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After the tropical storm Cristobal, we performed special adult entomological collections in the peri-domicile of 35 houses from 25 neighborhoods of Merida, Yucatan, Mexico in response to complaints from the community about an increased nuisance due to an abundance of mosquitoes. A total of 1,275 specimens from four genera and 13 species were collected: Aedes taeniorhynchus (92%), Culex quinquefasciatus (72%), Aedes aegypti (72%), Psorophora mexicana (36%), Psorophora cyanescens (32%), Aedes scapularis (24%), Culex nigripalpus (24%), Aedes albopictus (8%), Psorophora ferox (4%), Haemagogus equinus (4%), Aedes trivittatus (4%), Culex coronator (4%), Culex iolambdis (4%). From these collections, the increased mosquito nuisance was mainly the result of invasive species such as Aedes taeniorhynchus and Psorophora. City wide, vehicle mounted ULV spraying was performed by the MoH and the municipality of Merida to control adult mosquito populations. We report Culex iolambdis for the first time in Merida and Psorophora mexicana for the state of Yucatan.

Objective To evaluate the protective effect of house-screening (HS) on indoor Ae. aegypti infestation, abundance and arboviral infection in Merida, Mexico. Methods In 2019, we performed a cluster randomized controlled trial (6 control and 6 intervention areas: 100 households/area). Intervention clusters received permanently fixed fiberglass HS on all windows and doors. The study included two cross-sectional entomologic surveys, one baseline (dry season in May 2019) and one post-intervention (PI, rainy season between September-October 2019). The presence and number of indoor Aedes females and blood-fed females (indoor mosquito infestation) as well as arboviral infections with dengue (DENV) and Zika (ZIKV) viruses were evaluated in a subsample of 30 houses within each cluster. Results HS houses had significatively lower risk for having Aedes aegypti female mosquitoes (odds ratio [OR]=0.56, 95% C. I. 0.33-0.97, P=0.04) and blood-fed females (OR=0.53, 95% C. I. 0.28-0.97, P=0.04) than unscreened households from the control arm. Compared to control houses, HS houses had significantly lower indoor Ae. aegypti abundance (rate ratio [RR]=0.50, 95% C. I. 0.30-0.83, P=0.01), blood-fed Ae. aegypti females (RR=0.48, 95% C. I. 0.27-0.85, P=0.01) and female Ae. aegypti positive for arboviruses (OR=0.29, 95% CI 0.10-0.86, P=0.02). The estimated intervention efficacy in reducing Ae. aegypti arbovirus infection was 71%. Conclusions These results provide evidence supporting the use of HS as an effective pesticide-free method to control house infestations with Aedes aegypti and reduce the transmission of Aedes-transmitted viruses such as DENV, chikungunya (CHIKV), and ZIKV.

We conducted a baseline characterization of the abundance and seasonality of Aedes aegypti (Linnaeus, 1762)—a vector of dengue, chikungunya, and Zika—in two suburban localities of Yucatan, Mexico, as the first step in the implementation of an integrated vector management (IVM) plan combining ‘traditional Aedes control’ (source reduction/truck-mounted ultra-low volume [ULV] spraying) and incompatible insect technique/sterile insect technique for population suppression in Yucatan, Mexico. Weekly entomological collections with ovitraps and BG-sentinel traps were performed in 1-ha quadrants of both localities for 1 yr. Three distinct periods/phases were identified, closely associated with precipitation: 1) a phase of low population abundance during the dry season (weekly average of Aedes eggs per ovitrap and adults per BG trap = 15.51 ± 0.71 and 10.07 ± 0.88, respectively); 2) a phase of population growth and greatest abundance of Aedes (49.03 ± 1.48 eggs and 25.69 ± 1.31 adults) during the rainy season; and finally 3) a phase of decline among populations (20.91 ± 0.97 eggs and 3.24 ± 0.21 adults) after the peak of the rainy season. Seasonal abundance and dynamics of Ae. aegypti populations suggest that it is feasible to develop and implement time-specific actions as part of an IVM approach incorporating integrating novel technologies (such as rear-and-release of Wolbachia-infected males) with classic (insecticide-based) approaches implemented routinely for vector control. In agreement with the local vector control program, we propose a pilot IVM strategy structured in a preparation phase, an attack phase with traditional vector control, and a suppression phase with inundative releases, which are described in this paper.

Commercial aerosolized insecticides can be implemented as a community-based approach to targeted indoor residual spraying against Aedes aegypti, but their efficacy on pyrethroid-resistant mosquitoes has not yet been evaluated. Two commercial aerosolized products (H24 Poder Fulminante Ultra Eficaz®, carbamate, and Baygon Ultra Verde®, pyrethroid) were sprayed on common indoor surfaces e.g., cement, plywood, and cloth, and tested for their residual efficacy on susceptible and field-derived pyrethroid-resistant Ae. aegypti strains using the WHO cone bioassays. Overall, ≥80% 24-h mortality was observed for both products for at least 4 wk regardless of the mosquito strain or surface type used. H24 Poder Fulminante Ultra Eficaz showed the highest residual potency, sustaining >80% mortality for 7-wk posttreatment regardless of mosquito strain and surface type. For Baygon Ultra Verde, the mean mortality of female Ae. aegypti remained >80% for a shorter period (4–6 wk). Nonpyrethroid commercial aerosolized formulations can provide a lasting residual effect indoors compatible with the need for rapid and lasting mosquito control during outbreaks and may be suitable for community-based targeted indoor residual spraying.

Background There is an increased need to mitigate the emergence of insecticide resistance and incorporate new formulations and modes of application to control the urban vector Aedes aegypti. Most research and development of insecticide formulations for the control of Ae. aegypti has focused on their peridomestic use as truck-mounted ULV-sprays or thermal fogs despite the widespread knowledge that most resting Ae. aegypti are found indoors. A recent modification of indoor residual spraying (IRS), termed targeted IRS (TIRS) works by restricting applications to 1.5 m down to the floor and on key Ae. aegypti resting sites (under furniture). TIRS also opens the possibility of evaluating novel residual insecticide formulations currently being developed for malaria IRS. Methods We evaluated the residual efficacy of chlorfenapyr, formulated as Sylando 240SC, for 12 months on free-flying field-derived pyrethroid-resistant Ae. aegypti using a novel experimental house design in Merida, Mexico. On a monthly basis, 600 female Ae. aegypti were released into the houses and left indoors with access to sugar solution for 24 hours. After the exposure period, dead and alive mosquitoes were counted in houses treated with chlorfenapyr as well as untreated control houses to calculate 24-h mortality. An evaluation for these exposed cohorts of surviving mosquitoes was extended up to seven days under laboratory conditions to quantify “delayed mortality”. Results Mean acute (24-h) mortality of pyrethroid-resistant Ae. aegypti ranged 80–97% over 5 months, dropping below 30% after 7 months post-TIRS. If delayed mortality was considered (quantifying mosquito mortality up to 7 days after exposure), residual efficacy was above 90% for up to 7 months post-TIRS application. Generalized Additive Mixed Models quantified a residual efficacy of chlorfenapyr of 225 days (ca. 7.5 months). Conclusions Chlorfenapyr represents a new option for TIRS control of Ae. aegypti in urban areas, providing a highly-effective time of protection against indoor Ae. aegypti females of up to 7 months., Author summary Vector control (VC) for managing Aedes aegypti and reducing transmission of Aedes-borne diseases is largely focused on peridomestic insecticide applications. However, the indoor resting behavior of Ae. aegypti and the acceleration of insecticide resistance owed to reduced modes of action have diminished the effectiveness of many VC tools. A targeted Indoor residual spraying (TIRS) modality in experimental housing units was employed to investigate the potential of chlorfenapyr, a pyrrole-class insecticide with known effectiveness to resistant mosquito species. This was the first investigation for chlorfenapyr use against locally resistant Ae. aegypti (Merida, Mexico) with this approach. Two treatment arms were investigated in the present study: TIRS and a control house where only water was sprayed. A comparison of entomological efficacy for TIRS applied to interior perimeter walls below 1.5 m with chlorfenapyr (formulated as Sylando 240SC) at 250 mg/m2 over 12 months was assessed. TIRS chlorfenapyr treatments were highly efficacious and led to acute mortalities (after 24 exposure) above 80% up to 5 months; delayed mortalities (to Ae. aegypti) were monitored over seven days post exposures vs untreated controls. When delayed mortality was considered, residual efficacy of chlorfenapyr extended to 7 months. These data provide evidence that TIRS chlorfenapyr is an effective Aedes management tool that surpassed efficacy profiles for other TIRS insecticides that have been previously reported with this method. Further, Chlorfenapyr emerges as a novel addition to Ae. aegypti VC, and future studies should focus on its effectiveness and residual power as part of Phase II-III TIRS trials.

We evaluated the efficacy of bendiocarb (Ficam W® 80%) and pirimiphos-methyl (Actellic 300CS® 28.16%), applied to different surfaces potentially sprayable within houses during the application of a targeted indoor residual spraying (TIRS) against a field pyrethroid-resistant strain of Aedes aegypti. Bioassays with cones were performed on cement (walls), wood (doors), and textile (cloth) surfaces within typical houses in the Mexican city of Merida (n = 10). Optimal residual efficacy (>80% of mean mortality) of bendiocarb ranged from 3 months (cement) to 2 months (wood and textiles). Residual efficacy of pirimiphos-methyl ranged from 5 months (cement) to 2 months (wood and textiles). Both insecticides proved to be effective as adulticides against field Ae. aegypti and may be useful in mosquito control programs implementing TIRS with pyrethroid-resistant populations.

We evaluated the efficacy of aerial ultra-low-volume (ULV) insecticide spraying in field bioassays with caged Aedes aegypti in May 2017 in Puerto Vallarta, Jalisco, Mexico. The insecticides tested included an organophosphate (Mosquitocida UNO ULV) and a neonicotinoid–pyrethroid combination (Cielo). Two Ae. aegypti populations were evaluated: a field pyrethroid-resistant local strain (Puerto Vallarta) and an insecticide-susceptible laboratory strain (New Orleans). Knockdown after 1 h by both products was ≥97.0%, and mortality after 24 h was ≥98% for the susceptible laboratory strain. Knockdown of the local Puerto Vallarta field strain by both products after 1 h was ≥96.5%; and mosquito mortality after 24 h was also very high (≥98%). Meteorological conditions during this evaluation were favorable for aerial mosquito control and represented conditions that typically occur during adulticide space spray applications. Temperature oscillated between 24°C and 26°C with winds between 6 and 10 km/h. The majority of droplets met the droplet distribution criteria required for the insecticides. The evaluation demonstrated an acceptable performance of both products for Ae. aegypti control when applied undiluted at a rate of 199.4 ml/ha and 73.07 ml/ha for Mosquitocida UNO ULV and Cielo, respectively. The volume median diameter (VMD) droplet size was characterized at 31.3 μm and 37.3 μm, respectively.

A cluster-randomized controlled trial quantified the entomological efficacy of aerial ultra-low volume (AULV) applications of the insecticide chlorpyrifos against Aedes aegypti in Puerto Vallarta, México, during November–October 2017. The trial involved 16 large (1 × 1 km) clusters distributed between treatment-control arms. Primary endpoint was the abundance of Ae. aegypti indoors (total adults, females, and blood-fed females) collected using Prokopack aspirators. After four consecutive weekly cycles of AULV, all adult Ae. aegypti infestation indices were significantly lower in the treatment arm (OR and IRR ≤ 0.28). Efficacy in reducing indoor Ae. aegypti increased with each weekly application cycle from 30 to 73% (total adults), 33 to 76% (females), and 45.5 to 89% (blood-fed females). Entomological indices remained significantly lower in the treatment arm up to 2 wk after the fourth spraying round. Performing AULV spraying can have significant and lasting entomological impact on Ae. aegypti as long as multiple (ideally four) spray cycles are implemented using an effective insecticide.

Summary Background Effective Aedes aegypti control is limited, in part, by the difficulty in achieving sufficient intervention coverage. To maximise the effect of vector control, areas with persistently high numbers of Aedes-borne disease cases could be identified and prioritised for preventive interventions. We aimed to identify persistent Aedes-borne disease hotspots in cities across southern Mexico. Methods In this spatial analysis, geocoded cases of dengue, chikungunya, and Zika from nine endemic Mexican cities were aggregated at the census-tract level. We included cities that were located in southern Mexico (the arbovirus endemic region of Mexico), with a high burden of dengue cases (ie, more than 5000 cases reported during a 10-year period), and listed as high priority for the Mexican dengue control and prevention programme. The Getis-Ord Gi*(d) statistic was applied to yearly slices of the dataset to identify spatial hotspots of each disease in each city. We used Kendall's W coefficient to quantify the agreement in the distribution of each virus. Findings 128 507 dengue, 4752 chikungunya and 25 755 Zika clinical cases were reported between Jan 1, 2008, and Dec 31, 2016. All cities showed evidence of transmission heterogeneity, with a mean of 17·6% (SD 4·7) of their total area identified as persistent disease hotspots. Hotspots accounted for 25·6% (SD 9·7; range 12·8–43·0) of the population and 32·1% (10·5; 19·6–50·5) of all Aedes-borne disease cases reported. We found an overlap between hotspots of 61·7% for dengue and Zika and 53·3% for dengue and chikungunya. Dengue hotspots in 2008–16 were significantly associated with dengue hotspots detected during 2017–20 in five of the nine cities. Heads of vector control confirmed hotspot areas as problem zones for arbovirus transmission. Interpretation This study provides evidence of the overlap of Aedes-borne diseases within geographical hotspots and a methodological framework for the stratification of arbovirus transmission risk within urban areas, which can guide the implementation of surveillance and vector control. Funding USAID, the US Centers for Disease Control and Prevention, the Canadian Institutes of Health Research, International Development Research Centre, Fondo Mixto CONACyT (Mexico)-Gobierno del Estado de Yucatan, and the US National Institutes of Health. Translation For the Spanish translation of the abstract see Supplementary Materials section.

Resumen Introducción. El programa de enfermedades transmitidas por vectores en México tiene una red establecida de ovitrampas para la vigilancia entomológica de Aedes spp. Los servicios de salud del estado de Yucatán, en respuesta a reportes de Aedes albopictus en la periferia de Mérida, capital del estado, incrementaron la especificidad de dicha vigilancia. Objetivo. Describir la presencia y distribución de Ae. albopictus en Mérida y su abundancia relativa comparada con Aedes aegypti, en ovitrampas del programa de control de vectores. Materiales y métodos. Durante octubre de 2019, se seleccionaron al azar 91 ovitrampas en 31 barrios de Mérida. Los mosquitos adultos se obtuvieron del insectario de la Unidad Colaborativa para Bioensayos Entomológicos de la Universidad Autónoma de Yucatán a partir de huevos recolectados en campo. Se determinó la abundancia relativa de individuos adultos de cada especie identificada y por barrios evaluados. Resultados. En el 32 % de los barrios muestreados, se detectó Ae. albopictus y, en todos ellos, Ae. aegypti. Se recolectaron 28 adultos de Ae. albopictus (10 hembras y 18 machos) en las ovitrampas. No se observó correlación entre la abundancia de adultos ni de hembras Ae. aegypti y Ae. albopictus por barrio (p>0,05). Conclusiones. Los resultados confirmaron que Ae. albopictus estaba coexistiendo con Ae. aegypti en Mérida en el momento del estudio. La baja abundancia relativa sugiere que Ae. albopictus se encontraba en la fase inicial de invasión. Abstract Introduction: The vector-borne diseases program in México has an established network of ovitraps for entomological surveillance of Aedes spp. In response to reports of Aedes albopictus in the periphery of Mérida, the state capital of Yucatán, the Ministry of Health increased the specificity of this surveillance. Objective: To describe the presence and distribution of Ae. albopictus in Mérida and its relative abundance compared to Aedes aegypti in ovitraps of the vector control program. Materials and methods: During October, 2019, 91 ovitraps were randomly selected from 31 neighborhoods of Mérida. Mosquitoes were reared at the insectary of the Collaborative Unit for Entomological Bioassays of the Autonomous University of Yucatán from eggs collected in the field. Relative abundance was determined for adult individuals of each identified species and neighborhood. Results: 32 % of the neighborhoods were positive for Ae. albopictus and 100 % for Ae. aegypti. A total of 28 adults of Ae. albopictus (10 females and 18 males) were obtained from ovitraps. No correlation was observed between the abundance of Ae. aegypti and Ae. albopictus for both adults and females (p>0.05) at the neighborhood level. Conclusions: The results confirm that Ae. albopictus coexisted with Ae. aegypti in Mérida at the time of the study. The low relative abundance suggests that Ae. albopictus was in the initial phase of invasion.

Aedes aegypti and Aedes albopictus vector dengue, chikungunya and Zika viruses. With both species expanding their global distributions at alarming rates, developing effective surveillance equipment is a continuing priority for public health researchers. Sound traps have been shown, in limited testing, to be highly species-specific when emitting a frequency corresponding to a female mosquito wingbeat. Determining male mosquito capture rates in sound traps based on lure frequencies in endemic settings is the next step for informed deployment of these surveillance tools. We field-evaluated Male Aedes Sound Traps (MASTs) set to either 450 Hz, 500 Hz, 550 Hz or 600 Hz for sampling Aedes aegypti and/or Aedes albopictus and compared catch rates to BG-Sentinel traps within Pacific (Madang, Papua New Guinea) and Latin American (Molas, Mexico and Orange Walk Town, Belize) locations. MASTs set to 450–550 Hz consistently caught male Ae. aegypti at rates comparable to BG-Sentinel traps in all locations. A peak in male Ae. albopictus captures in MASTs set at 550 Hz was observed, with the lowest mean abundance recorded in MASTs set to 450 Hz. While significantly higher abundances of male Culex were sampled in MASTs emitting lower relative frequencies in Molas, overall male Culex were captured in significantly lower abundances in the MASTs, relative to BG-Sentinel traps within all locations. Finally, significant differences in rates at which male Aedes and Culex were positively detected in trap-types per weekly collections were broadly consistent with trends in abundance data per trap-type. MASTs at 550 Hz effectively captured both male Ae. aegypti and Ae. albopictus while greatly reducing bycatch, especially male Culex, in locations where dengue transmission has occurred. This high species-specificity of the MAST not only reduces staff-time required to sort samples, but can also be exploited to develop an accurate smart-trap system—both outcomes potentially reducing public health program expenses., Author summary The continued global expansion of Aedes aegypti and Aedes albopictus, which transmit viruses causing dengue and Zika, necessitates the further development of effective mosquito traps for monitoring and predicting transmission risk. Mosquito sound traps attract male mosquitoes by producing a frequency which mimics the wingbeat sound of female mosquitoes. As few insects will respond to such sounds, these traps can be highly species-specific, saving significant person-time to sort samples, potentially paving the way for more accurate smart-trap systems and reduced surveillance costs. To date, limited research has occurred within field-settings investigating the capture rates of male mosquitoes in sound traps set to different frequencies. To this point, we performed trials in dengue endemic environments to quantify capture rates of mosquitoes in Male Aedes Sound Traps set to different frequencies in Papua New Guinea, Mexico and Belize. We found that both male Ae. aegypti and Ae. albopictus responded positively to frequencies between 450 and 600 Hz. Additionally, male Culex mosquitoes were also caught, but at lower abundances in traps set to higher sound frequencies. These traps, when set to 550 Hz, effectively capture male Ae. aegypti or Ae. albopictus with limited bycatch.

Background In the absence of vaccines or drugs, insecticides are the mainstay of Aedes-borne disease control. Their utility is challenged by the slow deployment of resources, poor community compliance and inadequate household coverage. Novel application methods are required. Methodology and principal findings A 10% w/w metofluthrin “emanator” that passively disseminates insecticide from an impregnated net was evaluated in a randomized trial of 200 houses in Mexico. The devices were introduced at a rate of 1 per room and replaced at 3-week intervals. During each of 7 consecutive deployment cycles, indoor resting mosquitoes were sampled using aspirator collections. Assessments of mosquito landing behaviours were made in a subset of houses. Pre-treatment, there were no differences in Aedes aegypti indices between houses recruited to the control and treatment arms. Immediately after metofluthrin deployment, the entomological indices between the trial arms diverged. Averaged across the trial, there were significant reductions in Abundance Rate Ratios for total Ae. aegypti, female abundance and females that contained blood meals (2.5, 2.4 and 2.3-times fewer mosquitoes respectively; P, Author summary Insecticidal control tools are heavily relied on for the control of mosquito-borne viruses such as dengue, chikungunya and Zika, but the logistics associated with conventional insecticide use (e.g. space sprays and residual formulations) are challenging. Considerable time and resources are required to treat household interiors; an impediment exacerbated by the difficulty in gaining entrance to households, and sometimes by limited compliance in the community. Another constraint to effective insecticide use is that many mosquito populations are resistant to the chemicals used. Volatile pyrethroids, exhibiting both lethal and behavioural effects on mosquitoes are available in formulations that release insecticides passively to the air, at room temperature. These may be suitable for deployment in houses with the aim of creating “bite-free” spaces. By removing the need for conventional application methods, these devices might be rapidly deployed with minimum disruption to households. This is the first large-scale, randomized control trial to evaluate the entomological impacts of volatile pyrethroids in an urban environment. Using metofluthrin as an example, we confirm that some formulations have a significant impact on Aedes aegypti densities and landing behaviour indoors. These effects occur despite the presence of pyrethroid-resistance alleles associated with conventional insecticide resistance.

Arbovirus infection in Aedes aegypti has historically been quantified from a sample of the adult population by pooling collected mosquitoes to increase detectability. However, there is a significant knowledge gap about the magnitude of natural arbovirus infection within areas of active transmission, as well as the sensitivity of detection of such an approach. We used indoor Ae. aegypti sequential sampling with Prokopack aspirators to collect all mosquitoes inside 200 houses with suspected active ABV transmission from the city of Mérida, Mexico, and tested all collected specimens by RT-PCR to quantify: a) the absolute arbovirus infection rate in individually tested Ae. aegypti females; b) the sensitivity of using Prokopack aspirators in detecting ABV-infected mosquitoes; and c) the sensitivity of entomological inoculation rate (EIR) and vectorial capacity (VC), two measures ABV transmission potential, to different estimates of indoor Ae. aegypti abundance. The total number of Ae. aegypti (total catch, the sum of all Ae. aegypti across all collection intervals) as well as the number on the first 10-min of collection (sample, equivalent to a routine adult aspiration session) were calculated. We individually tested by RT-PCR 2,161 Aedes aegypti females and found that 7.7% of them were positive to any ABV. Most infections were CHIKV (77.7%), followed by DENV (11.4%) and ZIKV (9.0%). The distribution of infected Aedes aegypti was overdispersed; 33% houses contributed 81% of the infected mosquitoes. A significant association between ABV infection and Ae. aegypti total catch indoors was found (binomial GLMM, Odds Ratio > 1). A 10-min indoor Prokopack collection led to a low sensitivity of detecting ABV infection (16.3% for detecting infected mosquitoes and 23.4% for detecting infected houses). When averaged across all infested houses, mean EIR ranged between 0.04 and 0.06 infective bites per person per day, and mean VC was 0.6 infectious vectors generated from a population feeding on a single infected host per house/day. Both measures were significantly and positively associated with Ae. aegypti total catch indoors. Our findings provide evidence that the accurate estimation and quantification of arbovirus infection rate and transmission risk is a function of the sampling effort, the local abundance of Aedes aegypti and the intensity of arbovirus circulation., Author summary Aedes-borne diseases comprise a serious public health burden in many parts of the world, usually affecting low income areas. The ability to detect virus circulation within a population may be key in responding to the threat of outbreaks, providing a cost-effective approach for triggering vector control. Unfortunately, gaps in the knowledge of natural Aedes-borne virus (ABV) infection in Aedes aegypti have led to uncertainties in the consideration of arbovirus surveillance in mosquitoes. Here, we show that the natural infection rate in a mosquito population may not be a function of where Aedes aegypti are, but rather where key human-mosquito contacts occur. Sampling 200 houses with suspected ABV active transmission led us to quantify high virus infection rates in all Aedes aegypti present in the house and use such information to estimate the sensitivity of indoor aspiration with Prokopack devices and two measures of ABV transmission potential. Our findings provide evidence that the accurate quantification of arbovirus infection rate and transmission risk is a function of the sampling effort, the local abundance of Aedes aegypti and the intensity of arbovirus circulation. Results from this study are relevant to understand the value of virus testing of vector populations, and for the design of entomological endpoints relevant for epidemiological trials quantifying the impact of vector control on ABVs.

This study reports the results of a molecular screening for Wolbachia (Wb) infection in Aedes albopictus (Skuse) populations recently established in the Yucatan Peninsula, Mexico. To do so, collections of free-flying adults with BG traps and emerged adults from eggs after ovitrap field collections were performed in three suburban localities of the city of Merida, Yucatan. Overall, local populations of Ae. albopictus present a natural Wb infection rate of ~40% (18 of 45). Wb infection was detected in both field-collected adults (76.5%, 13 of 17) and eggs reared (17.8%, 5 of 28) and in 37.9% (11/29) of females and 43.7% (7/16) of male Ae. albopictus mosquitoes. An initial screening for Wolbachia strain typing showed that native Ae. albopictus were naturally coinfected with both wAlbA and wAlbB strains. The knowledge of the prevalence and diversity of Wolbachia strains in local populations of Aedes mosquitoes is part of the baseline information required for current and future Wolbachia-based vector control approaches to be conducted in Mexico.

Fitting long-lasting insecticidal nets (LLIN) as screens on doors/windows has a significant impact on indoor-adult Aedes aegypti (L.), with entomological reductions measured in a previous study being significant for up to 2 yr post-installation, even in the presence of pyrethroid-resistant Aedes populations. To better understand the mode of LLIN protection, bioassays were performed to evaluate the effects of field deployment (0, 6, and 12 mo) and damage type (none, central, lateral, and multiple) on LLIN efficacy. Contact bioassays confirmed that LLIN residual activity (median knockdown time, in minutes, or MKDT) decreased significantly over time: 6.95 (95% confidence interval [CI]: 5.32–8.58) to 9.24 (95% CI: 8.69–9.79) MKDT at 0- and 12-mo age, respectively, using a pyrethroid-susceptible Aedes strain. Tunnel tests (exposing human forearm for 40 min as attractant) showed that deployment time affected negatively Aedes passage inhibition from 54.9% (95% CI: 43.5–66.2) at 0 mo to 35.7% (95% CI: 16.3–55.1) at 12 mo and blood-feeding inhibition from 65.2% (95% CI: 54.2–76.2) to 48.9% (95% CI: 26.4–71.3), respectively; both the passage/blood-feeding inhibition increased by a factor of 1.8–2.9 on LLINs with multiple and central damages compared with nets with lateral damage. Mosquito mortality was 74.6% (95% CI: 65.3–83.9) at 0 mo, 72.3% (95% CI: 64.1–80.5) at 6 mo, and 59% (95% CI: 46.7–71.3) at 12 mo. Despite the LLIN physical integrity could be compromised over time, we demonstrate that the remaining chemical effect after field conditions would still contribute to killing/repelling mosquitoes.

Background The integration of house-screening and long-lasting insecticidal nets, known as insecticide-treated screening (ITS), can provide simple, safe, and low-tech Aedes aegypti control. Cluster randomised controlled trials in two endemic localities for Ae. aegypti of south Mexico, showed that ITS conferred both, immediate and sustained (~2 yr) impact on indoor-female Ae. aegypti infestations. Such encouraging results require further validation with studies quantifying more epidemiologically-related endpoints, including arbovirus infection in Ae. aegypti. We evaluated the efficacy of protecting houses with ITS on Ae. aegypti infestation and arbovirus infection during a Zika outbreak in Merida, Yucatan, Mexico. Methodology/Principal findings A two-arm cluster-randomised controlled trial evaluated the entomological efficacy of ITS compared to the absence of ITS (with both arms able to receive routine arbovirus vector control) in the neighbourhood Juan Pablo II of Merida. Cross-sectional entomological surveys quantified indoor adult mosquito infestation and arbovirus infection at baseline (pre-ITS installation) and throughout two post-intervention (PI) surveys spaced at 6-month intervals corresponding to dry/rainy seasons over one year (2016–2017). Household-surveys assessed the social reception of the intervention. Houses with ITS were 79–85% less infested with Aedes females than control houses up to one-year PI. A similar significant trend was observed for blood-fed Ae. aegypti females (76–82%). Houses with ITS had significantly less infected female Ae. aegypti than controls during the peak of the epidemic (OR = 0.15, 95%CI: 0.08–0.29), an effect that was significant up to a year PI (OR = 0.24, 0.15–0.39). Communities strongly accepted the intervention, due to its perceived mode of action, the prevalent risk for Aedes-borne diseases in the area, and the positive feedback from neighbours receiving ITS. Conclusions/Significance We show evidence of the protective efficacy of ITS against an arboviral disease of major relevance, and discuss the relevance of our findings for intervention adoption., Author summary We evaluated the efficacy of protecting houses with insecticide-treated nets permanently fixed with aluminium frames on external doors and windows on Ae. aegypti infestation and arbovirus infection during a Zika outbreak in Merida, Yucatan, Mexico. Houses protected with screens were ≈80% less infested with Aedes females and very importantly, had significantly less infected female Ae. aegypti during the peak of the epidemic. Communities strongly accepted the intervention, due to its perceived mode of action, the prevalent risk for Aedes-borne diseases in the area, and the positive feedback from neighbours. House screening provides a simple, affordable sustainable method to reduce human-vector contact inside houses and can protect against dengue, chikungunya and Zika.

Background There is a need for effective methods to control Aedes aegypti and prevent the transmission of dengue, chikungunya, yellow fever and Zika viruses. Insecticide treated screening (ITS) is a promising approach, particularly as it targets adult mosquitoes to reduce human-mosquito contact. Methodology/Principal findings A cluster-randomised controlled trial evaluated the entomological efficacy of ITS based intervention, which consisted of the installation of pyrethroid-impregnated long-lasting insecticide-treated netting material fixed as framed screens on external doors and windows. A total of 10 treatment and 10 control clusters (100 houses/cluster) were distributed throughout the city of Merida, Mexico. Cross-sectional entomological surveys quantified indoor adult mosquito infestation at baseline (pre-intervention) and throughout four post-intervention (PI) surveys spaced at 6-month intervals corresponding to dry/rainy seasons over two years (2012–2014). A total of 844 households from intervention clusters (86% coverage) were protected with ITS at the start of the trial. Significant reductions in the indoor presence and abundance of Ae. aegypti adults (OR = 0.48 and IRR = 0.45, P, Author summary An ITS based intervention, screened houses with insecticide-treated netting (long-lasting insecticidal nets permanently fixed with aluminium frames on external doors and windows), in Merida city, Mexico. Screened houses had >50% less chance of having Ae. aegypti mosquitoes indoors and importantly, >50% fewer female Ae. aegypti in comparison with non-screened houses (control houses). The impact was sustained over 2 years. House screening could provide a feasible sustainable method to reduce human-vector contact inside houses and could potentially be scaled up to protect against mosquito-borne diseases, particularly in locations where the simultaneous transmission, or threat, of dengue, chikungunya, yellow fever and Zika is occurring.

The operational impact of deltamethrin resistance on the efficacy of indoor insecticide applications to control Aedes aegypti was evaluated in Merida, Mexico. A randomized controlled trial quantified the efficacy of indoor residual spraying (IRS) against adult Ae. aegypti in houses treated with either deltamethrin (to which local Ae. aegypti expressed a high degree of resistance) or bendiocarb (to which local Ae. aegypti were fully susceptible) as compared to untreated control houses. All adult Ae. aegypti infestation indices during 3 months post-spraying were significantly lower in houses treated with bendiocarb compared to untreated houses (odds ratio, Author summary Insecticide resistance has emerged as a worrisome outlook for the implementation of insecticide-only approaches. Particularly for Aedes aegypti, it is generally argued that this rapid rise of insecticide resistance may compromise the effectiveness of control programs. Yet, empirical evidence of such negative operational impact is lacking. This article provides quantitative evidence of the impact of insecticide resistance, primarily to the pyrethroid insecticide deltamethrin, on the entomological effectiveness of interventions against Aedes aegypti mosquitoes. Within an area of high resistance to pyrethroids, performing high-quality insecticide applications using deltamethrin had no entomological impact in comparison to the application of an insecticide to which Ae. aegypti was susceptible. Deltamethrin did not protect against resistant Ae. aegypti, whereas the application of bendiocarb led to an average efficacy of 60% during a 3-month period. This study provides strong evidence of the dramatic operational treatment failure that can occur when the background insecticide resistance level of Ae. aegypti populations is not taken into consideration when performing vector control.

Dengue is one of the most important vector-borne diseases worldwide and is a public health problem in Mexico. Most programs in dengue endemic countries rely on insecticides for Aedes control. In Mexico, pyrethroid insecticides (mainly permethrin and deltamethrin) have been extensively used over a decade as adulticides and represented a strong selection for insecticide resistance for dengue vectors in several parts of the country. We studied the type, frequency and distribution of insecticide resistance mechanisms in Aedes aegypti from six municipalities in the state of Guerrero selected on the basis of historically intense chemical control and a high risk for dengue transmission. Ae. aegypti eggs were collected from October 2009 to January 2010 using ovitraps. F1 adults, emerged from these collections, were exposed to permethrin, deltamethrin and DDT in WHO diagnostic tests and showed high resistance levels to both pyrethroids and DDT. This was consistent with the presence of increased metabolic enzyme activities and target site insensitivity due to kdr mutations. Biochemical assays showed elevated esterase and glutathione S-transferase activities in the six municipalities. The V1016I kdr mutation on the IIS6 domain of the sodium channel gene was present in an overall frequency of 0.80. A second mutation, F1534C on the IIIS6 domain of the same gene was also detected, being the first report of this mutation in Guerrero. The multiple resistance mechanisms present in Ae. aegypti from Guerrero state represent a warning for the efficacy of the pyrethroid usage and consequently for the success of the dengue control program.

OBJETIVO: Determinar la importancia relativa de los tipos de criadero de Aedes aegypti para proponer intervenciones de control enfocadas en Morelos. MATERIAL Y METODOS: Se realizaron muestreos transversales con colecta de pupas en Cuautla, Jojutla y Tlaquiltenango en temporada de sequia (1713 casas) y lluvias (1677) del ano 2008. La importancia relativa de cada tipo de criadero se determino por su contribucion (%) a la produccion pupal total por localidad. RESULTADOS: En Cuautla, la mayoria de pupas se recolectaron en temporada de sequia de tanques/pilas (48.5%), tambos y botes/cubetas (15% c/u); en lluvias, los diversos chicos (21.3%), botes/cubetas (19.3%) y macetas/macetones (12.9%) fueron mas productivos. En Jojutla y Tlaquiltenango, 97% de las pupas se colectaron de macetas/macetones en secas; durante las lluvias la mayoria de pupas se recolectaron de diversos chicos (26.3%), trastes de cocina/lavado (13.9%), botes/cubetas (12.9%) y macetas/macetones (12.7%), respectivamente. CONCLUSION: La prevencion y control del vector del dengue deben basarse en este tipo de evidencias para focalizar las acciones sobre los criaderos mas productivos.

Background \ud Long-lasting insecticidal net screens (LLIS) fitted to domestic windows and doors in combination with targeted treatment (TT) of the most productive Aedes aegypti breeding sites were evaluated for their impact on dengue vector indices in a cluster-randomised trial in Mexico between 2011 and 2013.\ud \ud Methods \ud Sequentially over 2 years, LLIS and TT were deployed in 10 treatment clusters (100 houses/cluster) and followed up over 24 months. Cross-sectional surveys quantified infestations of adult mosquitoes, immature stages at baseline (pre-intervention) and in four post-intervention samples at 6-monthly intervals. Identical surveys were carried out in 10 control clusters that received no treatment.\ud \ud Results \ud LLIS clusters had significantly lower infestations compared to control clusters at 5 and 12 months after installation, as measured by adult (male and female) and pupal-based vector indices. After addition of TT to the intervention houses in intervention clusters, indices remained significantly lower in the treated clusters until 18 (immature and adult stage indices) and 24 months (adult indices only) post-intervention.\ud \ud Conclusions \ud These safe, simple affordable vector control tools were well-accepted by study participants and are potentially suitable in many regions at risk from dengue worldwide.

Dengue prevention efforts rely on control of virus vectors. We investigated use of insecticide-treated screens permanently affixed to windows and doors in Mexico and found that the screens significantly reduced infestations of Aedes aegypti mosquitoes in treated houses. Our findings demonstrate the value of this method for dengue virus vector control.

We carried out dengue virus surveillance in Aedes aegypti populations from 47 neighborhoods of Acapulco during the rainy season of 2011 following a standard national protocol and as an improvement of the entomological surveillance of the Mexican Dengue Control Program. A total of 4,146 Ae. aegypti adults collected indoors and/or emerged from eggs, larvae, or pupae from households with dengue reports (probable or confirmed cases), were grouped into pools and processed using a standardized serotype-specific 4-plex real-time reverse transcriptase-polymerase chain reaction assay. Overall, only 2 (0.9%) of 226 pools of Ae. aegypti adults (1 pool of adults emerged from field-collected larvae, and another of indoor-collected adults) were positive for dengue virus 1 (DENV-1). This is appears to be the 1st report of evidence on the vertical and transovarial transmission of DENV-1 in field-caught Ae. aegypti in Mexico.

We compared the number of adult Aedes aegypti emerging from subsurface catch basins located in the streets against the number of pupae (as a proxy of adults emerging) from the entire container larval habitats found at residential premises within 1 ha of a neighborhood in the Mexican city of Merida during 8 days in the dry season of 2012. Aedes aegypti adults were collected from 60% of the subsurface catch basins. They produced 12 adults/day/ha (95% confidence interval [CI], 6.4 to 17.9), 5 females (95% CI, 2.1 to 7.7), and 7 males (95% CI, 3.8 to 10.7). In contrast, only 7 containers holding water were identified in 30 premises inspected, 1 bucket was positive for Ae. aegypti larvae, but no pupae-positive containers were found. No other mosquito species were found. This study revealed the importance of this type of nonresidential and subterranean aquatic habitat for Ae. aegypti adult production in this neighborhood of Merida during the dry season.

We report the collection of Aedes aegypti, Culex quinquefasciatus, Cx. interrogator, Cx. thriambus, Cx. coronator, and Cx. salinarius larvae from storm sewers within an endemic area for dengue transmission in Merida, Mexico, during the rainy season of 2011. This is the first record of the dengue vector Ae. aegypti breeding in storm sewers in the southeast of Mexico.

Background Dengue is a major public health problem in Mexico, where the use of chemical insecticides to control the principal dengue vector, Aedes aegypti, is widespread. Resistance to insecticides has been reported in multiple sites, and the frequency of kdr mutations associated with pyrethroid resistance has increased rapidly in recent years. In the present study, we characterized patterns of insecticide resistance in Ae. aegypti populations in five small towns surrounding the city of Merida, Mexico. Methods A cross-sectional, entomological survey was performed between June and August 2013 in 250 houses in each of the five towns. Indoor resting adult mosquitoes were collected in all houses and four ovitraps were placed in each study block. CDC bottle bioassays were conducted using F0-F2 individuals reared from the ovitraps and kdr allele (Ile1016 and Cys1534) frequencies were determined. Results High, but varying, levels of resistance to chorpyrifos-ethyl was detected in all study towns, complete susceptibility to bendiocarb in all except one town, and variations in resistance to deltamethrin between towns, ranging from 63–88 % mortality. Significant associations were detected between deltamethrin resistance and the presence of both kdr alleles. Phenotypic resistance was highly predictive of the presence of both alleles, however, not all mosquitoes containing a mutant allele were phenotypically resistant. An analysis of genotypic differentiation (exact G test) between the five towns based on the adult female Ae. aegypti collected from inside houses showed highly significant differences (p