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Abundance and distribution of immature mosquitoes in urban rivers proximate to their larval habitats
Abstract
Whether ecological restoration of polluted urban rivers would provide suitable breeding habitats for some mosquitoes was not clear yet. It was therefore important to determine how altered river conditions influence mosquito ecology. Monthly data on water quality and larval density were obtained to determine the effects of river systems on the distribution and abundance of immature mosquitoes in two coastal cities in Eastern China. In total, 5 species within two genera of mosquitoes were collected and identified in habitat with vegetation from three positive rivers. Culex pipiens pallens was the most abundant and widely distributed species. A new species (Culex fuscanus) was reported in certain districts. Physico-chemical parameters of river water were important, but not the only, set of influences on immature mosquito breeding. Aquatic vegetation could increase the likelihood of mosquito breeding while artificial aeration might prevent the approach of mosquitoes. Slow-moving water might be a new potential marginal habitat type for some Culex and Aedes albopictus. Variation of river system with ecological restoration might influence the abundance and distribution of immature mosquitoes.
... Sehubungan dengan sumber makanan, beberapa penelitian menunjukkan bahwa masukan detritus adalah salah satu sumber energi utama untuk larva Ae. aegypti di habitat akuatik. Telah terungkap bahwa kelimpahan bakteri berkurang oleh aktivitas makan Ae. triseriatus (Ma, Huang, & Leng, 2016). Cyanobacteria tampaknya memiliki peran penting dalam diet, terbukti dari lambung Ae. aegypti memiliki konsentrasi tinggi dari mikroorganisme fitoplankton ini. ...
... Faktor yang mempengaruhi pertumbuhan larva adalah nutrisi (Ray et al., 2009;Telang, Frame, & Brown, 2007;Padmanabha et al., 2011), yang akan memiliki konsekuensi pada fekunditas dewasa (Perez & Noriega, 2014;Perez & Noriega, 2014), massa larva, massa dewasa, cadangan gizi dan profil produksi ekdisteroid (Telang, Frame, & Brown, 2007). Faktor lain yang mempengaruhi pertumbuhan lainnya adalah suhu (Ma et al., 2016;Mohammed & Chadee, 2011;Farjana, Tuno, & Higa, 2012). Pada suhu 24-25 0 C keberhasilan telur menetas adalah 98%, namun pada 34-35 0 C telur menetas menurun menjadi 1,6%. ...
... Kadar oksigen terlarut (DO) dalam air mengakibatkan kelangsungan hidup larva berkurang dan waktu pengembangan yang lebih lama (Silberbush, Abramsky, & Tsurim, 2015). Oksigen terlarut merupakan faktor yang signifikan mempengaruhi kelimpahan larva C. Annulirostris (Ma et al., 2016). Garcia-Sánchez, Pinilla, & Quintero, (2017) melaporan bahwa ditemukan pembeda faktor fisiko kimia dari tempat perindukan yang ditemukan larva Ae. ...
... The larval stages of all species of Anopheles require water, so the presence of a water source is associated with an increased distribution and density of larvae, as well as an increased incidence of adult mosquitoes and thus malaria [11,12]. Several factors are correlated with the presence of larvae, including pH, temperature, dissolved oxygen (DO) level, alkalinity, and phosphate and chloride concentrations [12]. ...
... The larval stages of all species of Anopheles require water, so the presence of a water source is associated with an increased distribution and density of larvae, as well as an increased incidence of adult mosquitoes and thus malaria [11,12]. Several factors are correlated with the presence of larvae, including pH, temperature, dissolved oxygen (DO) level, alkalinity, and phosphate and chloride concentrations [12]. Moreover, different species occupy different habitats, with An. minimus and An. ...
... Finally, the width of the river was significantly negatively correlated with the abundance of both species. Larger rivers tend to have stronger currents, which are very dangerous to mosquito larvae [12]. Consequently, mosquito larvae tend to be associated with stagnant and slow running water in the The Scientific World Journal 7 wild, and nearly all larvae will be eliminated by currents of >15 kilogallons/min [12,27]. ...
Malaria is transmitted by female mosquitoes in the genus Anopheles and is a major public health issue. Different species of Anopheles mosquitoes have different epidemiological characteristics, behaviors, and ecological requirements, and so an understanding of their biology and ecology in a particular area is critical for successful disease control. The aim of this study was to determine which environmental factors are associated with Anopheles larvae in a malaria-endemic area in Ratchaburi Province, Thailand, which shares a border with Myanmar. In October 2016, we collected mosquito larvae and measured six environmental factors at 10 study sites located along Lam Pachi River, which flows through Huay Nam Nak village in Ratchaburi Province. We found two species of Anopheles larvae (An. subpictus sensu lato (s.l.) Grassi and An. barbirostris s.l. van der Wulp) at 7 of the 10 study sites, the numbers of which significantly differed between sites (p < 0.05). Pearson correlation analysis showed that the numbers of larvae of both species were significantly positively correlated with the dissolved oxygen level (p < 0.01) and significantly negatively correlated with the width of the river (p < 0.05) and pH (p < 0.01). By contrast, turbidity, water depth, and water temperature were not associated with larval abundance. Mosquito species which belong to genus Anopheles are considered to be of public health and medical importance. Therefore, Anopheles mosquito surveillance and control in the study sites are essential. This information will facilitate vector-borne disease control and improve our understanding of the biology of Anopheles vectors in rivers located along international borders, further reducing the number of patients in this malaria-endemic area.
... Dense vegetation provides shaded areas and increased moisture, creating suitable resting and breeding sites for mosquitoes. Dense vegetation with thick foliage can provide shade and retain water, creating favorable conditions for mosquito breeding [77]. Overgrown vegetation can also make it di cult to detect and eliminate mosquito breeding sites. ...
This review aims to provide a comprehensive overview of the important predictors, and additionally spatial modeling tools capable of producing Dengue Hemorrhagic Fever (DHF) risk maps. A literature search was conducted in PubMed, Scopus, Science Direct, and Google Scholar for studies reporting DHF risk factors. The Preferred Reporting Items for Systematic Reviews (PRISMA) 2020 statement is used to report this scoping review. It lasted from January 2011 to August of 2022. Initially 1329 articles were found, after inclusion and exclusion criteria, 45 manuscripts were selected. A variety of models and techniques were used to identify DHF risk areas with an arrangement of various multiple-criteria decision-making, statistical, and Machine Learning technique. We found that There was no pattern of predictor use associated with particular approaches; instead, a wide range of predictors was used to create DHF risk maps. Predictors are various variables or factors that are considered when assessing the likelihood or intensity of DHF outbreaks in a specific area in the context of DHF risk mapping. These predictors can include climatology factors (e.g., temperature, rainfall, humidity), socio-economic indicators (e.g., population density, urbanization level), environmental factors (land-use, elevation) and other relevant factors (e.g., mosquito abundance, previous DHF cases). The spatial model of DHF risk is a valuable tool for public health authorities, policymakers, and communities to identify areas at higher risk of dengue transmission, but its limitations underscore the importance of complementing it with other approaches and considering contextual factors for a more holistic assessment of DHF outbreaks. It enables targeted interventions, such as vector control measures and public awareness campaigns, to be implemented in high-risk areas, ultimately helping to mitigate the impact of dengue outbreaks and protect public health.
... The other type refers to environmental factors that can be further classified as built-up or socioeconomic environmental variables. The former includes vegetation (Gleiser and Gorla, 2007;Hendy et al., 2020;Lourenço et al., 2011), roads (Madewell et al., 2019;Regilme et al., 2021) and rivers (Carver et al., 2009;Ma et al., 2016); the latter consists of the human population (Romeo-Aznar et al., 2018;Schmidt et al., 2011) and housing prices. Apart from variables chosen by following previous studies (e.g., vegetation, roads, and population), we also introduced indicators that could, to some extent, reflect the socioeconomic characteristics of a community. ...
Aedes albopictus (Diptera: Culicidae) is a major vector of multiple diseases. While vaccines have been developed, preventing these Aedes-borne diseases continues to primarily depend on monitoring and controlling the vector population. Despite increasing research on the impacts of various factors on Ae. albopictus population dynamics, there is still no consensus on how meteorological or environmental factors affect vector distribution. In this study, the relationships between mosquito abundance and meteorological and environmental indicators were examined at the town level based on data collected from July to September, the peak abundance period of 2019 in Shanghai. In addition to performing Poisson regression, we employed the geographically weighted Poisson regression model to account for spatial dependency and heterogeneity. The result showed that the environmental factors (notably human population density, the Normalized Difference Vegetation Index (NDVI), socioeconomic deprivation, and road density) had more significant impacts than the meteorological variables in accounting for the spatial variation of mosquito abundance at a city scale. The dominant environmental variable differed in urban and rural places. Furthermore, our findings indicated that deprived townships are more susceptible to higher vector densities compared to non-deprived townships. Therefore, it is crucial not only to allocate more resources but also to increase attention towards controlling the vectors responsible for their transmission in these townships.
... Malaria risk stratification of Rivers State from 2007 to 2017 also showed that Ikwerre LGA recorded very high malaria risk ( Figure 13) including Eleme, Ogu-Bolo and Opobo/Nkoro LGAs whereas Abua-Odual, Akuku-Toru and Degema had very low malaria risk. These LGAs with very low malaria risk are riverine communities and according to [17], the quality of water bodies could determine the presence and abundance of adult malaria vectors and consequently affect malaria transmission in the region. It is therefore highly probable that the water bodies are not conducive for malaria vector breeding and hence the very low risk recorded in the area. ...
Rivers State is the centre of Nigeria's oil industry and has the presence of oil prospectors including expatriates who are at risk of malaria infection. Periodic analysis of epidemiological data will enable malaria control programmers to appraise the interventions carried out over the years and assist in the development of sustainable and adaptive strategies directed from an informed local level. This study, therefore, examined spatiotemporal variations in malaria incidence in the State using Annual Parasite Incidence (API) as an indicator. Monthly reported malaria cases from 2007-2017 at the local government area (LGA) level were retrieved from the Integrated Disease Surveillance Response (IDSR) system of Rivers State Ministry of Health while projected population data for the same period were obtained from the National Bureau of Statistics. API of the LGAs from 2007 to 2017 were computed, integrated into GIS, and subjected to weighted overlay analysis to delineate the risk zones. The eleven-year retrospective study of malaria in Rivers State displayed geographical variations which were statistically significant between the LGAs. Malaria incidence fluctuated throughout the study period. API values increased from 13.746 in 2007 to 34.067 in 2013 and dropped to 8.721 in 2017. All the LGAs recorded API values below 100, indicating a very low malaria burden in a controlled setting. However, none of the LGAs has reached the WHO standard level for the elimination of transmission. Ikwerre, Eleme, Ogu-Bolo and Opobo/Nkoro LGAs were assigned to the very high malaria risk stratum (362.615 to 490.005) whereas Abua-Odual, Akuku-Toru and Degema LGAs were assigned to very low-risk malaria stratum (103.281 to 113.897). The findings of this research will aid stakeholders in evaluating the impact of control strategies employed over the years and possibly, revisit malaria extant interventions for improved malaria control outcomes.
... The abundance of rainfall and vegetation cover in a breeding habitat can influence the distribution and density of larvae, which in turn can influence the abundance of adult Anopheles vectors [32,34,35]. Water temperature can also affect the development of eggs or allow the development of more microorganisms that are required by the larvae for food [32,36]. ...
Background
Mosquito larval source management (LSM) is a valuable additional tool for malaria vector control. Understanding the characteristics of mosquito larval habitats and its ecology in different land use types can give valuable insight for an effective larval control strategy. This study determined the stability and productivity of potential anopheline larval habitats in two different ecological sites: Anyakpor and Dodowa in southern Ghana.
Methods
A total of 59 aquatic habitats positive for anopheline larvae were identified, and sampled every two weeks for a period of 30 weeks using a standard dipping method. Larvae were collected using standard dippers and were raised in the insectary for identification. Sibling species of the Anopheles gambiae sensu lato (s.l.) were further identified by polymerase chain reaction. The presence of larval habitats, their stability and larvae positive habitats were compared between the two sites using Mann–Whitney U and the Kruskal–Wallis test. Factors affecting the presence of An. gambiae larvae and physicochemical properties at the sites were determined using multiple logistic regression analysis and Spearman’s correlation.
Results
Out of a total of 13,681 mosquito immatures collected, 22.6% (3095) were anophelines and 77.38% (10,586) were culicines. Out of the 3095 anophelines collected, An. gambiae s.l. was predominant (99.48%, n = 3079), followed by Anopheles rufipes (0.45%, n = 14), and Anopheles pharoensis (0.064%, n = 2). Sibling species of the An. gambiae consisted of Anopheles coluzzii (71%), followed by An. gambiae s.s. (23%), and Anopheles melas (6%). Anopheles mean larval density was highest in wells [6.44 (95% CI 5.0–8.31) larvae/dip], lowest in furrows [4.18 (95% CI 2.75–6.36) larvae/dip] and man-made ponds [1.20 (95% CI 0.671–2.131) larvae/dip].The results also revealed habitat stability was highly dependent on rainfall intensity, and Anopheles larval densities were also dependent on elevated levels of pH, conductivity and TDS.
Conclusion
The presence of larvae in the habitats was dependent on rainfall intensity and proximity to human settlements. To optimize the vector control measures of malaria interventions in southern Ghana, larval control should be focused on larval habitats that are fed by underground water, as these are more productive habitats.
Graphical Abstract
... Although this species is source of nuisance due to its biting pattern. The high abundance of this species was reported in different countries globally (22) and locally in Pakistan (23). This species could transmit filarial parasites to humans and in immunocompromised individuals. ...
Background: Mosquitoes (Diptera: Culicidae) are haemotophagus insects and are vectors of many arthropod-borne
diseases. Present study aimed to explore species composition, seasonal abundance, spatial distribution and physio-
chemical properties of larval breeding sites of mosquitoes in District Mardan, Khyber Pakhtunkhwa, Pakistan.
Methods: Both adults and larvae of mosquitoes were collected through light traps, insecticide spray, mouth aspirator
and larval standard dipping method in District Mardan from May to November 2017. Water samples from larval sites
were physio-chemically analysed.
Results: 5078 (3704 adults and 1374 larvae) mosquito specimens were collected in Mardan, Katlang and Takhtbhai
tehsils. Six species in four genera were reported. Culex pipiens (89.80%) and Armigeres subalbatus (9.20%) were the
most abundant species. Diversity was high in Takhtbhai (0.29) followed by Katlang (0.28) and Mardan (0.25). Greater
number of specimens were recorded in peridomestic sites (93.97%) as compared to domestic habitats (6.03%). Culex
pipiens larval abundance had negative correlation with pH whereas it correlated positively with electric conductivity,
salinity, and TDS (total dissolved sulphur). Mosquito abundance peaked in August and July while the lowest was in
May. Their monthly abundance had positive correlation with rainfall (r= 0.5069), relative humidity (r= 0.4439) and mean
minimum temperature (r= 0.2866). Number of mosquitoes was highest at low elevation < 347m asl (above sea level) in
agriculture land and near to water bodies (streams).
Conclusion: Culex pipiens being the most abundant species, was susceptible to high pH. Mosquitoes preferred habitats
were at low elevation in agriculture land.
... Various water-holding containers ranging from small to large and natural to manmade have been reported to support Aedes mosquito breeding. They include tires, flower pots, plastic or metal recipients, drains, swimming pools, storm water, flooding water, bamboo sticks, and plant axils (8)(9)(10). Moreover, any standing water body represents a potential mosquito breeding site. ...
Background
The knowledge of key elements of the ecosystem affecting mosquito distribution and their population dynamics is essential for designing mosquito-borne disease interventions. The present study characterized the physicochemical properties of Aedes mosquito breeding habitats in Democratic Republic of the Congo.
Methods
A cross-sectional survey was carried out in Kinshasa, from February to April 2021. The physicochemical characteristics of the natural and artificial aquatic habitats of Aedes were measured using a multiparametric device.
Results
Out of 438 breeding habitats inspected, 273 (62.3%) contained mosquito larvae. The Aedes mosquitoes identified in 76.19% of positive breeding sites were Aedes albopictus (67.30%) and Aedes aegypti (37.98%). The median values of dissolved oxygen (DO) (1.0), turbidity (19.15), and salinity (0.115) in water breeding sites of Aedes were respectively 0.8, 55.0, and 0.29 in Culex breeding sites ( p < 0.05). The physicochemical characteristics of the breeding habitat for Ae. aegypti and Ae. albopictus were almost identical. In urban areas, the median temperature was 29.82 while it was 29.60 in suburban areas ( p < 0.05). Significantly, the salinity was higher in bamboo and metal containers while DO was higher in tins. After analysis using simple linear regression, total dissolved solids (r = 0.23; p = 0.000), conductivity (r = 0.23), salinity (r = 0.23), and temperature (r = 0.13) were associated with larval density ( p < 0.05). In the final model (r = 0.30, p = 0.01), salinity (r = 0.23) and DO (r = 0.138) adjusted to temperature, pH, and turbidity were associated positively to larvae density.
Conclusion
The Aedes breeding sites and mosquito density were significantly influenced by water salinity, DO, temperature, pH, and turbidity.
... dan Culex sp. (Ma, Huang, and Leng 2016). Nyamuk yang dapat ditemukan di taman perkotaan yaitu Aedes aegypti, Aedes albocpitus, Culex quiquefasciatus (Medeiros-Sousa et al. 2015). ...
... Culex pipiens pallens, commonly found north of 37 • N in China, Japan and Korea, is one of the major mosquito species responsible for biting human and disease transmission (Kim and Tsuda, 2015). Previous study has shown that since slow-moving urban creeks were polluted, Cx. pipiens pallens was the most abundant and widely distributed species in positive sites (Ma et al., 2016). We hypothesize that PACl coagulation-flocculation could drive larval Cx. ...
Larval mosquitoes have a more limited home range and lower resistance to adverse environment than adults, thus can be ideal targets for vector control in some cases. Coagulation-flocculation technology, which could be used for water treatment in breeding sites of several vector mosquito species, can significantly change both the distribution of organic particles and surface sediment characteristics in water environment. The aim of this study was to explore the effect, principle and possibility of using coagulation-flocculation technology in immature mosquitoes killing. In this study, dechlorinated water was treated with Poly Aluminum Chloride (PACl, sewage treatment using), and we observed the impacts of PACl treatment on the development and survival of immature Culex pipiens pallens mosquitoes. When exposed to PACl treatment, physical effect is believed to be a main reason of coagulation-flocculation caused high larvae mortality: Ⅰ) alum floc layer increases the difficulty of larvae foraging, leads larvae starving to death; (Ⅱ) the little floc particles could attach to the lateral hair of larvae, which impede floatation process and then surface respiration by larval mosquitoes. The alum floc layer had a good killing effect on the mosquito larvae, presented the half lethal time (LT50) of 2d, the 90% lethal time (LT90) of 8.7±7.3 ∼ 14±4.5 d, and the pupation rate of 0 ∼ (6.5±0.5)%, respectively. Our results indicates alum floc, produced by PACl coagulation-flocculation, was shown to be highly active against 1st∼2nd instar larvae, the high mortality rate of immature mosquitoes as a result of physical effect. The observations suggest that coagulation-flocculation technology offers a novel potential approach to a sustainable and low-impact mosquito control method.
... Reducing the number of Aedes mosquitoes is recognized as an effective means to reduce risks and control the outbreak of dengue fever (Ma et al. 2016;Weeratunga et al. 2016). For controlling Ae. aegypti populations, there is an intense focus on larvae eradication, because breeding sites are often close to human populations, especially man-made containers (Chaiphongpachara et al. 2018;Rohani et al. 2014). ...
Laojun S, Chaiphongpachara T. 2020. Comparative study of larvicidal activity of commercial essential oils from aromatic rosemary, vanilla, and spearmint against the mosquito Aedes aegypti. Biodiversitas 21: 2383-2389. Dengue fever is a dangerous mosquito-borne viral disease of humans. This disease is caused by dengue virus, a member of the genus Flavivirus of the family Flaviviridae. The Aedes aegypti mosquito is a principal vector for this virus. To control Ae. aegypti populations, there is extensive focus on larval eradication, because breeding sites are often close to human populations, especially man-made containers. The objective of this research was to evaluate the efficacy of commercial essential oils from rosemary (Rosmarinus officinalis), vanilla (Vanilla planifolia), and spearmint (Mentha spicata) with regard to larvicidal activity against Ae. aegypti larvae after 24 and 48-hours of exposure in the laboratory. The results showed highly efficacious larvicidal activity, with median lethal doses (LC50) of 0.23, 0.10, and 0.12 ppm after 24-hour exposure to commercial rosemary, vanilla, and spearmint oil, respectively. The results of this study will be useful for the control of a common dengue vector and may replace the use of pesticides that may have broad environmental impacts.
... DO is important for several species of larval mosquitoes [12] and other aquatic invertebrates [15]. A study of urban rivers proximate to larval habitats in Chinese urban areas found that DO in breeding containers was negatively associated with overall larval abundance [16]. Another study in central Colombia found DO significantly affected Ae. aegypti larvae, with a range of 5.85-6.25 mg/l [17]. ...
Purpose
The purpose of this paper is to investigate the influence of breeding containers on the production of Aedes mosquitoes after a vector-control program in households that might support dengue transmission in tourist attraction areas of Bang Kachao Riverbend, Thailand.
Design/methodology/approach
A cross-sectional study was conducted in an ecotourism area of Bang Kachao Riverbend, Thailand, during the period October 2016 to September 2017. A total of 832 households from five villages participated in the study. Data collection employed an interview questionnaire, larval mosquito survey and measurements of the chemical properties of the water in each container. A binary logistic regression model was used to investigate the characteristics of water containers influencing the presence or absence of Aedes immatures.
Findings
The study found that water containers located inside households had a highly presence of Aedes immatures (2.22 times) compared with outdoor containers. Water containers without lids and water containers with ineffective had a high presence of Aedes immatures (3.69 and 2.54 times, respectively). In addition, the chemical properties of the water inside the containers, such as pH, influenced the presence of Aedes immatures (1.76 times) (OR=1.76, 95% CI=1.59–1.96).
Originality/value
The study results emphasized the characteristics of water containers in households located in a tourist attraction area. The findings may inform public health vector-control messages for households located in the tourist attraction area.
... In fact, a considerable number of biotic and abiotic factors, such as habitat types and aquatic vegetation, seasonal variation and physicochemical parameters of water, affect the abundance and distribution of immature mosquitoes (Gardner et al. 2013;Ma et al. 2016). In addition, different mosquito species choose various types of habitats for diurnal rest, either having a solid background or within vegetation (Clements, 1999). ...
Oases are semi-natural woodlots surrounded by an inhospitable desert environment. This insular-like habitat system is known to support a mixture of sedentary and migratory bird species originating from different areas. However, little is known about the interactions between these birds and parasites. In this study, we investigated the diversity, prevalence and host specificity of avian haemosporidian parasites in southern Tunisian oases in two sedentary and common bird species, the laughing dove Spilopelia senegalensis and hybrid sparrow Passer domesticus × hispaniolensis , in six sites that differ regarding vegetation structure and distance to the coast. Two new Haemoproteus lineages, related to other Haemoproteus transmitted by biting midges, were detected in doves. With regard to sparrows, all detected parasites have previously been reported in other sparrow populations, except for one new Haemoproteus lineage. Our results also showed that densely vegetated sites were characterized by the higher prevalence of Plasmodium but a lower prevalence of Haemoproteus compared with less-vegetated sites. This is the first study aiming to explore avian parasites in the oasis habitat. Gathering data on a larger sample of oases with different sizes and isolation levels will be the next step to better understand factors shaping the transmission dynamics of avian parasites in such ecosystems.
... DO was negatively associated with A. aegypti infestation in both models (Tables 2 and 3), but there were no differences in DO levels between urban and rural sites ( Table 5). Ma et al. [70] also found a significantly negative association between DO and overall larval abundance in Chinese urban river systems, although these larvae mainly consisted of Culex species. On the other hand, A. aegypti has been observed to oviposit and develop normally in raw sewage with low levels of dissolved oxygen, suggesting a wide tolerance spectrum [36]. ...
Background
Aedes aegypti, the major vector of dengue, breeds in domestic water containers. The development of immature mosquitoes in such containers is influenced by various environmental, ecological and socioeconomic factors. Urban and rural disparities in water storage practices and water source supply may affect mosquito immature abundance and, potentially, dengue risk. We evaluated the effect of water and container characteristics on A. aegypti immature abundance in urban and rural areas. Data were collected in the wet season of 2011 in central Colombia from 36 urban and 35 rural containers, which were either mosquito-positive or negative. Immature mosquitoes were identified to species. Data on water and container characteristics were collected from all containers.
Results
A total of 1452 Aedes pupae and larvae were collected of which 81% were A. aegypti and 19% A. fluviatilis. Aedes aegypti immatures were found in both urban and rural sites. However, the mean number of A. aegypti pupae was five times higher in containers in the urban sites compared to those in the rural sites. One of the important factors associated with A. aegypti infestation was frequency of container washing. Monthly-washed or never-washed containers were both about four times more likely to be infested than those washed every week. There were no significant differences between urban and rural sites in frequency of washing containers. Aedes aegypti immature infestation was positively associated with total dissolved solids, but negatively associated with dissolved oxygen. Water temperature, total dissolved solids, ammonia, nitrate, and organic matter were significantly higher in urban than in rural containers, which might explain urban-rural differences in breeding of A. aegypti. However, many of these factors vary substantially between studies and in their degree of association with vector breeding, therefore they may not be reliable indices for vector control interventions.
Conclusions
Although containers in urban areas were more likely to be infested with A. aegypti, rural containers still provide suitable habitats for A. aegypti. Containers that are washed more frequent are less likely to produce A. aegypti. These results highlight the importance of container washing as an effective vector control tool in both urban and rural areas. In addition, alternative designs of the highly productive washbasins should continue to be explored. To control diseases such as dengue, Zika and chikungunya, effective vector breeding site control must be implemented in addition to other interventions.
Background
Creating a spatial model of dengue fever risk is challenging duet to many interrelated factors that could affect dengue. Therefore, it is crucial to understand how these critical factors interact and to create reliable predictive models that can be used to mitigate and control the spread of dengue.
Methods
This scoping review aims to provide a comprehensive overview of the important predictors, and spatial modelling tools capable of producing Dengue Haemorrhagic Fever (DHF) risk maps. We conducted a methodical exploration utilizing diverse sources, i.e., PubMed, Scopus, Science Direct, and Google Scholar. The following data were extracted from articles published between January 2011 to August 2022: country, region, administrative level, type of scale, spatial model, dengue data use, and categories of predictors. Applying the eligibility criteria, 45 out of 1,349 articles were selected.
Results
A variety of models and techniques were used to identify DHF risk areas with an arrangement of various multiple-criteria decision-making, statistical, and machine learning technique. We found that there was no pattern of predictor use associated with particular approaches. Instead, a wide range of predictors was used to create the DHF risk maps. These predictors may include climatology factors (e.g., temperature, rainfall, humidity), epidemiological factors (population, demographics, socio-economic, previous DHF cases), environmental factors (land-use, elevation), and relevant factors.
Conclusions
DHF risk spatial models are useful tools for detecting high-risk locations and driving proactive public health initiatives. Relying on geographical and environmental elements, these models ignored the impact of human behaviour and social dynamics. To improve the prediction accuracy, there is a need for a more comprehensive approach to understand DHF transmission dynamics.
Mosquito-borne diseases (MBDs) are emerging in response to climate and land use changes. As mosquito (Diptera: Culicidae) habitat selection is often contingent on water availability for egg and larval development, studies have recognized water quality also influences larval habitats. However, underlying species-, genera-, and mosquito level preferences for water quality conditions are varied. This systematic review and meta-analysis aimed to identify, characterize, appraise, and synthesize available global data on the relationships between water quality and mosquito presence and abundance (MPA); with the goal to further our understanding of the geographic expansion of MBD risks. A systematic review was conducted to identify studies investigating the relationships between water quality properties and MPA. Where appropriate, random-effects meta-analyses were conducted to provide pooled estimates for the association between the most reported water quality properties and MPA. The most reported water quality parameters were pH (87%), nitrogen concentrations (56%), turbidity (56%), electrical conductivity (54%), dissolved oxygen (43%), phosphorus concentrations (30%), and alkalinity (10%). Overall, pH (P = 0.05), turbidity (P < 0.0001), electrical conductivity (P = 0.005), dissolved oxygen (P < 0.0001), nitrogen (P < 0.0001), and phosphorus (P < 0.0001) showed significantly positive pooled correlations with MPA, while alkalinity showed a nonsignificant null pooled correlation (P = 0.85). We observed high heterogeneity in most meta-analyses, and climate zonation was shown to influence the pooled estimates. Linkages between MPA and water quality properties will enhance our capacity to predict MBD risks under changing environmental and land use changes.
We evaluate the links between wetland breeding mosquitoes (Diptera: Culicidae), vector-borne disease transmission, human incidence of disease and the underlying mechanisms regulating these relationships. Mosquitoes are a diverse taxonomic group that plays a number of important roles in healthy wetlands. Mosquitoes are also the most important insect vectors of pathogens to wildlife, livestock and humans, transmitting many important diseases such as malaria, West Nile virus, and Ross River virus. Mosquitoes interact with a variety of invertebrates and vertebrates in complex communities within wetlands. These interactions regulate populations of key vector species. Healthy wetlands are characterized by intact wetland communities with increased biodiversity and trophic structure that tend to minimize dominance and production of vector mosquito species, reservoir host species and minimize risk of disease to surrounding human and animal populations. In a public health paradigm, these natural ecological interactions can be considered a direct ecosystem service—natural mitigation of vector-borne disease risk. Anthropogenic disruptions, including land-use, habitat alterations, biodiversity loss and climatic changes can compromise natural ecological processes that regulate mosquito populations and have severe human health and economic implications. Maintenance of healthy wetlands is likely to be beneficial for human and ecosystem health, and more cost effective and sustainable than chemical control of vector species.
Freshwater ecosystems worldwide are subjected to a vari-ety of anthropogenic threats (Malmqvist and Rundle 2002). Inappropriate land use practices, pollutants, overexploita-tion, and overpopulation have simplified/fragmented aquatic habitats and degraded biodiversity and water quality. In fluvial systems, human threats result from rel-atively slight use, such as, sports activities (e.g., canoeing and rafting), to severe pollution of water quality (inflow of nutrient-enriched sewage and a large amount of nonpoint source pollution loads), and damage to stream morphology (e.g., channelization and straightening) and the flow con-tinuum (e.g., impoundment by large dams and weirs). Thus, conserving and reviving freshwater health and bio-diversity are increasingly becoming global aims to ensure ecosystem integrity and freshwater ecosystem sustainability. Freshwater is a crucial resource for nature and man, and a biodiversity hotspot, which supports almost 10 % of all known animal species (Strayer and Dudgeon 2010), but they are much more vulnerable to disturbances than other ecosystems (Cushing and Allan 2001). Nevertheless, despite global attention on biodiversity imperilment in freshwater ecosystems for decades, increasing human pressures will accelerate species loss. Dudgeon et al. (2006) apprehended the extinction of freshwater animal species at a rate of 4 % per decade in North America, which exceeded by several fold that is expected of terres-trial species. In the case of Korean freshwater fishes, 63 of the 215 species (29.3 %) are endemic and 26 (12.1 %) are designated as 'Critically Endangered,' 'Endangered,' or 'Vulnerable' based on the IUCN (International Union for the Conservation of Nature and Natural Resources) red list, which portends a consistent decrease in their numbers (MOE/NIBR 2012). Intensive human-centered land use practices, such as, agricultural activities and urbanization, over decades have severely altered most stream and river ecosystems in Korea through excessive water use, which threatens water security and biodiversity (Jeong et al. 2010). Consequently, very few Korean streams and rivers remain undisturbed, and currently these compose only 5 % of reference streams listed in the National Aquatic Eco-logical Monitoring Program (NAEMP) database (Jun et al. 2012). ''Restoration of the ecological integrity of the nation's water'' is one of the most important objectives of legisla-tion concerning water environment management and con-servation and related policies in many countries (e.g., US EPA 2011). This is also the case in Korea, where the Water Quality and Aquatic Ecosystem Conservation Act, and water environment management programs declare the importance of the health and integrity of aquatic ecosys-tems (MOE 2007). Given the implementation of national investment in water infrastructure and regulation, much work has been done to restore aquatic ecosystems, partic-ularly rivers and streams. However, although major water quality improvements have been achieved (e.g., BOD) over the past three decades, many environmental challenges remain, such as, loss and destruction of habitat, altered
Caloric restriction (CR) and chemical agents, such as resveratrol and rapamycin that partially mimic the CR effect, can delay morbidity and mortality across a broad range of species. In humans, however, the effects of CR or other life-extending agents have not yet been investigated systematically. Human maximal lifespan is already substantially greater compared to that of closely related primate species. It is therefore possible that humans have acquired genetic mutations that mimic the CR effect. Here, we tested this notion by comparing transcriptome differences between humans and other primates, with the transcriptome changes observed in mice subjected to CR. We show that the human transcriptome state, relative to other primate transcriptomes, does not match that of the CR mice or mice treated with resveratrol, but resembles the transcriptome state of ad libitum fed mice. At the same time, the transcriptome changes induced by CR in mice are enriched among genes showing age-related changes in primates, concentrated in specific expression patterns, and can be linked with specific functional pathways, including insulin signalling, cancer, and the immune response. These findings indicate that the evolution of human longevity was likely independent of CR-induced lifespan extension mechanisms. Consequently, application of CR or CR-mimicking agents may yet offer a promising direction for the extension of healthy human lifespan.
Anopheles arabiensis (Diptera: Culicidae) is a potential malaria vector commonly present at low altitudes in remote areas in Reunion Island. Little attention has been paid to the environmental conditions driving larval development and abundance patterns in potential habitats. Two field surveys were designed to determine whether factors that discriminate between aquatic habitats with and without An. arabiensis larvae also drive larval abundance, comparatively in man-made and naturally occurring habitats.
Background:
An important determinant of mosquito-borne pathogen transmission is the spatial distribution of vectors. The primary vectors of West Nile virus (WNV) in Illinois are Culex pipiens Linnaeus (Diptera: Culicidae) and Culex restuans Theobald. In urban environments, these mosquitoes commonly oviposit in roadside storm water catch basins. However, use of this habitat is inconsistent, with abundance of larvae varying significantly across catch basins at a fine spatial scale.
Methods:
We tested the hypothesis that attributes of the biotic and abiotic environment contribute to spatial and temporal variation in production of mosquito vectors, characterizing the relationship between terrestrial vegetation and aquatic chemistry and Culex abundance in Chicago, Illinois. Larvae were sampled from 60 catch basins from June 14 to October 3, 2009. Density of shrubs and 14 tree genera surrounding the basins were quantified, as well as aquatic chemistry content of each basin.
Results:
We demonstrate that the spatial pattern of Culex abundance in catch basins is strongly influenced by environmental characteristics, resulting in significant variation across the urban landscape. Using regression and machine learning techniques, we described landscape features and microhabitat characteristics of four Chicago neighborhoods and examined the implications of these measures for larval abundance in adjacent catch basins. The important positive predictors of high larval abundance were aquatic ammonia, nitrates, and area of shrubs of height <1 m surrounding the catch basins, whereas pH and area of flowering shrub were negatively correlated with larval abundance. Tree density, particularly of arborvitae, maple, and pear, also positively influenced the distribution of Culex during the fruit-bearing periods and early senescent periods in August and September.
Conclusions:
This study identifies environmental predictors of mosquito production in urban environments. Because an abundance of adult Culex is integral to efficient WNV transmission and mosquitoes are found in especially high densities near larval habitats, identifying aquatic sites for Culex and landscape features that promote larval production are important in predicting the spatial pattern of cases of human and veterinary illness. Thus, these data enable accurate assessment of regions at risk for exposure to WNV and aid in the prevention of vector-borne disease transmission.
Background
Over the past 20 years, numerous studies have investigated the ecology and behaviour of malaria vectors and Plasmodium falciparum malaria transmission on the coast of Kenya. Substantial progress has been made to control vector populations and reduce high malaria prevalence and severe disease. The goal of this paper was to examine trends over the past 20 years in Anopheles species composition, density, blood-feeding behaviour, and P. falciparum sporozoite transmission along the coast of Kenya.
Methods
Using data collected from 1990 to 2010, vector density, species composition, blood-feeding patterns, and malaria transmission intensity was examined along the Kenyan coast. Mosquitoes were identified to species, based on morphological characteristics and DNA extracted from Anopheles gambiae for amplification. Using negative binomial generalized estimating equations, mosquito abundance over the period were modelled while adjusting for season. A multiple logistic regression model was used to analyse the sporozoite rates.
Results
Results show that in some areas along the Kenyan coast, Anopheles arabiensis and Anopheles merus have replaced An. gambiae sensu stricto (s.s.) and Anopheles funestus as the major mosquito species. Further, there has been a shift from human to animal feeding for both An. gambiae sensu lato (s.l.) (99% to 16%) and An. funestus (100% to 3%), and P. falciparum sporozoite rates have significantly declined over the last 20 years, with the lowest sporozoite rates being observed in 2007 (0.19%) and 2008 (0.34%). There has been, on average, a significant reduction in the abundance of An. gambiae s.l. over the years (IRR = 0.94, 95% CI 0.90–0.98), with the density standing at low levels of an average 0.006 mosquitoes/house in the year 2010.
Conclusion
Reductions in the densities of the major malaria vectors and a shift from human to animal feeding have contributed to the decreased burden of malaria along the Kenyan coast. Vector species composition remains heterogeneous but in many areas An. arabiensis has replaced An. gambiae as the major malaria vector. This has important implications for malaria epidemiology and control given that this vector predominately rests and feeds on humans outdoors. Strategies for vector control need to continue focusing on tools for protecting residents inside houses but additionally employ outdoor control tools because these are essential for further reducing the levels of malaria transmission.
This review brings together information on mosquitoes, the diseases they transmit and the wetlands that provide habitats for
the immature stages (eggs and larvae). Wetland values are mentioned, though the main literature on this does not generally
overlap the mosquito issue. Mosquito management is overviewed to include: the use of larvicides, source reduction in intertidal
wetlands and management in freshwater systems. There is not a great deal of information on mosquitoes and freshwater systems,
except for constructed wetlands and they are considered separately. We then consider restoration mainly in the context of
wetlands that have been the subject of habitat modification for mosquito control. Land use and climate change, as they affect
mosquitoes and the diseases they transmit, are also reviewed, as this will affect wetlands via management activities. Finally
the review addresses the critical issue of balancing health, both human and environmental, in an adaptive framework. It concludes
that there is a need to ensure that both mosquito and wetland management communicate and integrate to sustain wetland and
human health.
To classify mosquito species based on common features of their habitats, samples were obtained fortnightly between June 2001-October 2003 in the subtropical province of Chaco, Argentina. Data on the type of larval habitat, nature of the habitat (artificial or natural), size, depth, location related to sunlight, distance to the neighbouring houses, type of substrate, organic material, vegetation and algae type and their presence were collected. Data on the permanence, temperature, pH, turbidity, colour, odour and movement of the larval habitat's water were also collected. From the cluster analysis, three groups of species associated by their degree of habitat similarity were obtained and are listed below. Group 1 consisted of Aedes aegypti. Group 2 consisted of Culex imitator, Culex davisi, Wyeomyia muehlensi and Toxorhynchites haemorrhoidalis separatus. Within group 3, two subgroups are distinguished: A (Psorophora ferox, Psorophora cyanescens, Psorophora varinervis, Psorophora confinnis, Psorophora cingulata, Ochlerotatus hastatus-oligopistus, Ochlerotatus serratus, Ochlerotatus scapularis, Culex intrincatus, Culex quinquefasciatus, Culex pilosus, Ochlerotatus albifasciatus, Culex bidens) and B (Culex maxi, Culex eduardoi, Culex chidesteri, Uranotaenia lowii, Uranotaenia pulcherrima, Anopheles neomaculipalpus, Anopheles triannulatus, Anopheles albitarsis, Uranotaenia apicalis, Mansonia humeralis and Aedeomyia squamipennis). Principal component analysis indicates that the size of the larval habitats and the presence of aquatic vegetation are the main characteristics that explain the variation among different species. In contrast, water permanence is second in importance. Water temperature, pH and the type of larval habitat are less important in explaining the clustering of species.
The current status of insecticide resistance in mosquitoes and the effects of insecticides on non-target insect species have raised the need for alternative control methods for malaria vectors. Predation has been suggested as one of the important regulation mechanisms for malaria vectors in long-lasting aquatic habitats, but the predation efficiency of the potential predators is largely unknown in the highlands of western Kenya. In the current study, we examined the predation efficiency of five predators on Anopheles gambiae s.s larvae in 24 hour and semi- field evaluations.
Predators were collected from natural habitats and starved for 12 hours prior to starting experiments. Preliminary experiments were conducted to ascertain the larval stage most predated by each predator species. When each larval instar was subjected to predation, third instar larvae were predated at the highest rate. Third instar larvae of An. gambiae were introduced into artificial habitats with and without refugia at various larval densities. The numbers of surviving larvae were counted after 24 hours in 24. In semi-field experiments, the larvae were counted daily until they were all either consumed or had developed to the pupal stage. Polymerase chain reaction was used to confirm the presence of An. gambiae DNA in predator guts.
Experiments found that habitat type (P < 0.0001) and predator species (P < 0.0001) had a significant impact on the predation rate in the 24 hour evaluations. In semi-field experiments, predator species (P < 0.0001) and habitat type (P < 0.0001) were significant factors in both the daily survival and the overall developmental time of larvae. Pupation rates took significantly longer in habitats with refugia. An. gambiae DNA was found in at least three out of ten midguts for all predator species. Gambusia affins was the most efficient, being three times more efficient than tadpoles.
These experiments provide insight into the efficiency of specific natural predators against mosquito larvae. These naturally occurring predators may be useful in biocontrol strategies for aquatic stage An. gambiae mosquitoes. Further investigations should be done in complex natural habitats for these predators.
Sampling of Culex larval habitat plays an important role in West Nile virus surveillance and control programs. Although many cities have established mosquito sampling programs and abatement districts, there is relatively little information describing the extent and ecology of urban surface waters and stormwater systems in different geographic areas and how these parameters affect mosquito communities and control strategies. An aerial survey of the city of Madison, Wisconsin revealed 521 above-ground wet sites. These included both constructed stormwater systems (ditches, retention ponds, detention ponds) and natural wetlands (marshes, flood areas, creeks, and rivers). Repeat sampling of 351 of these sites was conducted during 2004 and 2005. The majority of sites, 58% in 2004 and 72% in 2005, yielded no mosquito larvae, suggesting that physical and biological features of these wet sites limit the development of mosquito larvae. For both years, analysis of the positive samples revealed that less than 25% of sites produced Culex spp. while a small number of ditches and detention ponds were consistent "superproducers" of Culex larvae from year to year. This information will facilitate comparisons across geographical areas and provides insight into local variation in the public health risk due to mosquito transmission of human disease agents.
Mosquitoes (Diptera: Culicidae) are important vectors of human disease-causing pathogens. Mosquitoes are found both in rural and urban areas. Deteriorating infrastructure, poor access to health, water and sanitation services, increasing population density, and widespread poverty contribute to conditions that modify the environment, which directly influences the risk of disease within the urban and peri-urban ecosystem. The objective of this study was to evaluate the mosquito vector abundance and diversity in urban, peri-urban, and rural strata in Malindi along the Kenya coast. The study was conducted in the coastal district of Malindi between January and December 2005. Three strata were selected which were described as urban, peri-urban, and rural. Sampling was done during the wet and dry seasons. Sampling in the wet season was done in the months of April and June to cover the long rainy season and in November and December to cover the short rainy season, while the dry season was between January and March and September and October. Adult mosquito collection was done using Pyrethrum Spray Collection (PSC) and Centers for Disease Control and Prevention (CDC) light traps inside houses and specimens were identified morphologically. In the three strata (urban, peri-urban, and rural), 78.5% of the total mosquito (n = 7,775) were collected using PSC while 18.1% (n = 1,795) were collected using the CDC light traps. Using oviposition traps, mosquito eggs were collected and reared in the insectary which yielded 329 adults of which 83.8% (n = 276) were Aedes aegypti and 16.2% (n = 53) were Culex quinquefasciatus. The mosquito distribution in the three sites varied significantly in each collection site. Anopheles gambiae, Anopheles funestus and Anopheles coustani were predominant in the rural stratum while C. quinquefasciatus was mostly found in urban and peri-urban strata. However, using PSC and CDC light trap collection techniques, A. aegypti was only found in urban strata. In the three strata, mosquitoes were mainly found in high numbers during the wet season. Further, A. gambiae, C. quinquefasciatus, and A. aegypti mosquitoes were found occurring together inside the houses. This in turn exposes the inhabitants to an array of mosquito-borne diseases including malaria, bancroftian filariasis, and arboviruses (dengue fever, Yellow fever, Rift Valley fever, Chikungunya fever, and West Nile Virus). In conclusion, our findings provide useful information for the design of integrated mosquito and disease control programs in East African environments.
As the ecology of mosquito larvae can be complex there is need to develop a rational framework for undertaking larval ecological studies. Local environmental characteristics, such as altitude, climate and land use, can significantly impact on phenology and population dynamics of mosquito larvae, and indirectly affect the dynamics of mosquito-borne diseases. The aim of this study was to assess the feasibility of implementing an integrated approach to larval source management under the distinct ecological settings.
The study was conducted in two highland villages and one village, at a lower altitude, in the Lake Victoria basin, where malaria is endemic and transmitted by the same Anopheles mosquito species. In each village the stability of mosquito larval habitats was classified as either temporary or permanent. The productivity of these habitat types was quantified by carrying out weekly larval sampling using a standard dipping method for a period of two years. During sampling the physical characteristic of the larval habitat, including the vegetation cover were noted. Ambient temperature, rainfall and relative humidity were recorded on a 21 × Micro-datalogger in each study site.
Anopheles gambiae sensu lato larvae were found in all study sites. Anopheles arabiensis was more abundant (93%) in Nyalenda (Lake Victoria basin) and Fort Ternan (highland area; 71%). In Lunyerere (highland area), An. gambiae sensu stricto comprised 93% of the total An. gambiae s.l. larvae. Larvae of An. gambiae s.l. mosquitoes were present in both temporary and permanent habitats with monthly variations dependent on rainfall intensity and location. Anopheles larvae were more likely to be found in man-made as opposed to natural habitats. Grassy habitats were preferred and were, therefore, more productive of Anopheles larvae compared to other habitat types. Weekly rainfall intensity led to an increase or decrease in mosquito larval abundance depending on the location.
The majority of mosquito breeding habitats were man made in all sites. Both temporary and permanent habitats were suitable for An. gambiae breeding. In Fort Ternan temporary sites were favoured for mosquito breeding above permanent sites. Significant differences in larval abundance were found depending on weekly rainfall intensity. Larval source management programmes should target permanent and temporary habitats equally and work closely with land and home owners as a majority of the breeding habitats are man made.
Larvae of Aedes albopictus Skuse typically inhabit natural and artificial containers. Since these larval habitats are replenished by rainfall, Ae. albopictus may experience increased loss of immature stages in areas with high levels of rainfall. In this study, we investigated the effects of rainfall and container water level on population density, and oviposition activity of Ae. albopictus. In field and laboratory experiments, we found that rainfall resulted in the flushing of breeding habitats. Excess rain negatively impacted larval and pupal retention, especially in small habitats. When filled with water to overflowing, container habitats were significantly repellent to ovipositing females. Taken together, these data suggest that rainfall triggers population loss of Ae. albopictus and related species through a direct detrimental effect (flushing out) and an indirect effect (ovipositional repellency).
A crucial component for developing insect management strategies is the understanding of the ecological parameters involved
in habitat selection by proliferating species. The key ecological drivers underlying habitat selection in the mosquito Coquillettidia sp. have been investigated in natura. Vegetation analysis suggested that the most suitable habitats were ponds with a high vegetation cover maintaining a high
degree of humidity in the air. The optimal biotope for Coquillettidia was associated with the presence of larval host plants such as Typha sp., Phragmites sp., and Juncus sp. Water quality was also found to be a key factor in larval habitat distribution. The presence of larvae was significantly
correlated with physico-chemical factors and the optimal water characteristics were neutral pH, low salt concentration, and
a relatively low level of suspended particulate matter. A significant correlation was observed between chemical cues and the
Coquillettidia distribution pattern. For instance, 2,6-di-tert-butyl-p-cresol was positively correlated to larval habitat, whereas high lauric acid and heptadecanoic acid concentrations may be
limiting factors. This study underlines the fact that mosquito habitat selection is driven by a complex process based on discriminating
levels of several ecological factors. Multivariate analysis helps understand such processes, which is this case will assist
in managing expanding populations of a species that threatens human health.
Landuse changes, including deforestation, agriculture, and urbanization, have coincided with an increase in vector-borne diseases worldwide. Landuse changes may alter mosquito populations by modifying the characteristics of aquatic larval habitats, but we still poorly understand the physical, chemical, and biological factors involved. We examined a total of 81 mosquito larval habitats for immature mosquitoes and 17 environmental variables in native forest, pastureland, and urbanland, at three locations in the Kapiti region, New Zealand. Significantly higher immature mosquito densities, predominantly of the endemic species Cx. pervigilans, were collected from urbanland and pastureland compared to native forest. Urbanland and pastureland habitats were mostly artificial containers compared to ground pools in native forest. Generalized linear modeling (GLM) revealed nine environmental variables that were significantly different between landuses. Of these variables, mosquito density was significantly (positively) correlated with bacteria and dissolved organic carbon. When location and date were controlled for in GLM, mosquito density was (negatively) related to the presence of vegetation and combined predators. The findings of this study support those from prior surveys in warmer climates suggesting greater mosquito-borne disease risk in anthropogenically-modified environments because of ecosystem disruption. Unlike most previous field-based work, this study suggests that in addition to habitat type, the presence of vegetation, water quality, and predators are also associated with mosquito density and may be involved in causal mechanisms. Urban containers and stock drinking troughs had high mosquito densities, suggesting that an initial step in directing control operations should be to focus on these habitats.
Mosquitoes are serious biting pests and obligate vectors of many vertebrate pathogens. Their immature larval and pupal life stages are a common feature in most tropical and many temperate water bodies and often form a significant proportion of the biomass. Control strategies rely primarily on the use of larvicides and environmental modification to reduce recruitment and adulticides during periods of disease transmission. Larvicides are usually chemical but can involve biological toxins, agents or organisms. The use of insect predators in mosquito control has been exploited in a limited fashion and there is much room for further investigation and implementation. Insects that are recognized as having predatorial capacity with regard to mosquito prey have been identified in the Orders Odonata, Coleoptera, Diptera (primarily aquatic predators), and Hemiptera (primarily surface predators). Although their capacity is affected by certain biological and physical factors, they could play a major role in mosquito control. Furthermore, better understanding for the mosquitoes-predators relationship(s) could probably lead to satisfactory reduction of mosquito-borne diseases by utilizing either these predators in control programs, for instance biological and/or integrated control, or their kairomones as mosquitoes' ovipoisting repellents. This review covers the predation of different insect species on mosquito larvae, predator-prey-habitat relationships, co-habitation developmental issues, survival and abundance, oviposition avoidance, predatorial capacity and integrated vector control.
Discarded vehicle tires are a common habitat for container mosquito larvae, although the environmental factors that may control their presence or abundance within a tire are largely unknown. We sampled discarded vehicle tires in six sites located within four counties of central Illinois during the spring and summer of 2006 to determine associations between a suite of environmental factors and community composition of container mosquitoes. Our goal was to find patterns of association between environmental factors and abundances of early and late instars. We hypothesized that environmental factors correlated with early instars would be indicative of oviposition cues, whereas environmental factors correlated with late instars would be those important for larval survival. We collected 13 species of mosquitoes, with six species (Culex restuans, Cx. pipiens, Aedes albopictus, Cx. salinarius, Ae. atropalpus, and Ae. triseriatus) accounting for r95% of all larvae. There were similar associations between congenerics and environmental factors, with Aedes associated with detritus type (fine detritus, leaves, seeds) and Culex associated with factors related to the surrounding habitat (human population density, canopy cover, tire size) or microorganisms (bacteria, protozoans). Although there was some consistency in factors that were important for early and late instar abundance, there were few significant associations between early and late instars for individual species. Lack of correspondence between factors that explain variation in early versus late instars, most notable for Culex, suggests a difference between environmental determinants of oviposition and survival within tires. Environmental factors associated with discarded tires are important for accurate predictions of mosquito occurrence at the generic level.
Mosquito-borne pathogen transmission exhibits spatial-temporal variability caused by ecological interactions acting at different scales. We used local spatial statistics and geographically weighted regression (GWR) to determine the spatial pattern of malaria incidence and persistence in northeastern Venezuela. Seven to 11 hot spots of malaria transmission were detected by using local spatial statistics, although disease persistence was explained only for four of those hot spots. The GWR models greatly improved predictions of malaria risk compared with ordinary least squares (OLS) regression models. Malaria incidence was largely explained by the proximity to and number of Anopheles aquasalis habitats nearby (1-3 km), and low-elevation terrains. Disease persistence was associated with greater human population density, lower elevations, and proximity to aquatic habitats. However, there was significant local spatial variation in the relationship between malaria and environmental variables. Spatial modeling improves the understanding of the causal factors operating at several scales in the transmission of malaria.
Biotic interactions involving mosquito larvae are context dependent, with effects of interactions on populations altered by ecological conditions. Relative impacts of competition and predation change across a gradient of habitat size and permanence. Asymmetrical competition is common and ecological context changes competitive advantage, potentially facilitating landscape-level coexistence of competitors. Predator effects on mosquito populations sometimes depend on habitat structure and on emergent effects of multiple predators, particularly interference among predators. Nonlethal effects of predators on mosquito oviposition, foraging, and life history are common, and their consequences for populations and for mosquito-borne disease are poorly understood. Context-dependent beneficial effects of detritus shredders on mosquitoes occur in container habitats, but these interactions appear to involve more than simple resource modification by shredders. Investigations of context-dependent interactions among mosquito larvae will yield greater understanding of mosquito population dynamics and provide useful model systems for testing theories of context dependence in communities.
Although they provide a number of valuable ecological services, wetlands also may harbor mosquitoes that are vectors of human pathogens. During 2002 and 2003, we measured biological (i.e., abundances of mosquitoes, other insects, and total heterotrophic bacteria, vegetational cover, and dead organic material), chemical (i.e., pH, dissolved nitrate, dissolved nitrite, dissolved phosphate, total alkalinity, and electrical conductivity), and physical (i.e., water temperature, dissolved oxygen, depth, and turbidity) attributes at fixed survey sites in Beaver Valley Wetlands, a small reconstructed palustrine wetland in Black Hawk County, Iowa. The number of immature mosquitoes was significantly correlated with dissolved nitrate and dissolved phosphate concentrations in both years. During the second year of the study, the number of immature mosquitoes was significantly correlated with nonpredators and water turbidity, but not with other measured variables. Independent variables explained 87 and 70% of the variability in mosquito numbers per survey site for the 2 yr of the study, respectively. The most common species of mosquitoes developing in Beaver Valley Wetlands were Aedes vexans (Meigen) Culex territans Walker, Uranotaenia sapphirina (Osten Sacken), and Culex tarsalis Coquillet. We compared relative risks of disease transmission by the mosquitoes developing in wetland microhabitats based upon published species-specific infection rates and propensities to bite humans. The majority of mosquitoes and the greatest potential disease risks were associated with temporary pools, which represented a small proportion of the wetlands. Although relatively few mosquitoes developed in Beaver Valley Wetlands, targeted control efforts could dramatically reduce the numbers of mosquitoes produced with minimal impacts upon nontarget species.
Concentrations and distribution of cadmium, chromium, copper, iron, lead, manganese and zinc in mosquito larval habitats in urban Kisumu and Malindi, Kenya and their effect on the presence of Anopheles gambiae, Aedes aegypti, Culex quinquefasciatus and Anopheles funestus larvae were investigated. Manganese and iron were the most prevalent heavy metals in water of larval habitats in urban Kisumu and Malindi, respectively. Iron was the most prevalent heavy metal in bottom sediments in larval habitats in both cities. The highest concentrations of all heavy metals, except cadmium and iron, were recorded in the poorly planned-well drained stratum in the two cities. All heavy metals were more concentrated in human-made than in natural larval habitats. Copper was positively associated with the presence of Ae. aegypti, and lead was associated with the presence of An. gambiae and Ae. aegypti in urban Kisumu. Absence of significant correlation between the other metals and mosquito species in both cities, despite relatively high concentrations, suggest that the local larval populations, including key malaria vectors have adapted to the detected levels of these metals.
A longitudinal study of mosquito ecology in Tanyard Creek, an urban stream in Atlanta, GA, that receives combined storm and waste water effluent from the Atlanta combined sewage overflow system, was undertaken in 2006. Culex quinquefasciatus was the dominant species found, but Culex restuans was also abundant during the spring with limited numbers of Culex nigripalpis and Anopheles punctipennis also collected. Significant differences in mosquito densities were found with greater densities associated with side pools of water and stagnant water. Mosquito numbers are regulated largely by flooding of the stream by effluent discharges exceeding 15 kgal/min. These floods are associated with significant immediate reductions, but not complete elimination, of mosquitoes from Tanyard Creek. Mosquito numbers rebound within 5-10 days after such floods and rapidly reach high densities.
Immature stages of the malaria mosquito Anopheles gambiae experience high mortality, but its cause is poorly understood. Here we study the impact of rainfall, one of the abiotic factors to which the immatures are frequently exposed, on their mortality.
We show that rainfall significantly affected larval mosquitoes by flushing them out of their aquatic habitat and killing them. Outdoor experiments under natural conditions in Kenya revealed that the additional nightly loss of larvae caused by rainfall was on average 17.5% for the youngest (L1) larvae and 4.8% for the oldest (L4) larvae; an additional 10.5% (increase from 0.9 to 11.4%) of the L1 larvae and 3.3% (from 0.1 to 3.4%) of the L4 larvae were flushed away and larval mortality increased by 6.9% (from 4.6 to 11.5%) and 1.5% (from 4.1 to 5.6%) for L1 and L4 larvae, respectively, compared to nights without rain. On rainy nights, 1.3% and 0.7% of L1 and L4 larvae, respectively, were lost due to ejection from the breeding site.
This study demonstrates that immature populations of malaria mosquitoes suffer high losses during rainfall events. As these populations are likely to experience several rain showers during their lifespan, rainfall will have a profound effect on the productivity of mosquito breeding sites and, as a result, on the transmission of malaria. These findings are discussed in the light of malaria risk and changing rainfall patterns in response to climate change.
Many invasive species succeed in becoming established in new locations because of their competitive superiority to native species. This has been shown in several examples involving mosquitoes. In this study, we examined the interspecific competition between mosquito larvae of a well-established, non-native species, Culex pipiens, and those of its ecologically similar, native congener Culex restuans. Small but significant differences in survival, growth, and development rates were found in Cx. restuans as a response to varying proportions of Cx. pipiens, suggesting that Cx. restuans is a slightly superior competitor. However, the overall differences between the species were small, and they may be nearly ecological equivalents as larvae. Nevertheless, the observed seasonal pattern of feeding and oviposition activity suggests some phenological avoidance of competition, thus demanding further study of the interaction of these two species.
Hennig’s (1966) concept of hierarchies of monophyletic taxons based on common ancestors (with plesiomorphies or retained primitive, ancestral characters) and shared synapomorphies (homologous shared characters inferred to have been present in the nearest common ancestor but not in earlier ancestors nor in the taxa outside this group), has provided the theoretical basis for taxa formation. During the first decades following its proposal, it resulted in the establishment of cladistic trees where recency of common ancestry is the sole criterion for grouping of the taxa. The problem of ranking taxa and tree formation in a Darwinian evolutionary context was the next scientific step (Eldridge and Cracraft 1980). Opinions about what different nodes represent, how to deal with branch lengths, and how to rank monophyletic entities, have become part of a scientific field of its own (Britton et al. 2007). Applying both morphologic and genetic taxonomic methods, and working with different groups of characters to reveal evolutionary relationships between insect orders or families as monophyletic groups, is now becoming standard. In the new millennium this work has resulted in several new hypotheses of phylogenetic trees of Insecta. Wheeler et al. (2001) established the relationship between Diptera and Strepsiptera. Grimaldi and Engel (2005) in their comprehensive work on extinct and extant Insecta, summarized different hypotheses for Diptera. They accepted five suborders of Lower Diptera (Nematocera): Tipulomorpha, Psychodomorpha, Culicomorpha, Blephariceromorpha and Bibionomorpha. They placed Anisopodidae as a sistergroup to Brachycera (all higher Diptera) and discarded Nematocera as a paraphyletic group (including a most recent common ancestor and some, but not all, of it descendants). This view has been strongly advocated by Amorim et al. (2006). They recognised seven suborders/infraorders instead of Nematocera and added Brachycera as the eighth suborder/infraorder for the rest of the Diptera.
Mosquitoes are responsible for the transmission of many medically important pathogens and parasites such as viruses, bacteria, protozoans, and nematodes, which cause serious diseases such as malaria, dengue, yellow and Chikungunya fever, encephalitis or filariasis (Kettle 1995; Beaty and Marquardt 1996; Lehane 1991; Eldridge and Edman 2000). Transmission can be mechanical (e.g. Myxoma virus causing myxomatosis in rabbits) or biological. The latter is more complex because it involves an obligatory period of replication and/or development of the pathogen or parasite in the vector insect. Due to their blood-sucking behaviour, mosquitoes are able to acquire the pathogens or parasites from one vertebrate host and pass them to another, if the mosquito’s ecology and physiology is appropriate for transmission. Highly efficient vectors have to be closely associated with the hosts and their longevity has to be sufficient enough to enable the pathogens/parasites to proliferate and/or to develop to the infective stages in the vector. For successful transmission, multiple blood-meals are necessary.
We investigated how ambient temperature under fluctuating conditions affects the larval-pupal immature traits of Aedes aegypti and Culex quinquefasciatus mosquitoes from Córdoba city, Argentina, and established each species development threshold and physiological time. Based on life tables, three cohorts of each mosquito species were reared in the laboratory under small fluctuating temperatures conditions of 15.2±1.7°C, 17.9±1.6°C, 21.6±0.7°C and 25.3±0.4°C for Ae. aegypti, and 16.6±1.7°C, 18.7±1.7°C and 25.2±0.3°C for Cx. quinquefasciatus. Immature development time and survival values, and also thermal development threshold and physiological time were estimated. Development times of all larval and pupal stages of Ae. aegypti and Cx. quinquefasciatus were significantly affected by the rearing temperatures, decreasing when temperature increased. Mean Ae. aegypti total (larva+pupa) development time ranged from 21.9 to 8.6 days, at 15.2 and 25.3°C, whereas, for Cx. quinquefasciatus varied between 23.5 to 9.2 days at 16.6 and 25.2°C, respectively. Larval and pupal survival of both species was affected by different rearing temperatures, increasing in general as temperature increased. For Ae. aegypti the total immature survival ranged from 26% at 15.2°C to 92% at 21.6°C; however, temperature did not have significant effect on this variable. The total immature survival of Cx. quinquefasciatus was significantly and positively affected by temperatures, ranging from 32 to 88%, at 16.6 and 25.2°C. The temperature development threshold and the physiological time estimated for Ae. aegypti and Cx. quinquefasciatus were 11.11°C and 93.74 degree-days, and 10.96°C and 136.87 degree-days, respectively. The results of the present study showed that temperature significantly affects the larval-pupal immature traits of these mosquito species of sanitary importance, from the central region of Argentina. All the parameters recorded are useful for the development of mosquito management models.
Copyright © 2015. Published by Elsevier B.V.
This study evaluated the temporal and spatial variations of water quality data sets for the Xin'anjiang River through the use of multivariate statistical techniques, including cluster analysis (CA), discriminant analysis (DA), correlation analysis, and principal component analysis (PCA). The water samples, measured by ten parameters, were collected every month for three years (2008-2010) from eight sampling stations located along the river. The hierarchical CA classified the 12 months into three periods (First, Second and Third Period) and the eight sampling sites into three groups (Groups 1, 2 and 3) based on seasonal differences and various pollution levels caused by physicochemical properties and anthropogenic activities. DA identified three significant parameters (temperature, pH and E.coli) to distinguish temporal groups with close to 76% correct assignment. The DA also discovered five parameters (temperature, electricity conductivity, total nitrogen, chemical oxygen demand and total phosphorus) for spatial variation analysis, with 80.56% correct assignment. The non-parametric correlation coefficient (Spearman R) explained the relationship between the water quality parameters and the basin characteristics, and the GIS made the results visual and direct. The PCA identified four PCs for Groups 1 and 2, and three PCs for Group 3. These PCs captured 68.94%, 67.48% and 70.35% of the total variance of Groups 1, 2 and 3, respectively. Although natural pollution affects the Xin'anjiang River, the main sources of pollution included agricultural activities, industrial waste, and domestic wastewater.
There are currently five invasive Aedes mosquito species known to be established in Europe, namely Aedes albopictus, Aedes aegypti, Aedes japonicus, Aedes atropalpus and Aedes koreicus. Aedes albopictus and Aedes aegypti are the incriminated vectors in the recent outbreaks of chikungunya and dengue fever in Europe. However, both laboratory experiments and field observations indicate that these invasive mosquitoes have a potential to also transmit other pathogens of public health importance. Increasing travel and pathogen introduction, expansion of vector distribution, and both environmental and climatic changes are likely to raise the risk of pathogen transmission by these invasive Aedes mosquitoes. Their vector status and their involvement in pathogen transmission are dynamic processes that shape the future of mosquito-borne disease epidemiology in Europe. Beside vector surveillance, enhanced disease surveillance will enable the early detection of cases and the prompt implementation of control measures.
Distributions of mosquito larvae likely are a consequence of multiple factors, although two commonly studied factors (quality
of the larval environment and the terrestrial matrix in which these habitats reside) have rarely and simultaneously been varied
in the field to understand distributions of larvae. We monitored aquatic containers of two leaf detritus levels within a forest,
prairie, and industrial habitat across five months to understand the temporal and spatial colonization of aquatic invertebrates
in Northcentral Illinois, USA. Data were collected monthly on mosquito populations and the composition of other invertebrates
colonizing containers. Overall, six species of mosquitoes colonized containers, with Culex restuans and Aedes triseriatus having the highest relative abundances. There were strong seasonal abundance patterns for these two mosquito species, with
the dominant species changing over time in the forest habitat. The responses of other mosquito taxa were more variable, with
abundances reflective of either the terrestrial matrix or larval habitat quality. High detritus containers supported the highest
abundances of most species encountered, regardless of habitat. Non-mosquito taxa were less common numerically, but analyses
suggested that some taxa, such as syrphid larvae, often co-occurred with mosquitoes. Nested subset analysis indicated communities
were strongly nested, and that both habitat type and detritus level were important in explaining nested patterns of aquatic
invertebrates. Our data show that both the larval habitat and the surrounding terrestrial matrix shape patterns of container
mosquitoes, and that other container invertebrates vary in similar ways as mosquitoes.
Many rural areas in the United States and throughout much of the postindustrial world are undergoing significant ecological, socioeconomic, and political transformations. The migration of urban and suburban dwellers into rural areas has led to the subdivision of large tracts of land into smaller parcels, which can complicate efforts to govern human-environmental problems. Non-point source (NPS) pollution from private rural lands is a particularly pressing human-environmental challenge that may be aggravated by changing land tenure. In this article, I report on a study of the governance and management of sediment (a common NPS pollutant) in the North Coastal basin of California, a region undergoing a transition from traditional extractive and agricultural land uses to rural residential and other alternative land uses. I focus on the differences in the governance and management across private timber, ranch, residential, vacation, and other lands in the region. I find that (1) the stringency and strength of sediment regulations differ by land use, (2) nonregulatory programs tend to target working landscapes, and (3) rural residential landowners have less knowledge of sediment control and report using fewer sediment-control techniques than landowners using their land for timber production or ranching. I conclude with an exploration of the consequences of these differences on an evolving rural landscape.
Studies were conducted between May and June, 2006 to investigate the environmental factors affecting the distribution of An. arabiensis Patton and Culex quinquefasciatus Say in Mwea, Kenya. The sampling unit comprised all non-paddy aquatic habitats and ten randomly selected paddies and canals located within a 200 m radius from the periphery of the study site. Thirteen physico-chemical variables were recorded for each sampling site in each sampling occasion and a sample of mosquito larvae and other aquatic invertebrates collected. The non-paddy aquatic habitats identified included pools and marshes. Morphological identification of 1,974 mosquito larvae yielded four species dominated by Cx. quinquefasciatus (73.2%) and An. arabiensis (25.0%). Pools were associated with significantly higher Cx. quinquefasciatus larval abundance and less diversity of other aquatic invertebrates compared with other habitat types. In contrast, the abundance of An. arabiensis did not differ significantly among habitat types. Culex quinquefasciatus habitats had higher water conductivity and exhibited a higher abundance of other aquatic invertebrates than An. arabiensis habitats. Chi-square analysis indicated that the two species were more likely to coexist in the same habitats than would be expected by chance alone. Anopheles arabiensis larvae were positively associated with dissolved oxygen and adults of family Haliplidae and negatively associated with emergent vegetation and Heptageniidae larvae. Culex quinquefasciatus larvae were positively associated with dissolved oxygen, total dissolved solids, Chironomidae larvae, and Microvelidae adults and negatively associated with emergent vegetation. These findings suggest that both biotic and abiotic factors play a significant role in niche partitioning among Cx. quinquefasciatus and An. arabiensis, a factor that should be considered when designing an integrated vector control program.
A total of 13,214 larvae specimens representing eight species (Culex pipiens, Culiseta annulata, Ochlerotatus cantans, Ochlerotatus communis, Ochlerotatus excrucians, Ochlerotatus sticticus, Aedes vexans, and Anopheles maculipennis) from twelve sampling places in the Wrocław area in Poland were collected between May and October, 1998-2000. The development rate of each mosquito species depended on hydrological types and various plant communities in water bodies. The water quality (temperature, pH and ion concentration) influenced mosquito larvae dynamics as well. The most abundant and constant species was Cx. pipiens. Its monthly population was significantly higher in the water bodies located in the city center as compared to those in the suburbs.
The population dynamics of the larval and adult life stages of the malaria vector Anopheles gambiae Giles were studied in Miwani, western Kenya, in relation to meteorological conditions. Larval density within a habitat, the number of larval habitats and sibling species composition were investigated as determinants of larval population dynamics. Female vector densities inside local houses and sibling species composition were investigated as determinants of adult population dynamics. Larval densities were estimated using a modified area-sampling method. Within the habitats, all instars showed a highly aggregated distribution, with the exception of second instars. A longitudinal study on the larval populations of A. gambiae s.l. in two different types of habitat (dirt track and ditch) was carried out, using a novel sampling procedure. A. gambiae s.s. and Anopheles arabiensis, the two sibling species occurring sympatrically in the study area, showed some spatial segregation between the two types of habitat. Rainfall was significantly correlated with the number of A. gambiae s.l. larval habitats during the first 6 weeks of study taking 1 week time lag into account, while over the entire 5-month study period correlations were less clear. With 1 week time lag, rainfall was also significantly correlated with the number of female A. gambiae s.l. collected from CDC-light traps in the study houses. Both larval and adult populations showed a significant increase in the proportion of A. gambiae s.s. within the mixed population of A. gambiae s.s. and A. arabiensis over time. Although not significantly correlated, the ratio of rainfall over precipitation/potential evapotranspiration (P/PE), indicative of the humidity conditions in the area, was probably the driving force of this increase.