Abstract The goal of this project is to break fundamentally new ground by investigating the molecular basis of vision in the daytime mosquito vector, Aedes (Ae.) aegypti. This mosquito is a major disease vector, which transmits the viruses that cause dengue, yellow fever, Zika and other diseases that affect many tens of millions of people each year. Due to climate change and travel, this invasive species is spreading to new locations, including multiple areas in the United States. Therefore, innovative strategies to control mosquito borne disease are urgently needed. Female Ae. aegypti detect and integrate multiple sensory cues to locate human hosts. Once they sense CO2 odor plumes emanating from human breath at distances of up to 10-15 meters, their visual attention to potential hosts is greatly increased. They then rely on visual information along with other human- derived cues, such as organic olfactory stimuli, to home in on people. Despite the important contribution of vision in promoting the ability of Ae. aegypti to find humans, there has been no comprehensive approach to apply molecular genetics to define the mechanisms underlying vision and odor-stimulated vision-guided host attraction. The objective of the proposed research is to address this gap. Aim 1 is to define the roles of the TRP and TRPL channels in Aedes vision. We have recently used CRISPR/Cas9 to generate mutations that disrupt the trp and trpl genes. We propose to examine the roles of these channels for the light response in photoreceptor cells. We also outline experiments to investigate potential roles for these channels in several vision- and light-driven behaviors, including CO2-stimulated vision-guided target attraction. The goal of aim 2 is to test the idea that the two phospholipase C genes expressed in the eyes of Ae. aegypti (NORPA and PLC21C) have distinct roles in visual transduction and in multiple vision- and light-driven behaviors, including circadian rhythms. We will also address the impact of mutations disrupting norpA and plc21C in combination with mutations that disrupt cryptochrome, which encodes a light sensitive protein in the insect brain. Ae. aegypti are most active and bite primarily after sunrise and before sunset. Therefore, understanding the regulation of circadian rhythms in this organism is important, and the contributions of retinal proteins to this behavior represents another major gap in our understanding of the biology of Ae. aegypti. Aim 3 focuses on testing an iconoclastic role for the Gaq in the light response. In addition to its classical role as an effector protein for rhodopsin, we will test the idea that Gaq directly regulates the TRP and TRPL channels. To accomplish our goals, we propose to employ a multidisciplinary approach, including electrophysiology, molecular genetics, biochemistry, cell biology and a wide diversity of behavioral assays. We propose that these studies will provide the conceptual framework for devising innovative s...