Presence of the a.i. imidacloprid on vegetation near corn fields sown with Gaucho ® dressed seeds

In recent years the widespread use of corn seed hybrids dressed with the systemic insecticide Gaucho ® (a.i. imidacloprid), has been frequently linked, by beekeepers with bee colony losses registered during the corn sowing season. On the basis of a preliminary experiment, where the loss of imidacloprid from the pneumatic seed drills was highlighted, the aim of the study was to verify both the amount of contamination and the persistence of the active ingredient on leaves and flowers of spontaneous plants growing near corn fields in which Gaucho ® dressed seeds had been used. The observations were carried out in north eastern Italy on five different commercial corn hybrid seeds, three dressed with Gaucho ® [hybrids 2 (H2), 4 (H4) and 5 (H5)], one with a new adjuvant (H5). The escape of the active ingredient from the fan drain of the pneumatic seed drill was monitored using paper filters, whereas samples of grass and flowers were collected from the borders of sown fields. Meteorological data were registered. The samples (paper filters, grass and flowers) were analyzed using a gas chromatography method. Paper filters on the output of the drill fan have shown, at different concentrations, an escape of imidacloprid from the fan for each kind of Gaucho ® dressed seed; the order of magnitude of the escape ranged on average for H2, H4 and H5 from 120 to 240 µg of imidacloprid for 1 g of paper filter at 240 seconds. Therefore the new adjuvant did not eliminate the loss of active ingredient. Even if at different concentrations for each kind of Gaucho ® dressed hybrid, imidacloprid was found the same day of sowing on