Larval Development Sites Research Articles

Larval development sites of the main Culicoides species (Diptera: Ceratopogonidae) in northern Europe and distribution of coprophilic species larvae in Belgian pastures

Some Culicoides species of biting midges (Diptera: Ceratopogonidae) are biological virus vectors worldwide and have indeed been associated with outbreaks of important epizoonoses in recent years, such as bluetongue and Schmallenberg disease in northern Europe. These diseases, which affect domestic and wild ruminants, have caused considerable economic losses. Knowledge of substrates suitable for Culicoides larval development is important, particularly for the main vector temperate species. This study, realized during two years, aimed to highlight the larval development sites of these biting midge species in the immediate surroundings of ten Belgian cattle farms. Moreover, spatial distribution of the coprophilic Culicoides larvae (C. chiopterus and C. dewulfi) within pastures was studied with increasing distance from farms along linear transects (farm–pasture–woodland). A total of 4347 adult specimens belonging to 13 Culicoides species were obtained by incubation of 2131 soil samples belonging to 102 different substrates; 18 of these substrates were suitable for larval development. The Obsoletus complex (formed by two species) was observed in a wide range of substrates, including silage residues, components of a chicken coop, dung adhering to walls inside stables, leftover feed along the feed bunk, a compost pile of sugar beet residues, soil of a livestock trampling area, and decaying wood, while the following served as substrates for the other specimens: C. chiopterus, mainly cow dung; C. dewulfi, cow dung and molehill soil; C. circumscriptus, algae; C. festivipennis, algae and soil in stagnant water; C. nubeculosus, algae and silt specifically from the edge of a pond; C. punctatus, mainly wet soil between silage reserves; C. salinarius, algae; and C. stigma, algae and wet soil between silage reserves. We also recorded significantly higher densities of coprophilic larvae within pastures in cow dung located near forests, which is likely due to the localization of potential hosts; the presence of these larvae within cow dung is, however, uninfluenced by relative distance from farms.A better knowledge of the microhabitats of Culicoides biting midges and their spatial distribution may allow the development of targeted species-specific vector control strategies, and may help to prevent the creation of new larval development sites.

Evaluation of Vegetation Treatment With Lambda-Cyhalothrin to Control Aedes vexans and Simulium maculatum in Northern China.

The mosquito Aedes vexans and black fly Simulium maculatum are important blood-sucking pests in northern China. Control of these pests using current methods is difficult because of complex larval developmental sites. In the present study, lambda-cyhalothrin was applied as a barrier spray to vegetation and various structures surrounding human dwellings for control against the adults of each species. The barrier spray resulted in an 88.2-99.4% reduction in Ae. vexans abundance and a 67.8-89.6% reduction in S. maculatum abundance for 2wk postapplication. Our results indicated that lambda-cyhalothrin applied as a barrier spray to vegetation and other structures that serve as harborage for adults of both species could be adopted as part of an integrated pest management approach against these pests.

Aedes(Stegomyia)aegyptiin the Continental United States: A Vector at the Cool Margin of Its Geographic Range

After more than a half century without recognized local dengue outbreaks in the continental United States, there were recent outbreaks of autochthonous dengue in the southern parts of Texas (2004-2005) and Florida (2009-2011). This dengue reemergence has provoked interest in the extent of the future threat posed by the yellow fever mosquito, Aedes (Stegomyia) aegypti (L.), the primary vector of dengue and yellow fever viruses in urban settings, to human health in the continental United States. Ae. aegypti is an intriguing example of a vector species that not only occurs in the southernmost portions of the eastern United States today but also is incriminated as the likely primary vector in historical outbreaks of yellow fever as far north as New York, Philadelphia, and Boston, from the 1690s to the 1820s. For vector species with geographic ranges limited, in part, by low temperature and cool range margins occurring in the southern part of the continental United States, as is currently the case for Ae. aegypti, it is tempting to speculate that climate warming may result in a northward range expansion (similar to that seen for Ixodes tick vectors of Lyme borreliosis spirochetes in Scandinavia and southern Canada in recent decades). Although there is no doubt that climate conditions directly impact many aspects of the life history of Ae. aegypti, this mosquito also is closely linked to the human environment and directly influenced by the availability of water-holding containers for oviposition and larval development. Competition with other container-inhabiting mosquito species, particularly Aedes (Stegomyia) albopictus (Skuse), also may impact the presence and local abundance of Ae. aegypti. Field-based studies that focus solely on the impact of weather or climate factors on the presence and abundance of Ae. aegypti, including assessments of the potential impact of climate warming on the mosquito's future range and abundance, do not consider the potential confounding effects of socioeconomic factors or biological competitors for establishment and proliferation of Ae. aegypti. The results of such studies therefore should not be assumed to apply in areas with different socioeconomic conditions or composition of container-inhabiting mosquito species. For example, results from field-based studies at the high altitude cool margins for Ae. aegypti in Mexico's central highlands or the Andes in South America cannot be assumed to be directly applicable to geographic areas in the United States with comparable climate conditions. Unfortunately, we have a very poor understanding of how climatic drivers interact with the human landscape and biological competitors to impact establishment and proliferation of Ae. aegypti at the cool margin of its range in the continental United States. A first step toward assessing the future threat this mosquito poses to human health in the continental United States is to design and conduct studies across strategic climatic and socioeconomic gradients in the United States (including the U.S.-Mexico border area) to determine the permissiveness of the coupled natural and human environment for Ae. aegypti at the present time. This approach will require experimental studies and field surveys that focus specifically on climate conditions relevant to the continental United States. These studies also must include assessments of how the human landscape, particularly the impact of availability of larval developmental sites and the permissiveness of homes for mosquito intrusion, and the presence of other container-inhabiting mosquitoes that may compete with Ae. aegypti for larval habitat affects the ability of Ae. aegypti to establish and proliferate. Until we are armed with such knowledge, it is not possible to meaningfully assess the potential for climate warming to impact the proliferation potential for Ae. aegypti in the United States outside of the geographic areas where the mosquito already is firmly established, and even less so for dengue virus transmission and dengue disease in humans.

Evidence of Habitat Structuring Aedes albopictus Populations in Réunion Island

Arbovirus vector dynamics and spread are influenced by climatic, environmental and geographic factors. Major Chikungunya and Dengue fever outbreaks occurring the last 10 years have coincided with the expansion of the mosquito vector Aedes albopictus to nearly all the continents. We characterized the ecological (larval development sites, population dynamics, insemination and daily survival rates) and genetic (diversity, gene flow, population structure) features of two Aedes albopictus populations from distinct environments (rural and urban) on Réunion Island, in the South-West Indian Ocean. Microsatellite analysis suggests population sub-structuring Ae. albopictus populations. Two genetic clusters were identified that were significantly linked to natural versus urban habitats with a mixed population in both areas. Ae. albopictus individuals prefer urban areas for mating and immature development, where hosts and containers that serve as larval development sites are readily available and support high population densities, whereas natural environments appear to serve as reservoirs for the mosquito.

Larval development and emergence sites of farm‐associated Culicoides in the United Kingdom

Culicoides biting midges (Diptera: Ceratopogonidae) are the biological vectors of internationally important arboviruses of livestock including bluetongue virus (BTV). Information on the habitats used by Culicoides for larval development is valuable for establishing targeted vector control strategies and for improving local scale models of vector abundance. This study combines emergence trap collections of adult Culicoides identified using molecular markers and physiochemical measurements of habitats to investigate larval development sites of Palaearctic Culicoides in South East England. The known range of larval habitats for several Culicoides species is extended and the potential BTV vector species C. obsoletus and C. scoticus are confirmed to co-occur in many larval habitats. The presence of emerging C. obsoletus was favoured by increasing substrate moisture level [odds ratio (OR) 6.94 (2.30; 20.90)] and substrate pH [OR 4.80 (1.66; 13.90)] [bias-corrected Dxy : 0.68; area under the curve (AUC): 0.86] rather than any particular larval habitat type, as expected for a species with relatively wide larval habitat preference. Of the newly emerged sub-genus Avaritia individuals collected, 23% were observed to have a degree of abdominal pigmentation commonly inferred to indicate parity. If consistent across species and locations, this observation represents a potential source of error for age structure analyses of Culicoides populations.

Larvae of cryptic species of Anopheles gambiae respond differently to cues of predation risk

Summary Predation is a major evolutionary force driving speciation. Identifying the stimuli prompting anti‐predator responses is essential for unravelling the proximate mechanisms of anti‐predator adaptations and for understanding how predation impacts species diversification. Here, we explore for the first time the divergence in the use of cues of predation risk by different incipient species of mosquitoes within the Anopheles gambiae complex. We examined the anti‐predator responses to various predation cues by the aquatic larvae of Anopheles arabiensis and the two molecular forms, M and S, of Anopheles gambiae s.s. sampled from wild populations in Burkina Faso naturally exposed to different predator densities. The larvae altered their behaviour in response to various predation cues, shifting from the surface of the water to a less exposed location on the walls of the experimental arena. There were important differences in the use of predation cues between populations sharing the same larval development sites and, within the M form, related to predation pressure at their site of origin. Anopheles arabiensis larvae, which develop in small temporary waterbodies, relied only on physical cues signalling the presence of a predator to mount a vigilance response, whereas the sympatric larvae of the M and S forms of An. gambiae used both physical and chemical cues to fine‐tune their response. M‐form larvae, developing in permanent aquatic habitats with high densities of predators, responded chiefly to chemical stimuli ensuing from acute predation. Our results suggest that predation might play a role as a disruptive selective force promoting ecological divergence within the An. gambiae complex and, more recently, between the M and S molecular forms. Notably, beyond interspecific differences in the use of predation cues, our study also documented phenotypic differences within the M form based on predation pressure at their site of origin, suggesting that a process of ecological divergence is generating species ‘forerunners’ within the An. gambiae complex in the wild.

Hosts or habitats: What drives the spatial distribution of mosquitoes?

Understanding the factors that influence the distribution of vectors is critical to assess the risk of disease transmission across landscapes. For mosquitoes, existing spatial models use only habitat elements (hydrologic and floristic) to predict the distribution of disease vectors within the landscape, ignoring the potential importance of the distribution of hosts. We tested the hypothesis that the distribution of hosts would better explain the spatial distribution of mosquitoes than habitat variables using Information Theory and Poisson Regression. We analyzed the abundance of ectotherm‐biting mosquitoes and their hosts from 37 points over a 28‐km2 area in Tuskegee National Forest, Alabama, USA. We compared models built using information regarding habitat, hosts, or both for their ability to explain the abundance of Culex peccator and Culex territans, two mosquito species that specialize on reptiles and amphibians. Models built using both host and habitat information were the best models for both species, suggesting that information regarding the distribution of mosquito hosts greatly improves models of mosquito distributions. Moreover, when differences in habitat makeup among stations were accounted for, mosquitoes were found to be significantly more abundant at locations with greater host abundance. Since most mosquitoes feed on only a limited range of hosts and successful blood feeding is one of the most crucial bottlenecks in the life cycle of mosquitoes, it follows that mosquitoes would aggregate in areas of greatest host density. Habitat influences the availability of suitable larval development sites, and to some extent, distribution of hosts. Our analysis, however, shows that within the landscape the distribution of host animals is a crucial factor in determining the spatial distribution of vectors. This has clear and important implications for determining which areas are at a greater risk for zoonotic arboviruses and is a potentially transformative paradigm for understanding the factors that influence the spatial distribution of disease vectors.

Aerobic to anaerobic transition in Biomphalaria glabrata (Say, 1818) infected with different miracidial doses of Echinostoma paraensei (Lie and Basch, 1967) by high-performance liquid chromatography

The glucose content in the hemolymph and glycogen content in the digestive gland-gonad complex (DGG) and cephalopedal mass of Biomphalaria glabrata exposed to different parasite doses (5 and 50 miracidia) of Echinostoma paraensei as well as the activity of lactate dehydrogenase were evaluated. HPLC (high-performance liquid chromatography) analyses were also performed to determine the concentrations of four organic acids (oxalic, succinic, pyruvic and lactic) present in the hemolymph of infected and uninfected snails, to better understand the effect of infection on the host's energetic/oxidative metabolism. The snails were dissected 1-4 weeks after infection to collect the hemolymph and separate the tissues. There was alteration in the glycemia of the snails at both parasite doses, with a significant increase of glycemia from of the third week after infection in comparison to the control group. Changes were also observed in the lactate dehydrogenase activity, with increased activity as the infection progressed. In parallel, there was a decrease in the glycogen content in the storage tissues, with a markedly greater reduction in the digestive gland-gonad complex (larval development site) in comparison with the cephalopedal mass. Additionally, the infection by both miracidial doses resulted in an increase of oxalic and lactic acid levels, as well as in a decline of piruvic and succinic acid levels in B. glabrata, thus explaining the reduction of the oxidative decarboxylation rate in the tricarboxylic acid cycle and acceleration of the anaerobic degradation of carbohydrates in the snails, through lactic fermentation, which is essential to ensure energy supply and success of the infection.

Modelling the spatial distribution of Culicoides biting midges at the local scale

Summary Culicoides midges (Diptera: Ceratopogonidae) are ubiquitous on farms in the United Kingdom (UK), but little research has explored their abundance, an important determinant of disease risk. Models to explain and predict variation in their abundance are needed for effective targeting of control methods against bluetongue virus (BTV) and other Culicoides‐borne diseases. Although models have been attempted at the national scale (e.g. Scotland), no investigations have taken place at a finer spatial scale. Midge abundances were estimated using light traps on 35 farms in Bala, north Wales. Culicoides catches were combined with remotely sensed ecological correlates, and on‐farm host and environmental data, within a GLM model. Drivers of local‐scale variation were determined at the 1‐km resolution. Local‐scale variation in abundance exhibited an almost 500‐fold difference (74–33 720) between farms in maximum Obsoletus Group catches. The Obsoletus Group model explained 81% of this variance and was dominated by normalized difference vegetation index (NDVI). This is consistent with previous studies suggesting strong impacts of forest cover and vegetation activity on distribution, as well as shaded breeding site requirements. The variance explained was consistently high for the Pulicaris Group, C. pulicaris and C. punctatus (80%, 73% and 74%), the other probable BTV vector species in the United Kingdom. The abundance of all vector species increased with the number of sheep on farms, but this relationship was missing from any of the non‐vector models. This is particularly interesting given that none of the species concerned are known to utilize sheep‐associated larval development sites. Performance of the non‐vector models was also high (65–87% variance explained), but species differed in their associations with satellite variables. Synthesis and application. At a large spatial scale, there is significant variation in Culicoides Obsoletus Group abundance, which undermines attempts to record their nationwide distribution in larger‐scale models. Satellite data can be used to explain a high proportion of this variation and, if shown to be generalizable, they may produce effective predictive models of disease vector abundance. We recommend undertaking a prior survey for farms with high Culicoides catches within the sampling area and checking stability in catch size between seasons and years.

Aedes(Stegomyia)aegyptiandAedes (Howardina) cozumelensisin Yucatán State, México, with a summary of published collection records forAe. cozumelensis

We collected mosquito immatures from artificial containers during 2010-2011 from 26 communities, ranging in size from small rural communities to large urban centers, located in different parts of Yucatán State in southeastern México. The arbovirus vector Aedes (Stegomyia) aegypti was collected from all 26 examined communities, and nine of the communities also yielded another container-inhabiting Aedes mosquito: Aedes (Howardina) cozumelensis. The communities from which Ae. cozumelensis were collected were all small rural communities (<6,000 inhabitants) in the north-central part of Yucatán State. These new collection records for Ae. cozumelensis demonstrate that this mosquito has a far broader geographic range in the Yucatán Peninsula than previously known. Ae. cozumelensis immatures were collected from both residential premises and cemeteries, with specimens recovered from rock holes as well as various artificial containers including metal cans, flower vases, buckets, tires, and a water storage tank. The co-occurrence with Ae. aegypti in small rural communities poses intriguing questions regarding linkages between these mosquitoes, including the potential for direct competition for larval development sites. Additional studies are needed to determine how commonly Ae. cozumelensis feeds on human blood and whether it is naturally infected with arboviruses or other pathogens of medical or veterinary importance. We also summarize the published records for Ae. cozumelensis, which are restricted to collections from México's Yucatán Peninsula and Belize, and uniformly represent geographic locations where Ae. aegypti can be expected to occur.

The Dengue Virus Mosquito Vector Aedes aegypti at High Elevation in México

México has cities (e.g., México City and Puebla City) located at elevations > 2,000 m and above the elevation ceiling below which local climates allow the dengue virus mosquito vector Aedes aegypti to proliferate. Climate warming could raise this ceiling and place high-elevation cities at risk for dengue virus transmission. To assess the elevation ceiling for Ae. aegypti and determine the potential for using weather/climate parameters to predict mosquito abundance, we surveyed 12 communities along an elevation/climate gradient from Veracruz City (sea level) to Puebla City (∼2,100 m). Ae. aegypti was commonly encountered up to 1,700 m and present but rare from 1,700 to 2,130 m. This finding extends the known elevation range in México by > 300 m. Mosquito abundance was correlated with weather parameters, including temperature indices. Potential larval development sites were abundant in Puebla City and other high-elevation communities, suggesting that Ae. aegypti could proliferate should the climate become warmer.

Pyriproxyfen and House Flies (Diptera: Muscidae): Effects of Direct Exposure and Autodissemination to Larval Habitats

Pyriproxyfen is an insect growth regulator with juvenile hormone-like activity that has potential uses for dipterans that are difficult to manage with conventional insecticides, such as house flies (Musca domestica L.). The objectives of this study were to determine the efficacy of this insect growth regulator against house flies using variety of delivery systems and target life stages, including an evaluation of the potential for autodissemination by female flies to larval development sites. Adult female house flies exposed to filter paper (3.75% active ingredient) or sugar treated with pyriproxyfen (0.01-0.1%) produced significantly fewer F1 pupae than untreated flies. Adult emergence from pupae was unaffected. In contrast, treatment of larval rearing medium with 0.35 ml/cm2 of a 12 mg pyriproxyfen/liter preparation had no effect on the number of pupae developing from eggs but markedly inhibited adult emergence from those pupae. There was little difference in susceptibility between an insecticide-susceptible and a wild strain of house fly. The LC50 for inhibiting fly emergence of dust formulations in diatomaceous earth incorporating commercial pyriproxyfen products ranged from 8 to 26 mg/liter, with little difference among products. Compared with untreated flies, significantly fewer pupae were produced at concentrations > 0.5% and no adults were produced at concentrations > 0.05% pyriproxyfen. When gravid females were exposed for 1 h to treated fabric (6 mg pyriproxyfen/cm2) and allowed to oviposit in rearing media containing eggs, sufficient pyriproxyfen was autodisseminated to reduce adult emergence from those eggs by > 99%. Intermittent contact with treated fabric over 2 d reduced adult emergence by 63-76%.

Aedes albopictusMosquitoes, Yucatan Peninsula, Mexico

To the Editor: We collected Asian tiger mosquitoes, Aedes albopictus (Skuse), in Cancun in the Yucatan Peninsula of Mexico in September 2011. This mosquito is a nuisance biter of humans and a vector of numerous arboviruses, including those causing dengue, yellow fever, and chikungunya (1). Ae. albopictus mosquitoes, which are native to Southeast Asia, emerged in the continental United States in 1985 and thereafter spread rapidly across the southeastern United States and into northern Mexico (2,3). These mosquitoes have also been found in the states of Tamaulipas, Coahuila, and Nuevo Leon in northern Mexico, Chiapas in southern Mexico, and south of Mexico in Guatemala and Belize (3–9). These findings are now complemented by our collection of Ae. albopictus mosquitoes from Cancun in Quintana Roo State, which with Yucatan and Campeche States compose the Yucatan Peninsula. A previous study of the mosquito fauna of Quintana Roo conducted in 2006 did not report any Ae. albopictus mosquitoes (10). During September 2011, Ae. albopictus mosquitoes were collected from a cemetery in Cancun, which is located in the eastern part of the Yucatan Peninsula (21°8.53′Ν, 86°52.79′W) (Figure). The collection location was shaded by trees. Water in containers from which larvae were collected had an average temperature of 24.5°C and a pH of 8.5. The larval collection included ≈30 specimens of different developmental stages that were collected from vases and other artificial containers in the cemetery. The containers were examined as part of routine surveillance activities by Servicios Estatales de Salud de Quintana Roo. Larvae suspected to be those of Ae. albopictus mosquitoes were reared to adults for identification, and a colony of Ae. albopictus mosquitoes from Cancun was established. Figure Notable locations (pushpins) in Mexico, the United States, and Central America where Aedes albopictus mosquitoes were collected and year of the first collection (reference) (A), including the current collection in 2011 from Cancun, Quintana Roo State, ... F0 or F1 adult specimens were confirmed to be Ae. albopictus mosquitoes by species identification at Servicios Estatales de Salud de Quintana Roo (Quintana Roo, Mexico), Universidad Autonoma de Yucatan (Merida, Mexico), and Colorado State University (Fort Collins, CO, USA). The initial mosquito larval collection was composed of 26 Ae. albopictus, 3 Ae. aegypti, and 1 Culex sp. In addition, 6 Ae. albopictus female mosquitoes were collected from the cemetery by landing catches. Finding Ae. albopictus mosquitoes in Cancun was not surprising because these mosquitoes have been found in nearby Belize (9). Cancun is also a major port for ships carrying tourists and goods that originate in areas to which Ae. albopictus mosquitoes are endemic, including Florida and Texas. Nevertheless, the introduction of Ae. albopictus mosquitoes into Cancun and the high potential for establishment and spread across the Yucatan Peninsula has major public health implications. The Yucatan Peninsula is hyperendemic for dengue, with all 4 dengue virus (DENV) serotypes circulating in this region. Should Ae. albopictus mosquitoes persist in this region, they may spread and come to play a secondary role to Ae. aegypti mosquitoes as local vectors of DENV. Ae. albopictus mosquitoes may also change local virus transmission dynamics. For example, DENV transmission may be intensified in rural areas because Ae. albopictus mosquitoes are more likely than Ae. aegypti mosquitoes to be found in this setting. Ae. albopictus and Ae. aegypti mosquitoes also may differ in their potential for vertical transmission of DENV, which could affect virus transmission dynamics, especially during interepidemic periods or parts of the year that have low mosquito activity and infrequent human–mosquito contact. Other concerns regarding introduction of Ae. albopictus mosquitoes into the Yucatan Peninsula are their role as an aggressive nuisance biter of humans, which may necessitate intensified mosquito control to protect the local tourist industry; and their potential role as a vector of chikungunya virus, which is a major threat to immunologically naive populations in the Americas should the virus emerge there. Introduction of Ae. albopictus mosquitoes into the Yucatan Peninsula requires research on local biology of the mosquito and their potential role as an arbovirus vector in this part of Mexico. Studies are needed to determine how fine-scale spatial segregation of Ae. albopictus and Ae. aegypti mosquitoes might result from competition for containers that serve as larval development sites, from differential survival related to container type, and from hydrologic microclimates or nutrient conditions. One possible scenario is for Ae. albopictus mosquitoes to outcompete and exclude Ae. aegypti mosquitoes from certain settings. Other issues include how effectively Ae. albopictus mosquitoes can transmit locally circulating DENV strains and, because this species bridges the transitional zone from urban to forested environments and may bite a wide range of mammals, what role it might play in the urban emergence of arboviruses that are currently restricted to sylvatic forest transmission cycles in the Yucatan Peninsula.

Weather variability affects abundance of larval Culex (Diptera: Culicidae) in storm water catch basins in suburban Chicago.

Culex pipiens L. (Diptera: Culicidae) and Culex restuans Theobald are the primary enzootic and bridge vectors of West Nile virus in the eastern United States north of 36 degrees latitude. Recent studies of the natural history of these species have implicated catch basins and underground storm drain systems as important larval development sites in urban and suburban locales. Although the presence of larvae in these habitats is well-documented, the influence of abiotic factors on the ecology of Culex larvae developing in them remains poorly understood. Therefore, we examined the effects of multiple abiotic factors and their interactions on abundance of Culex larvae in catch basins in the Chicago, IL, metropolitan area. Low precipitation and high mean daily temperature were associated with high larval abundance, whereas there was no correlation between catch basin depth or water depth and larval abundance. Rainfall was an especially strong predictor of presence or absence of larvae in the summer of 2010, a season with an unusually high precipitation. Regression tree methods were used to build a schematic decision tree model of the interactions among these factors. This practical, visual representation of key predictors of high larval production may be used by local mosquito abatement districts to target limited resources to treat catch basins when they are particularly likely to produce West Nile virus vectors.

Ecological Modeling of Aedes aegypti (L.) Pupal Production in Rural Kamphaeng Phet, Thailand

Background Aedes aegypti (L.) is the primary vector of dengue, the most important arboviral infection globally. Until an effective vaccine is licensed and rigorously administered, Ae. aegypti control remains the principal tool in preventing and curtailing dengue transmission. Accurate predictions of vector populations are required to assess control methods and develop effective population reduction strategies. Ae. aegypti develops primarily in artificial water holding containers. Release recapture studies indicate that most adult Ae. aegypti do not disperse over long distances. We expect, therefore, that containers in an area of high development site density are more likely to be oviposition sites and to be more frequently used as oviposition sites than containers that are relatively isolated from other development sites. After accounting for individual container characteristics, containers more frequently used as oviposition sites are likely to produce adult mosquitoes consistently and at a higher rate. To this point, most studies of Ae. aegypti populations ignore the spatial density of larval development sites.MethodologyPupal surveys were carried out from 2004 to 2007 in rural Kamphaeng Phet, Thailand. In total, 84,840 samples of water holding containers were used to estimate model parameters. Regression modeling was used to assess the effect of larval development site density, access to piped water, and seasonal variation on container productivity. A varying-coefficients model was employed to account for the large differences in productivity between container types. A two-part modeling structure, called a hurdle model, accounts for the large number of zeroes and overdispersion present in pupal population counts.FindingsThe number of suitable larval development sites and their density in the environment were the primary determinants of the distribution and abundance of Ae. aegypti pupae. The productivity of most container types increased significantly as habitat density increased. An ecological approach, accounting for development site density, is appropriate for predicting Ae. aegypti population levels and developing efficient vector control programs.

Dispersal of Stable Flies (Diptera: Muscidae) From Larval Development Sites in a Nebraska Landscape

Seven mark-recapture studies were conducted over 3 yr to assess dispersal of newly emerging adult stable flies, Stomoxys calcitrans L., from larval development sites in a mixed agricultural environment in northeastern Nebraska. Infested hay debris piles were marked by dusting their surfaces with fluorescent pigments, adults were captured with surrounding grids of Alsynite sticky traps, and specimens were dissected to determine feeding histories and reproductive age. Distances and directions of 3,889 marked specimens indicated males and females dispersed equally and in all directions. Midguts of males and females were equally likely to contain blood-meal remnants. Percentage with blood remnants and percentage of females with yolk increased with distance from mark origin, indicating survival and spread were positively associated with host finding success. A time-integrated diffusion model fit to results from the seven studies indicated 50% of stable fly adults had dispersed beyond 1.6 km of their natal site, but only 5% had dispersed beyond 5.1 km. These results indicate that stable fly adults on cattle in a given area are most likely to have originated from larval development sites within an ≈ 5 km radius of the subject cattle.

Combining Google Earth and GIS mapping technologies in a dengue surveillance system for developing countries

BackgroundDengue fever is a mosquito-borne illness that places significant burden on tropical developing countries with unplanned urbanization. A surveillance system using Google Earth and GIS mapping technologies was developed in Nicaragua as a management tool.Methods and ResultsSatellite imagery of the town of Bluefields, Nicaragua captured from Google Earth was used to create a base-map in ArcGIS 9. Indices of larval infestation, locations of tire dumps, cemeteries, large areas of standing water, etc. that may act as larval development sites, and locations of the homes of dengue cases collected during routine epidemiologic surveying were overlaid onto this map. Visual imagery of the location of dengue cases, larval infestation, and locations of potential larval development sites were used by dengue control specialists to prioritize specific neighborhoods for targeted control interventions.ConclusionThis dengue surveillance program allows public health workers in resource-limited settings to accurately identify areas with high indices of mosquito infestation and interpret the spatial relationship of these areas with potential larval development sites such as garbage piles and large pools of standing water. As a result, it is possible to prioritize control strategies and to target interventions to highest risk areas in order to eliminate the likely origin of the mosquito vector. This program is well-suited for resource-limited settings since it utilizes readily available technologies that do not rely on Internet access for daily use and can easily be implemented in many developing countries for very little cost.

Why Arboviruses Can Be Neglected Tropical Diseases

Why Arboviruses Can Be Neglected Tropical Diseases

Geographic Distribution and Breeding Site Preference ofAedes albopictusandAedes aegypti(Diptera: Culicidae) in Cameroon, Central Africa

Presence in Cameroon of the recently introduced Aedes (Stegomyia) albopictus (Skuse) in association with the indigenous Aedes aegypti (L.) raises public heath concerns because it might alter the risk of arbovirus transmission. The breeding site and distribution of the two Stegomyia species are updated and reported following entomological surveys carried out in 22 localities throughout Cameroon, with a total of 1,353 containers with water visited. Ae. aegypti was found in every location sampled, showing higher infestation rates in northern Cameroon. Breeding populations of Ae. albopictus were observed in all 19 southern localities, up to the Adamaoua mountains, but the species was not recorded further north. In the area where both species are present, they were often sampled in the same larval developmental sites, suggesting convergent habitat segregation. The most frequently encountered artificial and natural breeding sites were used tires, discarded tins and plastic containers, abandoned car parts, brick holes, dead leaves on the ground, tree holes, and rock pools. Further monitoring of the demographic as well as geographic expansion of Ae. albopictus in this Afrotropical environment and its relationships with indigenous Ae. aegypti should provide insight into the biology of this highly invasive species and help to implement arboviruses surveillance programs in the area.

A new species of Wyeomyia (Hystatomyia) (Diptera: Culicidae) from Colombia and a redescription of Wy. (Hystatomyia) intonca Dyar &amp;amp; Knab

Species within the Wyeomyia subgenus Hystatomyia represent one of the dominant mosquito groups utilizing tank bromeliads as larval development sites in mangrove and adjacent forest habitats on the northern Pacific Coast of Colombia. Surveys of phytotelm plants in this region found larval stages of Wy. intonca Dyar &amp; Knab frequently associated with large tank bromeliads, especially of the genus Werauhia, growing in mangrove. Wyeomyia intonca was originally described in 1910 on the basis of a male from the Canal Zone, Panama, and the larval stage was partial described in the 1920s. These incomplete descriptions have led to confusion over its identity and differentiation from Wy. circumcincta Dyar &amp; Knab. Consequently, Wy. intonca is redescribed here. In addition, Wy. chocoensis sp.n. is described from specimens reared from tank bromeliads in the same region where Wy. intonca occurred. The descriptions of these two species, accompanied with relevant illustrations, are of adult males and females and of the pupal and larval stages.