2nd Place: D3113: The effect of urban road salts on West Nile virus vector mosquito (Culex sp.) sex ratios

With high road densities, temperate cities experience high de-icing salt use during the winter. When road salts runoff into freshwater environments, they can decimate ecological communities by wiping out salt-intolerant taxa and promoting salt-tolerant taxa. One salt-tolerant taxon of concern is mosquitoes (Culicidae), which are potential disease vectors. While increased mosquito abundance can lead to higher disease transmission risk for urban residents, mosquito sexual dimorphism means that only female mosquitoes transmit zoonotic diseases like West Nile Virus; only adult females require bloodmeals from their hosts to reproduce. Interestingly, many mosquito species display male-biased emergence sex ratios, which may be exacerbated by prolonged exposure to aquatic stressors during their aquatic juvenile period. Yet, little is known about how common urban stressors, like road salt, affect the sex ratios of emergent mosquitoes across a season. To test this, we manipulated road salt concentrations (0 g/L NaCl or 4.5 g/L NaCl) in 10 mesocosms in Mississauga, Ontario, Canada from May to September 2022. We measured the sex ratio of emerging mosquitoes by collecting adults in emergence traps from mesocosms on a weekly basis. We show that salinity increases male-biased sex ratios at emergence. By encouraging a male-biased ratio, road salts may have the potential to decrease female mosquito success and indirectly reduce disease transmission in cities.