The ecology and establishment of Aedes aegypti in tropical, sub-tropical, and temperate areas makes them one of the most medically relevant mosquito species. While they have been reported to be highly anthropophilic, several studies indicate a broader host range. They also reportedly take multiple blood meals between gonotrophic cycles, which makes determination of host usage difficult when using common blood meal analysis methods. In this study, we examined host usage of Ae. aegypti in Harris County, Texas (Houston), and Maricopa County, Arizona (Phoenix), using a nanopore-based third-generation sequencing protocol to resolve host usage and multiplicity. Using this method, approximately 80% of samples from each location with evidence of blood feeding resulted in blood meal identification, with a single host blood meal identified in about 80% of samples and approximately 20% containing evidence of multiple blood meals. Overall, we observed a wide host range with human DNA being the most prevalent followed by feline (Felis catus) and canine (Canis lupus). We also identified avian, rodent, ungulate and even ectotherm usage by Ae. aegypti from Maricopa County. This study demonstrates the utility of a third-generation sequencing method to identify less common hosts, like ectotherms in Arizona, and to resolve multiple feedings which remain difficult to resolve by current Sanger-based methods.

BACKGROUND:Mosquitoes are vectors of diseases globally, making development of models that better explain mosquito abundance imperative. Mosquito population dynamics are particularly sensitive to local weather conditions, and mosquito-borne disease outbreaks can be spatially concentrated. There is a need for improved modeling studies to address whether spatial variation in disease outbreaks is driven by spatial variation in weather conditions, especially in dry and hot environments. In the present study, we built a climate-driven model of mosquito population dynamics and compared whether predictions of mosquito abundance at the county scale were improved by accounting for subcounty weather variation. METHODS:Using a 5-year time series of weekly Culex quinquefasciatus abundance data collected for each zip code in Maricopa County, USA, we assessed how local variation in weather could explain and predict mosquito population dynamics. We built a mechanistic model of mosquito population dynamics influenced by daily maximum temperature and 30-day accumulated precipitation. We grouped zip codes on the basis of similar patterns of temperature and precipitation using functional clustering. We compared two approaches: one using county-level average weather and another using data from the identified weather clusters. We used Markov chain Monte Carlo simulations to fit the mechanistic model using averaged weather data in each cluster, then compared the model fit with observed data between the county-level model and the model on the basis of weather-based clusters. RESULTS:Simple, weather-forced modeling accurately estimated detailed Cx. quinquefasciatus abundance trajectories throughout the 5-year period. Modeling mosquito abundances in the subcounty spatial clusters demonstrated that the same effects of temperature and precipitation on population growth rates could explain small-scale changes in mosquito abundances. However, when we aggregated the subcounty model fits to the county-scale, the resulting fits were more precise but sometimes overly confident, leading to lower overall accuracy and predictive performance. CONCLUSIONS:Our study demonstrated the importance of collecting fine-scale mosquito abundance data to improve our understanding and the predictability of mosquito population dynamics. The strong performance of both the cluster-based and county-level models illustrated the value of spatially sensitive modeling in this application. We anticipate that such modeling efforts will aid in using weather forecasts to predict increases in mosquito populations, thereby aiding in efforts to control the spread of infectious disease.

Abstract Mosquito-borne diseases pose a growing public health challenge as climate change reshapes vector population dynamics. West Nile virus (WNV), transmitted between birds and Culex mosquitoes, disproportionately affects Maricopa County, Arizona, one of the nation’s highest-burden counties, yet whether models that include weather and avian dynamics improve forecast accuracy remains unclear. Using a 15-year weekly time series of mosquito abundance, mosquito infection prevalence, and human cases, we developed four mechanistic model configurations of varying complexity, from mosquito-human dynamics alone to full models incorporating avian dynamics and weather forcing. We fitted each model to the weekly-observed data, generated probabilistic 1- and 2-week-ahead forecast horizons, and evaluated forecasts against a historical baseline. All configurations fit the data equally regardless of weather or avian dynamics. However, models incorporating both birds and weather created more accurate forecasts of mosquito abundance and mosquito infection prevalence, and all configurations outperformed the baseline for forecasting human cases. Forecast accuracy was highest in summer and fall, and ensemble aggregation sometimes outperformed every individual model, stabilizing predictions across the 15-year record. These findings indicate that avian and weather dynamics are most critical for predicting mosquito-specific data, positioning this framework as a scalable tool for public health planning for WNV surveillance under climate change.

Abstract Here we report a newly developed method utilizing long-range PCR and long-read Pacific Biosciences HiFi sequencing that successfully obtained two full-length and annotated mitochondrial genomes from Culex quinquefasciatus Say, 1823 and Culex tarsalis Coquillett, 1896, both from Maricopa County, Arizona, USA. Given the substantial burden of West Nile virus in Maricopa County over the past decade, and that these vectors are primarily responsible for spillover to human populations in the county, it is critical to better understand their distribution over time and space. This study begins to approach this need by contributing a novel approach that has resulted in the first West Nile virus vector mitochondrial genomes from Arizona. Our circular Cx. quinquefasciatus mitogenome is 15,587 bp in length, making it the first USA-based mitogenome sequenced through the AT-rich control region. The Cx. tarsalis mitochondrial genome is 16,416 bp long, longer than recently published California-based CTarK1 and Texas-based PQ585801 mitogenomes. The increased length of the Cx. tarsalis mitogenome is a result of a 905 bp insertion in the AT-rich control region, not present in the species’ publicly available mitogenomes. A maximum likelihood-based phylogenetic reconstruction supports the species designation of these newly-sequenced mitogenomes. The newly developed methodology offers a unique approach to study medically-important vector species around the globe, providing a solution to study populations through pooled vector pathogen surveillance programs.

Locally acquired arboviral infections are an increasing public health concern in the United States. Aedes aegypti and Culex quinquefasciatus, vectors of dengue virus and West Nile virus, respectively, are established in regions where local transmission has been reported. Seasonal variation in mosquito abundance affects vector density, human-vector contact, and arbovirus transmission risk. The aim of this study is to investigate seasonal variations in Ae. aegypti and Cx. quinquefasciatus population dynamics in Miami-Dade County, Florida; Maricopa County, Arizona; and Clark County, Nevada. Monthly relative abundance, average mosquitoes collected per trap-night, normalized abundance ratios, and seasonal-trend decomposition were used to evaluate species- and location-specific seasonal patterns. Mosquito population dynamics differed by species and location. In Miami-Dade County, the two species showed seasonal turnover, with Cx. quinquefasciatus peaking during winter and spring and Ae. aegypti peaking during summer. In Maricopa and Clark counties, both species peaked primarily between August and September. Species dominance also differed by site, with Ae. aegypti more abundant than Cx. quinquefasciatus in Maricopa County and Cx. quinquefasciatus more abundant than Ae. aegypti in Clark and Miami-Dade counties. Seasonal decomposition showed that Ae. aegypti peaked earlier in Miami-Dade County than in Maricopa and Clark counties, whereas Cx. quinquefasciatus showed a spring peak in Miami-Dade County and bimodal seasonal patterns in Maricopa and Clark counties. These results suggest that mosquito population dynamics are species- and location-specific and support the use of local surveillance data to guide the timing of mosquito control and arbovirus preparedness.

Background:Mosquitoes are vectors for diseases globally, making development of models that better explain mosquito abundances imperative. Mosquito population dynamics are particularly sensitive to local weather conditions, and mosquito-borne disease outbreaks can be spatially concentrated. There is a need for improved modeling studies to address whether spatial variation in disease outbreaks is driven by spatial variation in weather conditions, especially in dry and hot environments. In this study, we build a climate-driven model of mosquito population dynamics and compare whether predictions of mosquito abundance at the county scale are improved by accounting for sub-county climate variation. Methods:Using a 5-year time series of weekly mosquito abundance data collected for each zip code in Maricopa County, USA, we assess how local variation in climate can explain and predict mosquito population dynamics. We built a mechanistic model of mosquito population dynamics influenced by daily temperature and 30-day accumulated precipitation. We grouped zip codes based on similar patterns of temperature and precipitation using functional clustering. We compared two approaches: one using county-level average climate and another using data from the identified climate clusters. We use MCMC to fit the mechanistic model using averaged climate data in each cluster, then compare the modeling fit to observed data of the county-level model to the model based on climate-based clusters. Results:Simple, climate-forced modeling accurately estimates detailed mosquito abundance trajectories throughout a five-year period. Modeling mosquito abundances in the sub-county spatial clusters demonstrated that the same effects of temperature and precipitation on population growth rates could explain small-scale changes in mosquito populations. However, when we aggregate the sub-county model fits to the county-scale, the resulting fits are more precise but are sometimes overly confident, leading to lower overall accuracy and predictive performance. Conclusions:Our study demonstrates the importance of collecting fine-scale mosquito abundance data to improve our understanding and the predictability of mosquito population dynamics. The strong performance of both the cluster-based and county-level models illustrates the value of spatially sensitive modeling in this application. We anticipate that such modeling efforts will also aid in using weather forecasts to predict mosquito populations, aiding in efforts to control the spread of infectious disease.

Aedes aegypti (L.), the primary mosquito vector of arboviruses such as dengue and Zika, has a global distribution that includes the southern United States. Control of this peridomestic mosquito is challenging. Ultra-low volume (ULV) pyrethroid sprays are commonly used against adult mosquitoes to break transmission during a disease outbreak, although efficacy data are limited. This study examined the impacts of ULV sprays on Ae. aegypti vectorial capacity as measured by vector abundance and age structure in two cities in Maricopa County, AZ with robust Ae. aegypti populations and a well-developed vector management program. We assessed impacts of routine ULV applications conducted by Maricopa Vector Control Division during the summer rainy seasons of 2017 to 2019 to determine whether existing practices mainly targeting Culex spp. also suppressed Ae. aegypti. The insecticide formulations applied for Culex spp. control (Duet and Permanone 30-30) did not affect Ae. aegypti abundance, but Duet applications slightly reduced female mosquito age. Deltagard, the insecticide product used specifically against Ae. aegypti, was only applied three times in 2018 over small areas, so efficacy assessment was difficult. Deltagard was associated with a small decline in Ae. aegypti abundance. CDC bottle bioassays of Ae. aegypti collected in the study area showed resistance to permethrin and deltamethrin. Overall, the lack of significant mosquito population suppression or age structure changes after insecticide applications suggest that current tools used by Maricopa Vector Control Division are unlikely to effectively control Ae. aegypti populations in the event of a disease outbreak.

West Nile virus (WNV) (Orthoflavivirus nilense) and Saint Louis encephalitis virus (SLEV) (Orthoflavivirus louisense) are transmitted by Culex quinquefasciatus Say and Culex tarsalis Coquillett in Maricopa County, Arizona, where a significant increase in the number of WNV cases was reported in 2021. We used data collected between 2014 and 2021 from a network of CO2-baited surveillance traps to assess whether particular land use categories may have contributed to this rise in WNV cases. For each vector species and year, we estimated the association between the areas of each of 10 land use categories neighboring the traps and vector abundance or the odds of detecting WNV or SLEV in females from the traps. Across years, the percentage of traps detecting WNV in each vector was positively associated with the number of reported WNV human cases. Positive associations between areas of the land use categories Single-Family Residential, Industrial, and Golf Course and the odds of detecting WNV only occurred in 2021, indicating that a greater occurrence of WNV in vectors from within these land use categories may have contributed to the rise in WNV human cases in 2021. Areas of the land use categories Golf Course and Vacant were consistently negatively associated with Cx. quinquefasciatus abundance and the odds of detecting SLEV. Agriculture was consistently positively associated with Cx. tarsalis abundance and the odds of detecting SLEV. By identifying land use categories that may have mediated arbovirus transmission at landscape scale, our results provide valuable information for developing targeted vector control strategies.

Aedes aegypti is the primary vector of several viruses of international public health concern, including Zika, dengue, yellow fever, and chikungunya. Their synanthropic ecology and establishment in tropical, sub-tropical, and temperate areas make Ae. aegypti one of the most medically relevant mosquito species. While they have been reported to be highly anthropophilic, several studies indicate a broader host range. They are also reported to take multiple blood meals between gonotrophic cycles. Consumption of multiple blood meals makes determination of host usage difficult when using common blood meal analysis methods. In this study, we examined host usage of Ae. aegypti in Harris County, Texas (Houston), and Maricopa County, Arizona (Phoenix), using a Nanopore-based third-generation sequencing protocol to successfully resolve host usage multiplicity and identify a broad range of host usage. Using this method, approximately 80% of samples from each location with evidence of blood feeding resulted in a blood meal species identification, with a single host blood meal in about 80% of samples and approximately 20% containing evidence of multiple blood meals. Overall, we observed a wide host range with human DNA the most prevalent followed by feline and canine. We also identified avian, rodent, ungulate and even ectotherm usage by Ae. aegypti from Maricopa County. The discovery of hosts other than humans expands the understanding of host usage dynamics in Ae. aegypti and their involvement in arbovirus transmission systems in highly urbanized areas such as Harris and Maricopa Counties. Synopsis The yellow fever mosquito, Aedes aegypti , is a vector of several viral pathogens that frequently cause human disease in tropical and subtropical locations but many of these pathogens are not controlled by vaccination. As such, control of this mosquito is critical to reduce disease transmission and better understanding of the ecology of this species helps to improve the efficacy of operational control. In this study, researchers used a deep sequencing method to define patterns of host usage in two large US metropolitan areas, Houston, TX and Phoenix, AZ, with substantial Ae. aegypti infestations. Results identified frequent multiple blood feeding by individual mosquitoes and that the primary host sources were humans and their pets. Results from Phoenix indicated a broad host usage, including feeding on livestock, birds, and even reptiles. This may provide useful information about Ae. aegypti resting sites and could be used to improve treatment by operational personnel. ### Competing Interest Statement The authors have declared no competing interest.

Arizona is home to many mosquito species, some of which are known vectors of infectious diseases that harm both humans and animals. Here, we provide an overview of the 56 mosquito species that have been identified in the State to date, but also discuss their known feeding preference and the diseases they can (potentially) transmit to humans and animals. This list is unlikely to be complete for several reasons: (i) Arizona’s mosquitoes are not systematically surveyed in many areas, (ii) surveillance efforts often target specific species of interest, and (iii) doubts have been raised by one or more scientists about the accuracy of some collection records, which has been noted in this article. There needs to be an integrated and multifaceted surveillance approach that involves entomologists and epidemiologists, but also social scientists, wildlife ecologists, ornithologists, representatives from the agricultural department, and irrigation and drainage districts. This will allow public health officials to (i) monitor changes in current mosquito species diversity and abundance, (ii) monitor the introduction of new or invasive species, (iii) identify locations or specific populations that are more at risk for mosquito-borne diseases, and (iv) effectively guide vector control.

Understanding drivers of disease vectors’ population dynamics is a pressing challenge. For short-lived organisms like mosquitoes, landscape-scale models must account for their highly local and rapid life cycles. Aedes aegypti, a vector of multiple emerging diseases, has become abundant in desert population centers where water from precipitation could be a limiting factor. To explain this apparent paradox, we examined Ae. aegypti abundances at > 660 trapping locations per year for 3 years in the urbanized Maricopa County (metropolitan Phoenix), Arizona, USA. We created daily precipitation layers from weather station data using a kriging algorithm, and connected localized daily precipitation to numbers of mosquitoes trapped at each location on subsequent days. Precipitation events occurring in either of two critical developmental periods for mosquitoes were correlated to suppressed subsequent adult female presence and abundance. LASSO models supported these analyses for female presence but not abundance. Precipitation may explain 72% of Ae. aegypti presence and 90% of abundance, with anthropogenic water sources supporting mosquitoes during long, precipitation-free periods. The method of using kriging and weather station data may be generally applicable to the study of various ecological processes and patterns, and lead to insights into microclimates associated with a variety of organisms’ life cycles.

West Nile virus (WNV) is the leading mosquito-borne disease causing-pathogen in the United States. Concerningly, there are no prophylactics or drug treatments for WNV and public health programs rely heavily on vector control efforts to lessen disease incidence. Insecticides can be effective in reducing vector numbers if implemented strategically, but can diminish in efficacy and promote insecticide resistance otherwise. Vector control programs which employ mass-fogging applications of insecticides, often conduct these methods during the late-night hours, when diel temperatures are coldest, and without a-priori knowledge on daily mosquito activity patterns. This study's aims were to 1) quantify the effect of temperature on the toxicity of two conventional insecticides used in fogging applications (malathion and deltamethrin) to Culex tarsalis, an important WNV vector, and 2) quantify the time of host-seeking of Cx. tarsalis and other local mosquito species in Maricopa County, Arizona. The temperature-toxicity relationship of insecticides was assessed using the WHO tube bioassay, and adult Cx. tarsalis, collected as larvae, were exposed to three different insecticide doses at three temperature regimes (15, 25, and 35°C; 80% RH). Time of host-seeking was assessed using collection bottle rotators with encephalitis vector survey traps baited with dry ice, first at 3h intervals during a full day, followed by 1h intervals during the night-time. Malathion became less toxic at cooler temperatures at all doses, while deltamethrin was less toxic at cooler temperatures at the low dose. Regarding time of host-seeking, Cx. tarsalis, Aedes vexans, and Culex quinquefasciatus were the most abundant vectors captured. During the 3-hour interval surveillance over a full day, Cx. tarsalis were most-active during post-midnight biting (00:00-06:00), accounting for 69.0% of all Cx. tarsalis, while pre-midnight biting (18:00-24:00) accounted for 30.0% of Cx. tarsalis. During the 1-hour interval surveillance overnight, Cx. tarsalis were most-active during pre-midnight hours (18:00-24:00), accounting for 50.2% of Cx. tarsalis captures, while post-midnight biting (00:00-06:00) accounted for 49.8% of Cx. tarsalis. Our results suggest that programs employing large-scale applications of insecticidal fogging should consider temperature-toxicity relationships coupled with time of host-seeking data to maximize the efficacy of vector control interventions in reducing mosquito-borne disease burden.

The Arizona State University (ASU) Tempe campus is inhabited by some 55,000 enrolled students as well as several mosquito species that can transmit West Nile virus, dengue, Zika, chikungunya, and yellow fever. The time of host-seeking of these vectors has not been quantified on the ASU Tempe campus, but this information is important to inform ground and/or truck-mount fogging operations targeting mosquitoes to prevent or control disease outbreaks. We quantified the time of host-seeking of the predominant mosquito vector species at the ASU Tempe campus during the post-monsoon season in 2021, using collection bottle rotators with encephalitis vector survey traps that were baited with CO2, at 3 h intervals during a full day. Culex quinquefasciatus, Aedes aegypti, and Culex tarsalis were the most abundant species captured. Pre-midnight host-seeking (18:00-00:00) accounted for 52% of all captures, whereas post-midnight host-seeking (00:00-06:00) accounted for 35% of all captures. Peak activity times were between 21:00 and 00:00 for Cx. quinquefasciatus and Cx. tarsalis, and between 15:00 and 18:00 for Ae. aegypti. Data can be used to inform local mosquito surveillance and control programs.

Aedes-borne diseases represent a major public health threat and mosquito control operations represent a key line of defense. Improving the real-time awareness of mosquito control authorities by providing reliable forecasts of the relative abundance of mosquito vectors could greatly enhance control efforts. To this aim, we developed an analytical tool that forecasts Aedes aegypti relative abundance 1 to 4 weeks ahead. Forecasts were validated against mosquito surveillance data (2,760 data points) collected over multiple years in four jurisdictions in the US. The symmetric absolute percentage error was in the range 0.43-0.69, and the 90% interquantile range of the forecasts had a coverage of 83-92%. Our forecasts consistently outperformed a reference "naïve" model for all analyzed study sites, forecasting horizon, and for periods with medium/high Ae. aegypti activity. The developed tool can be instrumental to address the need for evidence-based decision making.

We compared the effectiveness of 4 different carbon dioxide (CO2) sources (sugar-fermented BG-CO2, sugar-fermented Fleischmann yeast, dry ice, and compressed gas cylinders) in attracting different mosquito species in 2 separate 4 × 4 Latin square trials. The CO2 generated by dry ice and the gas cylinders collected more Culex quinquefasciatus than the sugar-fermented BG-CO2 and Fleischmann yeasts during the 1st trial (16-h surveillance periods), but there was no significant difference in Aedes aegypti numbers. There were no significant differences between the different CO2 sources in collecting Cx. quinquefasciatus and Ae. aegypti mosquitoes in the 2nd trial (24-h surveillance periods). Catches for Culiseta inornata and Cx. tarsalis were too low in both experiments for formal statistical analysis. Data can be used to inform local mosquito surveillance programs, but the selection of a CO2 source will also depend on financial and logistical constraints.

Cities across the USA are implementing urban policies to mitigate unwanted effects of urbanization. These policies may inadvertently promote the proliferation of mosquito vectors. Limited evidence exists regarding how urban policies impact arbovirus transmission risk. Models can evaluate public health interventions aimed at reducing arbovirus-related risks caused by urban policies.

West Nile virus (WNV) is a mosquitoborne disease primarily transmitted through bites of infected Culex species mosquitos (1). In the United States, WNV is the leading domestically acquired arboviral disease; it can cause severe illness affecting the brain and spinal cord with an associated case fatality rate of 10% (2,3). On September 2, 2021, Maricopa County Environmental Services Department, Vector Control Division (MCESD-VCD) notified the Maricopa County Department of Public Health (MCDPH) and the Arizona Department of Health Services (ADHS) that the WNV vector index (VI), a measure of infected Culex mosquitoes, was substantially elevated. By that date, at least 100 WNV cases had already been reported among Maricopa County residents to MCDPH by health care providers and laboratories. Within 2 weeks, the VI reached its highest ever recorded level (53.61), with an associated tenfold increase in the number of human disease cases. During 2021, a total of 1,487 human WNV cases were identified; 956 (64.3%) patients had neuroinvasive disease, and 101 (6.8%) died. MCESD-VCD conducted daily remediation efforts to mitigate elevated VI and address mosquito-related complaints from residents (i.e., large numbers of outdoor mosquitoes from an unknown source and unmaintained swimming pools potentially breeding mosquitoes). MCDPH increased outreach to the community and providers through messaging, education events, and media. This was the largest documented focal WNV outbreak in a single county in the United States (4). Despite outreach efforts to communities and health care partners, clinicians and patients reported a lack of awareness of the WNV outbreak, highlighting the need for public health agencies to increase prevention messaging to broaden public awareness and to ensure that health care providers are aware of recommended testing methods for clinically compatible illnesses.

Mosquito-borne diseases are a major global public health concern and mosquito surveillance systems are essential for the implementation of effective mosquito control strategies. The objective of our study is to determine the spatiotemporal distribution of vector mosquito species in Maricopa County, AZ from 2011 to 2021, and to identify the hotspot areas for West Nile virus (WNV) and St. Louis Encephalitis virus (SLEV) transmission in 2021. The Maricopa County Mosquito Control surveillance system utilizes BG-Sentinel and EVS-CDC traps throughout the entire urban and suburban areas of the county. We estimated specific mosquito species relative abundance per unit area using the Kernel density estimator in ArcGIS 10.2. We calculated the distance between all traps in the surveillance system and created a 4 km buffer radius around each trap to calculate the extent to which each trap deviated from the mean number of Culex quinquefasciatus and Culex tarsalis collected in 2021. Our results show that vector mosquito species are widely distributed and abundant in the urban areas of Mar-icopa County. A total of 691,170Cx. quinquefasciatus, 542,733 Cx. tarsalis, and 292,305 Aedes aegypti were collected from 2011 to 2022. The relative abundance of Ae. aegypti was highly seasonal peaking in the third and fourth quarters of the year. Culex quinquefasciatus, on the other hand, was abundant throughout the year with several regions consistently yielding high numbers of mosquitoes. Culex tarsalis was abundant but it only reached high numbers in well-defined areas near irrigated landscapes. We also detected high levels of heterogeneity in the risk of WNV and SLEV transmission to humans disregarding traps geographical proximity. The well-defined species-specific spatiotemporal and geographical patterns found in this study can be used to inform vector control operations.