Effects of methiocarb on Chironomus riparius survival and growth with and without tube-building.
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Slugs are major pests of oilseed rape that are poorly controlled by conventional bait pellets. A series of laboratory experiments investigated the potential of seed-dressings to control slug damage in this crop. Four compounds: metaldehyde, methiocarb, cinnamamide and 3,5-dimethoxycinnamic acid (DMCA) were tested at a range of doses for phytotoxicity and ability to reduce damage by Deroceras reticulatum (Müller). Metaldehyde and methiocarb were not phytotoxic at any doses, whereas all doses of cinnamamide and DMCA were. All compounds reduced slug damage, but metaldehyde and methiocarb consistently performed better than cinnamamide and DMCA. Metaldehyde and methiocarb seed-dressings were compared with baited pellets containing the same active ingredients at recommended field doses. The seed-dressings protected plants from damage by D reticulatum and Arion subfuscus (Draparnaud) as well as, or better than, baited pellets. We therefore recommend that metaldehyde and methiocarb should be field-tested as seed dressings to control slugs in oilseed rape.
Certain unconditioned stimuli (UCS) in flavor avoidance learning sometimes become ineffective after pairings with relatively stronger UCS. This failure of avoidance learning (avfail) has been demonstrated only with rodents. The present investigations were conducted to determine whether avfail might also occur with avian species, the food selection of which is guided primarily by visual cues. In Experiment 1, starlings were given pairings of methiocarb (a relatively weak UCS) and LiCl (a relatively strong UCS). In Experiment 2, red-winged blackbirds were given pairings of two concentrations of methiocarb (relatively weak and relatively strong UCS, respectively). Pairings were followed by a conditioning trial (UCS gavage in the presence of a color cue) and two-choice tests. Conditioned avoidance was always observed except when methiocarb preceded LiCl and when the low preceded the high methiocarb dose in preconditioning pairings. Experiment 3 demonstrated that UCS habituation could not account for the results of Experiments 1 and 2. The data reflect avfail in the visual modality, and a biological implication of the results is that birds may not learn strong avoidance of aposematic prey containing varied levels of toxicant.
Response of western flower thrips, Frankliniella occidentalis (Pergande), to selection for resistance to insecticides commonly used to control this pest in Murcia (south-east Spain) was studied under field and laboratory conditions. In the field, plots within sweet pepper crops in commercial and experimental greenhouses were treated under different selection strategies: insecticide rotation versus formetanate reiteration, formetanate reiteration versus acrinathrin reiteration, and formetanate reiteration versus methiocarb reiteration. Thrips populations were sampled monthly and bioassayed against methiocarb, methamidophos, acrinathrin, endosulfan, deltamethrin and formetanate. In the laboratory, F occidentalis strains were selected against each insecticide for several generations. To evaluate cross-resistance, each selected strain was bioassayed with the other insecticides. Frankliniella occidentalis populations showed a rapid development of acrinathrin resistance, reaching high levels in field and laboratory conditions. Formetanate and methiocarb resistance were also observed, although development was slower and at moderate levels. Cross-resistances between acrinathrin/deltamethrin and acrinathrin/formetanate were detected under field and laboratory conditions. Formetanate/methiocarb cross-resistance was suspected in laboratory selections, but not in field assays. Simultaneous moderate resistance levels to the three specific insecticides against thrips (formetanate, methiocarb and acrinathrin) were shown in laboratory selection strains, indicating a general mechanism of resistance, probably metabolic.
The cytochrome P450 (P450) and flavin-containing monooxygenase (FMO) enzymes are the major oxidative enzymes in phase I metabolism. Many organophosphate and carbamate thioether compounds are excellent substrates for these enzymes. Stereoselective sulfoxidation of fenthion and methiocarb by human liver, kidney, and microsomes was investigated. A high level of stereoselectivity in the formation of fenthion +-sulfoxide was observed in kidney and intestinal microsomes. This activity was not inhibited by the P450 inhibitor 1-aminobenzotriazole but was dramatically reduced following mild heat treatment. In liver, fenthion was metabolized to its sulfoxide in a nonstereoselective manner, and the activity was sensitive to both 1-aminobenzotriazole and heat treatment. The carbamate pesticide methiocarb also was sulfoxidated with a high degree of stereoselectivity in human kidney microsomes. Human liver microsomes formed both stereoisomers in equal amounts. Sulfoxide formation in kidney was not inhibited by 1-aminobenzotriazole but was abolished in liver microsomes. Formation of methiocarb sulfoxides was not observed in intestinal microsomes. The relative contribution of FMO1 and FMO3 to the sulfoxidation of carbophenothion, demeton-O, ethiofencarb, fonofos, and methiocarb also was investigated by using baculovirus-expressed recombinant proteins. FMO1 showed the highest catalytic activity for all pesticides. This study indicates that FMO1 may have a bigger role in extrahepatic metabolism than previously thought.
The occurrence of 4 pesticide residues, imidacloprid, carbendazim, methiocarb, and hexythiazox, was assessed in several fruits (oranges, tangerines, watermelons, and date plums) from the Valencian Community (Spain). A total of 227 samples--56 oranges, 134 tangerines, 13 watermelons, and 24 date plums--were taken from an agricultural cooperative representative of the area studied during 2001. The pesticides were determined by liquid chromatography/mass spectrometry after sample extraction with ethyl acetate and anhydrous sodium sulfate. Recoveries of 4 pesticides at 2 fortification levels (0.02 and 0.2 mg/kg), the lower of which was the quantification limit, ranged from 60 to 108%. Concentrations of imidacloprid, carbendazim, methiocarb, and hexythiazox ranged from 0.02 to 0.75 mg/kg in 184 samples (54 oranges, 119 tangerines, 3 watermelons, and 8 date plums). Nineteen samples contained methiocarb or hexythiazox residues that exceeded the maximum residue limits. Calculation of the estimated daily intakes of the 4 pesticides studied and their comparison with the Acceptable Daily Intakes established by the Food and Agriculture Organization of the World Health Organization demonstrated the safety of fruit consumption and showed the importance of monitoring for pesticide residues.
The interactions between six insecticides (methiocarb, formetanate, acrinathrin, deltamethrin, methamidophos and endosulfan) and three potential synergists (piperonyl butoxide (PBO), S,S,S-tributyl phosphorotrithioate (DEF) and diethyl maleate (DEM)) were studied by topical exposure in strains selected for resistance to each insecticide, and in a susceptible strain of Frankliniella occidentalis (Pergande). In the susceptible strain PBO produced appreciable synergism only of formetanate, methiocarb and methamidophos. Except for endosulfan, PBO synergized all the insecticides to varying degrees in the resistant strains. A very high level of synergism by PBO was found with acrinathrin, which reduced the resistance level from 3344- to 36-fold. PBO slightly synergized the carbamates formetanate (4.6-fold) and methiocarb (3.3-fold). PBO also produced a high synergism of deltamethrin (12.5-fold) and methamidophos (14.3-fold) and completely restored susceptibility to both insecticides. DEF did not produce synergism with any insecticide in the resistant strains and DEM was slightly synergistic to endosulfan (3-fold). These studies indicate that an enhanced detoxification, mediated by cytochrome P-450 monooxygenases, is the major mechanism imparting resistance to different insecticides in F occidentalis. Implications of different mechanisms in insecticide resistance in F occidentalis are discussed.