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Abstract Artificial light at night (ALAN) is an increasingly important form of environmental disturbance as it alters Light:Dark cycles that regulate daily and seasonal changes in physiology and phenology. The Northern house mosquito (Culex pipiens) and the tiger mosquito (Aedes albopictus) enter an overwintering dormancy known as diapause that is cued by short days. These two species differ in diapause strategy:Cx. pipiensdiapause as adult females whileAe. albopictusenter a maternally-programmed, egg diapause. Previous studies found that ALAN inhibits diapause in both species, but the mechanism is unknown. As the circadian clock is implicated in the regulation of diapause in many insects, we examined whether exposure to ALAN altered the daily expression of core circadian cloc genes (cycle,Clock,period,timeless,cryptochrome 1,cryptochrome 2, andPar domain protein 1) in these two species when reared under short-day, diapause-inducing conditions. We found that exposure to ALAN altered the abundance of several clock genes in adult females of both species, but that clock gene rhythmicity was maintained for most genes. ALAN also had little effect on clock gene abundance in mature oocytes that were dissected from femaleAe. albopictusthat were reared under short day conditions. Our findings indicate that ALAN may inhibit diapause initiation through the circadian clock in two medically-important mosquitoes. 

Cities are generally hotter than surrounding rural areas due to the Urban Heat Island (UHI) effect. These increases in temperature advance plant and animal phenology, development, and reproduction in the spring. However, research determining how increased temperatures affect the seasonal physiology of animals in the fall has been limited. The Northern house mosquito, Culex pipiens, is abundant in cities and transmits several pathogens including West Nile virus. Females of this species enter a state of developmental arrest, or reproductive diapause, in response to short days and low temperatures during autumn. Diapausing females halt reproduction and blood-feeding, and instead accumulate fat and seek sheltered overwintering sites. We found that exposure to increased temperatures in the lab that mimic the UHI effect induced ovarian development and blood-feeding, and that females exposed to these temperatures were as fecund as non-diapausing mosquitoes. We also found that females exposed to higher temperatures had lower survival rates in winter-like conditions, despite having accumulated equivalent lipid reserves relative to their diapausing congeners. These data suggest that urban warming may inhibit diapause initiation in the autumn, thereby extending the active biting season of temperate mosquitoes. 

The Northern house mosquito transmits West Nile virus and survives the winter by entering a state of dormancy called diapause. Light pollution has been shown to interfere with diapause initiation in this mosquito. The effects of light pollution on daily activity rhythms and metabolic products have not been thoroughly investigated in diapausing and non-diapausing Northern house mosquitoes. We found that light pollution affected mosquito activity levels and several metabolic products differently depending on photoperiod, indicating that light pollution may disrupt nutrient accumulation and possibly interfere with diapause initiation in this species. 

Abstract BackgroundCulexmosquitoes are the primary vectors of West Nile virus (WNV) across the USA. Understanding when these vectors are active indicates times when WNV transmission can occur. This study determined the proportion of femaleCulexmosquitoes that were in diapause during the fall and winter and when they terminated diapause and began blood feeding in the spring. MethodsMosquitoes were collected from parks using various traps and/or aspirated from culverts in Franklin County, Ohio, from October to mid-May from 2019 to 2022.Culexmosquitoes were morphologically identified to species, and the ovaries of females were dissected to determine their diapause and parity statuses. ResultsBy early October 2021, roughly 95% ofCulex pipienscollected in culverts were in diapause and 98% ofCx. erraticuswere in diapause. Furthermore, gravid and blood-fedCulex salinarius,Cx. pipiens, andCx. restuanswere collected in late November in 2019 and 2021 in standard mosquito traps. In the winter of 2021, the proportions of non-diapausingCulexdecreased within culverts. The last non-diapausingCx. erraticuswas collected in late December 2021 while the final non-diapausingCx. pipienswas collected in mid-January 2022, both in culverts. Roughly 50% ofCx. pipiensterminated diapause by mid-March 2022, further supported by our collections of gravid females in late March in all 3 years of mosquito collection. In fact, male mosquitoes ofCx. pipiens,Cx. restuans, andCx. territanswere collected by the 1st week of May in 2022, indicating that multiple species ofCulexproduced a second generation that reached adulthood by this time. ConclusionsWe collected blood-fed and gravidCulexfemales into late November in 2 of the 3 years of our collections, indicating that it might be possible for WNV transmission to occur in late fall in temperate climates like Ohio. The persistence of non-diapausingCx. pipiensandCx. erraticusthroughout December has important implications for the winter survival of WNV vectors and our overall understanding of diapause. Finally, determining whenCulexterminate diapause in the spring may allow us to optimize mosquito management programs and reduce the spread of WNV before it is transmitted to humans. Graphical Abstract