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1. Transmission of West Nile and five other temperate mosquito-borne viruses peaks at temperatures between 23°C and 26°C

   https://doi.org/10.7554/eLife.58511  

   Shocket, Marta S ; Verwillow, Anna B ; Numazu, Mailo G ; Slamani, Hani ; Cohen, Jeremy M ; El Moustaid, Fadoua ; Rohr, Jason ; Johnson, Leah R ; Mordecai, Erin A ( September 2020 , eLife)

   null (Ed.)

   The temperature-dependence of many important mosquito-borne diseases has never been quantified. These relationships are critical for understanding current distributions and predicting future shifts from climate change. We used trait-based models to characterize temperature-dependent transmission of 10 vector–pathogen pairs of mosquitoes ( Culex pipiens , Cx. quinquefascsiatus , Cx. tarsalis , and others) and viruses (West Nile, Eastern and Western Equine Encephalitis, St. Louis Encephalitis, Sindbis, and Rift Valley Fever viruses), most with substantial transmission in temperate regions. Transmission is optimized at intermediate temperatures (23–26°C) and often has wider thermal breadths (due to cooler lower thermal limits) compared to pathogens with predominately tropical distributions (in previous studies). The incidence of human West Nile virus cases across US counties responded unimodally to average summer temperature and peaked at 24°C, matching model-predicted optima (24–25°C). Climate warming will likely shift transmission of these diseases, increasing it in cooler locations while decreasing it in warmer locations. 

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2. Scoping review of Culex mosquito life history trait heterogeneity in response to temperature

   https://doi.org/10.1186/s13071-023-05792-3  

   Moser, S. Kane ; Barnard, Martha ; Frantz, Rachel M. ; Spencer, Julie A. ; Rodarte, Katie A. ; Crooker, Isabel K. ; Bartlow, Andrew W. ; Romero-Severson, Ethan ; Manore, Carrie A. ( June 2023 , Parasites & Vectors)

   Mosquitoes in the genusCulexare primary vectors in the US for West Nile virus (WNV) and other arboviruses. Climatic drivers such as temperature have differential effects on species-specific changes in mosquito range, distribution, and abundance, posing challenges for population modeling, disease forecasting, and subsequent public health decisions. Understanding these differences in underlying biological dynamics is crucial in the face of climate change.

   We collected empirical data on thermal response for immature development rate, egg viability, oviposition, survival to adulthood, and adult lifespan forCulex pipiens, Cx. quinquefasciatus, Cx. tarsalis, andCx. restuansfrom existing literature according to the PRISMA scoping review guidelines.

   We observed linear relationships with temperature for development rate and lifespan, and nonlinear relationships for survival and egg viability, with underlying variation between species. Optimal ranges and critical minima and maxima also appeared varied. To illustrate how model output can change with experimental input data from individualCulexspecies, we applied a modified equation for temperature-dependent mosquito type reproduction number for endemic spread of WNV among mosquitoes and observed different effects.

   Current models often input theoretical parameters estimated from a single vector species; we show the need to implement the real-world heterogeneity in thermal response between species and present a useful data resource for researchers working toward that goal.

    

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3. Transcriptome profiling reveals sex‐specific gene expressions in pupal and adult stages of the mosquito Culex pipiens

   https://doi.org/10.1111/imb.12735  

   Martynova, T. ; Kamanda, P. ; Sim, C. ( September 2021 , Insect Molecular Biology)

   Understanding the development process of male and female mosquitoes provides important basic information for sterile insect release programmes and is important for improving other vector control strategies. However, little is known about the molecular mechanisms that distinguish male from female‐specific developmental processes in this species. We used IlluminaRNA‐seq to identify sex‐specific genes during pupal and adult stages. One hundred and forty‐seven genes were expressed only in pupal males, 56 genes were expressed in adult males and another 82 genes were commonly expressed in both male samples. In addition, 26 genes were expressed only in the pupal females, 163 genes were found in the adult females and only one gene was expressed in both female samples. A further quantitative real‐time PCR validation of selected genes from the RNA sequencing (RNA‐seq) analysis confirmed upregulation of those genes in a sex‐specific manner, including: fibrinogen and fibronectin, a zinc finger protein, phospholipase A(2) and a serine protein for female pupae; venom allergen 3, a perlecan, testis‐specific serine/threonine‐protein kinase 1, testis‐specific serine/threonine‐protein kinase 6 and cytochrome c‐2 for male pupae; a salivary protein, D7 protein precursor, trypsin 7 precursor, D7 protein and nanos for female adults; and tetraspanin F139, cytosol aminopeptidase, testis‐specific serine/threonine‐protein kinase 1, a testis‐specific serine/threonine‐protein kinase 6 and a C‐type lectin for male adults. These findings provide insight into the development and physiology ofCulexmosquitoes, which will help in the development of more effective control methods for these disease vectors.

    

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4. Characterizing seasonal changes in the reproductive activity of Culex mosquitoes throughout the fall, winter, and spring in Ohio

   https://doi.org/10.1186/s13071-023-05806-0  

   Siperstein, Alden ; Pomeroy, Laura W. ; Robare, Sydney ; Sarko, Lucas ; Dehus, Hannah ; Lowmiller, Taylor ; Fyie, Lydia ; Meuti, Megan E. ( May 2023 , Parasites & Vectors)

   Culexmosquitoes 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.

   Mosquitoes 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.

   By 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.

   We 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.

    

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5. Human biting mosquitoes and implications for West Nile virus transmission

   https://doi.org/10.1186/s13071-022-05603-1  

   Uelmen, Jr., Johnny A. ; Lamcyzk, Bennett ; Irwin, Patrick ; Bartlett, Dan ; Stone, Chris ; Mackay, Andrew ; Arsenault-Benoit, Arielle ; Ryan, Sadie J. ; Mutebi, John-Paul ; Hamer, Gabriel L. ; et al ( January 2023 , Parasites & Vectors)

   West Nile virus (WNV), primarily vectored by mosquitoes of the genusCulex, is the most important mosquito-borne pathogen in North America, having infected thousands of humans and countless wildlife since its arrival in the USA in 1999. In locations with dedicated mosquito control programs, surveillance methods often rely on frequent testing of mosquitoes collected in a network of gravid traps (GTs) and CO₂-baited light traps (LTs). Traps specifically targeting oviposition-seeking (e.g. GTs) and host-seeking (e.g. LTs) mosquitoes are vulnerable to trap bias, and captured specimens are often damaged, making morphological identification difficult.

   This study leverages an alternative mosquito collection method, the human landing catch (HLC), as a means to compare sampling of potential WNV vectors to traditional trapping methods. Human collectors exposed one limb for 15 min at crepuscular periods (5:00–8:30 am and 6:00–9:30 pm daily, the time whenCulexspecies are most actively host-seeking) at each of 55 study sites in suburban Chicago, Illinois, for two summers (2018 and 2019).

   A total of 223 human-seeking mosquitoes were caught by HLC, of which 46 (20.6%) were mosquitoes of genusCulex. Of these 46 collectedCulexspecimens, 34 (73.9%) wereCx. salinarius, a potential WNV vector species not thought to be highly abundant in upper Midwest USA. Per trapping effort, GTs and LTs collected > 7.5-fold the number of individualCulexspecimens than HLC efforts.

   The less commonly used HLC method provides important insight into the complement of human-biting mosquitoes in a region with consistent WNV epidemics. This study underscores the value of the HLC collection method as a complementary tool for surveillance to aid in WNV vector species characterization. However, given the added risk to the collector, novel mitigation methods or alternative approaches must be explored to incorporate HLC collections safely and strategically into control programs.

    

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