Identification of two odorant receptors tuned to alarm pheromone compounds in the honey bee Apis mellifera

Being social insects, honey bees use an array of pheromones to facilitate intraspecific communication, ensuring colony cohesion in a wide range of contexts. The honey bee represents an attractive model for studying the neurobiological basis of pheromonal processing, given that their pheromones are well characterized and their olfactory pathway has been extensively studied. Despite substantial knowledge acquired on olfactory processing in this species, the mechanism of pheromonal coding remains poorly understood. In particular, olfactory receptors (ORs) detecting social pheromones are still unknown. In this study, we used heterologous expression in the Drosophila "empty neuron system", coupled with transcuticular calcium imaging and electrophysiology. We deorphanized two odorant receptors, AmelOR136 and AmelOR109, which detect constituents of the alarm pheromone. AmelOR136 exhibits a sparse coding strategy, suggesting a finely tuned mechanism for efficient communication in alarm situations. In contrast, AmelOR109 is a more broadly-tuned receptor, responding to diverse odorants, including pheromones.