Bestimmung der Nektarmenge von Blüten von clothianidin-gebeiztemRaps

In Germany large areas are cultivated with oilseed rape (Brassica napus). The attractiveness of this crop to insect pollinators, and so possible exposure of these beneficial insects to applied pesticides is given special attention. A field experiment was conducted in two different oilseed rape fields (Bochum, Germany); one crop was grown from with clothianidin treated seed and one from untreated. We used a new and accurate method to collect and quantitatively compare the nectar production of the flowers taken from the main and side shoots of flowering oilseed rape plants over the blooming period. The flowers were bagged one day before nectar collection to avoid insect visits. Then, individual flowers were collected, and their anthers were removed before they were centrifuged to extract their nectar. Nectar amounts were determined using semi-micro balances and sugar concentrations were measured with a digital refractometer. Our results showed significant effect of date and weather on nectar secretion in the both treated and untreated fields. Sugar concentrations and nectar amounts were clearly correlated. On average, amounts of nectar were approx. 2.4 mg/flower and ranged from 0.4-8.6 mg/flower. The sugar concentration was higher at the beginning of blooming (40.6% sugar) than at the end of the flowering(14.6 % sugar). To investigate the presence of clothianidin residues in nectar and pollen, samples wereanalyzed with tandem LC MS/MS. Analytical results showed that traces of clothianidin were detected in nectar (max. 0.68 μg/kg) as well as in pollen (max. 0.65 μg/kg).