Population dynamics, structure and behavior of Anopheles darlingi in a rural settlement in the Amazon rainforest of Acre, Brazil

Abstract

Background: Anopheles darlingi is the major vector of malaria in South America, and its behavior and distribution has epidemiological importance to biomedical research. In Brazil, An. darlingi is found in the northern area of the Amazon basin, where 99.5% of the disease is reported.

Methods: The study area, known as Ramal do Granada, is a rural settlement inside the Amazon basin in the state of Acre. Population variations and density have been analysed by species behaviour, and molecular analysis has been measured by ND4 mitochondrial gene sequencing.

Results: The results show higher density in collections near a recent settlement, suggesting that a high level of colonization decreases the vector presence. The biting activity showed higher activity at twilight and major numbers of mosquitos in the remaining hours of the night in months of high density. From a sample of 110 individual mosquitoes, 18 different haplotypes were presented with a diversity index of 0.895, which is higher than that found in other Anopheles studies.

Conclusions: An. darlingi depends on forested regions for their larval and adult survival. In months with higher population density, the presence of mosquitoes persisted in the second part of the night, increasing the vector capacity of the species. Despite the intra-population variation in the transition to rainy season, the seasonal distribution of haplotypes shows no change in the structure population of An. darlingi.

Figure 1

Study Area. A: Acrelândia, in northern Brazil. B: satellite image from "Ramal do Granada" (^©2010 Google-Images ^©2010 TerraMetrics, Nasa, Dados cartográficos ^©2010 Maplink). C: "Ramal do Granada" with the sampling sites km 24, km 30 and BR 364 (Point 0).

Figure 2

Collection points. Km 24 (A: indoor capture, B; outdoor capture, C: pasture behind the house) and Km 30 (D: indoor capture, E; outdoor capture, F: pasture behind the house).

Figure 3

An. darlingi 12-hour capture. Biting activity of An. darling in 12-hour capture at km 30.

Figure 4

An. darlingi seasonal density; rainfall (A) and temperature (B). The values correspond the monthly averages.

Figure 5

Statistical parsimony network. 18 haplotypes of An. darlingi populations for ND4 mitochondrial fragments. Black dots along the lines indicate mutational steps between haplotypes (unrepresented in the sample). The size of the sphere is proportional to the number of individuals carrying the haplotype.