Mosquito (Diptera: Culicidae) larval ecology in natural habitats in the cold temperate Patagonia region of Argentina

Abstract

Background: Knowledge of immature habitats is an important focus for investigations of mosquito community ecology, and may improve our understanding of how environmental variables increase risk of mosquito-borne diseases by influencing the distributions and abundances of species. In Patagonia region, where climatic and ecological factors could be only borderline suitable for mosquito development, relatively little is known about larval ecology. The present study focuses on associations of environmental conditions in natural aquatic habitats with abundances of mosquito species that have colonized such habitats in Patagonia.

Methods: We described the mosquito community composition within 26 natural temporary pools, and assessed the general relationships between environmental variables (pH, water temperature, conductivity, salinity, dissolved oxygen, aquatic plant cover and main nutrients) and larval abundances using redundancy analysis (RDA). Additionally, we compiled monthly climate data and vegetation indices for each larval habitat, and estimated the probability of presence for two of the most abundant species, describing through generalized linear models (GLM) the environmental, climatic and landscape variables-probability of occurrence relationships.

Results: Seven species belonging to the genera Culex and Aedes were identified, with Culex apicinus, Cx. acharistus and Aedes albifasciatus being the most abundant. Mean larval densities were low (6.8 ± 2.8 larvae/dip), and the highest species richness and larval densities were recorded in northern and central areas. Aedes albifasciatus, a species of sanitary importance, was widely distributed, being the only one collected south of the 45th parallel of S latitude. RDA indicated that aquatic conductivity, pH, water depth, dissolved oxygen, ammonia and soluble reactive phosphorous accounted for the main part of the variation in the species composition. According to GLMs, wind speed was the variable that best described the presence of Ae. albifasciatus, and the probability of finding this species was positively associated with high wind speed values. On the other hand, the EVI vegetation index was the only variable included in the Cx. apicinus model, whereby there was a great probability of presence in arid areas with lower EVI values.

Conclusions: Our results enhance our knowledge of larval habitat ecology under the extreme environmental conditions of Patagonia and will guide future efforts to understand how multiple effects can affect mosquito ecology and public health at higher latitudes.

Keywords: Models of probability of presence; Physicochemical parameters; Pools; Southern South America.

Fig. 1

Study area. a Map of Patagonia region (Argentina) showing the locations of the 26 mosquito larval habitats surveyed in this study in Neuquén (NQ), Río Negro (RN), Chubut (CH), Santa Cruz (SC) and Tierra del Fuego (TF) provinces. b Mean annual rainfall. c Mean annual temperature. d Mean annual wind speed. e Ecoregions. Software: QGIS v.2.14 [30]. Interprovincial boundaries, climatic variables and ecoregions were derived from data produced by the IGN [31], WorldClim v.2 [32] and Burkart et al. [33], respectively

Fig. 2

Spatial variation of mosquito species and environmental variables. Spatial variation of larval density, dissolved oxygen (DO), pH, conductivity, ammonia (NH₄⁺), nitrate+nitrite (NO₃⁻ + NO₂^-), soluble reactive phosphorous (PRS) and aquatic plant cover (APC) values measured in the 26 mosquito larval habitats. Software: QGIS v.2.14 [30]. Interprovincial boundaries were derived from data produced by the IGN [31]

Fig. 3

Redundancy analysis ordination diagram. RDA triplot with sites (circles), mosquito species (triangles), and environmental variables (arrows). The mosquito species are: Cx. apicinus, Cx. acharistus, Cx. brethesi, Cx. eduardoi, Cx. dolosus, Cx. tramazaiguesi and Ae. albifasciatus. The environmental variables are: dissolved oxygen (DO); water temperature (WT); pH; conductivity; soluble reactive phosphorous (PRS); ammonia (NH₄⁺); nitrate+nitrite (NO₃^-+NO₂^-); water depth (WD); aquatic plant cover (APC); and area. Sites are shown in colored dots grouped into provinces: Neuquén (NQ); Río Negro (RN); Chubut (CH); Santa Cruz (SC); and Tierra del Fuego (TF)

Fig. 4

Probability of Aedes albifasciatus and Culex apicinus presence. Fitted values (solid line) obtained by the binomial generalized linear models with associated 95% confidence interval (shaded area). The black dots are the observed values. a Probability of presence of Aedes albifasciatus as a function of wind speed. b Probability of presence of Culex apicinus as a function of EVI