Unveiling the Developmental Dynamics and Functional Role of Odorant Receptor Co-receptor (Orco) in Aedes albopictus: A Novel Mechanism for Regulating Tuning Odorant Receptor Expression

Abstract

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 tuning odorant receptors (ORs), which require the highly conserved odorant receptor co-receptor (Orco) to function. While Orcos role in enabling tuning 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 (ORNs) across embryonic, larval, pupal and adult stages of Ae. albopictus. We uncovered a dramatic reorganization of the olfactory system during metamorphosis: ORNs were observed as early as the embryonic stage and expanded during larval development before rapid degeneration and re-generation in the pupal stage resulting in the final population of adult ORNs. Orco expression in adults spanned the olfactory neurons of the antennae, labella, and maxillary palps in both male and female mosquitoes, consistent with its conserved peripheral distribution. 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 tuning Ors, suggesting that Orco may influence OR 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 elimination of host preference in females. Together, these findings reveal dynamic reorganization of ORNs during mosquito development and uncover the critical role of Orco in maintaining the integrity and function of the olfactory system, providing insights that may inform novel, next-generation vector control strategies.