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1. Characterizing the relative abundance of circadian transcription factors in diapausing and nondiapausing Northern house mosquitoes

   https://doi.org/https://doi.org/10.1016/j.jinsphys.2022.104404  

   Caitlin Peffers ; Megan E. Meuti ( June 2022 , Journal of insect physiology)

   The Northern house mosquito (Culex pipiens) is a major vector of West Nile virus. To survive harsh conditions in winter adult females of Cx. pipiens enter a state of arrested reproductive development called diapause. Diapause is triggered by the short daylengths of late summer and early fall. The methods by which Cx. pipiens measures daylength are still unknown. However, it is suspected that clock genes, which provide information on daylength, may also regulate diapause. The proteins produced by these genes often cycle in abundance throughout the day in diapausing and nondiapausing insects. Two clock genes suspected to control diapause are cycle (cyc) and Par domain protein1 (Pdp1) as they encode circadian transcription factors that may regulate genes that are involved in diapause. Using Western blotting we measured the relative protein abundance of CYC and PDP1 throughout the day in the whole bodies and the heads of Cx. pipiens reared under either long-day, diapause-averting conditions or short-day, diapause-inducing conditions. We found that in whole bodies there was no significant oscillation of CYC or PDP1 abundance in both long day and short day-reared mosquitoes. In the heads of long day-reared mosquitoes both CYC and PDP1 cycled. In contrast, only PDP1 abundance showed diel differences in abundance in the heads of short day-reared mosquitoes. These data bring us one step closer to understanding the role that CYC and PDP1 may play in regulating diapause and other biological processes. 

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2. Suppression of the gene encoding PDZ domain-containing protein decreases cold tolerance and overwintering survival of the mosquito, Culex pipiens (Culicidae: Diptera)

   https://doi.org/10.1093/jme/tjad059  

   King, Bryan ; Larsen, Mazie ; Ikenga, Arinze ; Sim, Cheolho ; Hillyer, ed., Julian ( May 2023 , Journal of Medical Entomology)

   In diapausing mosquitoes, cold tolerance and prolonged lifespan are important features that are crucial for overwintering success. In the mosquito Culex pipiens, we suggest that PDZ domain-containing protein (PDZ) (post synaptic density protein [PSD95], drosophila disc large tumor suppressor [Dlg1], and zonula occludens-1 protein [zo-1]) domain-containing protein is involved with these diapause features for overwintering survival in Culex mosquitoes. The expression level of pdz was significantly higher in diapausing adult females in the early stage in comparison to their nondiapausing counterparts. Suppression of the gene that encodes PDZ by RNA interference significantly decreased actin accumulation in the midgut of early-stage adult diapausing females. Inhibition of pdz also significantly reduced the survivability of diapausing females which indicates that this protein could play a key role in preserving the midgut tissues during early diapause.

    

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3. 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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4. Characterizing the seasonal abundance and reproductive activity of overwintering Anopheles (Diptera: Culicidae) mosquitoes

   https://doi.org/10.1093/jme/tjae024  

   Dehus, Hannah ; Siperstein, Alden ; Pomeroy, Laura W. ; Meuti, Megan E. ; Sallum, ed., Maria Anice ( February 2024 , Journal of Medical Entomology)

   In temperate regions of the United States, female Anopheles mosquitoes respond to low temperatures and short photoperiods by entering an overwintering dormancy or diapause. Diapause in Anopheles results in reduced frequency of blood-feeding and reproductive arrest, indicating a period when pathogen transmission by these mosquitoes is unlikely. However, it is unclear precisely how late into the fall and how early in the spring these mosquitoes are biting, reproducing, and potentially transmitting pathogens. This is further complicated by the lack of clear markers of diapause in Anopheles (e.g., changes in egg follicle length). Our goal was to characterize the seasonal reproductive activity of female Anopheles in central Ohio, United States and evaluate egg follicle length as an indicator of Anopheles diapause. We used traditional mosquito traps and aspirators to collect Anopheles from urban woodlots and culverts, respectively, from late September 2021 through mid-May 2022 in central Ohio. By measuring their egg follicle length, reproductive status, and blood-feeding status, we found that egg follicle length is not a reliable indicator of Anopheles diapause. We also found that a small proportion of An. punctipennis (Say), An. perplexens (Ludlow), and An. quadrimaculatus (Say) continued to bite and reproduce into early November 2021 and that females of these species terminated reproductive dormancy and began biting by mid-March 2022. This period of reproductive activity extends beyond current mosquito surveillance and control in Ohio. Our findings suggest that within temperate regions of North America, Anopheles have the capacity to transmit pathogens throughout the spring, summer, and fall.

    

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5. 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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