A comparison of mosquito densities,weather and infection rates of Aedes aegypti during the first epidemics of Chikungunya (2014) and Zika (2016) in areas with and without vector control in Puerto Rico

In Puerto Rico, the first records of the transmission of Chikungunya (CHIKV) and Zika (ZIKV) viruses were confirmed in May 2014 and December 2015, respectively. Transmission of CHIKV peaked in September 2014, whereas that of ZIKV peaked in August 2016. The emergence of these mosquito‐transmitted arboviruses in the context of a lack of human population immunity allowed observations of whether the outbreaks were associated with Aedes aegypti (Diptera: Culicidae) densities and weather. Mosquito density was monitored weekly in four communities using sentinel autocidal gravid ovitraps (AGO traps) during 2016 in order to provide data to be compared with the findings of a previous study carried out during the 2014 CHIKV epidemic. Findings in two communities protected against Ae. aegypti using mass AGO trapping (three traps per house in most houses) were compared with those in two nearby communities without vector control. Mosquito pools were collected to detect viral RNA of ZIKV, CHIKV and dengue virus. In areas without vector control, mosquito densities and rates of ZIKV detection in 2016 were significantly higher, similarly to those observed for CHIKV in 2014. The density of Ae. aegypti in treated sites was less than two females/trap/week, which is similar to the putative adult female threshold for CHIKV transmission. No significant differences in mosquito density or infection rates with ZIKV and CHIKV at the same sites between years were observed. Although 2016 was significantly wetter, mosquito densities were similar.     

Field evaluations of disposable sticky lures for surveillance of Aedes aegypti (Stegomyia aegypti) and Culex quinquefasciatus in Jakarta

From December 1997 to April 1998, disposable sticky lures (1608 lure days) were trialled in homes in north Jakarta, Indonesia as surveillance tools for Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae) and Culex quinquefasciatus (Diptera: Culicidae), referenced to indoor resting adult collections (92 × 10 min). The lures collected 89.4% of the total of 1339 Ae. aegypti and 92.1% of the total of 1272 Cx. quinquefasciatus collected by all methods. Because there were no significant differences with respect to numbers collected in bedrooms, living rooms and kitchens, bedrooms were selected for subsequent trials for reasons of convenience. The main trials involved a replicated complete block design with L‐lysine and sodium carbonate. Lures without attractant or with four different dilutions of L‐lysine collected 3.4–8.5 times more Ae. aegypti and 4.2–8.1 times more Cx. quinquefasciatus than were collected by mouth aspirator. Lures with or without dilutions of sodium carbonate collected 2.7–5.0 times more Ae. aegypti and 1.8–4.2 times more Cx. quinquefasciatus than aspirator collections. The precision associated with catches of sticky lures was better than that for aspirator collections. Although olfactants generally improved the numbers of mosquitoes collected, the differences in catch between lures with and without attractants were usually non‐significant. Any deficit in catch may be offset by increasing the surveillance period to ≥30 days to detect all four dengue serotypes from infected mosquitoes.     

First report of Stegomyia aegypti (= Aedes aegypti) in Mexico City,Mexico

Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) is a species of mosquito that is currently widespread in Mexico. Historically, the mosquito has been distributed across most tropical and subtropical areas lower than 1700 m a.s.l. Currently, populations that are found at higher altitudes in regions with cold and dry climates suggest that these conditions do not limit the colonization and population growth of S. aegypti. During a survey of mosquitoes in September 2015, larvae of S. aegypti mosquitoes were found in two different localities in Mexico City, which is located at about 2250 m a.s.l. Mexico City is the most populous city in Mexico and has inefficient drainage and water supply systems. These factors may result in the provision of numerous larval breeding sites. Mosquito monitoring and surveillance are now priorities for the city.     

Septic tanks as larval habitats for the mosquitoes Aedes aegypti and Culex quinquefasciatus in Playa‐Playita,Puerto Rico

Adult Aedes aegypti (Linnaeus) (Diptera: Culicidae) were previously recovered from emergence traps on septic tanks in southeastern Puerto Rico. In this study we quantified immature mosquito abundance and its relationship with structural variables of the septic tanks and chemical properties of the water containing raw sewage. A miniaturized floating funnel trap was used to sample 89 septic tanks for larvae in the Puerto Rican community of Playa‐Playita. Aedes aegypti larvae were recovered from 18% of the sampled tanks (10.3 larvae per septic tank per day). Larval presence was positively associated with cracking of the septic tank walls and uncovered access ports. Larval abundance was positively associated with cracking of the septic tank walls and larger tank surface areas, and inversely associated with the total dissolved solids (TDS). Culex quinquefasciatus (Say) larvae were also recovered from 74% of the septic tanks (129.6 larvae per septic tank per day). Larval presence was negatively associated with TDS in the water and larval abundance was positively associated with cracking of the septic tank walls. A screened, plastic emergence trap was used to sample 93 septic tanks within the community for Ae. aegypti and Cx. quinquefasciatus adults. Aedes aegypti adults were recovered from 49% of the sampled tanks (8.7 adults per septic tank per day) and Cx. quinquefasciatus adults were recovered from 97% of the sampled tanks (155.5 adults per septic tank per day). Aedes aegypti adult presence was positively associated with cracking, uncapped openings and septic water pH. The Ae. aegypti adult counts were positively associated with cracking and inversely associated with TDS and conductivity. This study marks the first published record of the recovery of Ae. aegypti larvae from holding tanks containing raw sewage in the Caribbean region. Our study indicates that Ae. aegypti larvae are present in sewage water and that septic tanks have at least the potential to maintain dengue transmission during the dry season.     

The challenge of invasive mosquito vectors in the U.K. during 2016–2018: a summary of the surveillance and control of Aedes albopictus

Mosquito‐borne diseases resulting from the expansion of two key vectors, Aedes aegypti and Aedes albopictus (Diptera: Culicidae), continue to challenge whole regions and continents around the globe. In recent years there have been human cases of disease associated with Chikungunya, dengue and Zika viruses. In Europe, the expansion of Ae. albopictus has resulted in local transmission of Chikungunya and dengue viruses. This paper considers the risk that Ae. aegypti and Ae. albopictus represent for the U.K. and details the results of mosquito surveillance activities. Surveillance was conducted at 34 points of entry, 12 sites serving vehicular traffic and two sites of used tyre importers. The most common native mosquito recorded was Culex pipiens s.l. (Diptera: Culicidae). The invasive mosquito Ae. albopictus was detected on three occasions in southern England (September 2016, July 2017 and July 2018) and subsequent control strategies were conducted. These latest surveillance results demonstrate ongoing incursions of Ae. albopictus into the U.K. via ground vehicular traffic, which can be expected to continue and increase as populations in nearby countries expand, particularly in France, which is the main source of ex‐continental traffic.     

Rift Valley fever virus and European mosquitoes: vector competence of Culex pipiens and Stegomyia albopicta (= Aedes albopictus)

Rift Valley fever (RVF) is a mosquito‐borne disease caused by the Rift Valley fever virus (RVFV). Rift Valley fever affects a large number of species, including human, and has severe impact on public health and the economy, especially in African countries. The present study examined the vector competence of three different European mosquito species, Culex pipiens (Linnaeus, 1758) form molestus (Diptera: Culicidae), Culex pipiens hybrid form and Stegomyia albopicta (= Aedes albopictus) (Skuse, 1894) (Diptera: Culicidae). Mosquitoes were artificially fed with blood containing RVFV. Infection, disseminated infection and transmission efficiency were evaluated. This is the first study to assess the transmission efficiency of European mosquito species using a virulent RVFV strain. The virus disseminated in Cx. pipiens hybrid form and in S. albopicta. Moreover, infectious viral particles were isolated from saliva of both species, showing their RVFV transmission capacity. The presence of competent Cx. pipiens and S. albopicta in Spain indicates that an autochthonous outbreak of RVF may occur if the virus is introduced. These findings provide information that will help health authorities to set up efficient entomological surveillance and RVFV vector control programmes.     

Assessing the efficacy of candidate mosquito repellents against the background of an attractive source that mimics a human host

Mosquito repellents are used around the globe to protect against nuisance biting and disease‐transmitting mosquitoes. Recently, there has been renewed interest in the development of repellents as tools to control the transmission of mosquito‐borne diseases. We present a new bioassay for the accurate assessment of candidate repellent compounds, using a synthetic odour that mimics the odour blend released by human skin. Using DEET (N,N‐diethyl‐meta‐toluamide) and PMD (p‐menthane‐3,8‐diol) as reference compounds, nine candidate repellents were tested, of which five showed significant repellency to the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae). These included: 2‐nonanone; 6‐methyl‐5‐hepten‐2‐one; linalool; δ‐decalactone, and δ‐undecalactone. The lactones were also tested on the yellow fever mosquito Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae), against which they showed similar degrees of repellency. We conclude that the lactones are highly promising repellents, particularly because these compounds are pleasant‐smelling, natural products that are also present in human food sources.     

Insecticide resistance,associated mechanisms and fitness aspects in two Brazilian Stegomyia aegypti (= Aedes aegypti) populations

In Brazil, insecticide resistance in Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) populations to pyrethroids and to the organophosphate (OP) temephos is disseminated. Currently, insect growth regulators (IGRs) and the OP malathion are employed against larvae and adults, respectively. Bioassays with mosquitoes from two northeast municipalities, Crato and Aracaju, revealed, in both populations, susceptibility to IGRs and malathion (RR₉₅ ≤ 2.0), confirming the effectiveness of these compounds. By contrast, temephos and deltamethrin (pyrethroid) resistance levels were high (RR₉₅ > 10), which is consistent with the use of intense chemical control. In Crato, RR₉₅ values were > 50 for both compounds. Knock‐down‐resistant (kdr) mutants in the voltage‐gated sodium channel, the pyrethroid target site, were found in 43 and 32%, respectively, of Aracaju and Crato mosquitoes. Biochemical assays revealed higher metabolic resistance activity (esterases, mixed function oxidases and glutathione‐S‐transferases) at Aracaju. With respect to fitness aspects, mating effectiveness was equivalently impaired in both populations, but Aracaju mosquitoes showed more damaging effects in terms of longer larval development, decreased bloodmeal acceptance, reduced engorgement and lower numbers of eggs laid per female. Compared with mosquitoes in Crato, Aracaju mosquitoes exhibited lower OP and pyrethroid RR₉₅, increased activity of detoxifying enzymes and greater effect on fitness. The potential relationship between insecticide resistance mechanisms and mosquito viability is discussed.     

Evaluation of vector competence for West Nile virus in Italian Stegomyia albopicta (=Aedes albopictus) mosquitoes

West Nile virus (WNV) is a zoonotic arboviral pathogen transmitted by mosquitoes in a cycle that involves wild birds as reservoir hosts. The virus is responsible for outbreaks of viral encephalitis in humans and horses. In Europe, Culex pipiens (Diptera: Culicidae) is considered to be the main vector of WNV, but other species such as Stegomyia albopicta (=Aedes albopictus) (Diptera: Culicidae) may also act as competent vectors of this virus. Since 2008 human cases of WNV disease have been reported in northeast Italy. In 2011, new areas of southern Italy became involved and a first outbreak of WNV lineage 1 occurred on the island of Sardinia. On the assumption that a potential involvement of St. albopicta in WNV transmission cannot be excluded, and in order to evaluate the competence of this species for the virus, an experimental infection of an St. albopicta laboratory colony, established from mosquitoes collected in Sardinia, was carried out. The results were compared with those obtained in a colony of the main vector Cx. pipiens. The study showed St. albopicta collected on Sardinia to be susceptible to WNV infection, which suggests this Italian mosquito species is able to act as a possible secondary vector, particularly in urban areas where the species reaches high levels of seasonal abundance.     

Controversies over the scientific name of the principal mosquito vector of yellow fever virus – expediency versus validity

The history of the scientific name of the yellow fever mosquito, the vector of yellow fever virus, ranges from 1757 to the early twenty‐first century. In his 1757 work Iter Palæstinum, Frederic Hasselquist gave the name Culex aegypti to a mosquito species responsible for fierce attacks on humans in Egypt. That name was never later ascribed to Hasselquist as author, but to Linnaeus, although the name never appeared in any of Linnaeus’ publications. In Cuba, at the end of the nineteenth century, the vector of the unknown infectious agent of yellow fever was first identified as Culex mosquito and later more validly named Stegomyia fasciata. Mosquito taxonomists differed strongly about the name of the mosquito through much of the twentieth century. Interventions by the International Commission on Zoological Nomenclature imposed a biologically invalid specific name, and in the early twenty‐first century a phylogenetic analysis of the culicid tribe Aedini restored the genus Stegomyia from a century earlier. That action was short‐lived. A phylogenetic reassessment resulted in the return of Stegomyia to subgeneric rank in Aedes; thus, the name of the yellow fever mosquito survives in the traditional classification of convenience as the trinomial Aedes (Stegomyia) aegypti (Linnaeus).     

Temporal genetic stability of Stegomyia aegypti (= Aedes aegypti) populations

The mosquito Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) is the primary vector of viruses that cause yellow fever, dengue and Chikungunya fever. In the absence of effective vaccines, the reduction of these diseases relies on vector control strategies. The success of these strategies is tightly linked to the population dynamics of target populations. In the present study, 14 collections from St. aegypti populations separated by periods of 1–13 years were analysed to determine their temporal genetic stability. Although temporal structure is discernible in most populations, the degree of temporal differentiation is dependent on the population and does not obscure the geographic structure of the various populations. The results suggest that performing detailed studies in the years prior to and after population reduction‐ or modification‐based control interventions at each target field site may be useful in assessing the probability of success.     

Experience‐ and age‐mediated oviposition behaviour in the yellow fever mosquito Stegomyia aegypti (=Aedes aegypti)

In repeated behaviours such as those of feeding and reproduction, past experiences can inform future behaviour. By altering their behaviour in response to environmental stimuli, insects in highly variable landscapes can tailor their behaviour to their particular environment. In particular, female mosquitoes may benefit from plasticity in their choice of egg‐laying site as these sites are often temporally variable and clustered. The opportunity to adapt egg‐laying behaviour to past experience also exists for mosquito populations as females typically lay eggs multiple times throughout their lives. Whether experience and age affect egg‐laying (or oviposition) behaviour in the mosquito Stegomyia aegypti (=Aedes aegypti) (Diptera: Culicidae) was assessed using a wind tunnel. Initially, gravid mosquitoes were provided with a cup containing either repellent or well water. After ovipositing in these cups, the mosquitoes were blood‐fed and introduced into a wind tunnel. In this wind tunnel, an oviposition cup containing repellent was placed in the immediate vicinity of the gravid mosquitoes. A cup containing well water was placed at the opposite end of the tunnel so that if the females flew across the chamber, they encountered the well water cup, in which they readily laid eggs. Mosquitoes previously exposed to repellent cups became significantly more likely to later lay eggs in repellent cups, suggesting that previous experience with suboptimal oviposition sites informs mosquitoes of the characteristics of nearby oviposition sites. These results provide further evidence that mosquitoes modify behaviour in response to environmental information and are demonstrated in a vector species in which behavioural plasticity may be ecologically and epidemiologically meaningful.     

Evaluation of collection methods for Culex quinquefasciatus,Aedes aegypti,and Aedes simpsoni in northeastern Tanzania

In East Africa, significant morbidity and mortality are caused by infections spread by Culex quinquefasciatus and Aedes aegypti. Sticky traps have been shown to be effective tools for sampling populations of Aedes mosquitoes and have been found to catch Cx. quinquefasciatus. Thus, they could potentially be used to sample populations of this species. This study compared Sticky ovitraps (SO) and MosquiTraps (MQT) with the CDC Gravid trap (CDC‐GT) for collection of Culex and Aedes mosquito populations in Tanzania. A follow‐up experiment was carried out using traps set for a 24‐h period to accommodate the oviposition habits of Aedes aegypti and Ae. simpsoni s.l. mosquitoes. The results showed that the CDC‐GT caught significantly more Cx. quinquefasciatus and Ae. aegypti than the SO or MQT, but there was no significant difference in the number of mosquitoes caught between the two sticky traps or of Ae. simpsoni s.l. caught among the three trap types. The results suggest that CDC‐GTs are the most appropriate in sampling of Cx. quinquefasciatus. Although CDC‐GTs collected more Ae. aegypti than the sticky traps, the simplicity and cost benefit of sticky traps facilitates large scale studies. All three trap types should be considered for monitoring Aedes mosquitoes.     

Productivity and population density estimates of the dengue vector mosquito Aedes aegypti (Stegomyia aegypti) in Australia

New mosquito control strategies centred on the modifying of populations require knowledge of existing population densities at release sites and an understanding of breeding site ecology. Using a quantitative pupal survey method, we investigated production of the dengue vector Aedes aegypti (L.) (Stegomyia aegypti) (Diptera: Culicidae) in Cairns, Queensland, Australia, and found that garden accoutrements represented the most common container type. Deliberately placed ‘sentinel’ containers were set at seven houses and sampled for pupae over 10 weeks during the wet season. Pupal production was approximately constant; tyres and buckets represented the most productive container types. Sentinel tyres produced the largest female mosquitoes, but were relatively rare in the field survey. We then used field‐collected data to make estimates of per premises population density using three different approaches. Estimates of female Ae. aegypti abundance per premises made using the container‐inhabiting mosquito simulation (CIMSiM) model [95% confidence interval (CI) 18.5–29.1 females] concorded reasonably well with estimates obtained using a standing crop calculation based on pupal collections (95% CI 8.8–22.5) and using BG‐Sentinel traps and a sampling rate correction factor (95% CI 6.2–35.2). By first describing local Ae. aegypti productivity, we were able to compare three separate population density estimates which provided similar results. We anticipate that this will provide researchers and health officials with several tools with which to make estimates of population densities.     

Fine scale spatial urban land cover factors associated with adult mosquito abundance and risk in Tucson,Arizona

It is currently unclear what role microhabitat land cover plays in determining the seasonal spatial distribution of Aedes aegypti and Culex quinquefasciatus, disease vectors of dengue and West Nile Virus, respectively, in Tucson, AZ. We compared mosquito abundance to sixteen land cover variables derived from 2010 NAIP multispectral data and 2008 LiDAR height data. Mosquitoes were trapped with 30–9 traps from May to October of 2010 and 2011. Variables were extracted for five buffer zones (10–50 m radii at 10 m intervals) around trapping sites. Stepwise regression was performed to determine the best scale for observation and the influential land cover variables. The 30 m radius buffer was determined to be the best for observing the land cover‐mosquito abundance relationship. Ae. aegypti presence was positively associated with structure and medium height trees and negatively associated with bare earth; Cx. quinquefasciatus presence was positively associated with pavement and medium height trees and negatively associated with shrubs. These findings emphasize vegetation, impervious surfaces, and soil influences on mosquito presence in an urban setting. Lastly, the land cover‐mosquito abundance relationships were used to produce risk maps of seasonal presence that highlight high risk areas in Tucson, which may be useful for focusing mosquito control program actions.     

Comparative analysis of midgut bacterial communities in three aedine mosquito species from dengue‐endemic and non‐endemic areas of Rajasthan,India

Dengue viruses are transmitted to humans through the bites of infected female aedine mosquitoes. Differences in the composition and structure of bacterial communities in the midguts of mosquitoes may affect the vector's ability to transmit the disease. To investigate and analyse the role of midgut bacterial communities in viral transmission, midgut bacteria from three species, namely Stegomyia aegypti (= Aedes aegypti), Fredwardsius vittatus (= Aedes vittatus) and Stegomyia albopicta (= Aedes albopictus) (all: Diptera: Culicidae), from dengue‐endemic and non‐endemic areas of Rajasthan, India were compared. Construction and analyses of six 16S rRNA gene libraries indicated that Serratia spp.‐related phylotypes dominated all clone libraries of the three mosquito species from areas in which dengue is not endemic. In dengue‐endemic areas, phylotypes related to Aeromonas, Enhydrobacter spp. and uncultivated bacterium dominated the clone libraries of S. aegypti, F. vittatus and S. albopicta, respectively. Diversity indices analysis and real‐time TaqMan polymerase chain reaction assays showed bacterial diversity and abundance in the midguts of S. aegypti to be higher than in the other two species. Significant differences observed among midgut bacterial communities of the three mosquito species from areas in which dengue is and is not endemic, respectively, may be related to the vectorial capacity of mosquitoes to carry dengue viruses and, hence, to the prevalence of disease in some areas.     

First record of Stegomyia albopicta (= Aedes albopictus) in Morocco: a major threat to public health in North Africa?

The Asian tiger mosquito Stegomyia albopicta (= Aedes albopictus) (Diptera: Culicidae), native to Asian forests, is a nuisance mosquito and is responsible for the transmission of arboviruses of public health importance, such as dengue, chikungunya and Zika viruses. It has colonized parts of all continents, except Antarctica, over the past 30–40 years. However, to date, the only records of S. albopicta in North Africa refer to occasional collections in 2010 and 2014 in Algeria. In early September 2015, S. albopicta larvae and adults were collected in a district of Rabat, Morocco. Morphological identification was confirmed by molecular analysis. This is the first record of this invasive mosquito in Morocco. A national surveillance programme will be implemented in 2016 to establish its geographical distribution in Morocco and to instigate control measures to prevent the establishment of new populations and the transmission of arboviruses.     

Geographic and ecological distribution of the dengue and chikungunya virus vectors Aedes aegypti and Aedes albopictus in three major Cameroonian towns

Aedes albopictus (Diptera: Culicidae) was first reported in Central Africa in 2000, together with the indigenous mosquito species Aedes aegypti (Diptera: Culicidae). Because Ae. albopictus can also transmit arboviruses, its introduction is a public health concern. We undertook a comparative study in three Cameroonian towns (Sahelian domain: Garoua; equatorial domain: Douala and Yaoundé) in order to document infestation by the two species and their ecological preferences. High and variable levels of pre‐imaginal Ae. aegypti and Ae. albopictus infestation were detected. Only Ae. aegypti was encountered in Garoua, whereas both species were found in Douala and Yaoundé, albeit with significant differences in their relative prevalence. Peridomestic water containers were the most strongly colonized and productive larval habitats for both species. No major differences in types of larval habitat were found, but Ae. albopictus preferentially bred in containers containing plant debris or surrounded by vegetation, whereas Ae. aegypti tended to breed in containers located in environments with a high density of buildings. These findings may have important implications for vector control strategies.     

Insecticide susceptibility status in Mexican populations of Stegomyia aegypti (= Aedes aegypti): a nationwide assessment

In Mexico, mosquito vector‐borne diseases are of public health concern as a result of their impact on human morbidity and mortality. The use of insecticides against adult mosquitoes is one of the most common ways of controlling mosquito population densities. However, the use of these compounds has resulted in the development of insecticide resistance. The aim of this study was to estimate susceptibility to six pyrethroids, two carbamates and two organophosphates in Mexican populations of Stegomyia aegypti (Linnaeus, 1762) (= Aedes aegypti) (Diptera: Culicidae) mosquitoes. Bottle insecticide susceptibility tests, with 1 h exposure, were performed on adult mosquitoes from 75 localities across 28 states. At 30 min of exposure, the proportion of fallen mosquitoes was recorded. After 60 min of exposure, mosquitoes were recovered in non‐treated containers and mortality was determined at 24 h after the set‐up of the experiment. In general, the carbamate insecticides represented the most effective group in terms of the proportion of mosquitoes fallen at 30 min (72–100%) and 24‐h mortality (97–100%). High and widespread resistance to pyrethroids Types I and II and, to a lesser extent, to organophosphates was observed. Insecticide susceptibility among and within states was highly variable.