Unveiling the developmental dynamics and functional role of Odorant Receptor Co-receptor (Orco) in Aedes albopictus: A novel mechanism for regulating odorant receptor expression

As one of the most aggressive disease vectors, the Asian tiger mosquito Aedes albopictus relies heavily on its olfactory system to search for food in the larval stage, locate hosts after eclosion, and identify suitable oviposition sites after blood feeding. In mosquitoes and other insects, the olfactory system detects environmental odors primarily through a diverse repertoire of odorant receptors (ORs), which require the highly conserved odorant receptor co-receptor (Orco) to function. While Orco's role in enabling receptor function is well established, its cellular localization patterns, developmental expression dynamics, and system-wide impact on olfactory physiology and behavior remain understudied in Ae. albopictus. To address this knowledge gap, we leveraged the Q-system to systematically characterize Orco-expressing neurons across embryonic, larval, and adult stages of Ae. albopictus. Orco-expressing neurons were observed as early as in the embryonic stage and proliferated during larval development. Orco expression in adults spanned the olfactory sensory neurons (OSNs) of the antennae, labella, and maxillary palps in both male and female mosquitoes, consistent with its conserved peripheral distribution across various mosquito species. To further investigate the functional implications of Orco, we generated Orco knockout mutants and strikingly discovered that Orco knockout mutants displayed significant widespread downregulation of ORs, suggesting that Orco may influence ORs' expression or stability. Electrophysiological recordings confirmed significantly attenuated responses to human volatiles in Orco mutants, and behavioral assays demonstrated a marked decline in blood-feeding efficiency and decrease of human preference in females. Together, these findings reveal dynamic organization of OSNs during mosquito development and uncover the critical role of Orco in maintaining the integrity and function of the olfactory system, providing insights which may inform novel, next-generation vector control strategies.