A rapid identification guide for larvae of the most common North American container-inhabiting Aedes species of medical importance

Mosquito abundance and diversity in central Ohio, USA vary among stormwater wetlands, retention ponds, and detention ponds and their associated environmental parameters

Mosquitoes (Diptera: Culicidae) are one of the most impactful pests to human society, both as a nuisance and a potential vector of human and animal pathogens. Mosquito larvae develop in still aquatic environments. Eliminating these habitats near high human density or managing them to reduce the suitability for mosquitoes will reduce mosquito populations in these human environments and decrease the overall negative impact of mosquitoes on humans. One common source of standing water in urban and suburban environments is the water that pools in stormwater control measures. Previous studies have shown that some stormwater control measures generate large numbers of mosquitoes while others harbor none, and the reason for this difference remains unclear. Our study focuses on elucidating the factors that cause a stormwater control measure to be more or less suitable for mosquitoes. During the summers of 2021 and 2022, we collected and identified mosquito larvae from thirty stormwater control measures across central Ohio to assess variation in mosquito abundance and diversity among sites. Our goal was to determine if specific types of stormwater control measures (retention ponds, detention ponds, or constructed wetlands) harbored different abundances of mosquitoes or different community structures. We also assessed environmental parameters of these sites to elucidate their effects on mosquito abundance and diversity. Overall, we recorded the highest number of mosquito larvae and species in constructed wetlands. However, these sites were dominated by the innocuous species, Culex territans. Conversely, detention ponds held fewer mosquitoes but a higher proportion of known vector species, including Culex pipiens and Aedes vexans. The total number of mosquitoes across all sites was correlated with higher vegetation, more shade, lower water temperatures, and lower pH, suggesting stormwater control measures with these features may also be hotspots for mosquito proliferation.

First Record of Aedes Japonicus in St. Tammany Parish, Louisiana

Information of species presence and abundance is useful for taking a targeted approach to controlling populations of medically important and nuisance mosquito species. In April 2023, staff at St. Tammany Parish Mosquito Abatement District (STPMAD), in Slidell, Louisiana, identified Aedes japonicus (Theobald, 1901) mosquitoes from a larval sample brought in from the field for identification. Although invasive Aedes species like Aedes albopictus are commonly found in Louisiana, this is the first record of Ae. japonicus in St. Tammany Parish.

Insecticide susceptibility status on Aedes aegypti (Linn) and Aedes albopictus (Skuse) of Chittorgarh district, Rajasthan, India

Vector-borne diseases are a major burden to human health. It accounts for more than 17% of the total infectious diseases and causes more than 0.7 million deaths annually. Mosquitoes are potential vectors for many vector-borne diseases that cause illness to public health, globally. Vector species of the genus Aedes i.e., Aedes aegypti and Aedes albopictus are the vector for many arboviruses such as dengue, chikungunya, yellow fever, and Zika in India. Dengue is one of the most prevalent viral infections causing a high number of cases throughout the world and resistance to insecticides can be a reason for the failure of vector control strategies. This study was carried out to check the degree of resistance among these vectors in the Chittorgarh district of Rajasthan, India through standard World Health Organization protocol. The resistance was monitored to pyrethroids i.e., deltamethrin (0.05%), permethrin (0.75%), alphacypermethrin (0.05%); organochlorine i.e., DDT (4%), and an organophosphate larvicide i.e., temephos (0.02 mg/L) in both vector species. Complete resistance to DDT was observed among all tested populations of both species. All tested populations of Aedes albopictus were found susceptible to pyrethroids. Aedes aegypti was found resistant in the Mangalwad population, unconfirmed resistant in Bhopalsagar and Rashmi populations while the remaining are susceptible to permethrin. The Mangalwad population was also found unconfirmed resistant to deltamethrin and alphacypermethrin. Larvae of both species were found susceptible to temephos. Decreasing the use of DDT will help to reduce the impact on human health and environmental contamination. However, temephos as a larvicide, deltamethrin, and alphacypermethrin as an adulticide can be used in critical disease outbreaks at a minimum concentration as mosquitoes are found susceptible in the study area.

Origins of high latitude introductions of Aedes aegypti to Nebraska and Utah during 2019

Aedes aegypti (L.), the yellow fever mosquito, is also an important vector of dengue and Zika viruses, and an invasive species in North America. Aedes aegypti inhabits tropical and sub-tropical areas of the world and in North America is primarily distributed throughout the southern US states and Mexico. The northern range of Ae. aegypti is limited by cold winter months and establishment in these areas has been mostly unsuccessful. However, frequent introductions of Ae. aegypti to temperate, non-endemic areas during the warmer months can lead to seasonal activity and disease outbreaks. Two Ae. aegypti incursions were reported in the late summer of 2019 into York, Nebraska and Moab, Utah. These states had no history of established populations of this mosquito and no evidence of previous seasonal activity. We genotyped a subset of individuals from each location at 12 microsatellite loci and ~ 14,000 single nucleotide polymorphic markers to determine their genetic affinities to other populations worldwide and investigate their potential source of introduction. Our results support a single origin for each of the introductions from different sources. Aedes aegypti from Utah likely derived from Tucson, Arizona, or a nearby location. Nebraska specimen results were not as conclusive, but point to an origin from southcentral or southeastern US. In addition to an effective, efficient, and sustainable control of invasive mosquitoes, such as Ae. aegypti, identifying the potential routes of introduction will be key to prevent future incursions and assess their potential health threat based on the ability of the source population to transmit a particular virus and its insecticide resistance profile, which may complicate vector control.

Assessing the distribution of invasive Asian mosquitoes in Northern Italy and modelling the potential spread of Aedes koreicus in Europe

In the last decade, Aedes koreicus and Aedes japonicus japonicus mosquitoes, which are competent vectors for various arboviruses of public health relevance, colonised Italy and other European countries. Nevertheless, information about their current and potential distribution is partial. Accordingly, in this study four regions of Northern Italy (Lombardy, Liguria, Piedmont and Aosta Valley) were surveyed during 2021 for the presence of eggs, larvae and pupae of these two invasive species. We found evidence for a widespread presence of Ae. koreicus in pre-Alpine territories of Lombardy and Piedmont. Larvae from the invasive subspecies of Ae. j. japonicus were also collected in the same geographic areas, though they were less frequent. Occurrence data from this study and results from previous monitoring campaigns were used to generate a Maxent model for the prediction of habitat suitability for Ae. koreicus mosquitoes in Northern Italy and the rest of Europe. Peri-urban areas located in proximity to forests, pastures and vineyards were revealed as highly suitable environments for colonisation by this invasive species. Maps of the potential distribution also suggest the presence of further suitable areas in currently uncolonized countries. We conclude that this invasive mosquito species has the potential for a broad expansion at the European level in the coming decades.

The role of anthropogenic container habitats as mosquito oviposition habitats in rural settlements in northern Tanzania

In many areas, the main sources of mosquito vectors are not natural habitats but small artificial water bodies that are provided unintentionally by humans. Such container habitats have been linked to outbreaks of dengue fever and other arboviral diseases. However, in many parts of the world the possible risks associated with container habitats have not been assessed. Here, we focused on a human population expansion area in northern Tanzania with a high incidence of dengue and other cases of high fever. We explored the importance of anthropogenic container habitats for mosquito production in the Lake Manyara Basin. We also assessed how biotic and physicochemical habitat characteristics limit mosquito abundance in containers. Results showed that Aedes aegypti (Linnaeus), vector of dengue and other arboviruses, and Culex quinquefasciatus (Say), vector of filarial worms, were the dominant mosquitoes ovipositing in large numbers in different containers. Old tires were the dominant and most productive container habitat for mosquitoes in the region. However, there were strong differences among villages, illustrating that the mosquito burden associated with container habitats varies locally. We concluded that in this region, removal of artificial container habitats could be a simple strategy to reduce the mosquito-mediated disease burden within the local population.

The Effectiveness of Net to Reduce the Entomological Indices in Dengue-Endemic Areas in Balikpapan, Indonesia

BACKGROUND: Drums and cisterns are ubiquitous water storages in Indonesian households, seldom being drained and left open to create access for the rainwater, providing a favorable breeding site for dengue vector. The bigger the container, the more it produces immature mosquitoes that are soon to be mature, increasing the entomological indices and raising the potency of cases in the area. Previous studies revealed that the net covering the reservoir was able to effectively protect the water from mosquito oviposition; therefore, a modification of the net was made. AIM: The aim of this study is to discover whether the net as a cover for water containers is effective in reducing the entomological indices in dengue-endemic areas. METHODS: The quasi-experimental study with pretest and posttest control group design, involved 3 intervention and 3 control clusters, 150 houses which have 672 water-holding containers with 116 large containers were intervened with non-insecticide tulle nets for 3 months. The larval presence data were performed by larval survey. RESULTS: It revealed that net reduced the container index (CI) in intervened large containers 18%–84% as well as the environment entomological indices in general in study areas: CI decreased 75%–79%, house index decreased 65%–70%, and Breteau index decreased 75.5%–78.7%, while Free Larva Index rose 73.7%–88%. CONCLUSIONS: The nets had lowered the CI in the intervened large container and affected the entomological indices of the surrounding environment, by blocking the mosquitos-water contact and preventing the young mosquitos that had developed in the containers from flying out.

Keep your natural enemies close - native predators can maintain low mosquito densities in temporary ponds in a malaria expansion area in Northern Tanzania

Mosquitoes and the diseases they transmit are a global public health threat that affects most human populations. Mosquito abundances are strongly linked to the number of suitable larval habitats available. However, it is still not well understood how different land uses impact larval habitat quality in different parts of the world. We investigated links between land use practices and abundance of mosquito larvae in temporary ponds located in different land uses in a malaria expansion zone in Tanzania. Temporary ponds are often cited as important sources of mosquitoes but are also of substantial conservation concern being home to a unique fauna and flora. Often, they also have high socio-economic importance. Overall, encountered mosquito larval abundances were very low, both for the collected Anopheles gambiae s.l. and Culex quinquefasciatus. Although temporary ponds are important mosquito larval habitats in other parts of Africa, currently they are unlikely to be an important factor affecting the prevalence of mosquito borne diseases in the Manyara study region. Larval abundances in temporary ponds were higher in agricultural areas where more eutrophic conditions were found and minimal in residential areas. Overall, even though temporary ponds are often modified as rice paddies in the rainy season, they were in a good ecological condition and hosted a diverse assemblage of aquatic predators that likely prevented larval mosquitoes from reaching high densities. Maintaining this good condition by preventing pesticide and nutrient input as much as possible, can be important to prevent pond degradation that is likely to make these habitats more suitable for mosquitoes in the future.

Occurrence of the Mosquito Aedes triseriatus (Diptera: Culicidae) Beyond Its Most Northwestern Range Limits in Manitoba, Canada

Native to the Eastern United States and Eastern Canada, Aedes triseriatus (eastern tree hole mosquito) is an important vector of La Crosse virus and dog heartworm. Although its range has been well characterized in the United States, few studies have surveyed its distribution within Canada. In this study, mosquitoes were collected from a variety of urban and rural communities throughout Manitoba, Canada between the years of 2018 and 2020. Aedes triseriatus was identified and confirmed molecularly to be present in 13 communities. This includes localities that expand the species known distribution to new northern and western areas, and suggests that past surveillance efforts have not been comprehensive or environmental factors have caused this mosquito species to be present in areas in which it was not found previously. As Canada is showing signs of a changing climate, this may be driving the broader occurrence of Ae. triseriatus.

Diapause characterisation and seasonality of Aedes japonicus japonicus (Diptera, Culicidae) in the northeast of France

The invasive mosquito Aedes japonicus japonicus (Theobald, 1901) settled in 2013 in the Alsace region, in the northeast of France. In this temperate area, some mosquito species use diapause to survive cold winter temperatures and thereby foster settlement and dispersal. This study reports diapause and its seasonality in a field population of Ae. japonicus in the northeast of France. For two years, eggs were collected from May to the beginning of November. They were most abundant in summer and became sparse in late October. Diapause eggs were determined by the presence of a fully developed embryo in unhatched eggs after repeated immersions. Our study showed effective diapause of Ae. japonicus in this part of France. At the start of the egg-laying period (week 20), we found up to 10% of eggs under diapause, and this rate reached 100% in October. The 50% cut-off of diapause incidence was determined by the end of summer, leading to an average calculated maternal critical photoperiod of 13 h 23 min. Interestingly, diapause was shown to occur in part of the eggs even at the earliest period of the two seasons, i.e. in May of each year. Even though we observed that the size of eggs was positively correlated with diapause incidence, morphology cannot be used as the unique predictive indicator of diapause status due to overlapping measurements between diapausing and non-diapausing eggs. This study provides new knowledge on diapause characterisation and invasive traits of Ae. japonicus.

Natural Vertical Transmission of Dengue Virus Serotype 4 in Aedes aegypti Larvae from Urban Areas in Sinaloa, Mexico

Dengue virus (DENV) is transmitted to humans by the bite of the vector Aedes aegypti. Several researchers have suggested that the mechanism of vertical transmission of DENV in the vector is a key aspect for the prevalence of the virus in the environment and the potentiation of epidemic outbreaks of the disease. In this context and as part of an integrated study of DENV serotypes in mosquitoes of urban areas in Sinaloa, Mexico, the presence of DENV-4 in larval stages of Ae. aegypti was evaluated to demonstrate the vertical transmission of this serotype. In total, 672 larvae of Ae. aegypti were collected in 16 sectors and were grouped into 36 pools, of which 41.66% (15/36 pools) tested positive for DENV-4, with a minimum infection rate = 22.32. The analysis of the obtained sequences showed a 98% similarity to the DENV-4 with sequences previously reported in GenBank. These results show that Ae. aegypti acts as a natural reservoir for DENV-4 in this region.

The larval environment strongly influences the bacterial communities of Aedes triseriatus and Aedes japonicus (Diptera: Culicidae)

Mosquito bacterial communities are essential in mosquito biology, and knowing the factors shaping these bacterial communities is critical to their application in mosquito-borne disease control. This study investigated how the larval environment influences the bacterial communities of larval stages of two container-dwelling mosquito species, Aedes triseriatus, and Aedes japonicus. Larval and water samples were collected from tree holes and used tires at two study sites, and their bacteria characterized through MiSeq sequencing of the 16S rRNA gene. Bacterial richness was highest in Ae. japonicus, intermediate in Ae. triseriatus, and lowest in water samples. Dysgonomonas was the dominant bacterial taxa in Ae. triseriatus larvae; the unclassified Comamonadaceae was dominant in water samples from waste tires, while Mycobacterium and Carnobacterium, dominated Ae. japonicus. The two mosquito species harbored distinct bacterial communities that were different from those of the water samples. The bacterial communities also clustered by habitat type (used tires vs. tree holes) and study site. These findings demonstrate that host species, and the larval sampling environment are important determinants of a significant component of bacterial community composition and diversity in mosquito larvae and that the mosquito body may select for microbes that are generally rare in the larval environment.

Surveillance for Zika in Mexico: naturally infected mosquitoes in urban and semi-urban areas

Zika cases have been reported in 29 out of the 32 states of Mexico. Information regarding which mosquito species might be driving Zika virus transmission/maintenance in nature must be regularly updated. From January 2017 to November 2018, mosquitoes were collected indoors and outdoors using the CDC backpack aspirator in urban and semi-urban areas with evidence of mosquito-borne disease transmission. 3873 mosquito pools were tested for Zika infection using the CDC Trioplex real-time RT-PCR. For each collected specie, maximum likelihood estimator of infection rate (MLE) was estimated. Results showed 492 mosquito pools positive for Zika virus RNA. The majority of the positive pools were Aedes (Stegomyia) aegypti (Linnaeus) (54.6%, MLE = 19) (males and females) and Culex (Culex) quinquefasciatus (Say) (19.5%, MLE = 16.8). For the first time, ZIKV infection was detected in Ae. (Georgecraigius) epactius (Dyar and Knab) (MLE = 17.1), Cx. (Melanoconion) erraticus (Dyar and Knab) (MLE = non-estimable), Culiseta (Culiseta) inornata (Williston) (MLE = non estimable), and Cs (Cs.) particeps (Adams) (MLE = 369.5). Other detected species were: Ae. (Stg.) albopictus (Skuse) (MLE = 90.5), Cx. (Cx.) coronator s.l. (Dyar and Knab) (MLE = 102.8) and Cx. (Cx.) tarsalis (Coquillett) (MLE = 117.2). However, our results do not allow for the incrimination of these species as vectors of ZIKV. Routine surveillance should start to consider other mosquito species across the taxonomic spectrum of the Culicidae.

Trap Comparison for Surveillance of the Western Tree Hole Mosquito (Diptera: Culicidae)

The western tree hole mosquito, Aedes sierrensis (Ludlow), is a common nuisance mosquito and vector of Dirofilaria immitis (Leidy), the etiologic agent of dog heartworm, in western North America. Here, we compare weekly mosquito collections made with Mosquito Magnet (MM) traps, Biogents Sentinel (BGS) traps, and Biogents Bowl (BGS Bowl) traps set in Salt Lake City, UT, from the start of June to mid-August 2017. We found the number of mosquitoes decreased with rainfall and temperature independently of trap type. The highest number of mosquitoes were caught by BGS traps baited with carbon dioxide (CO2) and BG lure, which collected 62% (n = 422) of all mosquitoes, followed by the MM at 31% (n = 213), and both the BGS and BG Bowl with BG lure had 3.5% (n = 24) each. Aedes sierrensis females were caught weekly at similar densities (mean ± SD) in BGS with CO2 and lure (1.17 ± 2.93) and the MM (1.17 ± 2.66) traps during the study period. Given that BGS with CO2 and lure traps have several operational advantages over MM traps, including a quicker setup, smaller size, and lower cost, we consider BGS with CO2 and lure traps as the best suited surveillance tool to detect and remove Ae. sierrensis in the western United States and similar settings throughout North America.

Active dispersal of Aedes albopictus: a mark-release-recapture study using self-marking units

BACKGROUND

Understanding the dispersal dynamics of invasive mosquito species is fundamental to improve vector surveillance and to target control efforts. Aedes albopictus has been deemed a poor flyer as its range of active dispersal is generally assumed to be limited to a few hundred metres, while laboratory studies suggest this mosquito could actually fly several kilometres. The discrepancy may be due to differences in the local environment or to the methodological approach. In Switzerland, Ae. albopictus has been present since 2003 and has since then expanded its range. While passive dispersal is a key driver, it remains unclear how far this mosquito spreads through active flight and what the age structure and size of the local population are, all important parameters for vector surveillance and control.

METHOD

We investigated the active dispersal, daily survival rate and population size of Ae. albopictus in mark-release-recapture studies in Coldrerio and Lugano, two areas of intensive control in Switzerland. To mark mosquitoes emerging from breeding sites, we used self-marking units with fluorescent pigment that have minimal impact on mosquito survival and behaviour. We recaptured the adult mosquitoes with BG-Sentinel traps within a radius of 1 km from the marking units over 22 consecutive days.

RESULTS

We found that 77.5% of the recaptured Ae. albopictus individuals flew further than 250 m, the limit that is usually deemed sufficient for vector containment. The average age of females and males was 8.6 days and 7.8 days in Coldrerio and Lugano, respectively, while the estimated mosquito population densities were 134 mosquitoes/ha in Coldrerio and 767 mosquitoes/ha in Lugano.

CONCLUSIONS

Self-marking units are an effective tool to mark wild mosquitoes. Using this approach, we found that mosquitoes survive long enough to potentially transmit arboviral disease in our study area and that host-seeking Ae. albopictus females may travel further than previously assumed for European mosquito populations. This finding has direct implications for vector control as emergency treatments around positive cases, as well as surveillance and control around detections of new infestations, might need to be extended beyond the usual recommended range of just a few hundred metres.

Characteristics of water containers influencing the presence of Aedes immatures in an ecotourism area of Bang Kachao Riverbend, Thailand

Purpose

The purpose of this paper is to investigate the influence of breeding containers on the production of Aedes mosquitoes after a vector-control program in households that might support dengue transmission in tourist attraction areas of Bang Kachao Riverbend, Thailand.

Design/methodology/approach

A cross-sectional study was conducted in an ecotourism area of Bang Kachao Riverbend, Thailand, during the period October 2016 to September 2017. A total of 832 households from five villages participated in the study. Data collection employed an interview questionnaire, larval mosquito survey and measurements of the chemical properties of the water in each container. A binary logistic regression model was used to investigate the characteristics of water containers influencing the presence or absence of Aedes immatures.

Findings

The study found that water containers located inside households had a highly presence of Aedes immatures (2.22 times) compared with outdoor containers. Water containers without lids and water containers with ineffective had a high presence of Aedes immatures (3.69 and 2.54 times, respectively). In addition, the chemical properties of the water inside the containers, such as pH, influenced the presence of Aedes immatures (1.76 times) (OR=1.76, 95% CI=1.59–1.96).

Originality/value

The study results emphasized the characteristics of water containers in households located in a tourist attraction area. The findings may inform public health vector-control messages for households located in the tourist attraction area.

Aedes Mosquito Infestation in Socioeconomically Contrasting Neighborhoods of Panama City

The global expansion and proliferation of Aedes aegypti and Aedes albopictus represents a growing public health threat due to their capacity to transmit a variety of arboviruses to humans, including dengue, chikungunya, and Zika. Particularly important in urban regions, where these species have evolved to breed in man-made containers and feed nearly exclusively on human hosts, the threat of vector-borne disease has risen in recent decades due to the growth of cities, progression of climate change, and increase in globalization. While the dynamics of Aedes populations in urban settings have been well studied in relation to ecological features of the landscape, relatively less is known about the relationship between neighborhood socioeconomic status and Aedes infestation. Here, we compare infestation levels of both A. aegypti and A. albopictus in four socioeconomically contrasting neighborhoods of urban Panama City, Panama. Our results indicate that infestation levels for both Aedes species vary between neighborhoods of contrasting socioeconomic status, being higher in neighborhoods having lower percentage of residents with bachelor degrees and lower monthly household income. Additionally, we find that proximity between socioeconomically contrasting neighborhoods can predict infestation levels by species, with A. aegypti increasing and A. albopictus decreasing with proximity between neighborhoods. These findings hold key implications for the control and prevention of dengue, chikungunya, and Zika in Panama, a region with ongoing arbovirus outbreaks and high economic inequity.

Insecticide resistance in Aedes albopictus Skuse from sub-Himalayan districts of West Bengal, India

Dengue is one of the most rapidly spreading infectious diseases prevalent throughout the tropical and sub-tropical regions of the world. In absence of specific medications and vaccines, the sole method of disease prevention relies on vector control mainly using insecticides. But with the advent of Insecticide resistance, worldwide vector control programs are facing failure. In this study, eleven different Ae. albopictus population from sub-Himalayan districts of West Bengal, India were investigated as per WHO protocols to find out the current status of insecticide susceptibility against DDT, permethrin and propoxur. Also the role of three insecticide detoxifying enzymes underlying observed resistance was investigated through quantitative and synergistic assays to unveil the mechanism of insecticide resistance. It was found that majority of studied populations were resistant to 4% DDT. Two populations, namely Alipurduar (APD) and Jalpaiguri (JPG) were severely resistant to 0.75% permethrin, whereas only JPG population was found to exhibit severe resistance against 0.1% propoxur. Moreover, the involvement of detoxifying enzymes was also noted in conferring resistance against DDT and Permethrin. This study indicates the inefficacy of DDT in controlling Ae. albopictus populations in the study region. This study may help in implementation of an efficient vector control and insecticide resistance management strategies.

First Detection of Aedes albopictus (Diptera: Culicidae) and Expansion of Aedes japonicus japonicus in Wisconsin, United States

The 2015-2016 epidemic of Zika virus in the Americas raised concerns about the range of Aedes albopictus (Skuse) in the United States. In response, the University of Wisconsin Medical Entomology Laboratory coordinated with the Wisconsin Department of Health Services in 2016 to conduct Aedes spp. surveillance and set up an oviposition trap (ovitrap) network operated by local public health partners across southern and western Wisconsin. During 2016, 916 ovitrap events were processed, but only Aedes triseriatus Say (Diptera: Culicidae) and Aedes japonicus japonicus (Theobald) were detected. In 2017, a focused surveillance approach was employed to detect Ae. albopictus near sites with tires stored outdoors. Using this targeted approach, Ae. albopictus was detected from ovitraps in two out of seven counties surveyed during June, July, and August. This is the first record of Ae. albopictus in Wisconsin.

Effects of Plant Species, Insecticide, and Exposure Time On the Efficacy Of Barrier Treatments Against Aedes albopictus

The effect of 5 plant species (arborvitae [Thuja occidentalis], boxwood [Buxus sp., Japanese honeysuckle [Lonicera japonica], rhododendron [Rhododendron sp.], and zebra grass [Miscanthus sinensis]) and 2 rates of lambda-cyhalothrin (3.13 ml and 6.25 ml active ingredient [AI]/liter) on knockdown (1 h) and mortality (24 h) of adult female Aedes albopictus was evaluated over an 8-wk period. A significant difference in knockdown was observed between the 2 rates of lambda-cyhalothrin on the 5 plant species, with the highest proportion of knockdown observed on zebra grass and rhododendron treated at the higher rate. Although mortality was ≥60% and 85% on the 5 plant species at the low and high rates of lambda-cyhalothrin, respectively, a significant difference between the 2 rates was only observed on boxwood and Japanese honeysuckle (P < 0.0001). We also tested the residual toxicity of 3 barrier sprays (lambda-cyhalothrin, bifenthrin, and deltamethrin) and evaluated the efficacy of a short (5-min) exposure to the insecticides on knockdown and mortality of adults over time. Significantly higher knockdown was observed with lambda-cyhalothrin compared with bifenthrin and deltamethrin (P < 0.0001). Mean knockdown was ∼98%, 92%, and 20% for lambda-cyhalothrin, bifenthrin, and deltamethrin, respectively, at week 2, and ∼98%, 0%, and 44%, respectively, 8 wk after treatments were applied. Adult mortality from the 3 chemical treatments, however, remained above 90% throughout the study. Lastly, the trends in mean proportion of knockdown were similar for mosquitoes exposed for either 5 min or 24 h to the 3 chemicals. An overall decline in mean mortality over time, however, was observed for mosquitoes exposed for 5 min to the chemicals compared with mortality from the 24-h exposure. The results suggest that lambda-cyhalothrin can be an effective barrier spray treatment against Ae. albopictus adults because its efficacy is limited little by plant species, it has long residual toxicity, and it is effective following only 5 min of exposure.

Assessment of insecticide resistance in primary dengue vector, Aedes aegypti (Linn.) from Northern Districts of West Bengal, India

Aedes mosquitoes are the major vectors transmitting several arboviral diseases such as dengue, zika and chikungunya worldwide. Northern districts of West Bengal is home to several epidemics vectored by mosquito including dengue infections, proper control of which depends on efficient vector control. However the onset of insecticide resistance has resulted in failure of vector control approaches. This study was carried out to unveil the level of insecticide resistance prevailing among the primary dengue vector in this dengue endemic region of India. It was observed that, field caught populations of Ae. aegypti were moderately to severely resistant to majority of the insecticide classes tested, i.e. Organochlorine (DDT), Organophosphates (temephos, malathion), Synthetic Pyrethroids (deltamethrin, lambdacyhalothrin and permethrin) and carbamate (propoxur). In majority of the populations, metabolic detoxification seemed to play the underlying role behind the development of insecticide resistance. This study seems to be the first report revealing the pattern of insecticide resistance in Ae. aegypti from Northern West Bengal. Efficient disease management in this region can only be achieved through proper insecticide resistance management. This study may help the concerned authorities in the formulation of an effective vector control strategy throughout this region incorporating the knowledge gained through this study.

Multiple insecticide resistance mechanisms in primary dengue vector, Aedes aegypti (Linn.) from dengue endemic districts of sub-Himalayan West Bengal, India

Background

Mosquitoes belonging to genus Aedes are the prime vectors of several arboviral diseases such as Dengue, Zika and Chikungunya worldwide. Every year numerous cases of dengue infections occur throughout the world, proper control of which depends on efficient vector control. However the onset of insecticide resistance has resulted in failure of vector control approaches.

Principal findings

This study was carried out to unveil the degree of prevailing insecticide resistance along with its underlying mechanisms among the primary dengue vector in dengue endemic districts of West Bengal, India through standard WHO protocol. It was observed that, the majority of the tested populations were found to possess resistance to more than one insecticide. In adult bioassay, the toxicity levels of the six tested insecticides was found to decrease in the following order: deltamethrin > lambdacyhalothrin > malathion > propoxur > permethrin > DDT. In larval bioassay, one of the tested populations was found to possess moderate resistance against temephos, mortality percentage 92.5% and 79.8% for WHO (0.0200 ppm) and National Vector Borne disease Programme, India recommended dose (0.0125 ppm) respectively. Carboxylesterases were found to be involved in conferring resistance as revealed in synergistic and quantitative assay against temephos in North Dinajpur (NDP) population and malathion in Alipurduar (APD) and Darjeeling (DAR) populations. Similar correlations were also observed in the majority of the tested populations between reduced susceptibilities against pyrethroid insecticides and Cytochrome P₄₅₀s activity.

Conclusion

Efficient disease management in this region can only be achieved through proper integrated vector management along with tools to minimize insecticide resistance. This study may help the concerned authorities in the formulation of an effective vector control strategy throughout this region incorporating the knowledge gained through this study.

First Evidence of Vertical Infection of Dengue Virus 2 in Aedes aegypti Mosquitoes from Sinaloa, Mexico

Fourteen pools of Aedes aegypti larvae collected within the urban area of Culiacán, Sinaloa, were analyzed by RT-PCR. The results demonstrate, for the first time, the vertical infection of serotype-2 dengue virus (DENV-2) in Sinaloa, Mexico, suggesting that Ae. aegypti acts as a natural reservoir of DENV-2 in this region.

Characterizing environmental suitability of Aedes albopictus (Diptera: Culicidae) in Mexico based on regional and global niche models

The Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae), is an invasive species and a vector of numerous human pathogens, including chikungunya, dengue, yellow fever, and Zika viruses. This mosquito had been reported from 36 geographic locations in Mexico by 2005, increasing to 101 locations by 2010 and 501 locations (spanning 16 states) by 2016. Here we modeled the occupied niche for Ae. albopictus in Mexico to characterize the environmental conditions related to its presence, and to generate updated environmental suitability maps. The predictors with the greatest contribution to characterizing the occupied niche for Ae. albopictus were NDVI and annual mean temperature. We also estimated the environmental suitability for Ae. albopictus in regions of the country where it has not been documented yet, by means of: 1) transferring its occupied niche model to these regions and 2) modeling its fundamental niche using global data. Our models will help vector control and public health institutions to identify areas where Ae. albopictus has not yet been recorded but where it may be present. We emphasize that most of Mexico has environmental conditions that potentially allow the survival of Ae. albopictus, which underscores the need for systematic mosquito monitoring in all states of the country.

Duplex Real-Time PCR Assay Distinguishes Aedes aegypti From Ae. albopictus (Diptera: Culicidae) Using DNA From Sonicated First-Instar Larvae

Aedes aegypti (L.) and Ae. albopictus (Skuse) are important arbovirus vectors in the United States, and the recent emergence of Zika virus disease as a public health concern in the Americas has reinforced a need for tools to rapidly distinguish between these species in collections made by vector control agencies. We developed a duplex real-time PCR assay that detects both species and does not cross-amplify in any of the other seven Aedes species tested. The lower limit of detection for our assay is equivalent to ∼0.03 of a first-instar larva in a 60-µl sample (0.016 ng of DNA per real-time PCR reaction). The assay was sensitive and specific in mixtures of both species that reflected up to a 2,000-fold difference in DNA concentration. In addition, we developed a simple protocol to extract DNA from sonicated first-instar larvae, and used that DNA to test the assay. Because it uses real-time PCR, the assay saves time by not requiring a separate visualization step. This assay can reduce the time needed for vector control agencies to make species identifications, and thus inform decisions about surveillance and control.

Insecticide susceptibility status and major detoxifying enzymes' activity in Aedes albopictus (Skuse), vector of dengue and chikungunya in Northern part of West Bengal, India

Mosquitoes belonging to Aedes genus, Aedes aegypti and Aedes albopictus transmit many globally important arboviruses including Dengue (DENV) and Chikungunya (CHIKV). Vector control with the use of insecticide remains the suitable method of choice to stop the transmission of these diseases. However, vector control throughout the world is failing to achieve its target results because of the worldwide development of insecticide resistance in mosquitoes. To assess the insecticide susceptibility status of Aedes albopictus from northern part of West Bengal, the susceptibility of eight different Aedes albopictus populations were tested against a commonly used larvicide (temephos) and some adulticides (malathion, deltamethrin and lambda cyhalothrin) along with the major insecticide detoxifying enzymes' activity in them. Through this study, it was revealed that most of the populations were found susceptible to temephos except Nagrakata (NGK) and Siliguri (SLG), which showed both a higher resistance ratio (RR₉₉) and a lower susceptibility, thereby reflecting the development of resistance against temephos in them. However, all tested adulticides caused 100% mortality in all the population implying their potency in control of this mosquito in this region of India. Through the study of carboxylesterase activity, it was revealed that the NGK population showed a 9.6 fold higher level of activity than susceptible population. The same population also showed a lower level of susceptibility and a higher resistance ratio (RR₉₉), indicating a clear correlation between susceptibility to temephos and carboxylesterase enzymes' activity in this population. This preliminary data reflects that the NGK population is showing a trend towards resistance development and with time, there is possibility that this resistance phenomenon will spread to other populations. With the recurrence of dengue and chikungunya, this data on insecticide susceptibility status of Aedes albopictus could help the authorities engaged in vector control programmes to formulate effective measures against this mosquito in this region.

New Distribution Records of Mosquitoes In Washington State

Routine West Nile virus (WNV) surveillance in 2016 by the Washington State Department of Health resulted in 1 new state distribution record for Aedes hendersoni, bringing the total number of mosquito species reported from Washington to 52. We also report new county records for Aedes japonicus japonicus, Aedes togoi, and Culex salinarius .

Morphological Differentiation of the Eggs of North American Container-Inhabiting Aedes Mosquitoes

Aedes aegypti , Ae. albopictus, Ae. japonicus japonicus, and Ae. triseriatus eggs are described with the aid of color images and images from scanning electron microscopy. All eggs were broadly cigar shaped with Ae. triseriatus and Ae. j japonicus eggs being dull or matte black, while Ae. albopictus and Ae. aegypti eggs were shiny jet black. Aedes triseriatus eggs were lighter in color and had a rougher appearance when compared to those of Ae. j. japonicus. Aedes albopictus and Ae. aegypti eggs can be differentiated by the distinct presence of micropylar collars in Ae. aegypti. Our results reduce the need to rear these mosquitoes, reducing labor and time while providing an accurate identification of the vector mosquitoes.

The Eye of the Tiger, the Thrill of the Fight: Effective Larval and Adult Control Measures Against the Asian Tiger Mosquito, Aedes albopictus (Diptera: Culicidae), in North America

The Asian tiger mosquito, Aedes albopictus (Skuse), is a highly invasive container-inhabiting species with a global distribution. This mosquito, similar to other Stegomyia species such as Aedes aegypti (L.), is highly adapted to urban and suburban areas, and commonly oviposits in artificial containers, which are ubiquitous in these peridomestic environments. The increase in speed and amount of international travel and commerce, coupled with global climate change, have aided in the resurgence and expansion of Stegomyia species into new areas of North America. In many parts of their range, both species are implicated as significant vectors of emerging and re-emerging arboviruses such as dengue, chikungunya, and now Zika. Although rapid and major advances have been made in the field of biology, ecology, genetics, taxonomy, and virology, relatively little has changed in the field of mosquito control in recent decades. This is particularly discouraging in regards to container-inhabiting mosquitoes, because traditional integrated mosquito management (IMM) approaches have not been effective against these species. Many mosquito control programs simply do not possess the man-power or necessary financial resources needed to suppress Ae. albopictus effectively. Therefore, control of mosquito larvae, which is the foundation of IMM approaches, is exceptionally difficult over large areas. This review paper addresses larval habitats, use of geographic information systems for habitat preference detection, door-to-door control efforts, source reduction, direct application of larvicides, biological control agents, area-wide low-volume application of larvicides, hot spot treatments, autodissemination stations, public education, adult traps, attractive-toxic sugar bait methods, lethal ovitraps, barrier-residual adulticides, hand-held ultra-low-volume adulticides, area-wide adulticides applied by ground or air, and genetic control methods. The review concludes with future recommendations for practitioners, researchers, private industry, and policy makers.

The hitchhiker's guide to becoming invasive: exotic mosquitoes spread across a US state by human transport not autonomous flight

Not all exotic species establish and expand aggressively (i.e. become invasive). As potential vectors of disease agents, invasive mosquitoes can have considerable impact on public health, livestock and wildlife; therefore, understanding the species characteristics and ecological circumstances promoting their invasiveness is important. The mosquito Aedes japonicus japonicus, originally from north-east Asia, was introduced at least two separate times to the north-eastern USA, as surmised from the initial existence of two populations with distinct nuclear and mitochondrial genetic signatures that later intermixed. Since these original introductions in the late 1990s, Ae. j. japonicus has expanded across 31 US states, two Canadian provinces and five European countries. Although some of the expanded range was due to other independent introductions, to understand what drove the postintroduction expansion of Ae. j. japonicus within the north-eastern USA, we performed a high-resolution landscape genetic analysis of 461 specimens collected across Virginia, a state south of the original introductions. All specimens were genotyped at seven pre-optimized microsatellite loci, and a subsample was sequenced at one mitochondrial locus. We concluded that throughout Virginia this species has primarily expanded in association with humans: genetic distance and distance along roads remained correlated after controlling for geographic distance, and proximity to I-95, a major interstate highway, strongly predicted nuclear ancestry. In contrast, there was very limited evidence of diffusion even at distances potentially suitable for autonomous mosquito flight. This implies that its association with humans (rather than innate species characteristics) is the single most important determinant of invasiveness in this mosquito.

Intra-annual changes in abundance of Aedes (Stegomyia) aegypti and Aedes (Ochlerotatus) epactius (Diptera: Culicidae) in high-elevation communities in Mexico

We examined temporal changes in the abundance of the mosquitoes Aedes (Stegomyia) aegypti (L.) and Aedes (Ochlerotatus) epactius Dyar & Knab from June to October 2012 in one reference community at lower elevation (Rio Blanco; approximately 1,270 m) and three high-elevation communities (Acultzingo, Maltrata, and Puebla City; 1,670-2,150 m) in Veracruz and Puebla States, México. The combination of surveys for pupae in water-filled containers and trapping of adults, using BG-Sentinel traps baited with the BG-Lure, corroborated previous data from 2011 showing that Ae. aegypti is present at low abundance up to 2,150 m in this part of México. Data for Ae. aegypti adults captured through repeated trapping in fixed sites in Acultzingo--the highest elevation community (approximately 1,670 m) from which the temporal intra-annual abundance pattern for Ae. aegypti has been described--showed a gradual increase from low numbers in June to a peak occurrence in late August, and thereafter declining numbers in September. Ae. epactius adults were collected repeatedly in BG-Sentinel traps in all four study communities; this is the first recorded collection of this species with a trap aiming specifically to collect human-biting mosquitoes. We also present the first description of the temporal abundance pattern for Ae. epactius across an elevation gradient: peak abundance was reached in mid-July in the lowest elevation community (Rio Blanco) but not until mid-September in the highest elevation one (Puebla City). Finally, we present data for meteorological conditions (mean temperature and rainfall) in the examined communities during the study period, and for a cumulative measure of the abundance of adults over the full sampling period.

Taming a tiger in the city: comparison of motorized backpack applications and source reduction against the Asian tiger mosquito, Aedes albopictus

We evaluated 2 strategies to manage Aedes albopictus: 1) motorized backpack applications and 2) source reduction (coupled with hand-applied applications of larvicide). Backpack applications used a water-dispersible granular formulation (VectoBac WDG) of Bacillus thuringiensis var. israelensis (Bti), whereas source reduction used granular formulations of the insect growth regulator methoprene (Altosid) combined with a monomolecular film surfactant (Agnique). Six subplots (total 8.02 ha) were selected for backpack applications, source reduction, and control groups. The experiments were blind with applications conducted randomly and independently. Efficacy was determined through placement of bioassay cups with larvae within experimental plots 1 day before treatment. Backpack applications resulted in 76% (+/- 8.2% SE) and source reduction resulted in 92% (+/- 4.1% SE) larval mortality. Backpack applications required 50 times less labor than source reduction (0.25 versus 0.005 ha/h). The cost of backpack applications, including labor, was $159.88/ha, compared with $659.65/ha for source reduction. Although overall efficacy was slightly lower, motorized backpack applications of Bti were more efficient and cost-effective than source reduction methods to control Ae. albopictus in urban settings at the community level.

Susceptibility of field-collected mosquitoes in central New Jersey to organophosphates and a pyrethroid

Chemical insecticides are the primary means to control mosquitoes, and mosquito control programs must regularly monitor for resistance of mosquito vectors to commonly used insecticides to ensure the efficacy and sustainability of active ingredients. We performed insecticide resistance bioassays to test the susceptibility of field-collected mosquitoes in central New Jersey to 1 larvicide (temephos) and 2 adulticides (malathion and sumithrin). Larval susceptibility of Culex pipiens pipiens to temephos provided median concentration (LC50) and 95% lethal concentration (LC95) values of 1.108 microg/l and 2.02 microg/l, respectively. Bottle bioassays of adult Aedes albopictus showed that 100% mortality was achieved at 35-min exposure to sumithrin and at 40-min to malathion. Baseline values were obtained using both temephos and sumithrin. Our bioassays indicate satisfactory susceptibility to temephos and sumithrin in Ae. albopictus and Cx. p. pipiens field populations in central New Jersey. Despite constant field use, both products are still effective and can be used adequately for control of the test species. However, the susceptibility of target insects to various formulations should be closely monitored periodically to ensure continual efficacy.

Assessment of a direct application of two Bacillus thuringiensis israelensis formulations for immediate and residual control of Aedes albopictus

The bacterial agent Bacillus thuringiensis israelensis (Bti) is a highly effective larvicide against various medically important mosquito and black fly vector species. Recent formulations of this powerful larvicidal tool have been evaluated for their field efficacy in integrated mosquito management programs. Laboratory and controlled-condition trials have indicated long periods of residual efficacy, whereas field persistence is often much lower in duration. We investigated the residual persistence of high doses of 2 formulations of Bti, a water-dispersible granule (VectoBac WDG; 16 mg/liter) and an extruded pellet (VBC-60066; 80 mg/liter), for the management of natural larval populations of Aedes albopictus. Laboratory tests demonstrated 100% (WDG) and > or = 99.7% (VBC) average mortality across all treatments over 180 days. Field tests exhibited 100% efficacy (WDG and VBC) for 3 wk against Ae. albopictus and other coinhabiting mosquito species, with some residual efficacy lasting for > 4 wk. These results are discussed in relation to current field control of domestic Aedes vectors of public health significance.

Crouching tiger, hidden trouble: urban sources of Aedes albopictus (Diptera: Culicidae) refractory to source-reduction

Our ultimate objective is to design cost-effective control strategies for Aedes albopictus, the Asian tiger mosquito, an important urban nuisance and disease vector that expanded worldwide during the last 40 years.  We conducted mosquito larval surveys from May through October 2009 in the City of Trenton, New Jersey, USA, while performing intensive monthly source-reduction campaigns that involved removing, emptying, or treating all accessible containers with larvicides and pupicides. We examined patterns of occurrence of Ae. albopictus and Culex pipiens, another urban mosquito, among different container types by comparing observed and expected number of positive containers of each type. Expected use was based on the relative frequency of each container type in the environment. Aedes albopictus larvae and pupae were found significantly more often than expected in medium volumes of water in buckets and plant saucers but were rarely collected in small volumes of water found in trash items such as discarded cups and cans. They were also absent from large volumes of water such as in abandoned swimming pools and catch basins, although we consistently collected Cx. pipiens from those habitats. The frequency of Ae. albopictus in tires indicated rapid and extensive use of these ubiquitous urban containers. Standard larval-based indices did not correlate with adult catches in BG-Sentinel traps, but when based only on Ae. albopictus key containers (buckets, plant saucers, equipment with pockets of water, and tires) they did. Although we found that only 1.2% of the 20,039 water-holding containers examined contained immature Ae. albopictus (5.3% if only key containers were counted), adult populations were still above nuisance action thresholds six times during the 2009 mosquito season. We conclude that in urban New Jersey, effective source reduction for Ae. albopictus control will require scrupulous and repeated cleaning or treatment of everyday use containers and extensive homeowner collaboration.