP) pesticides can occur in free-living mammals in treated areas. Risk to nontarget animals from OPs usually is assessed with acute exposure data, but exposure of wild animals is likely to be intermittent and chronic. We compared the effects of single or repeated (hourly and daily) exposure to dimethoate on acetylcholinesterase (AChE) activity in laboratory mice to assess the suitability of standard laboratory tests for assessing risk. Mice were exposed either to a single dose (10 or 30 mg/kg) or to short-term repeated (three hourly doses of 10 mg/kg) intraperitoneal doses of dimethoate, and brain and serum AChE activity were measured. No significant difference was found in the degree of inhibition of AChE activity following acute and short-term repeated exposure. In a second experiment, mice were given three daily doses of 10 or 20 mg/kg of dimethoate, and both AChE activity and hepatic cytochrome P450 enzyme activity were measured. Daily exposure resulted in a dose-dependent decline in brain and serum AChE activity, and inhibition increased progressively with successively repeated exposures. However, this effect was relatively small compared to the effect of dose. Cytochrome P450 enzyme activity (CYP2B) was inhibited in the dimethoate-dosed mice. Our results indicate that acute dose-response toxicity studies are suitable models for predicting the likely occurrence of adverse effects from either short- or longer-term exposure of wild mammals to anticholinesterase compounds. Likely differences in exposure pattern between the laboratory and the natural environment are unlikely to bias the predictive power of these studies significantly.

Acetylcholinesterase↗
PubMed2003

Insecticide-resistant pollen beetles (Meligethes aeneus F) found in Danish oilseed rape (Brassica napus L) fields.

The pollen beetle is the most important pest in Danish oilseed rape fields. In 2001, we screened a broad range of pollen beetle populations for pyrethroid and dimethoate resistance. A standard dip-test was used to test insecticide resistance in 18 populations collected from oilseed winter and spring rape fields. The beetles were treated with four different insecticides: the pyrethroids tau-fluvalinate, lambda-cyhalothrin and esfenvalerate, and the organophosphate dimethoate. The results show that up to 99% of the pollen beetles survived Danish standard doses of pyrethroids and up to 36% of the beetles survived standard doses of dimethoate.

Animals↗