Sublethal effects of the organosilicone surfactant Silwet L-77 and its interactions with acetamiprid and sulfoxaflor on honeybee ( Apis mellifera ) sensory perception and cognition

Pesticides remain indispensable for global food security, yet their use must be reconciled with the preservation of biodiversity. Despite advances in developing ‘safer’ pesticides, their sublethal effects and synergistic potential with co-formulants in tank-mixtures, including ‘inert’ spray adjuvants, often remain poorly understood in beneficial insects like bees. In this study, we assessed the effects of acute oral exposure to field-realistic doses of Silwet™ L-77 (an organosilicone adjuvant; 0.1–2.5%), acetamiprid (a cyano-substituted neonicotinoid; 6–150 ng/bee), and sulfoxaflor (a sulfoximine; 3–27 ng/bee) on gustatory responsiveness, associative olfactory learning, and short-term memory retention in honeybees ( Apis mellifera L.). While we found no significant evidence of interaction effects at the exposure concentrations tested, the highest doses of Silwet™ L-77 and sulfoxaflor alone significantly reduced gustatory responsiveness. Furthermore, all three agrochemicals alone weakly affected associative learning without impacting memory retention. Although adjuvant-insecticide mixtures did not synergistically impair bee cognition, these adjuvants can impact sensory perception. Moving beyond mortality-based assessments and including sensory-cognitive thresholds is essential for a more holistic understanding of pollinator health.