A Compound Fungicide Impairs Cognitive Performance in Honey Bees (Apis mellifera)

Fungicides play a critical role in crop protection, yet their potential threats to pollinator remain a concern. This study investigated the sublethal effects of a commercial fungicide, Chunmanchun^® (a suspension-emulsion of 7% propiconazole and 28% carbendazim), on cognitive functions of the honey bee (Apis mellifera). Using the proboscis extension reflex (PER) assay, we evaluated sucrose sensitivity and olfactory learning and memory in workers exposed to the recommended field concentration (PC), along with sublethal (LD₁₀) and semi-lethal (LD₅₀) concentrations. Fungicide exposure significantly reduced sucrose sensitivity across all concentrations tested (0.1%, 1%, and 3%), with the strongest reductions occurring at the LD₁₀ and LD₅₀ levels. While olfactory associative learning was not significantly impaired, memory retention was adversely affected. Bees in the LD₅₀ group showed significantly reduced PER rates at both1 h and 6 h post-training, and LD₁₀ and LD₅₀ groups exhibited significant memory deficits by 1 h and 6 h relative to the control. These results demonstrate that Chunmanchun^® impairs both sucrose responsiveness and olfactory memory in honey bees, which may impair foraging efficiency and ultimately affect colony performance. This study highlights a potential ecological risk posed by this fungicide to pollinators in agricultural environments.