Higher early than late-season residue load of pesticides in honey bee bread in Slovakia

Bees are often exposed to pesticide residues during their foraging trips in agricultural landscapes. The
analysis of in-hive stored pollen reflects the spectrum of visited plants and can be almost used to link the exposure
to pesticides.In the current study, bee bread samples were collected in May and July from 17 sites located in
southern Slovakia. Samples were analysed using a multi-residue pesticide analysis method for a broad spectrum
of active substances and microscopic for pollen identification.Our results revealed a bee bread contamination with
19 different active substances, with fungicides being predominant. Sixteen of them are authorized in the EU, but
chlorpyrifos, chlorpyrifos-methyl, and chloridazon are not. The highest concentrations for pendimethalin (1400 μg/
kg), fluazifop-butyl (640 μg/kg), fenpropidin (520 μg/kg), fluopyram (130 μg/kg), and difenoconazole (95 μg/
kg) were detected. The total residue load in bee bread sampled in the early season (May) was significantly higher
than in the late season (July). The mean residue load of insecticides analysed in July comprised 46% of May’s
load, which is alarming due to the importance of bee bread in the diet for winter-rearing bees. Moreover, results
from both sampling periods showed that fungicides were positively associated with plant families Apiaceae and
Papaveraceae and herbicides with Aceraceae, Salicaceae, and Brassica-type/Brassicaceae.Hence, bee bread can be
considered a suitable matrix and a good bio-indicator reflecting honey bee exposure to pesticides over the season.