Functional dissection of mosquito humidity sensing reveals distinct Dry and Moist Cell contributions to blood feeding and oviposition

<i>Aedes aegypti</i> mosquitoes are major vectors of dengue, chikungunya, and other arboviral diseases. <i>Ae. aegypti</i>'s capacity to reproduce and to spread disease depends on the female mosquitoes' ability to obtain blood meals and find water-filled containers in which to lay eggs (oviposit). While humidity sensation (hygrosensation) has been implicated in these behaviors, the specific hygrosensory pathways involved have been unclear. Here, we establish the distinct molecular requirements and anatomical locations of <i>Ae. aegypti</i> Dry Cells and Moist Cells and examine their contributions to behavior. We show that Dry Cell and Moist Cell responses to humidity involve different ionotropic receptor (IR) family sensory receptors, with dry air-activated Dry Cells reliant upon the IR <i>Ir40a</i>, and humid air-activated Moist Cells upon <i>Ir68a</i>. Both classes of hygrosensors innervate multiple antennal sensilla, including sensilla ampullacea near the antennal base as well as two classes of coeloconic sensilla near the tip. Dry Cells and Moist Cells each support behaviors linked to mosquito reproduction but contribute differently: <i>Ir40a</i>-dependent Dry Cells act in parallel with <i>Ir68a</i>-dependent Moist Cells to promote blood feeding, while oviposition site seeking is driven specifically by <i>Ir68a-</i>dependent Moist Cells. Together these findings reveal the importance of distinct hygrosensory pathways in blood feeding and oviposition site seeking and suggest <i>Ir40a-</i>dependent Dry Cells and <i>Ir68a-</i>dependent Moist Cells as potential targets for vector control strategies.