Mosquito-borne Transmission Research Articles

Plant-Based Bioinsecticides for Mosquito Control: Impact on Insecticide Resistance and Disease Transmission.

Simple SummaryMosquito-borne diseases cause millions of deaths each year. There has been an increase in the use of insecticides to combat disease transmission caused by mosquitoes. Synthetic insecticides have been effectively used to protect humans from mosquito bites through insecticide-treated mosquito nets, fabrics, and indoor sprays. Despite the considerable progress made in reducing mosquito borne diseases, extensive usage of insecticides has caused serious health problems to humans and animals, insecticide resistance or insensitivity in mosquitoes, and environmental damage. A success in the fight with mosquito disease transmission can only be accomplished by adequate and effective implementation of insecticide resistance monitoring and management programs globally. For this purpose, extensive research focuses on exploring insecticide resistance mechanisms in mosquitoes and how they get resistant to chemical applications over time. The search also focuses on novel compounds that are more effective, safer, and eco-friendly for improved management of mosquito vectors. In this review, we provide the current literature on the synthetic insecticides and how mosquitoes develop resistance to them, with further emphasis on bioinsecticides that could replace conventional synthetic insecticides. In this context, plant-based compounds are explained in detail with their potential applications to control mosquitoes.The use of synthetic insecticides has been a solution to reduce mosquito-borne disease transmission for decades. Currently, no single intervention is sufficient to reduce the global disease burden caused by mosquitoes. Problems associated with extensive usage of synthetic compounds have increased substantially which makes mosquito-borne disease elimination and prevention more difficult over the years. Thus, it is crucial that much safer and effective mosquito control strategies are developed. Natural compounds from plants have been efficiently used to fight insect pests for a long time. Plant-based bioinsecticides are now considered a much safer and less toxic alternative to synthetic compounds. Here, we discuss candidate plant-based compounds that show larvicidal, adulticidal, and repellent properties. Our discussion also includes their mode of action and potential impact in mosquito disease transmission and circumvention of resistance. This review improves our knowledge on plant-based bioinsecticides and the potential for the development of state-of-the-art mosquito control strategies.

Effects of Sterile Males and Fertility of Infected Mosquitoes on Mosquito-Borne Disease Dynamics.

By studying an infection-age structured model, we consider the effects of releasing sterile males and the fertility of infected mosquitoes on the mosquito-borne diseases transmission including the extinction of mosquitoes, the elimination and persistence of diseases. Firstly, equivalent integral equations are established to prove the well-posedness of solutions. Then, the main results of disease dynamics are given. By taking chikungunya as a numerical simulation example, an optimal releasing threshold is given according to our presupposed control standard. When the fertility disturbance of infected mosquitoes is small, the high releasing amount plays a main role on the control of the disease; however, when the fertility disturbance is large, the initial distributions and the fertility of infected mosquitoes are the key factors to control the disease. Mathematically, the fertility of infected mosquitoes makes the system have complex dynamics with multiple positive equilibria and bistability.

The Impact of Deforestation, Urbanization, and Changing Land Use Patterns on the Ecology of Mosquito and Tick-Borne Diseases in Central America.

Simple SummaryCentral America is a region that possesses distinct ecological and socioeconomic characteristics, making it increasingly vulnerable to vector-borne diseases. The emergence and resurgence of these diseases has been linked to environmental changes driven by human activities, particularly land use changes associated with deforestation, forest degradation, and urbanization. However, the effects of these environmental modifications on the transmission dynamics and the increase of infection risks are not well understood in Central America where information is limited and scattered. In this article, we review and analyze the current knowledge and potential impacts of deforestation and urbanization on the risk and transmission dynamics of the most relevant mosquito-borne and tick-borne diseases in Central America. Disease events, such as the recent Zika and dengue epidemics, and the uneven progress towards regional malaria elimination highlight the need to increase awareness regarding the complex ecological interactions and environmental changes taking place in this region and how this information could be used to improve prevention and control strategies.Central America is a unique geographical region that connects North and South America, enclosed by the Caribbean Sea to the East, and the Pacific Ocean to the West. This region, encompassing Belize, Costa Rica, Guatemala, El Salvador, Honduras, Panama, and Nicaragua, is highly vulnerable to the emergence or resurgence of mosquito-borne and tick-borne diseases due to a combination of key ecological and socioeconomic determinants acting together, often in a synergistic fashion. Of particular interest are the effects of land use changes, such as deforestation-driven urbanization and forest degradation, on the incidence and prevalence of these diseases, which are not well understood. In recent years, parts of Central America have experienced social and economic improvements; however, the region still faces major challenges in developing effective strategies and significant investments in public health infrastructure to prevent and control these diseases. In this article, we review the current knowledge and potential impacts of deforestation, urbanization, and other land use changes on mosquito-borne and tick-borne disease transmission in Central America and how these anthropogenic drivers could affect the risk for disease emergence and resurgence in the region. These issues are addressed in the context of other interconnected environmental and social challenges.

Anthropogenic changes and associated impacts on vector-borne diseases

Urbanization impacts the community composition, abundance, and richness of mosquitoes. As urbanization processes increase globally, it is important to better understand the biodiversity loss caused by anthropogenic changes and associated impacts on vector-borne diseases. Mosquito surveillance and control are key for reducing the risk of mosquito-borne pathogen transmission.

A microfluidic platform for highly parallel bite by bite profiling of mosquito-borne pathogen transmission

Mosquito bites transmit a number of pathogens via salivary droplets deposited during blood-feeding, resulting in potentially fatal diseases. Little is known about the genomic content of these nanodroplets, including the transmission dynamics of live pathogens. Here we introduce Vectorchip, a low-cost, scalable microfluidic platform enabling high-throughput molecular interrogation of individual mosquito bites. We introduce an ultra-thin PDMS membrane which acts as a biting interface to arrays of micro-wells. Freely-behaving mosquitoes deposit saliva droplets by biting into these micro-wells. By modulating membrane thickness, we observe species-dependent differences in mosquito biting capacity, utilizable for selective sample collection. We demonstrate RT-PCR and focus-forming assays on-chip to detect mosquito DNA, Zika virus RNA, as well as quantify infectious Mayaro virus particles transmitted from single mosquito bites. The Vectorchip presents a promising approach for single-bite-resolution laboratory and field characterization of vector-pathogen communities, and could serve as a powerful early warning sentinel for mosquito-borne diseases.

Mosquitoes (Diptera: Culicidae) in the Dark-Highlighting the Importance of Genetically Identifying Mosquito Populations in Subterranean Environments of Central Europe.

The common house mosquito, Culex pipiens s. l. is part of the morphologically hardly or non-distinguishable Culex pipiens complex. Upcoming molecular methods allowed us to identify members of mosquito populations that are characterized by differences in behavior, physiology, host and habitat preferences and thereof resulting in varying pathogen load and vector potential to deal with. In the last years, urban and surrounding periurban areas were of special interest due to the higher transmission risk of pathogens of medical and veterinary importance. Recently, surveys of underground habitats were performed to fully evaluate the spatial distribution of rare members of the Cx. pipiens complex in Europe. Subterranean environments and their contribution to mosquito-borne pathogen transmission are virtually unknown. Herein, we review the underground community structures of this species complex in Europe, add new data to Germany and provide the first reports of the Cx. pipiens complex and usually rarely found mosquito taxa in underground areas of Luxembourg. Furthermore, we report the first finding of Culiseta glaphyroptera in Luxembourg. Our results highlight the need for molecular specimen identifications to correctly and most comprehensively characterize subterranean mosquito community structures.

Reducing mosquito-borne disease transmission to humans: A systematic review of cluster randomised controlled studies that assess interventions other than non-targeted insecticide.

Mosquito control interventions are widely used to reduce mosquito-borne diseases. It is unclear what combination of interventions are most effective in reducing human disease. A novel intervention study for Buruli ulcer targeting mosquito vectors was proposed for a Buruli ulcer-endemic area of Victoria, Australia. The local community expressed a preference for avoiding widespread residual spraying of pyrethroids. To inform the design of a future cluster randomised control study (cRCT) for Buruli ulcer prevention in Victoria, we conducted a systematic literature review. The aim was to describe cRCT designs which investigated interventions other than non-targeted insecticide for reducing mosquito-borne disease transmission, and comment on the strengths and weaknesses of these study designs. Five medical research databases were searched for eligible literature from the earliest available sources up to 5 July 2019 (Medline, Embase, Web of Science, EBM Reviews, CAB Direct). Reference lists of identified studies were hand searched. Eligible studies were cRCTs using targeted chemical or biological mosquito control interventions, or mosquito breeding source reduction, with the occurrence of mosquito-borne disease as an outcome. Eight eligible cRCTs, conducted between 1994-2013 were identified in a variety of settings in the Americas and Asia. Interventions to reduce dengue transmission were mass adult trapping and source reduction. Interventions to reduce malaria transmission were largescale larvicide administration and (topical and spatial) repellent use. Three studies showed the intervention was associated with statistically significant reductions in the disease of interest and entomological indicators. High community engagement with the intervention were common to all three. In two studies, large buffer zones reduced contamination between study arms. Heterogeneity was reduced through increasing study cluster numbers, cluster matching and randomisation. High community engagement is vital for a cRCT reducing mosquito-borne disease with a mosquito control intervention. These findings support a mosquito breeding source reduction intervention for Aedes control in a future study of Buruli ulcer prevention if local communities are supportive and very engaged. Regular administration of larvicide to sites unsuited to source reduction may supplement the intervention.

Public health messages on arboviruses transmitted by Aedes aegypti in Brazil

BackgroundThe outbreak of Zika virus in Brazil in 2015 followed the arrival of chikungunya in 2014 and a long history of dengue circulation. Vital to the response to these outbreaks of mosquito-borne pathogens has been the dissemination of public health messages, including those promoted through risk communication posters. This study explores the content of a sample of posters circulated in Brazil towards the end of the Zika epidemic in 2017 and analyses their potential effectiveness in inducing behaviour change.MethodsA content analysis was performed on 37 posters produced in Brazil to address outbreaks of mosquito-borne pathogens. The six variables of the Health Belief Model were used to assess the potential effectiveness of the posters to induce behaviour change.ResultsThree overarching key messages emerged from the posters. These included (i) the arboviruses and their outcomes, (ii) a battle against the mosquito, and (iii) a responsibility to protect and prevent. Among the six variables utilised through the Health Belief Model, cues to action were most commonly featured, whilst the perceived benefits of engaging in behaviours to prevent arbovirus transmission were the least commonly featured.ConclusionsThe posters largely focused on mosquito-borne transmission and the need to eliminate breeding sites, and neglected the risk of the sexual and congenital transmission of Zika and the importance of alternative preventive actions. This, we argue, may have limited the potential effectiveness of these posters to induce behaviour change.

Ligusticum sinense Nanoemulsion Gel as Potential Repellent against Aedes aegypti, Anopheles minimus, and Culex quinquefasciatus (Diptera: Culicidae).

Simple SummaryMosquito vectors can transmit diverse infectious pathogens and parasites that cause diseases such as dengue, Zika, Chikungunya, West Nile fever, and malaria. Botanical-derived repellents have been applied for personal protection against various species of mosquito vectors. In Thailand, numerous plant extracts have so far been investigated for mosquito repellent activity. Recently, Ligusticum sinense hexane extract (LHE) was reported as a potential candidate for the development of a new natural alternative to standard synthetic repellent. This study formulated LHE into nanoemulsion gel (LHE-NEG) and investigated its repellent activity against three mosquito vectors, including Aedes aegypti, Anopheles minimus, and Culex quinquefasciatus. The results revealed that LHE-NEG provided comparable protection times to N,N-diethyl-3-methylbenzamide nanoemulsion gel (DEET-NEG) against all mosquito species. Furthermore, LHE-NEG is safe for human health, based on the results of the skin irritation test. The repellent activity obtained from stored samples of LHE-NEG yielded satisfactory protection times of more than 2 h. Therefore, this gel formulation could be developed commercially, as an effective personal protection product against mosquito bites.Ligusticum sinense Oliv. cv. is a species of Umbelliferae (Apiaceae), a large plant family in the order Apiales. In this study, L. sinense hexane extract nanoemulsion gel (LHE-NEG) was investigated for mosquito repellency and compared to the standard chemical, N,N-diethyl-3-methylbenzamide (DEET), with the goal of developing a natural alternative to synthetic repellents in protecting against mosquito vectors. The results demonstrated that LHE-NEG afforded remarkable repellency against Aedes aegypti, Anopheles minimus, and Culex quinquefasciatus, with median protection times (MPTs) of 5.5 (4.5–6.0), 11.5 (8.5–12.5), and 11.25 (8.5–12.5) h, respectively, which was comparable to those of DEET-nanoemulsion gel (DEET-NEG: 8.5 (7.0–9.0), 12.0 (10.0–12.5), and 12.5 (10.0–13.5) h, respectively). Evaluation of skin irritation in 30 human volunteers revealed no potential irritant from LHE-NEG. The physical and biological stability of LHE-NEG were determined after being kept under heating/cooling cycle conditions. The stored samples of LHE-NEG exhibited some changes in appearance and differing degrees of repellency between those kept for 3 and 6 heating/cooling cycles, thus providing slightly shorter MPTs of 4.25 (4.0–4.5) and 3.25 (2.5–3.5) h, respectively, when compared to those of 5.0 (4.5–6.0) h in fresh preparation. These findings encourage commercially developed LHE-based products as an alternative to conventional synthetic repellents in preventing mosquito bites and helping to interrupt mosquito-borne disease transmission.

Lying in wait: the resurgence of dengue virus after the Zika epidemic in Brazil

After the Zika virus (ZIKV) epidemic in the Americas in 2016, both Zika and dengue incidence declined to record lows in many countries in 2017–2018, but in 2019 dengue resurged in Brazil, causing ~2.1 million cases. In this study we use epidemiological, climatological and genomic data to investigate dengue dynamics in recent years in Brazil. First, we estimate dengue virus force of infection (FOI) and model mosquito-borne transmission suitability since the early 2000s. Our estimates reveal that DENV transmission was low in 2017–2018, despite conditions being suitable for viral spread. Our study also shows a marked decline in dengue susceptibility between 2002 and 2019, which could explain the synchronous decline of dengue in the country, partially as a result of protective immunity from prior ZIKV and/or DENV infections. Furthermore, we performed phylogeographic analyses using 69 newly sequenced genomes of dengue virus serotype 1 and 2 from Brazil, and found that the outbreaks in 2018–2019 were caused by local DENV lineages that persisted for 5–10 years, circulating cryptically before and after the Zika epidemic. We hypothesize that DENV lineages may circulate at low transmission levels for many years, until local conditions are suitable for higher transmission, when they cause major outbreaks.

Spatial connectivity in mosquito-borne disease models: a systematic review of methods and assumptions.

Spatial connectivity plays an important role in mosquito-borne disease transmission. Connectivity can arise for many reasons, including shared environments, vector ecology and human movement. This systematic review synthesizes the spatial methods used to model mosquito-borne diseases, their spatial connectivity assumptions and the data used to inform spatial model components. We identified 248 papers eligible for inclusion. Most used statistical models (84.2%), although mechanistic are increasingly used. We identified 17 spatial models which used one of four methods (spatial covariates, local regression, random effects/fields and movement matrices). Over 80% of studies assumed that connectivity was distance-based despite this approach ignoring distant connections and potentially oversimplifying the process of transmission. Studies were more likely to assume connectivity was driven by human movement if the disease was transmitted by an Aedes mosquito. Connectivity arising from human movement was more commonly assumed in studies using a mechanistic model, likely influenced by a lack of statistical models able to account for these connections. Although models have been increasing in complexity, it is important to select the most appropriate, parsimonious model available based on the research question, disease transmission process, the spatial scale and availability of data, and the way spatial connectivity is assumed to occur.

Evidence for natural hybridization and novel Wolbachia strain superinfections in the Anopheles gambiae complex from Guinea.

Wolbachia, a widespread bacterium which can influence mosquito-borne pathogen transmission, has recently been detected within Anopheles (An.) species that are malaria vectors in Sub-Saharan Africa. Although studies have reported Wolbachia strains in the An. gambiae complex, apparent low density and prevalence rates require confirmation. In this study, wild Anopheles mosquitoes collected from two regions of Guinea were investigated. In contrast with previous studies, RNA was extracted from adult females (n = 516) to increase the chances for the detection of actively expressed Wolbachia genes, determine Wolbachia prevalence rates and estimate relative strain densities. Molecular confirmation of mosquito species and Wolbachia multilocus sequence typing (MLST) were carried out to analyse phylogenetic relationships of mosquito hosts and newly discovered Wolbachia strains. Strains were detected in An. melas (prevalence rate of 11.6%–16/138) and hybrids between An. melas and An. gambiae sensu stricto (prevalence rate of 40.0%–6/15) from Senguelen in the Maferinyah region. Furthermore, a novel high-density strain, termed wAnsX, was found in an unclassified Anopheles species. The discovery of novel Wolbachia strains (particularly in members, and hybrids, of the An. gambiae complex) provides further candidate strains that could be used for future Wolbachia-based malaria biocontrol strategies.

Ross River Virus Immune Evasion Strategies and the Relevance to Post-viral Fatigue, and Myalgic Encephalomyelitis Onset.

Ross River virus (RRV) is an endemic Australian arbovirus, and member of the Alphavirus family that also includes Chikungunya virus (CHIK). RRV is responsible for the highest prevalence of human disease cases associated with mosquito-borne transmission in Australia, and has long been a leading suspect in cases of post-viral fatigue syndromes, with extrapolation of this link to Myalgic Encephalomyelitis (ME). Research into RRV pathogenesis has revealed a number of immune evasion strategies, impressive for a virus with a genome size of 12 kb (plus strand RNA), which resonate with insights into viral pathogenesis broadly. Drawing from observations on RRV immune evasion, mechanisms of relevance to long term idiopathic fatigue are featured as a perspective on infection and eventual ME symptoms, which include considerations of; (1) selective pro-inflammatory gene suppression post antibody-dependent enhancement (ADE) of RRV infection, (2) Evidence from other virus families of immune disruption and evasion post-ADE, and (3) how virally-driven immune evasion may impact on mitochondrial function via target of rapamycin (TOR) complexes. In light of these RRV measures to counter the host immune - inflammatory responses, links to recent discoveries explaining cellular, immune and metabolomic markers of ME will be explored and discussed, with the implications for long-COVID post SARS-CoV-2 also considered. Compelling issues on the connections between virally-induced alterations in cytokine expression, for example, will be of particular interest in light of energy pathways, and how these perturbations manifest clinically.

Exploring the utility of social-ecological and entomological risk factors for dengue infection as surveillance indicators in the dengue hyper-endemic city of Machala, Ecuador.

The management of mosquito-borne diseases is a challenge in southern coastal Ecuador, where dengue is hyper-endemic and co-circulates with other arboviral diseases. Prior work in the region has explored social-ecological factors, dengue case data, and entomological indices. In this study, we bring together entomological and epidemiological data to describe links between social-ecological factors associated with risk of dengue transmission at the household level in Machala, Ecuador. Households surveys were conducted from 2014–2017 to assess the presence of adult Aedes aegypti (collected via aspiration) and to enumerate housing conditions, demographics, and mosquito prevention behaviors. Household-level dengue infection status was determined by laboratory diagnostics in 2014–2015. Bivariate analyses and multivariate logistic regression models were used to identify social-ecological variables associated with household presence of female Ae. aegypti and household dengue infection status, respectively. Aedes aegypti presence was associated with interruptions in water service and weekly trash collection, and household air conditioning was protective against mosquito presence. Presence of female Ae. aegypti was not associated with household dengue infections. We identified shaded patios and head of household employment status as risk factors for household-level dengue infection, while window screening in good condition was identified as protective against dengue infection. These findings add to our understanding of the systems of mosquito-borne disease transmission in Machala, and in the larger region of southern Ecuador, aiding in the development of improved vector surveillance efforts, and targeted interventions.

Malaria Surveillance - United States, 2017.

Malaria Surveillance - United States, 2017.

Impact of recent climate extremes on mosquito-borne disease transmission in Kenya.

Climate change and variability influence temperature and rainfall, which impact vector abundance and the dynamics of vector-borne disease transmission. Climate change is projected to increase the frequency and intensity of extreme climate events. Mosquito-borne diseases, such as dengue fever, are primarily transmitted by Aedes aegypti mosquitoes. Freshwater availability and temperature affect dengue vector populations via a variety of biological processes and thus influence the ability of mosquitoes to effectively transmit disease. However, the effect of droughts, floods, heat waves, and cold waves is not well understood. Using vector, climate, and dengue disease data collected between 2013 and 2019 in Kenya, this retrospective cohort study aims to elucidate the impact of extreme rainfall and temperature on mosquito abundance and the risk of arboviral infections. To define extreme periods of rainfall and land surface temperature (LST), we calculated monthly anomalies as deviations from long-term means (1983-2019 for rainfall, 2000-2019 for LST) across four study locations in Kenya. We classified extreme climate events as the upper and lower 10% of these calculated LST or rainfall deviations. Monthly Ae. aegypti abundance was recorded in Kenya using four trapping methods. Blood samples were also collected from children with febrile illness presenting to four field sites and tested for dengue virus using an IgG enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR). We found that mosquito eggs and adults were significantly more abundant one month following an abnormally wet month. The relationship between mosquito abundance and dengue risk follows a non-linear association. Our findings suggest that early warnings and targeted interventions during periods of abnormal rainfall and temperature, especially flooding, can potentially contribute to reductions in risk of viral transmission.

Comprehensive Quantitative Proteome Analysis of Aedes aegypti Identifies Proteins and Pathways Involved in Wolbachia pipientis and Zika Virus Interference Phenomenon.

Zika virus (ZIKV) is a global public health emergency due to its association with microcephaly, Guillain-Barré syndrome, neuropathy, and myelitis in children and adults. A total of 87 countries have had evidence of autochthonous mosquito-borne transmission of ZIKV, distributed across four continents, and no antivirus therapy or vaccines are available. Therefore, several strategies have been developed to target the main mosquito vector, Aedes aegypti, to reduce the burden of different arboviruses. Among such strategies, the use of the maternally-inherited endosymbiont Wolbachia pipientis has been applied successfully to reduce virus susceptibility and decrease transmission. However, the mechanisms by which Wolbachia orchestrate resistance to ZIKV infection remain to be elucidated. In this study, we apply isobaric labeling quantitative mass spectrometry (MS)-based proteomics to quantify proteins and identify pathways altered during ZIKV infection; Wolbachia infection; co-infection with Wolbachia/ZIKV in the A. aegypti heads and salivary glands. We show that Wolbachia regulates proteins involved in reactive oxygen species production, regulates humoral immune response, and antioxidant production. The reduction of ZIKV polyprotein in the presence of Wolbachia in mosquitoes was determined by MS and corroborates the idea that Wolbachia helps to block ZIKV infections in A. aegypti. The present study offers a rich resource of data that may help to elucidate mechanisms by which Wolbachia orchestrate resistance to ZIKV infection in A. aegypti, and represents a step further on the development of new targeted methods to detect and quantify ZIKV and Wolbachia directly in complex tissues.

Assessing the atmospheric fate of pesticides used to control mosquito populations in Houston, TX

During the summer months, urban areas are literal hot spots of mosquito-borne disease transmission and air pollution. Public health authorities release aerosolized pesticides directly into the atmosphere to help control adult mosquito populations and thereby reduce the threat of diseases, such as Zika Virus. The primary adulticides (i.e. pesticides used to control adult mosquito populations) in Houston, TX are permethrin and malathion. These adulticides are typically sprayed at night using ultra-low volume sprayers. Particulate matter (PM) samples including total suspended and fine PM (PM < 2.5 μm in aerodynamic diameter) were collected at four ground-based sites across Houston in 2013 and include daytime, nighttime, and 24 h samples. Malathion is initially sprayed as coarse aerosol (5–25 μm), but is measured in fine aerosol (<2.5 μm) and coarse aerosol in the urban atmosphere. Particle size is relevant both for deposition velocities and for human exposure. Atmospheric permethrin concentrations measured in nighttime samples peak at 60 ng m−3, while malathion nighttime concentrations peak near 40 ng m−3. Malaoxon, an oxidation product of malathion, was also frequently detected at concentrations >10 ng m−3, indicating significant nighttime oxidation. Based on the loss of malathion and the increase in malaoxon, the atmospheric half-life of malathion in Houston was estimated at <12 h, which was significantly shorter than previous half-life estimates (∼days). Importantly, malaoxon is estimated to be 22–33 times more toxic to humans than malathion. Both the aerosol size and the half-life are critical for mosquito control, human exposure, and risk assessment of these routine pesticides.

Habitat and microclimate affect the resting site selection of mosquitoes.

Mosquitoes (Diptera: Culicidae) use certain resting sites during their inactive phase. The microclimatic conditions of these resting sites might affect their physiology and vectorial capacity. In this study, we combined a field and a laboratory study to investigate the natural resting site and temperature preferences of mosquitoes. The field study was conducted at a forest close to Oldenburg (Lower Saxony, Germany) from May to October 2018. Mosquitoes were collected in five different natural habitats with seven replicates each. Temperature was recorded hourly at each site. Significantly more mosquitoes were collected in deadwood (predominantly Culiseta morsitans/fumipennis) and shaded herb layer (predominantly Aedes species) compared to unshaded herb layer or broadleaf and coniferous trees. GLMMs revealed resting site habitats as the best predictor to explain the observed preference patterns, but microclimatic conditions are also involved in mosquito resting site selection. Most mosquitoes were collected at resting sites with relatively colder and more stable temperatures. In concert, laboratory choice experiments with a thermal gradient ring demonstrated that Cs. morsitans/fumipennis avoid temperatures over 30 °C. Understanding the small-scaled resting site preferences and the related microclimatic conditions can improve mosquito collection techniques and refine the prediction of mosquito-borne pathogen transmission.

Outdoor Residential Water Use Restrictions during Recent Drought Suppressed Disease Vector Abundance in Southern California.

The California state government put restrictions on outdoor residential water use, including landscape irrigation, during the 2012-2016 drought. The public health implications of these actions are largely unknown, particularly with respect to mosquito-borne disease transmission. While residential irrigation facilitates persistence of mosquitoes by increasing the availability of standing water, few studies have investigated its effects on vector abundance. In two study sub-regions in the Los Angeles Basin, we examined the effect of outdoor residential water use restrictions on the abundance of the most important regional West Nile virus vector, Culex quinquefasciatus. Using spatiotemporal random forest models fit to Cx. abundance during drought and non-drought years, we generated counterfactual estimates of Cx. abundance under a hypothetical drought scenario without water use restrictions. We estimate that Cx. abundance would have been 44% and 39% larger in West Los Angeles and Orange counties, respectively, if outdoor water usage had remained unchanged. Our results suggest that drought, without mandatory water use restrictions, may counterintuitively increase the availability of larval habitats for vectors in naturally dry, highly irrigated settings and such mandatory water use restrictions may constrain Cx. abundance, which could reduce the risk of mosquito-borne disease while helping urban utilities maintain adequate water supplies.