Pesticide Contamination of Pollen in Container-Grown Blanket Flower

Pollinators, particularly bees, are essential for the reproduction of flowering plants, including ornamentals, and for maintaining ecosystem balance, benefitting gardens by supporting plant health and promoting robust flowering. However, pollinator populations are declining, with pesticide exposure recognized as one of several contributing stressors. Thiamethoxam, a commonly used systemic insecticide in ornamental horticulture (and its toxic metabolite clothianidin), has been found in nectar resources at levels harmful to bees. This study evaluated the impact of different thiamethoxam application rates on pollen contamination in blanket flower (Gaillardia pulchella L.), a popular source of pollen for bee pollinators. Container plants were drench-treated with low (0.30 g/L) and high (0.64 g/L) rates of thiamethoxam during the mature floral bud stage. The results show that thiamethoxam and clothianidin were present in pollen at both application rates. However, only clothianidin levels significantly increased with the application rate (p = 0.0009). When the pesticide concentrations measured in pollen were used to calculate the estimated exposure doses based on pollen consumption, the values exceeded published median lethal doses (LD50) for the common eastern bumble bee (Bombus impatiens Cresson) and buff-tailed bumble bee (Bombus terrestris L.), indicating substantial ecological risk. These findings underscore the potential threat posed to some pollinator species by thiamethoxam-treated ornamentals.