The effects of urban pollutants on mosquito dormancy and disease risk

Light pollution caused by artificial light at night (ALAN) and increased temperatures caused by the Urban Heat Island (UHI) effect could interfere with the environmental cues that temperate insects use to regulate their seasonal responses. Both ALAN and the UHI effect advance spring phenology. However, knowledge on the influences on seasonal responses in the fall remain limited. The Northern house mosquito, Culex pipiens, is a primary vector of West Nile virus. Females of this species enter a developmental arrest, or diapause, in response to short days and low temperatures during autumn. Diapausing females accumulate fat, and cease reproductive development and blood-feeding, halting disease transmission. Both ALAN and UHIs have the potential to interfere with the perception of changing seasons, inhibit diapause initiation, and thereby extend the active mosquito biting season. In two separate lab experiments we reared mosquitoes in environmental chambers with autumn daylengths and found that exposure to both dim ALAN or simulated UHI-temperatures altered seasonal phenotypes. Specifically, both ALAN and higher temperatures caused females to avert diapause, develop egg follicles, consume vertebrate blood and produce offspring. However, while ALAN caused female mosquitoes to accumulate less fat than diapausing mosquitoes, females exposed to UHI-temperatures had high levels of fat. Taken together, these results indicate that urbanization has the potential to interfere with normal seasonal responses in Cx. pipiens. This contributes to growing knowledge on how human-mediated changes to the environment affect disease transmission in cities, and provides important information for managing mosquitoes to improve urban public health.