Midgut and salivary gland barriers to La Crosse virus dissemination in mosquitoes of the Aedes triseriatus group

Vector competence for La Crosse virus (LACV) was compared for four species in the Aedes (Protomacleaya) triseriatus group: Ae. triseriatus (Say), Ae. hendersoni Cockerell, Ae. zoosophus Dyar and Knab and Ae. brelandi Zavortink (Diptera: Culicidae). Rates of replication and dissemination of virus in the mosquito hosts were compared and rates of oral transmission of virus to suckling mice were determined. Barriers to virus dissemination which limited the ability of each species to transmit virus were identified. Ae. zoosophus displayed the highest vector competence for LACV. Both infection and transmission rates were high: 99% and 85% respectively; no significant barriers to LACV were found. Disseminated infection of Ae. triseriatus with LACV was controlled primarily be a midgut escape barrier. When virus was introduced directly into the haemocoel, transmission rates were significantly increased (37% v. 79%). Ae. hendersoni showed high susceptibility to LACV infection but a very low rate of oral transmission (7%). Ae. brelandi was also highly susceptible to infection by LACV and transmitted virus at an intermediate rate (27%). Modulation of vector competence in both Ae. hendersoni and Ae. brelandi resulted from a salivary gland escape barrier. As these four species of mosquitoes comprise a closely related monophyletic series, their differences of vector competence for LACV provide an excellent model for studying the genetic basis of the barriers involved.     

The mosquitoes of eastern Tennessee: studies on abundance,habitat preferences,and host‐seeking behaviors

A significant increase in the number of reported cases of La Crosse virus (LACV) infections in eastern Tennessee has occurred in the last ten years. The objective of this study was to determine the abundance and habitat preferences of the potential vectors of LACV in this region. Adult host‐seeking mosquitoes were collected using CO₂‐baited CDC light traps and a series of human‐landing catches in eastern Tennessee from 2004 to 2006. A total of 4,200 female mosquitoes of 23 species was collected by CO₂‐baited CDC trapping at ten sites during the study period. Aedes albopictus (Skuse) was the most abundant mosquito collected at all sites and vegetation types, with the ratios of total Ae. albopictus to Ae. triseriatus (Say) females collected being 2.1:1 in 2004, 3.8:1 in 2005, and 4.9:1 in 2006. Ten species were collected during a series of human‐landing catches made at four different sites; one probable and three confirmed case sites of LACV infections, totaling 528 female mosquitoes. Aedes albopictus was the most abundant species collected, with a 4:1 ratio of Ae. albopictus to Ae. triseriatus females. Aedes albopictus exhibited two clear peaks of “landing” activity, one in the early morning and one in the late afternoon or early evening. Simple and multiple regression analyses of the predictors of the number of mosquitoes collected showed that populations of Ae. albopictus were three times more likely to be collected overall than Ae. triseriatus. Species (Ae. albopictus), vegetation (residential), and the previous cumulative precipitation for the four weeks prior to collection were significantly (P < 0.05) associated with the number of mosquitoes collected by CO₂‐baited CDC trapping. Aedes albopictus was also more likely to be collected than Ae. triseriatus at confirmed cases of LACV infections.     

Modeling a single season of Aedes albopictus populations based on host‐seeking data in response to temperature and precipitation in eastern Tennessee

In the southern Appalachia of the U.S., Aedes mosquitoes maintain and transmit La Crosse virus (LACV) which causes La Crosse encephalitis, a neuroinvasive disease of children. In response to mosquito outbreaks, communities organize prevention, detection, and response measures that are dependent on local characteristics of the mosquito population and the community. Knowing Ae. albopictus is an accessory vector of LACV and a nuisance biter, our objective was to build a system of ordinary differential equations to model dynamics in a single season using our data and readily available environmental variables that can reflect the abundance and activity of Ae. albopictus. Consequently, we built an Ae. albopictus single‐season mathematical model for eastern Tennessee to fit our 2013 mosquito collection data in order to understand the population fluctuations. We included precipitation, temperature, and rate of change of temperature in the model because Aedes mosquitoes oviposit desiccant tolerant eggs with peak activity occurring over 26° C and those data are readily available and used frequently as forecast predictors. Our ordinary differential equation model accurately fits the data and facilitates predictions and better understanding of Ae. albopictus populations in southern Appalachia.     

Oviposition habitat selection by container‐dwelling mosquitoes: responses to cues of larval and detritus abundances in the field

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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.     

Horizontal transfer of the insect growth regulator pyriproxyfen to larval microcosms by gravid Aedes albopictus and Ochlerotatus triseriatus mosquitoes in the laboratory

The insect growth regulator (IGR) pyriproxyfen is highly active against mosquitoes (Diptera: Culicidae). Through continuous emersion of large larvae (instars 3-4) the concentration causing 50% inhibition of adult emergence (EI50) was determined as 0.200 p.p.b. for Aedes albopictus (Skuse) and 3.5 to 7 times less for Ochlerotatus triseriatus (Say): IE50 0.0288 p.p.b. As a possible method of application to larval microcosms of these species that oviposit in water containers and phytotelmata, the horizontal transfer of pyriproxyfen to larval microcosms by adult mosquitoes was evaluated under laboratory conditions. Gravid females were forced to walk on surfaces treated with pyriproxyfen (tarsal contact exposure) and then allowed to oviposit in larval microcosms. Using replicate bioassay cages, each with an oviposition container, and a factorial experimental design, we assessed Ae. albopictus for the effects of (i) pyriproxyfen concentration (0.2, 0.3 and 0.4 mg/cm2) contacted by gravid females, and (ii) the number of treated gravid females added to bioassay cages (one, three or five females/cage), on the mortality of larvae in oviposition containers. Only 0.2 mg/cm2 treatment rate was tested on Oc. triseriatus. A significant (P < 0.05) curvilinear response in inhibition of emergence (IE) was achieved on both species. Densities of one or three treated Oc. triseriatus females/cage yielded IE rates of only 21-27%, whereas five treated females/cage resulted in 70% inhibition. With Ae. albopictus, densities of three or five treated females/cage yielded 48-67% and 59-73% IE, respectively, whereas one treated female/cage gave only 4-30% inhibition. Use of IGR-treated oviposition containers to achieve horizontal transfer of pyriproxyfen to mosquito oviposition sites could be a field management technique based on mosquito biology and behaviour. In binary choice tests with Ae. albopictus, horizontal transfer of pyriproxyfen from a container with a treated ovistrip (0.3 or 0.4 mg/cm2) to an untreated microcosm resulted in 14-38% inhibition. In larval bioassays, pyriproxyfen activity declined markedly within 10 days. Forcibly exposing gravid female mosquitoes to pyriproxyfen-treated paper surface did not affect their fecundity. However, from the 1st to 2nd gonotrophic cycles the egg hatch rate declined by 30% (P < 0.05). Some variation of results could be due to interactions between females at the oviposition site, possibly causing disproportionate transfer of pyriproxyfen to larval microcosms. Comparative studies of the oviposition behaviour of each mosquito are warranted and would potentially provide information needed to improve the technique.     

Satellite observation to assess dengue risk due to Aedes aegypti and Aedes albopictus in a subtropical city of Argentina

Earth observation environmental features measured through remote sensing and models of vector mosquitoes species Aedes aegypti and Ae. albopictus provide an advancement with regards to dengue risk in urban environments of subtropical areas of Argentina. The authors aim to estimate the effect of landscape coverage and spectral indices (Normalized Difference Vegetation Index [NDVI], Normalized Difference Water Index [NDWI] and Normalized Difference Built-up Index [NDBI]) on the larvae abundance of Ae. aegypti and Ae. albopictus in Eldorado, Misiones, Argentina using remote satellite sensors. Larvae of these species were collected monthly (June 2016 to April 2018), in four environments: tire repair shops, cemeteries, dwellings and an urban natural park. The proportion of landscape coverage (water, urban areas, bare soil, low vegetation and high vegetation) was determined from the supervised classification of Sentinel-2 images and spectral indices, calculated. The authors developed spatial models of both vector species by generalized linear mixed models. The model's results showed that Ae. aegypti larvae abundance was better modelled by NDVI minimum values, NDBI maximum values and the interaction between them. For Ae. albopictus proportion of bare soil, low vegetation and the interaction between both variables explained better the abundance.     

Investigating the distribution of prairie dogs in an urban landscape

Habitat fragmentation is a prevalent threat to biological diversity, and urbanization is a primary agent of fragmentation and a leading cause of species endangerment. Landscape biogeographic and local habitat characteristics can be important determinants of the distribution of species in habitat patches in urban landscapes. However, the specifics of which characteristics are most critical to maintaining biological diversity are not fully known for prairie ecosystems, especially in fragmented urban habitat. This study focuses on black-tailed prairie dogs along an urban gradient in Denver, CO. Prairie dogs have declined precipitously throughout the region and are an essential part of the prairie ecosystem, making them excellent study subjects. We identified a series of habitat fragments along a gradient of urbanization in the fully urbanized areas and south suburbs of Denver, CO, both containing and not containing prairie dogs. Local characteristics, including fragment slope and vegetative cover, and landscape characteristics, including fragment size, age and connectivity, were measured on each fragment. We used likelihood-based methods to explore which variables most accurately predicted prairie dog occurrence within our study area. Multiple factors influenced the distribution of prairie dogs in urban settings, with colony connectivity the strongest predictor of occupancy. Large and recently isolated fragments near other prairie dog colonies, flat areas and those with high graminoid cover were most likely to support prairie dog populations. Our study provides the first attempt to model prairie dog occurrence in highly fragmented urban habitat and has important implications for the management and conservation of prairie dogs.     

Loop‐mediated isothermal amplification (LAMP) for the identification of invasive Aedes mosquito species

Invasive Aedes mosquito species (Diptera: Culicidae) are of public health concern in Europe because they are either recognized or potential vectors of pathogens. Loop‐mediated isothermal amplification (LAMP) is a rapid and simple method for amplifying DNA with high specificity and efficiency, with the technique having potential for application in the field, including in high‐throughput format. Specific LAMP assays based on rDNA internal transcribed spacers 1 or 2 sequences, considering intraspecies variability at these loci, were developed for Aedes aegypti, Aedes albopictus, Aedes japonicus, Aedes koreicus and the indigenous Aedes geniculatus. No such assays could be developed for Aedes atropalpus and Aedes triseriatus because both loci were too short to serve as target. The assays rely on the clearly visible colour change from violet to sky blue after successful amplification. Sensitivity of egg detection was confirmed with ratios of up to one mosquito egg in 99 other eggs. Simple sample preparation of adults or eggs by mechanical homogenization in water required an additional heat treatment or centrifugation step to avoid non‐specific colour changes. Thus, further technical improvements are needed to render these assays truly field‐applicable, which would greatly facilitate surveillance of these invasive mosquito species and allow for prompt implementation of control measures.     

Fine‐scale variation within urban landscapes affects marking patterns and gastrointestinal parasite diversity in red foxes

1. Urban areas are often considered to be a hostile environment for wildlife as they are highly fragmented and frequently disturbed. However, these same habitats can contain abundant resources, while lacking many common competitors and predators. The urban environment can have a direct impact on the species living there but can also have indirect effects on their parasites and pathogens. To date, relatively few studies have measured how fine‐scale spatial heterogeneity within urban landscapes can affect parasite transmission and persistence.
2. Here, we surveyed 237 greenspaces across the urban environment of Edinburgh (UK) to investigate how fine‐scale variation in socio‐economic and ecological variables can affect red fox (Vulpes vulpes) marking behavior, gastrointestinal (GI) parasite prevalence, and parasite community diversity.
3. We found that the presence and abundance of red fox fecal markings were nonuniformly distributed across greenspaces and instead were dependent on the ecological characteristics of a site. Specifically, common foraging areas were left largely unmarked, which indicates that suitable resting and denning sites may be limiting factor in urban environments. In addition, the amount of greenspace around each site was positively correlated with overall GI parasite prevalence, species richness, and diversity, highlighting the importance of greenspace (a commonly used measure of landscape connectivity) in determining the composition of the parasite community in urban areas.
4. Our results suggest that fine‐scale variation within urban environments can be important for understanding the ecology of infectious diseases in urban wildlife and could have wider implication for the management of urban carnivores.

     

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.     

Accidental importation of the mosquito Aedes albopictus into the Netherlands: a survey of mosquito distribution and the presence of dengue virus

Abstract.  In the summer of 2005, the Asian tiger mosquito, Aedes albopictus (Skuse) (Diptera: Culicidae) was found for the first time in the Netherlands. It was collected on the premises of several horticultural companies that import the ornamental plant Dracaena sanderiana (Sparagalus: Dracaenaceae [Agavaceae]), known as Lucky bamboo, from southern China, an area endemic for this mosquito species and for arboviruses transmitted by this vector. Here we report the results of a 1-year survey of the distribution and vector status of Ae. albopictus in Lucky bamboo nurseries in the Netherlands (July 2006–June 2007). As it had been established previously that the presence of this species was linked to the import of Lucky bamboo, the survey was conducted only on sites owned by relevant import companies. In total, 569 adult Ae. albopictus were collected with mosquito traps from 15 of the 17 (88%) glasshouses used by Lucky bamboo importers, none of which were found to be infected with dengue virus. On two occasions there was evidence that Ae. albopictus had escaped from the glasshouses, but, overall, there was no evidence that a population had become established in the greenhouses or elsewhere.     

Entomological surveillance,spatial distribution,and diversity of Culicidae (Diptera) immatures in a rural area of the Atlantic Forest biome,State of São Paulo,Brazil

Because of the high adaptive capacity of mosquitoes, studies that focus on transitional environments become very important, such as those in rural areas, which are considered as bridges between wild diseases and human populations of urban areas. In this study, a survey of the existing species of mosquitoes was performed in an Atlantic Forest area of the city of Santa Bárbara d'Oeste, São Paulo state, Brazil, using traps for immatures and analyzing the frequency and distribution of these insects over the sampling months. Five mosquito species were found: Aedes albopictus (the most frequent species), Aedes aegypti, Aedes fluviatilis, Culex quinquefasciatus, and Toxorhynchites theobaldi. The 4,524 eggs collected in ovitraps showed the presence of the tribe Aedini. Aedes aegypti and Ae. albopictus were identified after larval hatching in the laboratory, with different spatial distributions: the first of which coincides with the area of greatest diversity calculated using the Simpson index, while the second does not. The association of ecological analysis of spatial diversity with simple methods of data collection enables the identification of possible epidemiological risk situations and is a strategy that may be implemented to monitor ecological processes resulting from the interaction among different species of mosquitoes.     

The behavioural ecology and population dynamics of a cryptic ground‐dwelling mammal in an urban Australian landscape

Urbanization results in widespread habitat loss and fragmentation and generally has a negative impact upon native wildlife, in particular ground‐dwelling mammals. The northern brown bandicoot (Isoodon macrourus; Marsupialia: Peramelidae) is one of relatively few native Australian ground‐dwelling mammals that is able to survive within urbanized landscapes. As a consequence of extensive clearing and urban development within the city of Brisbane, bandicoots are now restricted to the mostly small (<10 ha) bushland fragments scattered across the city landscape. Our study examined the behavioural ecology of northern brown bandicoots within habitat fragments located on a major creek‐line, using mark‐recapture population monitoring and radio telemetry. Bandicoots at monitored sites were found to occur at high densities (typically one individual ha^?1), although one‐third of the populations were transient. Radio tracking revealed that bandicoots had relatively small home ranges (mean 1.5 ± 0.2 ha) comprised largely of bushland/grassland with dense, often weed‐infested ground cover. Bandicoots sheltered by day in these densely covered areas and also spent most time foraging there at night, although they occasionally ventured small distances to forage in adjacent maintained parklands and residential lawns. We suggest that introduced tall grasses and other weeds contribute to high habitat quality within riparian habitat fragments and facilitate the persistence of high density populations, comprised of individuals with small home ranges. The generalized dietary and habitat requirements of northern brown bandicoots, as well as a high reproductive output, undoubtedly facilitate the survival of the species in urban habitat fragments. Further research is required on other native mammal species in urbanized landscapes to gain a greater understanding of how best to conserve wildlife in these heavily modified environments.     

Effects of an invasive species on refuge‐site selection by native fauna: The impact of cane toads on native frogs in the Australian tropics

Invasive species can induce shifts in habitat use by native taxa: either by modifying habitat availability, or by repelling or attracting native species to the vicinity of the invader. The ongoing invasion of cane toads (Rhinella marina) through tropical Australia might affect native frogs by affecting refuge‐site availability, because both frogs and toads frequently shelter by day in burrows. Our laboratory and field studies in the wet‐dry tropics show that native frogs of at least three species (Litoria tornieri, Litoria nasuta and Litoria dahlii) preferentially aggregate with conspecifics, and with (some) other species of native frogs. However, the frogs rarely aggregated with cane toads either in outdoor arenas or in standardized experimental burrows that we monitored in the field. The native frogs that we tested either avoided burrows containing cane toads (or cane toad scent) or else ignored the stimulus (i.e. treated such a burrow in the same way as they did an empty burrow). Native frogs selected a highly non‐random suite of burrows as diurnal retreat sites, whereas cane toads were less selective. Hence, even in the absence of toads, frogs do not use many of the burrows that are suitable for toads. The invasion of cane toads through tropical Australia is unlikely to have had a major impact on retreat‐site availability for native frogs.     

The extent of shifts in vegetation phenology between rural and urban areas within a human‐dominated region

Urbanization is one of the major environmental challenges facing the world today. One of its particularly pressing effects is alterations to local and regional climate through, for example, the Urban Heat Island. Such changes in conditions are likely to have an impact on the phenology of urban vegetation, which will have knock‐on implications for the role that urban green infrastructure can play in delivering multiple ecosystem services. Here, in a human‐dominated region, we undertake an explicit comparison of vegetation phenology between urban and rural zones. Using satellite‐derived MODIS‐EVI data from the first decade of the 20th century, we extract metrics of vegetation phenology (date of start of growing season, date of end of growing season, and length of season) for Britain's 15 largest cities and their rural surrounds. On average, urban areas experienced a growing season 8.8 days longer than surrounding rural zones. As would be expected, there was a significant decline in growing season length with latitude (by 3.4 and 2.4 days/degree latitude in rural and urban areas respectively). Although there is considerable variability in how phenology in urban and rural areas differs across our study cities, we found no evidence that built urban form influences the start, end, or length of the growing season. However, the difference in the length of the growing season between rural and urban areas was significantly negatively associated with the mean disposable household income for a city. Vegetation in urban areas deliver many ecosystem services such as temperature mitigation, pollution removal, carbon uptake and storage, the provision of amenity value for humans and habitat for biodiversity. Given the rapid pace of urbanization and ongoing climate change, understanding how vegetation phenology will alter in the future is important if we wish to be able to manage urban greenspaces effectively.     

Avian fitness consequences match habitat selection at the nest‐site and landscape scale in agriculturally fragmented landscapes

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Farms,pastures and woodlands: the fine‐scale distribution of Palearctic Culicoides spp. biting midges along an agro‐ecological gradient

The spatial epidemiology of Bluetongue virus (BTV) at the landscape level relates to the fine‐scale distribution and dispersal capacities of its vectors, midges belonging to the genus Culicoides Latreille (Diptera: Ceratopogonidae). Although many previous researches have carried out Culicoides sampling on farms, little is known of the fine‐scale distribution of Culicoides in the landscape immediately surrounding farms. The aim of this study was to gain a better understanding of Culicoides populations at increasing distances from typical dairy farms in north‐west Europe, through the use of eight Onderstepoort‐type black‐light traps positioned along linear transects departing from farms, going through pastures and entering woodlands. A total of 16 902 Culicoides were collected in autumn 2008 and spring 2009. The majority were females, of which more than 97% were recognized as potential vectors. In pastures, we found decreasing numbers of female Culicoides as a function of the distance to the farm. This pattern was modelled by leptokurtic models, with parameters depending on season and species. By contrast, the low number of male Culicoides caught were homogeneously distributed along the transects. When transects entered woodlands, we found a higher abundance of Culicoides than expected considering the distance of the sampling sites to the farm, although this varied according to species.