Search for: All records

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. 

IntroductionFemales of the Northern house mosquito,Culex pipiens, enter an overwintering dormancy, or diapause, in response to short day lengths and low environmental temperatures that is characterized by small egg follicles and high starvation resistance. During diapause,Culex pipiensMajor Royal Jelly Protein 1 ortholog (CpMRJP1) is upregulated in females ofCx. pipiens. This protein is highly abundant in royal jelly, a substance produced by honey bees (Apis mellifera), that is fed to future queens throughout larval development and induces the queen phenotype (e.g., high reproductive activity and longer lifespan). However, the role of CpMRJP1 inCx. pipiensis unknown. MethodsWe first conducted a phylogenetic analysis to determine how the sequence of CpMRJP1 compares with other species. We then investigated how supplementing the diets of both diapausing and nondiapausing females ofCx. pipienswith royal jelly affects egg follicle length, fat content, protein content, starvation resistance, and metabolic profile. ResultsWe found that feeding royal jelly to females reared in long-day, diapause-averting conditions significantly reduced the egg follicle lengths and switched their metabolic profiles to be similar to diapausing females. In contrast, feeding royal jelly to females reared in short-day, diapause-inducing conditions significantly reduced lifespan and switched their metabolic profile to be similar nondiapausing mosquitoes. Moreover, RNAi directed againstCpMRJPIsignificantly increased egg follicle length of short-day reared females, suggesting that these females averted diapause. DiscussionTaken together, our data show that consuming royal jelly reverses several key seasonal phenotypes ofCx. pipiensand that these responses are likely mediated in part by CpMRJP1. 

Culexmosquitoes transmit several pathogens to humans and animals, including viruses that cause West Nile fever and St. Louis encephalitis and filarial nematodes that cause canine heartworm and elephantiasis. Additionally, these mosquitoes have a cosmopolitan distribution and provide interesting models for understanding population genetics, overwintering dormancy, disease transmission, and other important and ecological questions. However, unlikeAedesmosquitoes that produce eggs that can be stored for weeks at a time, no obvious “stopping” point exists in the development ofCulexmosquitoes. Therefore, these mosquitoes require nearly continuous care and attention. Here, we describe some general considerations when rearing laboratory colonies ofCulexmosquitoes. We highlight different methods so that readers may choose what works best for their experimental needs and laboratory infrastructure. We hope that this information will enable additional scientists to conduct laboratory research on these important disease vectors. 

Culexlarvae are well adapted to growing and developing in containers, and therefore collecting and rearing field-collectedCulexto adulthood in the laboratory is relatively straightforward. What is substantially more challenging is simulating natural conditions that encourageCulexadults to mate, blood feed, and reproduce in laboratory settings. In our experience, this is the most difficult hurdle to overcome when establishing new laboratory colonies. Here, we detail how to collectCulexeggs from the field and establish a colony in the laboratory. Successfully establishing a new colony ofCulexmosquitoes in the laboratory will allow researchers to evaluate physiologically, behaviorally, and ecologically relevant aspects of their biology and better understand and manage these important disease vectors. 

After overcoming the significant obstacle of getting adultCulexmosquitoes to reproduce and blood feed in the laboratory, maintaining a laboratory colony is much more achievable. However, great care and attention to detail are still required to ensure that the larvae have adequate food without being overwhelmed by bacterial growth. Additionally, achieving the appropriate densities of larvae and pupae is essential, as overcrowding delays development, prevents pupae from successfully emerging as adults, and/or reduces adult fecundity and alters sex ratios. Finally, adult mosquitoes should have constant access to H₂O and nearly constant access to sugar sources to ensure that both males and females have adequate nutrition and can produce the maximum number of offspring. Here, we describe our methods for maintaining the Buckeye strain ofCulex pipiensand how other researchers might modify them to suit their specific needs. 

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.