Translocação e metabolismo do inseticida vamidothion em plantas de trigo (Triticum aestivum L.) e feijão (Phaseolus vulgaris L.)

Abstract

This work examines the metabolism and translocation of the insecticide vamidothion in wheat and common bean plants after foliar application of the chemical. The experiments were carried out using 4-week-old plants growing in a glasshouse. A solution of vamidothion in water was either injected into the petiole of a bean leaf or applied on the surface of a wheat or bean leaf, with a commercial formulation (KILVAL 300 EC) being used for surface application. At 4, 8 and 12 days after application, the amounts of vamidothion and its active metabolites sulphoxide and sulphone were measured in the treated leaf, non-treated leaves, stem and roots. The compounds were determined by gas-liquid chromatography with electron capture detector, after thin layer chromatography of plant extracts. Vamidothion was efficiently taken up by the leaves, with only 3 and 16% of the applied amount being removed by aceto ne washing, from wheat and bean leaves respectively, after 4 days since application. Vamidothion was extensevely oxidized to vami dothion sulphoxide in the plants, with the amounts of the sulphone remaining very low throughout the experiment. The degradation of vamidothion in the plants was moderately rapid, with half-life values of 6,5 and 10 days, respectively in wheat and bean plants. Vamidothion and/or its oxidation products were readily transported to the leaflet blade after injection of the Chemi cal into the petiole of a bean leaf. The compounds tended to accumulate in the margin of bean leaflets and were found predominantly in the apex of treated wheat leaves. Relatively small amounts of the compounds were found in non-treated parts of the plants, mainly in non-treated leaves and stem. The amounts found in non-treated parts of the plants increased with time (on the basis of the remaining amount in the whole plant), reaching 13% in wheat and 12% in bean plants, after 12 days since application. The amounts found in the root system were very low (less than 1% of the amount remaining in the whole plants), indicating that, although the compounds were transported from the treated leaf to other parts of the plant through the phloem, they were not retained in the lower parts of the plants and were transported subsequently to the leaves through the xylem.