Mosquito Reduction Research Articles

Targeting the diapause response of Aedes albopictus via CRISPR/Cas9-mediated genome editing to control the spread of mosquito-borne disease

Mosquito-borne infectious diseases such as malaria, dengue fever, chikungunya, and zika are responsible for hundreds of thousands of deaths across the globe each year. Due to the nature of the viruses and parasites that cause these diseases, targeting their mosquito vectors has become the most effective method for reducing transmission. However, an ecologically and evolutionarily sustainable method for mosquito population reduction has yet to be developed. This may be about to change due to the proven effectiveness of genome editing in mosquitoes using the CRISPR/Cas9 system. CRISPR/Cas9, found in nature as the adaptive immune system of bacteria and now adapted as a biological tool for use in any organism, is revolutionizing the study of genetics and now may also be the key to ending a global public health crisis. Current population control methods utilizing transgenic mosquitoes have ultimately failed at the hands of evolution due to unintended fitness costs. Here, we propose a novel control method for the invasive vector mosquito species, Aedes albopictus, using CRISPR/Cas9 to target genes that are essential for a period of developmental arrest known as photoperiodic diapause. Since diapause allows the species to invade temperate regions, genetic disruption of this pathway should result in the inability of Ae. albopictus to inhabit temperate environments, which in turn should inhibit the spread of mosquito-borne diseases in these regions.

Controlling vector-borne diseases by releasing modified mosquitoes.

Aedes mosquito-transmitted diseases, such as dengue, Zika and chikungunya, are becoming major global health emergencies while old threats, such as yellow fever, are re-emerging. Traditional control methods, which have focused on reducing mosquito populations through the application of insecticides or preventing breeding through removal of larval habitat, are largely ineffective, as evidenced by the increasing global disease burden. Here, we review novel mosquito population reduction and population modification approaches with a focus on control methods based on the release of mosquitoes, including the release of Wolbachia-infected mosquitoes and strategies to genetically modify the vector, that are currently under development and have the potential to contribute to a reversal of the current alarming disease trends.

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OBJECTIVES/SPECIFIC AIMS: Our objectives with this project are to engage communities through technology creating a communication channel with affected communities and stakeholders about mosquito-borne illness, vector control and environmental health risk. Furthermore, engaging communities to electronically map ecological risks that impact mosquito-borne illness with the goal of creating a mobile application that will work as an ecological surveillance against mosquito proliferation and potential mosquito population reduction, and finally pilot test and evaluate potential benefits in communities where the application was used. METHODS/STUDY POPULATION: We propose a methodology to perform formative community work that will underscore a distributed, democratized ecological surveillance through an integration of multidimensional health behavior theories that address the challenges of ZIKV in Culebra, a marginalized island community off the coast of the main island of Puerto Rico. Using participatory design, we will develop, test, and evaluate users’ experiences towards mobile applications using qualitative (interviews) and quantitative (survey) methodologies. A mobile application with the capacity of mapping, use of social-media, crowdsourcing, and photo-voice in a dynamic and simple way will allow community members to alert “hot-zone” locations to the stakeholders interested in creating ecological action in their community. This multidimensional concept integrates explanatory and prospective approaches and will generate systematic short-term solutions for mosquito control and long-term solutions providing the necessary tools for community empowerment. RESULTS/ANTICIPATED RESULTS: Our proposed design will facilitate better understanding of the interactions between community members and socio-environmental determinants of mosquito-borne diseases. Furthermore, our proposed project will not only facilitate communication among members of a community, but also it will provide a platform for engagement and empowerment, establishing a change in the preventive paradigm of how communities face the negative impacts of micro-ecologies that surround them. DISCUSSION/SIGNIFICANCE OF IMPACT: Our proposed community collaboratory mHealth tool mZAP! (Zonas, Accion y Proteccion) will address the lack of community participation efforts against mosquito-borne diseases contributed simultaneously by the disengagement and disempowerment of community members. mZAP! will serve as an innovative tool to engage marginalized and communities made vulnerable in Puerto Rico. This approach should be successful as Puerto Rico is one of the most digitally connected countries in Latin America, with high mobile phone usage rates and social media use. Using mZAP!, communities will report and map breeding sites, use social media and crowd sensing, targeting against powerful tools against mosquito ecologies in their own environments. This application could result in an effective way to change the paradigms for public health approaches to use Information Communications Technologies (ICTs) to empower communities.

Is outdoor vector control needed for malaria elimination? An individual-based modelling study

BackgroundResidual malaria transmission has been reported in many areas even with adequate indoor vector control coverage, such as long-lasting insecticidal nets (LLINs). The increased insecticide resistance in Anopheles mosquitoes has resulted in reduced efficacy of the widely used indoor tools and has been linked with an increase in outdoor malaria transmission. There are considerations of incorporating outdoor interventions into integrated vector management (IVM) to achieve malaria elimination; however, more information on the combination of tools for effective control is needed to determine their utilization.MethodsA spatial individual-based model was modified to simulate the environment and malaria transmission activities in a hypothetical, isolated African village setting. LLINs and outdoor attractive toxic sugar bait (ATSB) stations were used as examples of indoor and outdoor interventions, respectively. Different interventions and lengths of efficacy periods were tested. Simulations continued for 420 days, and each simulation scenario was repeated 50 times. Mosquito populations, entomologic inoculation rates (EIRs), probabilities of local mosquito extinction, and proportion of time when the annual EIR was reduced below one were compared between different intervention types and efficacy periods.ResultsIn the village setting with clustered houses, the combinational intervention of 50% LLINs plus outdoor ATSBs significantly reduced mosquito population and EIR in short term, increased the probability of local mosquito extinction, and increased the time when annual EIR is less than one per person compared to 50% LLINs alone; outdoor ATSBs alone significantly reduced mosquito population in short term, increased the probability of mosquito extinction, and increased the time when annual EIR is less than one compared to 50% LLINs alone, but there was no significant difference in EIR in short term between 50% LLINs and outdoor ATSBs. In the village setting with dispersed houses, the combinational intervention of 50% LLINs plus outdoor ATSBs significantly reduced mosquito population in short term, increased the probability of mosquito extinction, and increased the time when annual EIR is less than one per person compared to 50% LLINs alone; outdoor ATSBs alone significantly reduced mosquito population in short term, but there were no significant difference in the probability of mosquito extinction and the time when annual EIR is less than one between 50% LLIN and outdoor ATSBs; and there was no significant difference in EIR between all three interventions. A minimum of 2 months of efficacy period is needed to bring out the best possible effect of the vector control tools, and to achieve long-term mosquito reduction, a minimum of 3 months of efficacy period is needed.ConclusionsThe results highlight the value of incorporating outdoor vector control into IVM as a supplement to traditional indoor practices for malaria elimination in Africa, especially in village settings of clustered houses where LLINs alone is far from sufficient.

Mathematical modeling of Zika virus

Zika virus (ZIKV) mathematical model is formulated. Optimal control strategies are introduced into the model. The basic properties of the model without control strategies are determined including the reproduction number. Pontryagin's maximum principle is used to characterize the necessary conditions for optimal control of ZIKV. The preventive and treatment strategy without spraying the mosquitoes showed a great reduction in infected humans, however no significant reduction in the infected mosquitoes population. The use of preventive and insecticide techniques to minimize the spread of the virus showed a greater significance in the reduction of both infected humans and mosquitoes. The application of preventive, treatment and insecticide showed the best way of reducing the spread of ZIKV. The best strategy to minimize the spread of ZIKV is to use prevention, treatment and insecticide as control strategy at the same time.

Preliminary Report on the Reduction of Adult Mosquitoes in Housing Compounds in Western Kenya Using the ProVector Flower and Entobac Bait Pads Containing Bacillus thuringiensis israelensis With Honey Bait.

Reducing mosquito populations indoors and outdoors can have a significant impact on malaria and other mosquito-borne diseases. A new formulation and delivery system for Bacillus thuringiensis israelensis (Bti) was tested against adult mosquitoes. One Entobac bait with 7% Bti in a honey solution was placed within each ProVector Flower applicator. The applicators were placed in nine housing compounds, one on the outside of each home in Ahero and Nyalenda, Kenya, in June 2009. Seven housing compounds with no applicators were included as controls in the study area. After 1 mo, there was a significant reduction of mosquitoes in all nine compounds with the ProVector Flower compared to two of the seven control compounds. The overall mosquito population was reduced by 69% in housing compounds with the ProVector Flower whereas the mosquito population grew by nearly 15% in the control compounds. There was a significant reduction of the median number of mosquitoes in the test compounds than in the control compounds. The proportion of mosquitoes collected was significantly reduced in the test compounds within 1 mo for several species of Aedes, Anopheles, Coquillettidia, Culex, and Mansonia. This study provides evidence that Bti-laced bait may be used as an alternative adulticide and be delivered in an applicator to reduce mosquito populations of several species. This method may significantly reduce the cost of pesticide application through target specificity and by reducing the amount of pesticide placed into the environment.

Small-Scale Trials Suggest Increasing Applications of Natular™ XRT and Natular™ T30 Larvicide Tablets May Not Improve Mosquito Reduction in Some Catch Basins.

Stormwater catch basins are commonly treated with larvicides by mosquito control agencies to reduce local populations of mosquito species capable of transmitting West Nile virus. Recent evidence suggests that extended-release larvicides formulated to last up to 180 days in catch basins may not be effective in some basins due to chronic flushing, rapid dissolution, or burying of treatment in sump debris. To investigate if increasing the number of applications could improve effectiveness, a small study was performed over 13 weeks in 2015 to evaluate two extended-release larvicides (Natular™ XRT 180-day tablets and Natular™ T30 30-day tablets) and a larvicide oil (CocoBear™). Over the course of 13 weeks, three groups of eight basins were monitored for mosquitoes, each group receiving Natular™ XRT, Natular™ T30, or CocoBear™ larvicides. All basins received a single application at the beginning of the study period. Once mosquitoes in a basin surpassed the treatment threshold during weekly monitoring, an additional application of the associated larvicide was given to that basin. The number of applications during the study period ranged from 1 to 10 for CocoBear™ basins, 1 to 7 for T30 basins, and 2 to 8 for XRT basins. Overall, the average number of applications and the cost of larvicide per basin were 4.4 applications at $0.66 per Coco-Bear™ basin, 4.4 applications at $6.26 per T30 basin, and 4 applications at $16.56 per XRT basin. Basins treated with XRT and T30 needed reapplications more often than expected, yet were no more effective than CocoBear™, suggesting that increasing the frequency of application of these larvicide formulations may not provide increased mosquito reduction in some basins.

A G-protein-coupled receptor regulation pathway in cytochrome P450-mediated permethrin-resistance in mosquitoes, Culex quinquefasciatus.

Rhodopsin-like G protein-coupled receptors (GPCRs) are known to be involved in the GPCR signal transduction system and regulate many essential physiological processes in organisms. This study, for the first time, revealed that knockdown of the rhodopsin-like GPCR gene in resistant mosquitoes resulted in a reduction of mosquitoes’ resistance to permethrin, simultaneously reducing the expression of two cAMP-dependent protein kinase A genes (PKAs) and four resistance related cytochrome P450 genes. The function of rhodopsin-like GPCR was further confirmed using transgenic lines of Drosophila melanogaster, in which the tolerance to permethrin and the expression of Drosophila resistance P450 genes were both increased. The roles of GPCR signaling pathway second messenger cyclic adenosine monophosphate (cAMP) and downstream effectors PKAs in resistance were investigated using cAMP production inhibitor Bupivacaine HCl and the RNAi technique. Inhibition of cAMP production led to significant decreases in both the expression of four resistance P450 genes and two PKA genes and mosquito resistance to permethrin. Knockdown of the PKA genes had shown the similar effects on permethrin resistance and P450 gene expression. Taken together, our studies revealed, for the first time, the role of the GPCR/cAMP/PKA-mediated regulatory pathway governing P450 gene expression and P450-mediated resistance in Culex mosquitoes.

Insecticidal potency of Aspergillus terreus against larvae and pupae of three mosquito species Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti.

Microbial control agents offer alternatives to chemical pest control, as they can be more selective than chemical insecticides. The present study evaluates the mosquito larvicidal and pupicidal potential of fungus mycelia using ethyl acetate and methanol solvent extracts produced by Aspergillus terreus against Anopheles stephensi, Culex quinquefasciatus, and Aedes aegypti. The A. terreus mycelia were extracted after 15 days from Sabouraud dextrose broth medium. The ethyl acetate extracts showed lethal concentration that kills 50% of the exposed larvae (LC50) and lethal concentration that kills 90% of the exposed larvae (LC90) values of the first, second, third, and fourth instar larvae of An. stephensi (LC50 = 97.410, 102.551, 29.802, and 8.907; LC90 = 767.957, 552.546, 535.474, and 195.677 μg/ml), Cx. quinquefasciatus (LC50 = 89.584, 74.689, 68.265, and 67.40; LC90 = 449.091, 337.355, 518.793, and 237.347 μg/ml), and Ae. aegypti (LC50 = 83.541, 84.418, 80.407, and 95.926; LC90 = 515.464, 443.167, 387.910, and 473.998 μg/ml). Pupicidal activity of mycelium extracts was tested against An. stephensi (LC50 = 25.228, LC90 = 140.487), Cx. quinquefasciatus (LC50 = 54.525, LC90 = 145.366), and Ae. aegypti (LC50 = 10.536, LC90 = 63.762 μg/ml). At higher concentration (500 μg/ml), mortality starts within the first 6 h of exposure. One hundred percent mortality occurs at 24-h exposure. The overall result observed that effective activity against selected mosquito larvae and pupae after 24 h was a dose and time-dependent activity. These ensure that the resultant mosquito population reduction is substantial even where the larvicidal and pupicidal potential is minimal. The FTIR spectra of ethyl acetate extract reflect prominent peaks (3448.32, 3000.36, 2914.59, 2118.73, 1668.21, 1436.87, 1409.02, 954.33, 901.13, and 704.67 cm(-1)). The spectra showed a sharp absorption band at 1314.66 cm(-1) assigned to wagging vibration of the C-H group. The band at 1023.59 cm(-1) developed for C-O and C=N, respectively, and was commonly found in carboxylic acid and amine groups. GC-MS analysis of ethyl acetate extracts showed the presence of six compounds, of which the major compounds were identified as n-hexadecanoic acid (15.31%) and methyl 12,15-octadecadienoate (31.989%), based on their peak molecular weight. The HPLC analysis result highlights that the A. terreus ethyl acetate extract was compared with pure n-hexadecanoic acid which resulted in similar retention time of 19.52 and 19.38, respectively. Thus, the active compound produced by this species would be more useful against vectors responsible for diseases of public health importance. This is the first report on mosquito larvicidal and pupicidal activity of ethyl acetate extract produced by A. terreus species.

Seasonal Genetic Changes of Aedes aegypti (Diptera: Culicidae) Populations in Selected Sites of Cebu City, Philippines.

Aedes aegypti (L.) is the primary vector of dengue virus in the Philippines, where dengue is endemic. We examined the genetic changes of Ae. aegypti collected from three selected sites in Cebu city, Philippines, during the relatively wet (2011-2012) and dry seasons (2012 and 2013). A total of 493 Ae. aegypti adults, reared in the laboratory from field-collected larvae, were analyzed using 11 microsatellite loci. Seasonal variation was observed in allele frequencies and allelic richness. Average genetic differentiation (DEST=0.018; FST=0.029) in both dry seasons was higher, due to reduced Ne, than in the wet season (DEST=0.006; FST=0.009). Thus, average gene flow was higher in the wet season than in the dry seasons. However, the overall FST estimate (0.02) inclusive of the two seasons showed little genetic differentiation as supported by Bayesian clustering analysis. Results suggest that during the dry season the intense selection that causes a dramatic reduction of population size favors heterozygotes, leading to small pockets of mosquitoes (refuges) that exhibit random genetic differentiation. During the wet season, the genetic composition of the population is reconstituted by the expansion of the refuges that survived the preceding dry season. Source reduction of mosquitoes during the nonepidemic dry season is thus recommended to prevent dengue re-emergence in the subsequent wet season.

Fighting Arbovirus Transmission: Natural and Engineered Control of Vector Competence in Aedes Mosquitoes.

Control of aedine mosquito vectors, either by mosquito population reduction or replacement with refractory mosquitoes, may play an essential role in the fight against arboviral diseases. In this review, we will focus on the development and application of biological approaches, both natural or engineered, to limit mosquito vector competence for arboviruses. The study of mosquito antiviral immunity has led to the identification of a number of host response mechanisms and proteins that are required to control arbovirus replication in mosquitoes, though more factors influencing vector competence are likely to be discovered. We will discuss key aspects of these pathways as targets either for selection of naturally resistant mosquito populations or for mosquito genetic manipulation. Moreover, we will consider the use of endosymbiotic bacteria such as Wolbachia, which in some cases have proven to be remarkably efficient in disrupting arbovirus transmission by mosquitoes, but also the use of naturally occurring insect-specific viruses that may interfere with arboviruses in mosquito vectors. Finally, we will discuss the use of paratransgenesis as well as entomopathogenic fungi, which are also proposed strategies to control vector competence.

Observed loss and ineffectiveness of mosquito larvicides applied to catch basins in the northern suburbs of chicago IL, 2014.

In the northeastern part of the greater Chicago metropolitan area, the North Shore Mosquito Abatement District (NSMAD) treats approximately 50,000 catch basins each season with larvicide tablets as part of its effort to reduce local populations of the West Nile virus (WNV) vector Culex pipiens. During the 2014 season, an NSMAD technician monitored a subset of 60–195 basins weekly for 18 weeks among the communities of the District for the presence of mosquitoes. Monitoring found no clear evidence in the reduction of mosquitoes with the use of larvicides, and visual inspections of 211 larvicide-treated basins found that the majority (162, 76.8%) were missing tablets 1–17 weeks after applications. This loss of treatment may be due to the rapid dissolution or flushing of larvicides and would help explain why the larvicide appeared to be ineffective.

Community-based approach for dengue prevention and control in Sta. Cruz, Laguna, Philippines

Background: Despite having mandated health programs, dengue cases in Sta. Cruz had a marked increase of 106% in the past two years. Dengue ranked first on notifiable diseases in Sta. Cruz with a rate of 520 per 100000 populations. The occurrence of dengue in one barangay is a threat to nearby barangays and its spread intensified due to proliferating trade and travel. Therefore, dengue cannot be controlled if efforts are limited to only a few members of the community. Hence, strengthening the implementation of dengue programs must be pointed out. Methods: The community project aims to decrease the incidence of dengue cases in all the barangays of Sta. Cruz by 30% within one year. The strategic plan is designed that a Core Group has to be made in which the capacity of staff at different levels has to be increased. An assessment of their baseline knowledge, post-test results, return demonstration and field implementation was conducted. Strengthening communication for source reduction was made possible by posting dengue posters in conspicuous places and by sustained advertising of dengue jingle. Results: The Dengue-Rous Core Group acquired the knowledge, skills and capacity to deliver effective dengue prevention at the community level. The awareness and capacity building of each household to regularly practice search and destroy of mosquito breeding and resting places in their community were also enhanced. Conclusions: Our findings highlight the need for further information, education and communication on source reduction of mosquitoes. Identifying barriers to action and to seek ways to translate population knowledge about dengue into positive preventive practices are deemed essential.

Integrated Pest Management for Mosquito Reduction around Homes and Neighborhoods

This 40-page publication describes how homeowners can use an integrated pest management (IPM) program to help decrease pesticide use, reduce the risk of contracting mosquito-borne diseases, and ease the financial burden on local governments responsible for area-wide control. Modern mosquito control emphasizes source reduction to eliminate areas where mosquitoes thrive; surveillance to determine whether pesticide applications are necessary; screening; sanitation; and other techniques described in this document. The methods recommended in this publication are particularly effective in reducing mosquitoes that transmit diseases. Homeowners who take responsibility for identifying and eliminating sources of mosquito production around their homes and neighborhoods will improve health and quality of life for all Florida residents. Written by C. R. Connelly, E. Bolles, D. Culbert, J. DeValerio, M. Donahoe, K. Gabel, R. Jordi, J. McLaughlin, A. S. Neal, S. Scalera, E. Toro, and J. Walter, and published by the UF Department of Entomology and Nematology, September 2014.
 ENY-753/IN1045: Mosquitoes and their Control: Integrated Pest Management for Mosquito Reduction around Homes and Neighborhoods (ufl.edu)

An optimal control model of mosquito reduction management in a dengue endemic region

Aedes aegypti is known as the responsible vector in transmitting dengue flavivirus. Unavailability of medication to cure the transmission in human blood becomes a global health issue in recent decades. World epidemiologists are encouraged to focus on investigation toward an effective and inexpensive way to prevent dengue transmission, i.e. mosquito control. In this paper, we present a model depicting the dynamics of mosquito population based on indoor–outdoor life cycle classification. The basic mosquito offspring number is obtained and analysis of equilibria is shown. We bring along a discussion on application of optimal control model which engineers two simultaneous schemes. The first scheme is done by disseminating chemical like Temephos in spots where eggs and larvae develop, meanwhile the second scheme is done by conducting fumigation through areas where adult mosquitoes prevalently nest, indoor as well as outdoor. A version of gradient-based method is presented to set down a workflow in minimizing the objective functional with respect to control variable. Numerical results from analysis of the basic mosquito offspring number with constant control and from optimal control suggest that one has to enhance the usage of fumigation rather than Temephos. It is also suggested that applying both control schemes simultaneously gives the most significant reduction to the population.

Differences in male–female ratios of Aedes albopictus (Diptera: Culicidae) following ultra-low volume adulticide applications

Suppression of Aedes albopictus populations is a substantial challenge for mosquito control programs globally because juveniles of this species are found in numerous kinds of domestic artificial containers that are difficult to detect, access, and eliminate. We conducted a multi-year assessment of the effect of different interventions to control Ae. albopictus near the northernmost geographic boundary of the species in temperate North America and deployed an array of BG-Sentinel traps for adult surveillance. Here we present the results of a comparative examination of adult sex ratios in urban and suburban areas, shifts in sex ratios after control interventions, and a discussion of the critical drivers of population dynamics of Ae. albopictus in our area. We collected significantly more male mosquitoes in urban as compared to suburban areas in June through September, but not in May (p<0.001). The higher number of male mosquitoes in urban areas could be attributed to a higher number of larval habitats within a closer proximity of the surveillance traps and the lower flight dispersal of males. Following application of adulticides in urban areas, Ae. albopictus male populations were reduced by 88% on average, which was higher than the 69% reduction in female populations. The higher reduction of male mosquitoes could be attributed to the smaller body mass of the males and their higher susceptibility to adulticides. The results of this study are directly relevant to the development of suitable control strategies that depend on manipulation of males, such as the sterile insect technique. The results could also be used to refine mosquito abatement by providing more accurate methods to determine the need and timing of vector control.

Larval control of Anopheles (Nyssorhinchus) darlingiusing granular formulation of Bacillus sphaericus in abandoned gold-miners excavation pools in the Brazilian Amazon Rainforest

Use of a Bacillus sphaericus based mosquito larvicide was evaluated as an intervention for malaria vector control at a mining site in Amapá, Brazil. Impacts on larval and adult densities of the primary vector Anopheles darlingi were measured over the course of a 52 week study period. In Calçoene, State of Amapá, gold mining activity occurs in 19 mining sites in gold-miners of Lourenço. Large pools are formed in mining sites and naturally colonized by Anopheles darlingi. During one year, the impact of applications of VectoLex® CG to these larval sources was evaluated. Applications of 20kg/ha were made as needed, based on 10 immature (3rd, 4th instars and pupae) surveillance of health and established thresholds. One hundred percent initial control was observed 48h after each treatment. The pools received from 2-10 (5.3±1.6) treatments during the year. The average re-treatment interval in productive pools was 9.4±4.3 weeks. During weeks 3-52 of the study, mean density of late stage larvae was 78% and pupae were 93% lower in the treated pools than in untreated pools (p< 0.0001, n=51) while reduction of adult mosquitoes was 53% in comparison to the untreated area during the last five months of the study, which were the rainy season (p<0.001). VectoLex® CG reduced immature Anopheles darlingi infestation levels during the entire study period, and reduced adult mosquito populations during the rainy season.

Looking for new strategies to fight against mosquito-borne diseases: toward the development of natural extracts for mosquito control and reduction of mosquito vector competence

Looking for new strategies to fight against mosquito-borne diseases: toward the development of natural extracts for mosquito control and reduction of mosquito vector competence

The Resurgence of West Nile Virus

Cases of West Nile virus in 2012 in the United States have exceeded those of any other year. This commentary discusses the endemic cases and asks whether they stem from a new strain of the virus, a...

Willingness to Pay for Mosquito Control: How Important Is West Nile Virus Risk Compared to the Nuisance of Mosquitoes?

Public health programs that control mosquitoes and other disease vectors have the added benefit of reducing residents' exposure to pest insects. We surveyed homeowners in Madison, Wisconsin, and used an economic valuation method, stated-choice experiments, to measure willingness to pay (WTP) for control of West Nile virus (WNV)-transmitting and nuisance mosquitoes under current and increased levels of WNV risk. Under current WNV risk levels (approximately 1 in 250,000), the average Madison survey respondent was not willing to pay for programs that targeted West Nile-transmitting mosquitoes only (WTP=-$21, 95% [CI -$63, $20]), while WTP for a reduction in nuisance mosquitoes was substantial (WTP=$147, 95% [CI $109, $186]). As the risk of WNV was increased, WTP for control of disease-carrying mosquitoes also increased (WTP=$158; 95% CI [$111, $206] at the highest risk level), but WTP for nuisance control remained high (WTP=$108; 95% CI [$78, $138]). Among homeowners in our sample, the "nuisance factor" was more important than the "disease factor" in terms of respondents' demand for mosquito control.