Evaluating the influence of thiamethoxam on honeybee (Apis mellifera) foraging efficiency

Abstract

Honey bees (Apis mellifera) are vital pollinators, yet sublethal exposure to neonicotinoid insecticides such as thiamethoxam may impair their foraging performance and colony health. This two-year field study (rabi seasons 2022-2023 and 2023-2024) assessed the effects of environmentally realistic sublethal thiamethoxam exposure via foliar application to mustard (Brassica spp.) crops and/or contaminated sucrose feeding on foraging efficiency. Foraging activity was quantified by counting pollen-carrying foragers entering/exiting hives during 5-minute intervals at five diurnal time points, while individual foraging rate was measured as mean time spent per mustard flower. Thiamethoxam significantly reduced foraging traffic by 19-22% (outgoing and incoming bees), with greatest suppression during peak midday hours (11:00-13:00 h). Two-way ANOVA confirmed significant effects of treatment, time of day, and their interaction. Treated foragers also required 28.75-28.79% more time per flower (up to 40.56% on peak days), particularly during high-activity periods. These disruptions decreased traffic and prolonged visitation likely reflect impaired navigation, resource collection, and motivation, with potential consequences for colony productivity and pollination services. The results support temporally targeted pesticide applications and integrated pest management to minimize exposure risks.