Exploring the range of Culex mosquitoes in Western Argentinean Patagonia, unveiling the presence of Culex pipiens bioform pipiens in South America.

Culicids in Argentinean Patagonia are characterized by low species diversity and adaptation to extreme environmental conditions, yet few studies have been conducted in the region. To further assess the occurrence of Culicidae in Western Patagonia, and in particular the presence of Culex pipiens bioforms at the southernmost extent of their distribution, immature and adult specimens were collected aboveground across various land uses located in shrubland, steppe, and deciduous forest between 38.96 and 46.55°S. Mosquitoes were reported at 35 of the 105 inspected sites. Five species from the genus Culex were identified, all of which were present in the steppe and the forest, while only Cx. apicinus and members of the Cx. pipiens complex were collected in the shrubland. Within the latter, a total of 150 specimens were molecularly identified by PCR amplification of Ace-2 and CQ11 loci. The first-to-date occurrence of bioform pipiens in South America is reported, along with the first records of Cx. quinquefasciatus signatures in Patagonia. In addition, the distribution of Cx. acharistus and Cx. dolosus as south as Santa Cruz province is expanded, and the first record of Cx. eduardoi in Río Negro province is provided. Immature specimens of Cx. pipiens were conspicuous in human-made aquatic habitats (both containers and in the ground), while Cx. acharistus was more prominent in artificial containers and Cx. eduardoi was mainly in ground habitats, either natural or human-made. These findings provide valuable insights into the distribution and ecological roles of these mosquito species in a region of extreme environmental conditions.

Blood feeding habits of mosquitoes: hardly a bite in South America.

Mosquito blood feeding plays a key role in epidemiology. Despite its importance and large number of studies worldwide, less attention has been paid in South America. We summarized some general concepts and methodological issues related to the study of mosquito blood feeding habits, and compiled and analyzed all published information regarding the subject in the continent until 2020. Available literature comprised 152 scientific studies, that pursued different approaches: human landing catches (102 studies), baited trap (19), and blood meal analyses of collected specimens (38). Among the latter, 23 used serological and 15 molecular techniques. Species most frequently studied were those incriminated in malaria transmission, whereas relevant vectors such as Aedes aegypti, Ae. albopictus, and Haemagogus janthinomys were surprisingly neglected. Brazil was the leading country both in number of works and species studied. For over 70% of the species and three out of 13 South American countries there is no single information on mosquito blood feeding habits. Data from baited traps included 143 mosquito species, 83.9% of which were attracted to humans, either exclusively (10.5%) or in combination with other vertebrates (73.4%). Host blood identification of field collected specimens provided data on 102 mosquito species, and 60.8% of these fed on humans (55.9% combined with other vertebrates). Only 17 of the 73 species assessed by both methods yielded similar feeding patterns. Finally, supplementary tables are provided in a comprehensive summary of all information available and information gaps are highlighted for future research in the continent.

Aedes aegypti spreading in South America: new coldest and southernmost records.

The geographic distribution of Aedes (Stegomyia) aegypti (L.) in South America has been expanding during the last decades. Herein we present two new distribution records that extend its southern limits towards localities with extremer environmental conditions than reported to date. San Antonio Oeste constitutes the southernmost finding for the continent (40º44'S), whereas Tandil is the infested locality with the coldest mean annual temperature in Argentina (14.17ºC). The projection of a previous distribution model for Ae. aegypti predicts these two cities as positive and suggests several other localities with suitable conditions for vector proliferation beyond its assumed distribution limits.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit.

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Blood feeding patterns of the Culex pipiens complex in equestrian land uses and their implications for arboviral encephalitis risk in temperate Argentina.

Blood feeding patterns of mosquitoes are a key component in the dynamics of arboviral encephalitides transmission. In temperate Argentina, the members of the Culex pipiens complex include Cx. pipiens molestus, Cx. quinquefasciatus and their hybrids. To characterize their blood feeding patterns, adult resting mosquitoes were collected monthly during the warm season in urban and rural equestrian fields. The availability of birds and domestic mammals per site was characterized. The blood source and the complex member were successfully identified for 89 specimens using PCR. Blood of 19 vertebrate species was isolated including four mammals (most common feeds from dog, Canus lupus 19% of the blood meals; and horse, Equus caballus 18%) and 15 birds (picazuro pigeon, Patagioenas picazuro 11%; eared dove, Zenaida auriculata 10%; chicken, Gallus gallus 9%). The Forage Ratio (FR), calculated as the proportion of feeds taken from a given host species with respect to that host availability in the environment, suggested preference for dog by all members of the complex (FR ≥4.5). On the contrary, FR values suggested avoidance for horse by Cx. quinquefasciatus and the hybrid (FR ≤0.8), and a use proportional to its abundance by Cx. pipiens molestus (FR = 1.1-1.2 in urban and rural sites, respectively). FR values suggesting preference were obtained for avian species of the orders Passeriformes (7 species in total) and Columbiformes (5) by all members of the complex (FR ≥ 3.3), whereas values for monk parakeet (Myiopsitta monachus, Psiitaciformes) suggested avoidance by Cx. quinquefasciatus in urban sites (FR = 0.4) and by Cx. pipiens molestus in rural sites (FR = 0.3) but not in urban sites (FR = 1.4). A mammal-bird index (MBI, from -1 all avian to +1 all mammalian blood meals) was calculated for each member of the complex and urbanization category. Values were negative for Cx. quinquefasciatus (MBIurban  = -0.60, MBIrural  = -0.33) and positive for Cx. pipiens molestus (MBIurban  = 0.20, MBIrural  = 0.60), indicating a higher proportion of feeds taken on birds and mammals, respectively, regardless of the urbanization category. In temperate Argentina, the members of the Cx. pipiens complex fed both on horses and on birds, thus representing a real risk of transmission of arboviral encephalitides from avian enzootic cycles to horse epizootics.

Immature mosquitoes from groundwater habitats in a temperate wetland of Argentina: environmental associations and seasonal variation of community attributes.

We studied the seasonal patterns of 3 community attributes (breeding site index, richness, and diversity) of groundwater mosquito immatures and their associations with meso- and microhabitat factors in the Parana Lower Delta, Argentina, from December 2009 to November 2010. Monthly collections at 4 sites yielded 2,313 mosquito immatures, belonging to 19 species assigned to 6 genera. Immatures developed in a wide range of microenvironmental conditions (water temperature 4.0-30.2 degrees C, pH 5.4-9.1, electrical conductivity 0.02-6.33 mS/cm, and dissolved oxygen 0-235.6%), and their occurrence was significantly associated with lower water temperature and dissolved oxygen values. Most frequently captured species were Culex dolosus s.l. (58.6%), Aedes crinifer (22.9%), and Cx. intrincatus (19.0%). Breeding site index was highest in winter (0.76) and lowest in spring (0.54). Species richness and diversity varied significantly among seasons (peaking in summer), land uses, and habitat types.

Tire-breeding mosquitoes of public health importance along an urbanisation gradient in Buenos Aires, Argentina.

Used vehicle tires are a source of mosquito vectors and a means of their introduction and expansion. With the aim of assessing the effects of urbanisation on the main mosquito vectors in temperate Argentina, the infestation levels of Aedes aegypti (L.) and Culex pipiens L. were studied in used tires from highly urbanised cities to low-urbanised small towns in Buenos Aires. Immatures of both species accounted for 96% of the 9,722 individuals collected; the total individuals collected represented seven species. The percentage of water-filled tires containing mosquitoes [container index (CI)] was 33% and the percentage of infested sites [site index (SI)] was 65.2%. These indexes decreased significantly from low to high urbanisation levels for both mosquito species. The relative abundance (RA) of Ae. aegypti immatures was slightly higher toward large cities, but showed no difference for Cx. pipiens. The CI of shaded tires was significantly higher than the CI of exposed tires for both mosquito species. There was no difference in RA values between shaded and sunlit tires. The CI and the SI were highest during the summer across the urbanisation levels, except for Cx. pipiens, which continued to increase during the autumn in small towns. Results related to urbanisation gradient, sunlit exposure and seasonality are discussed.

Assessment of Environmental Hazards to Public Health in Temperate Urban Argentina.

Human health risk in urban areas depends on multiple environmental features. We performed a year-round survey in a highly urbanized district located in temperate Argentina (General San Martín, Buenos Aires) to establish baseline information about environmental hazards associated with health risks. Sampling was stratified into low and high hazardous zones according to estimated indexes previously developed for the area for four hazards: drinking water and air pollution, and mosquito and rodent infestation. Water from wells showed lower concentrations of aluminum, manganese and iron, and higher values of arsenic than tap samples, with the latter showing records above the maximum permitted for arsenic, aluminum and chromium. Benzene concentration in air was higher in summer than in winter, and in areas close to dumps and landfills, gas stations, high traffic pathways and industries with respect to low hazard areas. Adult mosquito collections were more abundant in high hazardous areas, three species from the genus Culex dominated the captures and the proportion of individuals from each species was variable seasonally and spatially. Rodent activity was recorded inside and outside dwellings, and its observed values did not differ between low and high hazardous areas. In the comparison between field data and estimated hazard maps, high accuracy was obtained for air pollution maps, intermediate accuracy for water pollution and mosquito infestation, and poor accuracy for rodent infestation. How to improve field surveys and estimated maps are both discussed, highlighting the need for dynamic feedback between GIS-based models and environmental monitoring.

An interdisciplinary approach to assess human health risk in an urban environment: A case study in temperate Argentina.

Unplanned urbanization increases the exposure of people to environmental hazards. Within a landscape ecology framework, this study is a diagnosis of human health risk in San Martín, an urban district of Buenos Aires, Argentina. Risk was estimated by combining four hazard indexes (water and air pollution, and mosquito and rodent infestation) and a vulnerability index. Each index was obtained by integrating environmental and socio-demographic layers in a Geographic Information System. Spatial autocorrelation was assessed for each hazard, vulnerability and risk indexes using Moran's tests. Also, spatial associations between pairs of variables were addressed by means of Geographically Weighted Regressions. The robustness of hazard and vulnerability indexes was checked by a sensitivity analysis. In General San Martín district, 83.3% of the population is exposed to relatively high levels of at least one hazard; 7.4% is exposed to relatively high levels of all hazards (11.5% of the total area) and only 16.7% lives in areas of relatively low levels of all hazards (15.4% of the total area). Areas where hazard intensity was relatively high corresponded to those areas where the most vulnerable population lives, enhancing human health risk. The models for hazards and vulnerability were reasonably robust to changes in the weights of the variables considered. Our results highlight the spatially heterogeneous nature of human health risk in an urban landscape, and reveal the location of critical risk hotspots where reduction or mitigation actions should be focused.

Aedes aegypti spreading in South America: new coldest and southernmost records

The geographic distribution of Aedes (Stegomyia) aegypti (L.) in South America has been expanding during the last decades. Herein we present two new distribution records that extend its southern limits towards localities with extremer environmental conditions than reported to date. San Antonio Oeste constitutes the southernmost finding for the continent (40º44'S), whereas Tandil is the infested locality with the coldest mean annual temperature in Argentina (14.17ºC). The projection of a previous distribution model for Ae. aegypti predicts these two cities as positive and suggests several other localities with suitable conditions for vector proliferation beyond its assumed distribution limits.

Assessment of Culex pipiens bioforms in the world's southernmost distribution limit

The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.

Community structure of ground-water breeding mosquitoes driven by land use in a temperate wetland of Argentina.

Wetlands have traditionally been associated with harbouring mosquitoes, but the effect of the land use on their communities has not been thoroughly studied. We characterized the ground-water habitat availability and mosquito species richness and composition during a year-round survey in the predominant land uses (domestic areas, Salicaceae plantations, secondary forests and Scirpus giganteus marshes) of the Paraná Lower Delta, Argentina. Each land use presented a characteristically different number, composition, and diversity of ground-water habitats, and harboured mosquitoes throughout the year. Nearly half of the 824 habitats examined, consisting of 10 types, were positive for immatures. We identified 23 species from 7 genera, with Culex and Ochlerotatus species accounting for 81.7% of all samples. Species richness was significantly lower in marshes than in the other land uses. Some species such as Culex dolosus s.l. and Ochlerotatus crinifer exhibited no habitat-type restrictions, while Uranotaenia nataliae and Mansonia indubitans presented specific habitat requirements. Our results strongly suggest that land use within temperate wetlands drives species richness and composition of ground-water mosquito communities through larval habitat availability.

Tire-breeding mosquitoes of public health importance along an urbanisation gradient in Buenos Aires, Argentina

Used vehicle tires are a source of mosquito vectors and a means of their introduction and expansion. With the aim of assessing the effects of urbanisation on the main mosquito vectors in temperate Argentina, the infestation levels of Aedes aegypti (L.) and Culex pipiens L. were studied in used tires from highly urbanised cities to low-urbanised small towns in Buenos Aires. Immatures of both species accounted for 96 percent of the 9,722 individuals collected; the total individuals collected represented seven species. The percentage of water-filled tires containing mosquitoes [container index (CI)] was 33 percent and the percentage of infested sites [site index (SI)] was 65.2 percent. These indexes decreased significantly from low to high urbanisation levels for both mosquito species. The relative abundance (RA) of Ae. aegypti immatures was slightly higher toward large cities, but showed no difference for Cx. pipiens. The CI of shaded tires was significantly higher than the CI of exposed tires for both mosquito species. There was no difference in RA values between shaded and sunlit tires. The CI and the SI were highest during the summer across the urbanisation levels, except for Cx. pipiens, which continued to increase during the autumn in small towns. Results related to urbanisation gradient, sunlit exposure and seasonality are discussed.