Sublethal λ-cyhalothrin disrupts sensory perception, learning, and memory, and induces oxidative stress in the...

The pyrethroid insecticide λ-cyhalothrin is an environmental hazard. It is known to affect honeybees adversely, yet reported acute oral LD₅₀ values vary considerably, and its sublethal effects on cognition and physiology remain poorly characterized. To address these gaps, we used λ-cyhalothrin in Apis mellifera L., and the survival analysis yielded an estimated acute oral LD₅₀ of 0.074 μg/bee after 24 h. Bees fed with 0.037 μg/bee (LD₅₀/2) exhibited reduced gustatory responsiveness and showed fewer proboscis extension responses (PERs) to water and sucrose. When this dose was administered 1 day or 3 h before differential olfactory conditioning, bees displayed selective deficits in learning and memory for the excitatory conditioned stimulus (CS+), while responses to the inhibitory conditioned stimulus (CS-) remained intact. Sublethal exposure after conditioning similarly impaired only the CS+ memory retention. Repeated exposure to a lower dose (0.0074 μg/bee; LD₅₀/10) for 3 days also produced comparable reductions in gustatory responsiveness and CS+ learning and memory. Sublethal treatments also elevated catalase (CAT) and superoxide dismutase (SOD) activities in both the heads and bodies, indicating systemic oxidative stress. Collectively, these results demonstrate that λ-cyhalothrin, even at low doses, disrupts sensory processing, cognitive performance, and physiological homeostasis in A. mellifera. This study provides an integrated evaluation combining acute toxicity, gustatory responsiveness, olfactory learning and memory retention, and oxidative stress biomarkers in honeybees exposed to λ-cyhalothrin, and the findings underscore the importance of incorporating subtle neurobehavioral and physiological endpoints into pollinator risk assessments to reflect the effects of environmentally relevant pyrethroid exposure.