Journal of Medical Entomology

Several endocrine signals are known to mediate mosquito egg development including insulin-like peptide, 20-hydroxyecdysone, and juvenile hormone. The objective of this study was to determine the effects of prostaglandin E2 (PGE2) as an additional mediator of oogenesis in the mosquitoes, Aedes albopictus and Anopheles gambiae. The injection of aspirin (an inhibitor of cyclooxygenase) shortly after blood-feeding significantly inhibited egg development at choriogenesis in a dose-dependent manner in Ae. albopictus. Moreover, oral administration of aspirin to An. albopictus and An. gambiae also inhibited egg production. The aspirin treatment suppressed expression of the genes (Yellow-g and Yellow-g2) associated with exochorion darkening and led to the production of a malformed egg shell in Ae. albopictus. These inhibitory effects of aspirin on egg development were rescued by the addition of PGE2, confirming the specificity of aspirin in inhibiting prostaglandin production. To validate these results, we identified a putative PGE2 receptor (Aa-PGE2R) in Ae. albopictus. Aa-PGE2R expression was highly inducible in adult ovary after blood-feeding. RNA interference of Aa-PGE2R expression resulted in the significant suppression of choriogenesis similar to aspirin treatment, where the addition of PGE2 to Aa-PGE2R-silenced females failed to rescue egg production. Together, these results suggest that PG synthesis and signaling are required for egg development across diverse mosquito taxa. Author SummaryProgstaglandins (PGs) play crucial roles in mediating various physiological processes in insects. Aspirin (ASP) inhibits PG biosynthesis and has been used as an anti-inflammatory drug. ASP injection or feeding to mosquitoes of Aedes albopictus or Anopheles gambiae significantly inhibits egg production at chorion formation. This led to significant reduction in fecundity and egg hatchability. PG signal is interrupted by RNA interference (RNAi) of PGE2 receptor. The RNAi treatment also gave a similar damage to females in egg production as seen in ASP treatment. Thus, PG signal is required for egg production of these mosquitoes. Data Availability StatementAll relevant data are within the manuscript and its Supporting Information file.

Mosquitoes such as Aedes aegypti, Aedes albopictus and Culex quinquefasciatus are vectors of many pathogens that greatly affect humankind. The maintenance of these mosquitoes in laboratory permit different studies that can help understanding their biology, as well as the vector-pathogen interaction. In addition to sugar meals, the blood feeding is essential for maintenance of the reproductive cycle in several vectors. The main blood sources for many mosquito colonies are direct feeding on live animal or the use of human/animal blood through artificial feeders. However, this latter process has some disadvantages, as artificial feeders can be very laborious for assembly and decontamination. Based on these observations, a simplified technique for feeding and artificial infection was developed with cotton-pads soaked (CS) and blood or blood and viral supernatant to simulate an artificial infection. The efficiency of the CS technique was investigated through the number of mosquitoes fed/infected, when compared to their respective control group. The CS technique, with blood at room temperature, promoted a feeding rate of 61.4% for Ae. albopictus, 70.8% for Cx. quinquefasciatus and 17% for Ae. aegypti. The control group (Hemotec-feeding) presented 47.9%, 16.5% and 59.1% of feeding success, respectively. To improve the CS technique for Ae. aegypti mosquitoes, the procedure was then performed with blood at 38{degrees}C, which was possible to observe a feeding rate of 47.3%, in comparison to 53.2% for the control group (Hemotec). When using the CS technique for artificial infection with Mayaro virus, more than 80% of infection was observed for Ae. aegypti and 100% for Ae. albopictus. In the traditional infection technique (glass feeder), the infection rate was 90% (Ae. aegypti) and 96.6% (Ae. albopictus). For Cx. quinquefasciatus, the infection was positive only with the CS technique, resulting in 1 (5%) mosquito infected with Mayaro virus. Our results suggest that this simplified technique of low-cost feeding and easy assembly, offers good results for feeding (maintenance of colonies) and artificial infection of different species of mosquitoes.

Dengue, Zika, and chikungunya, all transmitted by Aedes aegypti mosquitoes, present a significant and growing global health challenge. Contact-based insecticide such as pyrethroids, organophosphates, and organochlorines, are a core component of strategies to control Ae. aegypti. However, reliance on these chemical insecticides alone presents long-term challenges, particularly around increasing insecticide resistance. There are relatively few novel tools available that target adult mosquitoes through alternative mechanisms. Innovative, complementary approaches that can enhance the effectiveness and sustainability of existing mosquito control programs are urgently needed. Newly explored vector management tools are attractive toxic sugar baits (ATSBs), targeting the sugar-feeding behavior of both male and female mosquitoes, and allow for an ingested insecticide. Dried Attractive Bait Stations (DABS), a novel variant of ATSBs, have shown promising results for indoor Ae. aegypti control. We conducted cage and experimental house trials of DABS on laboratory-reared Ae. aegypti mosquitoes in Ponce, Puerto Rico. In cage trials, both male and female Ae. Aegypti that were exposed to DABS for 48 hours experienced near complete mortality, while control groups showed universal survival. All tested concentrations (1%, 2%, and 4% boric acid compounds) significantly reduced survival compared to controls (p < 0.001), with no significant differences between concentrations (p = 0.50). Water availability reduced DABS efficacy, lowering mortality by 47% in females (p < 0.001) and 32% in males (p < 0.001). In experimental house trials, DABS reduced mosquito survival by [~]75% (p < 0.001), with deployment of four DABS devices per room suggesting the greatest reduction in mosquito survival (p = 0.06-0.10). Optimal performance was observed at placing DABS 0.75 m above the floor (p < 0.001) and results suggest that medium-sized DABS may be more effective than larger (p = 0.09). Natural light increased mosquito survival (p = 0.028), but its interaction with DABS treatment was not significant (p = 0.322) and room-to-room variability was minimal. A notable limitation was the interference of ants during household trials, which led to the removal of mosquito carcasses and potential data loss, highlighting the need to further investigate alternative sugar sources and DABS interaction with non-target organisms. Despite these challenges, the results support DABS as a promising, scalable Aedes aegypti control tool. Future research should confirm effectiveness under varied field conditions, and assess the community acceptability for broader deployment.

BackgroundWest Nile virus (WNV), a mosquito-borne flavivirus, has circulated in the USA since 1999. In 2025, Florida was home to 24 million people, with projected increases in population and urbanization in a changing climate. The southern house mosquito, Culex quinquefasciatus, is found in every county, and is a major vector for WNV. Describing shifting WNV transmission risk is important to inform public health and vector control planning. Materials and MethodsUsing published estimates of thermal suitability of WNV transmission by Cx quinquefasciatus, with climate models and population data, we calculated and mapped baseline and projected county-level transmission suitability and people at risk (PAR) for 2000, 2030, and 2050. Five general circulation models (GCMs) and two mitigation scenarios (SSP2-4.5, SSP5-8.5) were used to explore future trajectories. ResultsAt baseline, all 67 counties in Florida experienced 5-9 months transmission suitability. Using the year 2000 census estimates, 2.33 million people in 2 counties experienced 9 months, and in 2030, across climate models, 8.93-12.26 million people (10-20 counties; SSP2-4.5), and 8.95-18.10 million people (11-26 counties; SSP5-8.5) are projected to experience 9 or more months of transmission suitability. In 2050, for both SSP2-4.5 and SSP5-8.5, 17.08-20.42 million people (23-26 counties), ranging to approximately 70% of the projected population of Florida will experience 9 or more months. The 10 most populated counties in 2000 are projected to experience 1-3 months of additional climate driven transmission suitability in the future. ConclusionThe southern house mosquito was previously managed as a seasonal nuisance in Florida but now represents an increasing public health exposure risk. Projections across climate trajectories underscore an increasing suitability and exposure risk for WNV in Florida, ranging as high as around 70% of the population exposed to suitable climate conditions for transmission for 9 or more months of the year in the 2050s. This means the types of operations and number of employees needed in vector control and public health will also increase.

Temperature is a major factor that impacts tick populations by limiting geographic range of different species. Little is known about the thermal characteristics of these pests outside of a few studies on survival related to thermal tolerance. In this study, thermal tolerance limits, thermal preference, impact of temperature on metabolic rate, and temperature-activity dynamics were examined in larvae for six species of ixodid ticks. Tolerance of low temperatures ranged from -15 to -24{degrees}C with Dermacentor andersoni surviving at the lowest temperatures. High temperature survival ranged from 41 to 47 {degrees}C, with Rhipicephalus sanguineus having the highest upper lethal limit. Ixodes scapularis showed the lowest survival at both low and high temperatures. Thermal preference temperatures were tested from 0-41{degrees}C. D. variabilis exhibited a significant distribution of individuals in the lower temperatures, while the majority of other species gathered around 20-30{degrees}C. Activity was measured from 10-60{degrees}C, and the highest activity was observed in most species was near 30{degrees}C. Metabolic rate was the highest for most species around 40{degrees}C. Both activity and metabolic rate dropped dramatically at temperatures below 10{degrees}C and above 50{degrees}C. In summary, tick species vary greatly in their thermal characteristics, and our results will be critical to predict distribution of these ectoparasites with changing climates.

Insecticide resistance is a serious threat to our ability to control mosquito vectors which transmit pathogens including malaria parasites and arboviruses. Understanding the underlying mechanisms is an essential first step in tackling the challenges presented by resistance. This study aimed to functionally characterise the carboxylesterase, CCEae3A, the elevated expression of which has been implicated in temephos resistance in Aedes aegypti and Aedes albopictus larvae. Using our GAL4/UAS expression system, already established in insecticide-sensitive Anopheles gambiae mosquitoes, we produced transgenic An. gambiae mosquitoes that express an Ae. aegypti CCEae3A ubiquitously. This new transgenic line permits examination of CCEae3A expression in a background which does not express the gene and allows comparison with existing An. gambiae GAL4-UAS lines. Insecticide resistance profiling of these transgenic An. gambiae larvae indicated significant increases in resistance ratio for three organophosphate insecticides, temephos (5.98), chloropyriphos (6.64) and fenthion (3.18) when compared to the parental strain. Cross resistance to adulticides from three major insecticide classes: organophosphates (malathion, fenitrothion and pirimiphos methyl), carbamates (bendiocarb and propoxur) and pyrethroid (alpha-cypermethrin) was also detected. Resistance to certain organophosphates and carbamates validates conclusions drawn from previous expression and phenotypic data. However, detection of resistance to pirimiphos methyl and alphacypermethrin has not previously been formally associated with CCEae3A, despite occurring in Ae. aegypti strains where this gene was upregulated. Our findings highlight the importance of characterising individual resistance mechanisms, thereby ensuring accurate information is used to guide future vector control strategies. Author SummaryInsecticides are vital disease control tools against pathogen-transmitting mosquitoes. However, they are becoming less effective as mosquitoes develop resistance. Among the molecular changes that contribute to resistance, increased production of enzymes that break down/sequester the insecticide is common. In Ae. aegypti mosquitoes, which spread many arboviruses, over-expression of the carboxylesterase enzyme, CEae3A, has been associated with resistance to certain insecticides used for vector control, particularly organophosphate compounds. However, multiple resistance enzymes/mechanisms are likely to be present in resistant mosquitoes at the same time. To examine the effect of CCEae3A expression in isolation, we utilised the An. gambiae mosquito with its convenient access to GAL4/UAS technology to regulate gene expression. This enabled production of CCEae3A in a normally insecticide-sensitive mosquito strain, permitting expression without interference from other resistance mechanisms. As anticipated, resistance to organophosphates was observed in larvae expressing CCEae3A. In adults, resistance was also found against compounds from organophosphate, carbamate and pyrethroid insecticide classes, including two compounds for which there had been no previous association. As well directly linking CCEae3A expression to specific insecticide resistance, this transgenic line can be included in a panel expressing alternative enzymes to screen new insecticidal compounds for liability to existing resistance mechanisms.

BackgroundAedes aegypti presence, human-vector contact rates, and Aedes-borne virus transmission are highly variable through time and space. The Lower Rio Grande Valley (LRGV), Texas, is one of the few regions in the U.S. where local transmission of Aedes-borne viruses occurs, presenting an opportunity to evaluate social, urbanistic, entomological, and mobility-based factors that modulate human exposure to Ae. aegypti. Methodology & Principal FindingsMosquitoes were collected using BG-Sentinel 2 traps during November 2021 as part of an intervention trial, with knowledge, attitudes, and practices (KAP) and housing quality surveys to gather environmental and demographic data. Human blood samples were taken from individuals and a Bitemark Assay (ELISA) was conducted to quantify human antibodies to the Ae. aegypti Nterm-34kDa salivary peptide as a measure of human exposure to bites. In total, 64 houses were surveyed with 142 blood samples collected. More than 80% of participants had knowledge of mosquito-borne diseases and believed mosquitoes to be a health risk in their community. Our best fit generalized linear mixed effects model found four fixed effects contributed significantly to explaining the variation in exposure to Ae. aegypti bites: higher annual household income, younger age, larger lot area, and higher female Ae. aegypti abundance per trap night averaged over 5 weeks prior to human blood sampling. ConclusionsMost surveyed residents recognized mosquitoes and the threat they pose to individual and public health. Urbanistic (i.e., lot size), social (i.e., income within a low-income community and age), and entomological (i.e., adult female Ae. aegypti abundance) factors modulate the risk of human exposure to Ae. aegypti bites. The use of serological biomarker assays, such as the Bitemark Assay, are valuable tools for surveillance and risk assessment of mosquito-borne disease, especially in areas like the LRGV where the transmission of target pathogens is low or intermittent. Author SummaryAedes aegypti is a mosquito vector with public health importance on the global scale as it transmits viruses such as dengue, chikungunya, and Zika. Although transmission rates of dengue and Zika are low in the U.S., there are a few regions, including south Texas, where local transmission has occurred. Our study aimed to evaluate the factors associated with risk of exposure to these viruses using a serological bioassay that measured antibody response to an Ae. aegypti salivary protein to assess human-vector contact. We collected mosquitoes, took human-blood samples, and conducted urbanistic and demographic surveys in November 2021 in eight communities in the Lower Rio Grande Valley, Texas. Our knowledge, attitude, and practices survey found that most residents recognized adult mosquitoes, though few individuals knew someone personally who been sick with a mosquito-borne disease. Outdoor adult female Ae. aegypti abundance was positively associated with exposure to mosquito bites. Household income, individual age, and lot area also significantly affected exposure levels. The Bitemark Assay we used in this study can be utilized as a tool for entomological risk assessment and could be used as an alternative to infection exposure in areas where mosquito-borne disease levels are low.

Three compounds derived from botanicals sources, ethyl perillyl carbonate, geranyl isovalerate, and citronellyl cyclobutane carboxylate, were tested for repellent activity against Ixodes scapularis Say in a semi-field trial. Tick drags were treated with the compounds or with N, N-diethyl-m-toluamide (DEET) at high (0.25mg/cm2) or low (0.15mg/cm2) concentrations. Negative controls included untreated drags and drags treated with acetone, the carrier for all repellents. Freshly treated drags (within 20 minutes) were used to collect I. scapularis ticks at a county park in Wisconsin. To assess effectiveness, we measured tick encounter rates, detachment rate, and time to detachment. None of the repellent treatments resulted in significantly fewer encounters compared to both control treatments. However, the percentage of ticks that detached within 3 min was significantly higher on drags treated with repellents compared to controls. DEET was the most effective, repelling 69.7 - 87% of ticks by 3 min, but the effectiveness of the three test compounds was still high, ranging from 42% to 87% of ticks detaching by 3 min. For time to detachment, there were no significant differences between DEET and the three test compounds. We conclude that these botanically-derived repellents were effective against I. scapularis in a semi-field trial and could be viable alternatives to DEET.

Aedes aegypti, as one of the vectors transmitting several arboviruses, is a main target in mosquito control programs. Permethrin remains the major adulticide used to control these mosquitoes. The increasing percentage of permethrin resistant Aedes aegypti has become an important issue around the world. Knockdown resistance (kdr) is one of the major mechanisms related to permethrin resistance. On the other hand, detoxification genes including cytochrome P450 monooxygenases (P450) and glutathione S-transferases (GSTs) are also suggested as permethrin resistance apparatus. Here we selected a permethrin resistant (p-s) Aedes aegypti population from Florida and compared its mortality after exposure, median lethal dose (LD50), adult survivorship and larval development to several field populations. We used allele-specific PCR genotyping of the S989P, V1016I and F1534C sites in the sodium channel gene and gene expression analysis of several p450 and GSTs genes before and after permethrin exposure to determine their involvement in permethrin sensitivity between Ae. aegypti populations. Results indicated the p-s population had the highest resistance to permethrin based on LD50 and the mortality test. The larval development time did not significantly differ between the populations, however the p-s adults survived longer than the other populations. In the genotype study, p-s population had mostly homozygous mutations in all three mutant sites of the sodium channel gene. Detoxification gene expression studies showed that two p450 genes, AAEL009124 (CYP6N12) and, AAEL009127 (CYP6M11), were upregulated and, accession # AAEL006802, AAEL014891 (CYP6P12) and AAEL014619 (CYP9J22) were downregulated after 120 minutes of permethrin exposure in the p-s population. These results suggest that in highly permethrin resistant Aedes aegypti populations both kdr mutations and xenobiotic metabolism might be involved. Involvement of multiple mechanisms to achieve resistance to permethrin supports the need for implementing comprehensive mosquito control measures, such as an integrated pest management strategy, so that selection pressure for resistance is decreased without compromising control efforts while new methodologies are being developed. Author summaryPyrethroids have been applied as a major type of insecticide targeted at Aedes aegypti, a key vector in the transmission of several flaviviruses. Resistance to pyrethroids has emerged and has become a worldwide threat to mosquito control. Pyrethroid resistance usually occurs with knockdown resistance (kdr) where the voltage gated sodium channel is mutated. We selected a permethrin resistant (p-s) Aedes aegypti population from Florida and, along with two other field populations, examined three mutation sites, S989P, V1016I and F1534C. The data showed the p-s population had the most homozygous mutations which correlated to the permethrin resistance level. Besides kdr, detoxification genes also have been identified to have pyrethroid metabolizing abilities. We found two cytochrome P450 monooxygenases genes, CYP6N12 and CYP6M11, were overexpressed in the p-s population after permethrin exposure, suggesting a role in resistance to permethrin. Together, our results provide information about potential mechanisms used in major vectors with high insecticide resistance.

Pyrethroids are the most widely used insecticides to control vector borne diseases including malaria. Physiological resistance mechanisms to these insecticides have been well described, whereas those for behavioral resistance remain overlooked. Field data suggest the presence of spatial sensory detection by Anopheles mosquitoes of the pyrethroid molecules used in insecticide-based control tools, such as long-lasting insecticide nets or insecticide residual spraying, opening the way to the emergence of a wide range of behavioral adaptations among malaria vectors. However, the spatial sensory detection of these molecules is controversial and needs to be demonstrated. The goal of this study was to behaviorally characterize the non-contact detection of three of the most common pyrethroids used for malaria vector control: permethrin, deltamethrin an -cypermethrin. To reach this goal, we recorded the behavior (takeoff response) of Anopheles gambiae pyrethroid-sensitive and resistant laboratory strains, as well as field collected mosquitoes from the Gambiae complex, when exposed to the headspace of bottles containing different doses of the insecticides at 25 and 35{degrees}C, in order to represent a range of laboratory and field temperatures. We found the proportion of laboratory susceptible and resistant female mosquitoes that took off was, in all treatments, dose and the temperature dependent. Sensitive mosquitoes were significantly more prone to take off only in the presence of -cypermethrin, whereas sensitive and resistant mosquitoes showed similar responses to permethrin and deltamethrin. Field-collected mosquitoes of the Gambiae complex were also responsive to permethrin, independently of the species identity (An. gambiae, An. coluzzi and An. arabiensis) or their genotypes for the kdr mutation, known to confer resistance to pyrethroids. The observed ability of Anopheles spp. mosquitoes to detect insecticides without contact could favor the evolution of behavioral modifications that may allow them to avoid or reduce the adverse effect of insecticides and thus, the development of behavioral resistance.

Precision-guided sterile insect technique (pgSIT) is an extremely promising vector control intervention that can reduce and potentially eliminate the unacceptable malaria burden, particularly in sub-Saharan Africa. The deployment of pgSIT shows the greatest promise and does not have a near peer competitor in the fight to eradicate malaria. Here we explore the cost effectiveness of using this approach in Africa using mathematical modeling and economical analysis. Overall, we find that pgSIT represents a cost-effective and promising approach to A. gambiae control in The Gambia, with the potential to deliver significant economic and social benefits. SummaryPrecision-guided sterile insect technique (pgSIT) is an extremely promising vector control intervention that can reduce and potentially eliminate the unacceptable malaria burden, particularly in sub-Saharan Africa. pgSIT is a safe, innovative, and highly targeted approach to mosquito control that combines the principles of the sterile insect technique (SIT) with advanced state-of-the-art technologies of genetic engineering (Akbari et al. 2023; M. Li et al. 2021; Kandul, Liu, and Akbari 2021; Kandul et al. 2019, 2022). The technique involves inundative releases of genetically sterile male mosquitoes into the environment to mate with their wild counterparts, sterilizing them in the process. After multiple releases, this method can suppress, and even eradicate pest populations without the use of chemical pesticides or other less specific agents. The use of pgSIT has the potential to be a lasting, safe, cost-effective, sustainable, and environmentally friendly method to suppress a target species, acting as a chemical-free, species-specific insecticide. Before this work is considered for field application, however, we need to have a robust, data-driven modeling framework that will accurately predict the outcome of pgSIT release scenarios for malaria control, and we need an assessment of the costs and health benefits of implementing this technology in a region in Africa. This cost assessment evaluates the economic feasibility of both capacity building and establishing the infrastructure for a pgSIT facility in The Gambia to control the deadly malaria mosquito vector Anopheles gambiae. We focused on the Upper River region (URR) for three key reasons: (1) this area is known to have the highest per capita malaria rates in The Gambia (2) this region has more comprehensive historical and current data on malaria incidence and prevalence, malaria-associated healthcare and prevention costs, and human demographic data and (3) its location could feasibly demonstrate that a single pgSIT production facility can support phased suppression on a regional scale and then upon local extinction be repurposed to support vector suppression on a country or continent-wide scale. The pgSIT treatment of the URR ([~]2069 km2) is predicted to prevent approximately 230 deaths and about 48,000 sick days per year. This estimate is based on a model for localized extinction of A. gambiae, reaching full epidemiological impact by the third year. There are multiple ways to calculate the value of this intervention monetarily, from the value of statistical life (VSL) to quality adjusted life years (QALY), which ranges from 367 million to 880 million USD saved in the first ten years of the facility being active. Other metrics such as willingness-to-pay (WTP), estimates the willingness of locals to contribute to malaria prevention financially, and estimates based on gross domestic product (GDP) growth predict this model to save either 53 million or 551 million USD, respectively, in the first ten years of intervention. This model assumes localized extinction of A. gambiae by the second year of intervention with repeated releases to maintain extinction despite seasonal mosquito migration from beyond the treatment area. Localized extinction, however, is expected to have a year-to-year suppression effect making it easier to suppress mosquito populations with reduced sterile male releases in subsequent years. It is, therefore, likely an underestimate of the costs and benefits of pgSIT sterile male releases. In later years, the release of sterile males from this facility could be redirected to new areas to expand the suppression region. Additionally, this facility would have a significant off-season where the facility is not producing sterile male A. gambiae. This off-season could, therefore, produce sterile males to suppress A. gambiae populations in other regions with seasonal malaria during the off-season in The Gambiae. It could even be used to mass produce pgSIT sterile males for other mosquito species, such as the dengue vector, Aedes aegypti, which have eggs that can be stored for many months and consequently can be stockpiled to aid in the suppression of dengue outbreaks, which are also common in the area. Initially, however, the off-season can be used to build local capacity for genetically engineered (GE) mosquitos, which would consist of training staff, optimizing procedures, and troubleshooting any issues that arose during the higher production phases. The costs for this approach will vary as there are some unknowns and variability in the expected efficiencies of the facility, equipment, and procedures. In particular, mosquito survival rates and fecundity may vary more widely at scale and selection of the rearing equipment and protocols, and the mosquito sorting technology will dictate production levels and procedures. This variability is factored into the cost, and, therefore, a range of technologies and costs are considered. The expected start-up costs range from 6 to 11.5 million USD, which includes all necessary development, field trials, equipment, facility construction, staffing, and other establishment costs. The major upfront costs vary by facility size and capital equipment, much of which is dependent on mosquito rearing efficiencies. The annual estimated operational costs range from approximately 315,000 USD, depending on equipment selection and the size of the facility. Annually, this intervention costs less than 1 USD per person to suppress mosquitoes in the URR and prevent malaria transmission, which is about 6% of a malaria prevention WTP based on current interventions or 0.3-11% when using the VSL or QALY metrics, with most variation from the VSL calculation method. This intervention costs 15 to 124 USD (2022) to save one life-year and prevents malaria infections at 13 to 113 USD per case prevented, making this method competitive with many current interventions. WTP demonstrates that this facility could be made locally sustainable long term by local funding. Overall, the estimates of the capital and operational costs associated with the production of pgSIT sterile males, and the construction and management of the production facility indicate the cost savings associated with the annual decrease in morbidity and mortality (value of life) resulting from the use of pgSIT are significantly higher than the implementation costs. These estimates suggest that pgSIT represents a cost-effective and promising approach to A. gambiae control in The Gambia, with the potential to deliver significant economic and social benefits.

Insecticides are widely used to control the insects that spread human infectious diseases, in particular falciparum malaria. This widespread use has driven insecticide resistance (IR) to high levels that may threaten the effectiveness of future control programmes. There is interest in identifying deployment methods that alleviate the pressures driving IR and we investigate three. Mixtures are, as already known, highly effective in slowing IR providing their effectiveness (ability to kill fully sensitive insects) remain close to 100%. Mixtures may be expensive and/or operationally difficult so two alternatives to mixtures were investigated. Panels, where different insecticides are physically closely adjacent, for examples, different panels on the same bednet; mosquitoes may therefore encounter both insecticides in the same foraging cycle. Micro-mosaics where different insecticides are deployed in slightly wider geographic proximity, for example in adjacent dwellings. The mosquitoes are unlikely to encountered both insecticides in the same foraging cycle but may encounter different insecticides in subsequent foraging. It is hoped that panels and/or micro-mosaics may, by allowing individual mosquitoes to potentially encounter both insecticides, be effective, lower-cost alternatives to mixtures. Our results suggest this is unlikely to be the case. When insecticides are fully effective then mixtures remain clearly the best strategy. As effectiveness falls then all three strategies are roughly equal. The operational decision of what deployment methods to use depends on how confident we are that insecticides will have high effectiveness that will be maintained in realistic field conditions post-deployment.

Urbanization is intensifying human interactions with mosquitoes, exacerbating public health challenges. Densely populated areas provide ideal conditions for container-dwelling mosquitoes, with increased host availability and the presence of artificial breeding sites. These anthropophilic mosquitoes often exhibit distinct ecological adaptations compared to their rural counterparts. Since mosquito eggs are immobile and remain at the site of oviposition, they provide a valuable lens for assessing how urbanization, climate-driven shifts in temperature, and drought affect mosquito reproductive success. This study examined Ae. aegypti egg viability under varying temperature and dry conditions over five months, focusing on lineages with distinct ancestries from West African populations. Mosquitoes collected from urban habitats with a high human preference demonstrated higher egg survival under prolonged arid conditions. Analysis of climatic factors revealed that dry season temperature and precipitation during wet periods are significant predictors of egg drought tolerance. Modeling future climate scenarios based on input from our egg viability results suggests a projected shift and expansion in the seasonal survival window for Ae. aegypti by the end of the century. This study highlights the importance of understanding environmental constraints on the drought tolerance of mosquito eggs to predict and mitigate future mosquito outbreaks.

BackgroundThe control of Aedes aegypti and Aedes albopictus mosquitoes, the main vectors of dengue, chikungunya and Zika viruses, presents several challenges. The difficulties encountered in acquiring funding, implementing measures, obtaining community participation, acceptability and effectiveness, and the problem of insecticide resistance demonstrate the need to develop and optimise innovative vector control strategies. The sterile insect technique (SIT), the incompatible insect technique (IIT) and a combination of both (SIT-IIT) show promise. Numerous trials are being carried out worldwide to obtain evidence of their effectiveness before implementing them in large-scale, integrated vector-control strategies. The main objective of our study is to build an analytical framework for the identification and standardisation of appropriate entomological indicators that could be used to compare the relative effectiveness of the SIT, IIT and SIT-IIT methods in reducing Aedes vector populations. MethodsWe reviewed the available scientific literature to compare the characteristics, methodologies, effectiveness indicators and results of various trials with the aim of standardising and comparing the indicators used in the trials, such as reductions in the egg hatch rate and in the adult populations. ResultsSeventeen trials, either published in peer-reviewed journals or posted as preprints, were selected. We found wide variation among them in experimental design, field implementation and the methods of calculating the indicators. Although limited by the amount of available published data, our results suggest that a reduction in egg hatching greater than 45% results in up to 60% fewer females, greater than 60% results in over 80% fewer females, and greater than 70% results in over 90% fewer females. Therefore, the quality of implementation, assessed on the basis of egg hatch reduction, is statistically associated with effectiveness, assessed on the basis of the reduction in Aedes females. ConclusionWe present results suggesting that, when implemented effectively, the incompatible and sterile insect techniques are substantially effective in reducing Aedes mosquito populations. Furthermore, these techniques are species specific, non-insecticidal and environmentally friendly. However, it has yet to be shown that they can be scaled up as cost-effective operational tools for vector control and that they substantially reduce arbovirus transmission.

Dengue cases in Bangladesh have surged in recent years. The existing insecticide-based control program, implemented in parts of the country, is challenged by issues of insufficient household coverage and high levels of insecticide resistance in the primary dengue virus (DENV) vector, Aedes aegypti. A more sustainable, effective alternative could be the implementation of a Wolbachia-mediated disease management strategy. Infecting mosquitoes with Wolbachia can change their reproductive compatibility and their ability to transmit DENV. These new phenotypes can be exploited to suppress or replace wild-type Ae. aegypti populations. Such strategies require the development of well-characterised Wolbachia-infected strains with biological characteristics that are comparable with local mosquitoes. We created and characterised a Wolbachia-infected Ae. aegypti strain with a Dhaka wild-type genetic background, and compared its reproductive compatibility, maternal inheritance, fitness, and virus-blocking ability to the parental strains (Dhaka wild-type and wAlbB2-F4). The new Ae. aegypti strain wAlbB2-Dhaka demonstrated complete cytoplasmic incompatibility with the wild-type strain and complete maternal transmission, retaining levels of pyrethroid resistance of the Dhaka wild-type (70% survival to 10 times the dose of permethrin expected to kill susceptible mosquitoes). No significant fitness costs were detected during laboratory comparisons of fecundity, fertility, survival, mating competitiveness, or desiccation tolerance. Compared to the wild-type strain, wAlbB2-Dhaka mosquitoes had a significantly reduced number of DENV genome copies in the bodies (44.4%, p = 0.0034); two-fold reduction in dissemination to legs and wings (47.6%, p < 0.0001); and >13-fold reduction of DENV in saliva expectorates (proxy of transmission potential) (92.7%, p < 0.0001) 14 days after ingesting dengue-infected blood. Our work indicates that the wAlbB2-Dhaka strain could be used for Ae. aegypti suppression or replacement strategies for dengue management in Bangladesh. Author summaryBangladesh is currently grappling with a series of severe dengue outbreaks, resulting in more than 300 thousand infections, 1700 fatalities, and a significant influx of patients requiring hospitalisation in 2023. These outbreaks coincide with the emergence of high levels of insecticide resistance in the Ae. aegypti population, which is contributing to the failure of conventional, insecticidal control strategies. In search of more sustainable, effective dengue control strategies, approaches using the endosymbiotic bacteria Wolbachia that render mosquitoes resistant to arbovirus infection are being trialled in a number of countries. We transinfected Dhaka wild-type Ae. aegypti with the Wolbachia strain wAlbB2 by backcrossing it with a Wolbachia wAlbB2-infected Ae. aegypti strain and assessed the new strains suitability for field release. We compared the fitness and virus-blocking ability of the backcrossed strain with its parental strains. We demonstrated that the new strain, wAlbB2-Dhaka, is as fit as the Dhaka wild-type strain and blocked [~]92% of dengue virus transmission. This strain has great potential for Wolbachia-mediated dengue management strategies in Bangladesh.

BackgroundAedes albopictus (Skuse 1894) mosquitoes can transmit deadly arboviruses and are globally invasive due to their ability to survive in both tropical and temperate climates. Although adults cannot survive harsh winters, females are capable of anticipating seasonal change and producing overwintering diapause (DP) eggs that remain in a state of arrested development over the winter and hatch when favorable conditions return in the spring. Previous work has shown that shortening photoperiod (day length) alone is sufficient for DP induction. While decreasing temperatures can facilitate DP entry, temperature signals alone are not sufficient to induce DP. Methodology/Principal FindingsTo identify maternal phenotypes predictive of DP egg production, we characterized aspects of maternal physiology and behavior to identify those that correlate with DP egg production and changes in photoperiod, versus changes in temperature. Neither changes in temperature nor photoperiod impacted protein preference, blood meal consumption, or total number of eggs produced per female. Egg retention and oviposition timing were influenced by temperature, independent of DP egg production. However, females housed under short photoperiod conditions showed increased starvation resistance, despite showing similar levels of locomotor activity and internal stores of triacylglycerols, glucose, glycogen, and trehalose compared to females housed in long photoperiods. Conclusions/SignificanceThese results suggest that temperature and photoperiod differentially affect maternal phenotypes and identify starvation resistance as a maternal phenotype that is influenced by photoperiod and can be used to predict DP egg status. AUTHOR SUMMARYAedes albopictus mosquitoes can survive in temperate climates because females are able to detect changes in temperature and day length in the autumn to produce "diapause" eggs that are provisioned with extra nutrients to survive harsh winters by remaining in a state of arrest and hatching in the spring. Although temperature and day length normally change in concert with each other throughout the year, studies have shown that day length is the most important cue used by female mosquitoes to initiate diapause egg production. In this study, the authors examined aspects of feeding and reproduction to determine which of these correlated with day length. Many aspects of reproduction were influenced by temperature; however, housing female mosquitoes under autumn-like short day conditions led to increased starvation resistance. Surprisingly these females survive longer even though they do not appear to expend less energy compared to females housed in spring-like long day conditions at the same temperature. This suggests that the mosquito mothers undergo changes in their metabolism that can be used predict whether she will produce eggs that can survive the winter. This new knowledge may lead to new targets to disrupt seasonal reproduction in mosquitoes and limit the parts of the world where they can survive.

BackgroundInsecticide resistance monitoring is key for evidence-based control of Anopheles and Aedes disease vectors in particular, since the vast majority of insecticide-based public health adult vector control tools are reliant on pyrethroids. While widespread pyrethroid resistance in Anopheles species and Aedes aegypti has been described in many countries, data for Papua New Guinea are scarce. Available data indicate the local Anopheles populations remain pyrethroid-susceptible, making regular insecticide resistance monitoring even more important. Knowledge on Aedes insecticide resistance in PNG is very limited, however, high levels of Aedes aegypti resistance have been described. Here we present insecticide resistance monitoring data from across PNG generated between 2017 and 2022. MethodsMosquito larvae were collected in larval habitat surveys and through ovitraps. Mosquitoes were reared to adults and subjected to insecticide treated filter papers in WHO insecticide susceptibility bioassays. Subsets of Aedes mosquitoes were subjected to sequencing of the voltage-sensitive sodium channel (Vssc) region to identify resistance mutations. ResultsOverall, nearly 20,000 adult female mosquitoes from nine PNG provinces were used in the tests. We show that in general, Anopheline mosquitoes in PNG remain susceptible to pyrethroids but with worrying signs of reduced 24 h mortality in some areas. In addition, some Anopheles populations were indicated to be resistant against DDT. We show that Ae. aegypti in PNG are pyrethroid, DDT and likely bendiocarb resistant with a range of Vssc resistance mutations identified. We demonstrate that Ae. albopictus is DDT resistant and is likely developing pyrethroid resistance based on finding a low frequency of Vssc mutations. ConclusionThis study represents the largest overview of insecticide resistance in PNG. While Ae. aegypti is highly pyrethroid resistant, the Anopheline and Ae. albopictus populations exhibit low levels of resistance in some areas. It is important to continue to monitor insecticide resistance in PNG and prepare for the widespread emergence of pyrethroid resistance in major disease vectors.

BackgroundMosquitoes are major vectors of arboviruses and other vector-borne diseases, making them a significant public health concern worldwide. Mitigation of arboviral outbreaks relies largely on the use of insecticides, but the effectiveness of such responses is threatened by the evolution of insecticide resistance. Monitoring mosquito susceptibility to different insecticides is therefore vital for informed decisions regarding outbreak responses. In this study, we elucidate the patterns of resistance to two insecticide classes within the primary vectors of West Nile virus in the northeast and midwestern regions of the continental United States, Culex pipiens and Culex restuans. Methodology/Principal FindingsEgg collections were performed throughout Illinois from 2018-2020, and adults were tested for insecticide resistance to permethrin and malathion. Individuals from each sampling location were sequenced to determine the presence of kdr target-site mutations, and biochemical assays were performed to determine increases in detoxification enzymes and insensitive acetylcholinesterase. Results from the bottle assays indicate variable resistance rates in Illinois, however lowered mortality was found in most of the regions that were tested. The kdr mutation (L1014F) was present in 50% of Culex pipiens sequenced, and more prevalent in southern Illinois compared with northern and central (p < 0.001). Different mechanisms were predictive of resistance by species and insecticide, with permethrin resistance being affected by kdr-allele frequency and oxidase levels and malathion resistance by - and {beta}-esterases in Cx. pipiens. For Cx. restuans -esterase and oxidase levels were predictive of permethrin resistance while {beta}-esterase and insensitive acetylcholinesterase levels were predictive of malathion resistance. Conclusions/SignificanceWe documented variation in insecticide resistance levels that appear to be driven by population differences in kdr mutation rates and metabolic resistance mechanisms. The presence of different mechanisms in species and regions has implications for approaches to resistance management and highlights the need to implement and maintain insecticide resistance monitoring practices. Author SummaryMosquitoes are the vectors of many major diseases including malaria, dengue, yellow fever, zika, and West Nile virus. Insecticides are often used to control mosquitoes and the outbreaks they cause. However, evidence has shown that populations of different mosquito species worldwide have developed resistance to our most common insecticides. This study shows that West Nile virus vectors in Illinois, (Culex pipiens and Culex restuans) are no exception to this trend. Egg collections were made throughout the state during the 2018-2020 field seasons and the resulting adults were tested for resistance to two common insecticides using the CDCs bottle bioassay protocol. The results indicate that rates of resistance vary throughout the state and population differences in resistance mechanisms are driving this variation.

Aedes albopictus is a cosmopolitan mosquito species capable of transmitting arboviral diseases such as dengue, chikungunya, and Zika. To control this and similar species, public and private entities often rely on pyrethroid insecticides. Insecticide resistance status and physiological traits, such as body size, may contribute to local patterns of abundance, which is important for planning vector control. In this study, we genetically screened Ae. albopictus collected from June to August, 2017, in Mecklenburg County, North Carolina, for mutations conferring pyrethroid resistance, and examined spatiotemporal patterns of specimen size, as measured by wing length. We hypothesized that size variation would be associated with factors found to influence abundance in similar populations of Ae. albopictus, and could therefore serve as a proxy measure. The genetic screening results indicated that known pyrethroid resistance alleles in two kdr regions are not present in this population. We detected no significant associations between wing length and socioeconomic and landscape factors, but mosquitoes collected in June had significantly longer wing length than in July or August. The lack of resistance indicators suggest that this population has not developed insecticide resistance via voltage-gated sodium channel mutations. The greater wing lengths in June are likely driven by meteorological patterns, suggesting that short-term weather cues may modulate morphological characteristics that, in turn, affect local fecundity and virus transmission potential.

BackgroundTriatoma infestans is the main vector of Chagas disease in the Southern Cone. The resistance to pyrethroid insecticides developed by populations of this species impairs the effectiveness of vector control campaigns in wide regions of Argentina. The study of the global transcriptomic response to pyrethroid insecticides is important to deepen the knowledge about detoxification in triatomines. Methodology and findingsWe used RNA-Seq to explore the early transcriptomic response of T. infestans after intoxication with deltamethrin. We were able to assemble a complete transcriptome of this vector and found evidence of differentially expressed genes belonging to diverse families such as chemosensory and odorant-binding proteins, ABC transporters and heat-shock proteins. Moreover, genes related to transcription and translation, energetic metabolism and cuticle rearrangements were also modulated. Finally, we characterized the repertoire of previously uncharacterized detoxification-related gene families in T. infestans and Rhodnius prolixus. Conclusions and significanceOur work contributes to the understanding of the detoxification response in vectors of Chagas disease. Given the absence of genomic information from T. infestans, the analysis presented here constitutes a resource for molecular and physiological studies in this species. The results increase the knowledge on detoxification processes in vectors of Chagas disease, and provide relevant information to explore new potential insecticide resistance mechanisms in these insects. Author summaryChagas disease affects millions of people worldwide. In the Southern Cone, the development of pyrethroid resistant populations from T. infestans is related to vector persistence and affects the efficiency of vector control campaigns. Several studies have explored the causes of insecticide resistance in T. infestans populations. However, the global transcriptomic response after insecticide treatment has not been analyzed in this species so far. In this study, we obtained transcriptomic information which allowed us to characterize important gene families despite the absence of genomic information. Furthermore, we performed a quantitative analysis of gene expression after deltamethrin intoxication. The results provided here increase the knowledge on detoxification processes in vectors of Chagas disease, which is essential for the design of new vector control strategies.