Olfactory gene dynamics in invasive Indian and non-invasive African malaria vectors at the crossroads of development, infection and resistance

Olfaction plays a pivotal role in a mosquito’s lifecycle, influencing vital functions such as finding food, mates, identifying hosts, and locating sites for laying eggs. However, a detailed catalog of the olfactory genes in mosquitoes has remained elusive—until now. In this study, we compiled the olfactory genes catalog for four key malaria vectors: two major Indian species, Anopheles stephensi and Anopheles culicifacies, along with two African species, Anopheles gambiae and Anopheles funestus. Using an extensive genome-wide approach, we uncovered crucial carrier proteins like odorant binding proteins (OBPs), chemosensory proteins (CSPs), and several receptors, including odorant receptors (ORs), ionotropic receptors (IRs), and gustatory receptors (GusRs). A particularly striking discovery was the significantly higher number of OBP, OR, and IR genes in African malaria vectors compared to their Indian counterparts, hinting at the gene gain and functional diversification in these species. The invasive A. stephensi—which has spread from Asia to Africa—showed closer genetic ties to A. minimus and A. gambiae than to A. culicifacies. Furthermore, when examining the expression of CSPs and SAPs in the larval stage of A. stephensi, we found that pyrethroid-resistant mosquito larvae exhibited elevated expression of SAP2 and SAP3, providing new evidence of their potential role in insecticide resistance. This study not only sheds light on the genetic basis of mosquito olfaction but also offers crucial insights into how these genes are linked to different physiological functions, paving the way for improved malaria control strategies.