Mosquitoes are the most medically significant insect pests in Arizona, responsible for transmitting West Nile virus, St. Louis encephalitis, and western equine encephalitis — all of which have caused human deaths and serious illness in the state. Three primary genera occur in Arizona: Culex mosquitoes (the primary West Nile virus vectors) breed in standing water including storm drains, neglected pools, bird baths, and irrigation water; Aedes mosquitoes (including the invasive Aedes aegypti, now established in the Phoenix metro area) are aggressive daytime biters that breed in small containers and can transmit dengue fever, Zika virus, and chikungunya; and Anopheles mosquitoes, which are the primary malaria vectors globally but pose minimal malaria risk in Arizona. The summer monsoon season dramatically increases mosquito populations by creating abundant standing water breeding sites. Maricopa County Vector Control conducts surveillance and control operations, but residential source reduction is essential.