New baseline environmental assessment of mosquito ecology in northern Haiti during increased urbanization

The catastrophic 2010 earthquake in Port‐au‐Prince, Haiti, led to the large‐scale displacement of over 2.3 million people, resulting in rapid and unplanned urbanization in northern Haiti. This study evaluated the impact of this unplanned urbanization on mosquito ecology and vector‐borne diseases by assessing land use and change patterns. Land‐use classification and change detection were carried out on remotely sensed images of the area for 2010 and 2013. Change detection identified areas that went from agricultural, forest, or bare‐land pre‐earthquake to newly developed and urbanized areas post‐earthquake. Areas to be sampled for mosquito larvae were subsequently identified. Mosquito collections comprised five genera and ten species, with the most abundant species being Culex quinquefasciatus 35% (304/876), Aedes albopictus 27% (238/876), and Aedes aegypti 20% (174/876). All three species were more prevalent in urbanized and newly urbanized areas. Anopheles albimanus, the predominate malaria vector, accounted for less than 1% (8/876) of the collection. A set of spectral indices derived from the recently launched Landsat 8 satellite was used as covariates in a species distribution model. The indices were used to produce probability surfaces maps depicting the likelihood of presence of the three most abundant species within 30 m pixels. Our findings suggest that the rapid urbanization following the 2010 earthquake has increased the amount of area with suitable habitats for urban mosquitoes, likely influencing mosquito ecology and posing a major risk of introducing and establishing emerging vector‐borne diseases.     

Identification of Aedes albopictus larval index thresholds in the transmission of dengue in Guangzhou,China

Entomological indices have been used to quantitatively express vector density, but the threshold of larval indices of Aedes albopictus in dengue epidemics is still undefined. We conducted a case‐control study to identify the thresholds of Aedes albopictus larval indices in dengue epidemics. Two unit levels of analysis were used: district and street. The discriminative power of the indices was assessed by receiver operating characteristic (ROC) curves. The association between the entomologic indices and dengue transmission was further explored by a logistic regression model. At the district level, there was no significant difference in the Breteau index (BI) between districts that reported cases and those did not (t=0.164, p>0.05), but the Container index (CI) did show a significant difference (t=2.028, p<0.01). The AUC (Area Under the Curve) of BI, CI, and prediction value were 0.540, 0.630, and 0.533, respectively. Predicting at the street level, the AUC of BI, CI, and prediction values were 0.684, 0.660, and 0.685, respectively, and 0.861, 0.827, and 0.867 for outbreaks. BI=5.1, CI=5.4, or prediction value =0.491were suggested to control the epidemic efficiently with the fewest resources, where BI=4.0, CI=5.1, or PRE =0.483 were suggested to achieve effectiveness.     

Oviposition substrate in Asian tiger mosquito surveillance: Do the sizes matter?

Ovitraps are regarded as a reliable system to monitor Aedes albopictus dynamics. However, the dimensions of the oviposition substrate are not standardized, and no studies have investigated which should be the most effective sizes. In this study, the effect of paddle sizes in tiger mosquito egg collection was evaluated. Egg count and density on the wide surfaces and margins of different‐sized oviposition substrates have been evaluated in two studies (A and B). In study A, a total of 29,995 Ae. albopictus eggs was counted in 250 classic oviposition substrates. Eggs were found on both wide surfaces (53.1%) and margins (46.9%). Egg density was significantly larger in margins compared to wide surfaces. Overall in study B, 983 Ae. albopictus eggs were collected. According to paddle sizes, 51.8% of eggs were on large and 48.2% on small paddles. Mean egg density of wide surfaces was significantly larger in small paddles (0.25 eggs/cm²) compared to large paddles (0.06 eggs/cm²). Results indicate that wider oviposition substrates do not mean larger number of Ae. albopictus eggs. Indeed, on paddles four times thinner than others, the number of eggs counted was not statistically different. These findings suggest that small paddles may be routinely employed in ovitraps, thus allowing savings of materials and money.     

Determining meteorological drivers of salt marsh mosquito peaks in tropical northern Australia

In northern Australia the northern salt marsh mosquito Aedes vigilax is a vector of Ross River virus and is an appreciable pest. A coastal wetland adjacent to Darwin's residential suburbs offers a favorable habitat for Ae. vigilax, and despite vigilant mosquito control efforts, peaks of Ae. vigilax occur in excess of 500/trap/night some months. To improve mosquito control for disease and nuisance biting to nearby residential areas, we sought to investigate meteorological drivers associated with these Ae. vigilax peaks. We fitted a cross‐sectional logistic regression model to weekly counts of female Ae. vigilax mosquitoes collected between July, 1998 and June, 2009 against variables, tide, rainfall, month, year, and larval control. Aedes vigilax peaks were associated with rainfall during the months September to November compared with January, when adjusted for larval control and tide. To maximize mosquito control efficiency, larval control should continue to be implemented after high tides and with increased emphasis on extensive larval hatches triggered by rainfall between September and November each year. This study reiterates the importance of monitoring and evaluating service delivery programs. Using statistical modelling, service providers can obtain solutions to operational problems using routinely collected data. These methods may be applicable in mosquito surveillance or control programs in other areas.     

Intraspecific variation in desiccation survival time of Aedes aegypti (L.) mosquito eggs of Australian origin

Aedes aegypti (L.) mosquitoes preferentially oviposit in natural and artificial receptacles where their eggs are able to withstand drying as water levels fluctuate. Desiccation‐resistant eggs also increase the potential for establishment in non‐native habitats while providing logistical impediments to control programs. Viability and mean survival times of eggs stored under three dryness conditions for up to 367 days were investigated among three field‐derived colonies of Australian Ae. aegypti to understand variation in desiccation survival. Further investigations compared egg survival between an established colony and its wild counterpart. Our results confirmed that Ae. aegypti eggs can withstand desiccation for extended periods of time with approximately 2–15% egg viability recorded after one year and viability remaining above 88% under all conditions through 56 days. Intraspecific variations in egg survival times were recorded, suggesting local adaptation while each of the colonies demonstrated a consistent preference for higher humidity. Egg volume varied between the populations, suggesting a relationship between egg volume and survival time, with the marginally larger eggs (Charters Towers and Innisfail) having greater desiccation resistance over the range of conditions. The strong survivorship of Charters Towers eggs in dry, warm conditions demonstrates the adaptive significance of a desiccation‐resistant egg.     

Organosulphur constituents in garlic oil elicit antennal and behavioural responses from the yellow fever mosquito

Garlic (Allium sativum) and its essential oil have long been used for their distinct flavour, therapeutic effects and as a topical and systemic insect repellent. We tested the hypothesis that the yellow fever mosquito, Aedes aegypti L. (Diptera: Culicidae), responds electrophysiologically and behaviourally to specific components of the steam‐distilled essential oil of garlic. In coupled gas chromatographic‐electroantennographic detection analyses of garlic oil, antennae of female Ae. aegypti responded to 14 compounds. Seven of them [diallyl disulphide, diallyl trisulphide, diallyl tetrasulphide, 2‐(2,3‐dithia‐5‐hexenyl)‐3,4‐dihydro‐2H‐thiopyran, 3‐(2,3‐dithia‐5‐hexenyl)‐3,4‐dihydro‐2H‐thiopyran, 6‐methyl‐4,5,8,9‐tetrathiadodeca‐1,11‐diene and 4,5,9,10‐tetrathiatrideca‐1,12‐diene] were isolated or synthesized and tested for their ability to repel host‐seeking female Ae. aegypti. A solution of diallyl trisulphide and diallyl tetrasulphide applied to a human forearm provided protection from female mosquitoes significantly longer than the paraffin oil control. All compounds had mean protection times significantly shorter than an equivalent dose of the ‘gold standard’N,N‐diethyl‐3‐methylbenzamide. Understanding the common moiety in organosulfur compounds that causes repellence could lead to the design of analogues that are more effective than their natural counterparts in repelling mosquitoes.     

The kinin receptor is expressed in the Malpighian tubule stellate cells in the mosquito Aedes aegypti (L.): a new model needed to explain ion transport?

It is known that insect kinins increase diuresis and fluid secretion in the Aedes aegypti Malpighian tubule, causing a rapid drop of the transepithelial resistance and increasing chloride conductance from the hemolymph towards the tubule lumen. The tubule is composed of both principal and stellate cells. The main route for increased chloride influx upon kinin treatment is proposed to be paracellular, with septate junctions acquiring increased chloride selectivity and conductance. Therefore, kinin treatment renders the Ae. aegypti tubule a “leaky epithelium”, and under this model the kinin receptor is postulated to be expressed in principal cells. However, in another dipteran, the fruit fly Drosophila melanogaster, the main route for chloride transport is transcellular through stellate cells. In both the fruit fly and the mosquito Anopheles stephensi the kinin receptor has been immunolocalized in stellate cells, where it regulates transepithelial chloride permeability. Here we show that in Ae. aegypti, similarly, the stellate cells express the kinin receptor. This was confirmed through immunohistochemistry with two specific anti-kinin receptor antibodies and confocal analysis. The receptor is detected as a 75 kDa band in western blot. These results indicate that the currently accepted model for chloride transport must be re-evaluated in Ae. aegypti and suggest the kinin regulatory signals controlling intercellular junctions originate in the stellate cells.     

Synthesis and bio-evaluation of aryl hydrazono esters for oviposition responses in Aedes albopictus

A novel series of aryl hydrazono esters (AHE) (1-13) were synthesized (yield 76-98%) to study the oviposition responses in Aedes albopictus (Skuse) mosquitoes for the first time. At a concentration of 10 μg ml⁻¹ in dual choice experiment, among the screened compounds, AHE-12 showed remarkable oviposition attractant activity with an oviposition activity index (OAI) of +0.299 (greater than 95% confidence limit) comparable to p-cresol (OAI +0.320) which is well-reported oviposition attractant for Aedes aegypti. Conversely, AHE-10 exhibited highest oviposition deterrent activity with OAI −0.247. The possible utilization of these compounds will be in integrated vector management strategies.     

Altitudinal variation in the morphometric characteristics of Aedes vexans Meigen from northeastern Turkey

Body size is one of the most significant features of organisms and is correlated with a large number of ecological and physiological variables. Similar to size, biological shape is one of the most conspicuous aspects of an organism's phenotype and provides a link between the genotype and the environment. Body size may change with altitude and also habitat differences associated with altitude may affect the biological shape and some morphological characteristics. Four populations of Aedes vexans Meigen occurring in different ecological subregions at altitudes between 808–1,620 m in the Aras Valley from northeastern Turkey were compared using traditional and geometric morphometrics. When the wing shape differences of populations were analyzed by UPGM, the cluster analyses recognized two main groups of populations. Gödekli (808 m) comprised the first group while Zülfikar (848 m), Sürmeli (944 m), and Cilehane (1,620 m) populations comprised the second group. In the second group, Zülfikar and Cilehane populations showed a similar grouping pattern while Sürmeli appeared as a different group. Centroid sizes were used as measures of overall wing size differences among different regions. Aedes vexans from the Sürmeli region had relatively larger wings.     

Abundance of West Nile virus mosquito vectors in relation to climate and landscape variables

It is currently unclear if the potential for West Nile virus transmission by mosquito vectors in the eastern United States is related to landscape or climate factors or both. We compared abundance of vector species between urban and suburban neighborhoods of Henrico County, VA, in relation to the following factors: temperature, precipitation, canopy cover, building footprint, and proximity to drainage infrastructure. Mosquitoes were collected throughout the 2005, 2006, and 2007 seasons and tested for West Nile virus (WNV) in pools of 10–50. Test results of mosquito pools were compared to average site abundance from 37 sites in Henrico County, VA; abundance was then examined in relation to ecological variables. Urban infrastructure was positively correlated with the abundance of Culex pipiens L./Cx. restuans, and our findings implicate combined sewer overflow systems as large contributors to Culex vector populations. No measure of urbanization examined in our study was correlated with Aedes albopictus abundance. Our study showed that certain landscape variables identified using Geographic Information Systems are valuable for predicting primary WNV vector abundance in Virginia, and that temperature along with low precipitation are strong predictors of population growth. Our results support other regional studies that found WNV proliferates under drought conditions.