5: Systemic insecticide residues in greenhouse annuals and implications for pest management

Accumulation of systemic insecticide residues in plant nectar may be one factor for the population decline of bees and other pollinators. We undertook a series of experiments to determine the amount of systemic insecticide residues in snapdragon (Antirihum majus) and annual salvia (Salvia splendens). Trade formulations of cyclaniliprole, flupyradifurone, dinotefuran, imidacloprid, and thiamethoxam were applied as foliar sprays or soil drenches using rates consistent with label directions to snapdragon and annual salvia plants grown in greenhouse after flower bud formation but prior to petal emergence. At periodic intervals, nectar was collected from flowers, frozen, and stored until analysis. Modified QuEChERS was used to extract and analyze samples for these actives and two major metabolites: olefin from imidacloprid, and clothianadin from thiamethoxam. Percent Brix for each samples was assessed. Residue amounts in ppb were normalized to average percent Brix within each experiment. To obtain average residue concentrations, samples with non-detectable residues were assigned one half the value of the limit of quantification based on sample volume. Across the three snapdragon experiments and two annual salvia, nectar residues in plants treated with foliar applications of systemic neonicotinoid insecticides tended to be lower than the EPA level of concern and were less than residues from plants treated with soil drenches. Cyclaniliprole and flupyradifurone residues, when detected, tended to be less than the EPA level of concern, regardless of application method. Growers can use neonicotinoid insecticides on annual plants for pest management with minimal risk to pollinating insects.