Determination of imidacloprid in beehive samples from an open field feeding study

MICHLIG, MELINA; MERKE, JULIETA; BULACIO CAGNOLO, NATALIA; ORELLANO, EMANUEL; SIGNORINI, MARCELO; SALTO, CÉSAR; BELDOMÉNICO, HORACIO; REPETTI, MARÍA ROSA

Workshop; European Pesticide Residue Workshop 2016; 2016

Neonicotinoids are characterized by a mode of action that affects the central nervous system of insects and its translocation capabilities. In Argentina imidacloprid is extensively used and this could be related with pollinator declines. Since in previous studies we had found imidacloprid residues in pollen and floral nectaries from sunflower plants, our group is conducting a new research. Therefore an open field study was carried out. For this purpose 30 beehives were displayed in a common field area, and submitted to 5 different feeding treatments, comprising 6 hives per treatment (n=6). Each treatment corresponded to the following concentrations of imidacloprid in sucrose solutions supplied to the colonies: a control without dose, and treatments I, II, III and IV with 15, 30, 120 and 240 ng/g respectively. The spiked sucrose solutions were provided once a week during a period of seven weeks in September-October 2014. Throughout the experiment on a weekly basis, several parameters regarding the behaviour of the colonies were studied, such as the number of bees and larvae per hive, and the pollen and honey store as well. Samples of all hives were obtained before starting the experience and in order to evaluate imidacloprid residues, bees from 2 hives per treatment were sampled at 0, 24 h and 48 h at the beginning, the middle and the end of the whole feeding period (7 weeks). After this point honey and beeswax samples were collected from all hives. An analytical methodology based on QuEChERS procedure was optimized and fully validated for bee and larvae matrices. After soak of samples and extraction with acetonitrile adding MgSO4 and NaCl salts, a dispersive-SPE step with MgSO4, PSA and C18 was applied. Extracts were evaluated in a UHPLC-MS/MS system. The LOD and LOQ were 0.05 and 0.2 ng/g respectively, and satisfactory recovery performance was achieved (100 ± 10 %). Preliminary results showed scarce differences in colony behaviour through evaluation of whole-hive parameters. Residue concentrations in bees evidenced the differences in the exposure through the different treatments. This field feeding study constitutes a first approach in the country regarding imidacloprid risk assessment for honeybees (Apis mellifera L.) at colony level, which may contribute to assess the potential for dietary exposure of this pesticide in further toxicity studies at this level.