Moderate use of pesticides in allotment gardens as indicated by their residues in larval food provisions of Osmia solitary bees

Urban Farm DB summary

This study investigated pesticide contamination using larval food provisions (a mix of pollen and nectar) of mason bees (Osmia spp.) nesting in artificial shelters at twelve allotment garden sites in Prague and Brno, with seven commercial croplands (fruit orchards, oilseed rape fields) selected for comparison. In total, 79 samples of larval provisions were analyzed using a validated UPLC-MS/MS method covering 262 pesticides and related metabolites. Fifty-six pesticide residues were detected in the allotments and 74 in cropland sites, with 50 compounds common to both; fewer residues were found in allotments (mean 14.3±0.9) than in croplands (21.5±1.1; df=17.4, t=-2.9), though some residues exceeded 10 ppb. The highest levels were observed for the fungicide pyrimethanil (mean 1,989 ppb, maximum 3,983 ppb) and, among insecticides, thiacloprid (mean 136 ppb, maximum 170 ppb). The results supported the view of a lower risk of pesticide exposure in urban allotment gardens than in croplands, though given limited knowledge of sublethal effects of pesticides, and especially pesticide mixtures, on solitary bee development, the study recommends regulation or control of pesticide use in allotment gardens.