Residues of neonicotinoid insecticides in pollen and nectar frommodel plants

Systemic insecticides used for ornamental horticulture crops can protect all portions of a plant with long-lasting effects. However, they may be hazardous to pollinators foraging on contaminated nectar or pollen. Two model plant cultivars were chosen based upon their ability to produce large quantities of pollen or nectar, enabling examination of the level of nectar or pollen contamination (e.g., insecticide ‘‘residues’’) following insecticide treatments, rather than for the need or advisability to treat these plants in production nurseries or the landscape with systemic insecticides. These plants were sunflower (Helianthus annuus L. ‘Taiyo’) for pollen, and swamp milkweed (Asclepius incarnata L. ‘Ice Ballet’) for nectar. Plants were treated at labeled nursery rates with imidacloprid, dinotefuran, or thiamethoxam via foliar spray or soil drench at various times before bloom. Insecticide residues from pollen and nectar varied based upon application method, insecticide, and rate. Assuming that residues should be considered hazardous when they exceed 25 parts per billion (ppb) for nectar or 100 ppb for pollen, potentially bee-toxic concentrations of insecticide in sunflower pollen only followed high-rate drench treatments. Toxic concentrations of neonicotinoids were found in milkweed nectar when applied either as a drench or as a foliar spray up to six weeks before bloom. Label directions for nursery and greenhouse plants permit very high application rates relative to agronomic crops. These high rates can create hazardous conditions for pollinators, and should be avoided for ornamental crops that are highly attractive to bees. Index words: sunflower (Helianthus annuus L.); swamp milkweed (Asclepius incarnata L.); dinotefuran; imidacloprid; thiamethoxam; pollinator; systemic insecticides. Chemicals used in this study: dinotefuran (Safari 20 SG); imidacloprid (Xytect 2F); thiamethoxam (Flagship 25 WG). Species used in this study: sunflower (Helianthus annuus L.); swamp milkweed (Asclepius incarnata L.). Significance to the Horticultural Industry Use of systemic pesticides in the production of ornamental horticulture crops presents a quandary: these materials can protect all portions of a plant with longlasting effects and can be compatible with integrated pest management programs, because the residues are translocated throughout and are presented from inside the plant. However, based upon their systemic nature, they may also inherently pose risks to pollinators which avail themselves of contaminated nectar or pollen resources. Pesticide labels permit high rate applications in ornamental horticulture use of neonicotinoid insecticides, relative to agronomic uses. These rates can lead to elevated residues in pollen, and especially in nectar, which are predicted to be toxic to bees. Nurseries and ornamental greenhouse growers do need to recognize the potential for harm to pollinators from the use of nitroguanidine neonicotinoid systemic insecticides. Ways to mitigate the risk to pollinators include substituting foliar sprays over drenches, using the lowest effective application rates, switching to systemic insecticides that have lower intrinsic toxicity to bees when treating beeattractive plants, or not using systemic insecticides on these plants. These mitigation approaches should be a high priority for research on establishing pollinator-safe practices in the ornamental horticulture industry.