Abstract Artificial light at night (ALAN) is a global, evolutionarily novel, anthropogenic environmental disturbance that can alter seasonal responses in plants and animals by interfering with their perception of daylength. This has profound implications for organisms that live in cities and experience both high levels of light pollution and higher temperatures from the Urban Heat Island effect. Understanding how these two disturbances interact to impact seasonality is important for predicting temporal population dynamics in cities for insects that transmit disease‐causing pathogens. Adult females of the Northern house mosquito, Culex pipiens f. pipiens , enter a state of developmental arrest, or diapause, primarily in response to short daylengths in autumn. While in diapause, females accumulate nutrient reserves, halt reproductive development, cease blood‐feeding, and therefore cannot transmit pathogens. We examined whether ALAN during autumn interacts with urban warming to inhibit diapause induction. Mosquito larvae were reared within enclosures on a temperature gradient of private properties in Columbus, Ohio, USA, during September and October. Each property hosted two enclosures: one placed in a location exposed to artificial light sources (i.e. porch lights) and the other in a dark location, and daily temperature was recorded within each enclosure. Approximately 1 week after adult emergence, mosquitoes were returned to the laboratory to evaluate their diapause status. We found that ALAN exposure inhibited diapause regardless of month and negated the effects of urban warming during September. Mosquitoes that were exposed to ALAN in both September and October had larger egg follicles, were less likely to be in diapause, were more likely to blood‐feed and produced larvae. Policy implications . Low intensities of warm white ALAN were a stronger inhibitor of diapause initiation than urban warming, indicating that changes in brightness or light colour may not be sufficient to mitigate ecological impacts and ALAN from common sources can extend seasonal mosquito biting activity and reproduction into late autumn. This study reveals a potential explanation for higher mosquito‐borne disease risk in cities. To mitigate this risk, we recommend increased mosquito surveillance and control interventions in areas with significant light pollution, as well as optimized changes to lighting structures.
Fyie et al. (Fri,) studied this question.