Mosquitoes (Diptera: Culicidae) From the Northwestern Brazilian Amazon: Araçá River

Land-use effects on mosquito biodiversity and potential arbovirus emergence in the Southern Amazon, Brazil

The Amazon rainforest is considered the largest reservoir of culicids and arboviruses in the world. It has been under intense human-driven alteration, especially in the so-called 'Arc of Deforestation', located in the eastern and southern regions. The emergence and transmission of infectious diseases are increasing, potentially due to land-use change. We used landscape-scale mosquito surveillance across a forest fragmentation gradient in the southern Amazon to evaluate the relationship between forest disturbance and the composition and structure of mosquito communities with a particular focus on the potential for arbovirus emergence in the region. Generalized linear models and logistic regression were used to associate the degree of landscape disturbance with arbovirus vectors' richness and abundance. A total of 1,960 culicids, belonging to 50 species, were collected from 2015 to 2016. Among these species, 20 have been associated with the transmission of arboviruses. Our results show an association of land use, more specifically small size of forest remnants with more irregular shape and higher edge density, with the increase of arbovirus vectors' richness and abundance. Six species of mosquito vectors exhibited a higher probability of occurrence in landscapes with medium or high degrees of disturbance. Our results indicate that land-use change influences mosquito communities with potential implications for the emergence of arboviruses.

Vector role and human biting activity of Anophelinae mosquitoes in different landscapes in the Brazilian Amazon

BACKGROUND

Environmental disturbance, deforestation and socioeconomic factors all affect malaria incidence in tropical and subtropical endemic areas. Deforestation is the major driver of habitat loss and fragmentation, which frequently leads to shifts in the composition, abundance and spatial distribution of vector species. The goals of the present study were to: (i) identify anophelines found naturally infected with Plasmodium; (ii) measure the effects of landscape on the number of Nyssorhynchus darlingi, presence of Plasmodium-infected Anophelinae, human biting rate (HBR) and malaria cases; and (iii) determine the frequency and peak biting time of Plasmodium-infected mosquitoes and Ny. darlingi.

METHODS

Anopheline mosquitoes were collected in peridomestic and forest edge habitats in seven municipalities in four Amazon Brazilian states. Females were identified to species and tested for Plasmodium by real-time PCR. Negative binomial regression was used to measure any association between deforestation and number of Ny. darlingi, number of Plasmodium-infected Anophelinae, HBR and malaria. Peak biting time of Ny. darlingi and Plasmodium-infected Anophelinae were determined in the 12-h collections. Binomial logistic regression measured the association between presence of Plasmodium-infected Anophelinae and landscape metrics and malaria cases.

RESULTS

Ninety-one females of Ny. darlingi, Ny. rangeli, Ny. benarrochi B and Ny. konderi B were found to be infected with Plasmodium. Analysis showed that the number of malaria cases and the number of Plasmodium-infected Anophelinae were more prevalent in sites with higher edge density and intermediate forest cover (30-70%). The distance of the drainage network to a dwelling was inversely correlated to malaria risk. The peak biting time of Plasmodium-infected Anophelinae was 00:00-03:00 h. The presence of Plasmodium-infected mosquitoes was higher in landscapes with > 13 malaria cases.

CONCLUSIONS

Nyssorhynchus darlingi, Ny. rangeli, Ny. benarrochi B and Ny. konderi B can be involved in malaria transmission in rural settlements. The highest fraction of Plasmodium-infected Anophelinae was caught from midnight to 03:00 h. In some Amazonian localities, the highest exposure to infectious bites occurs when residents are sleeping, but transmission can occur throughout the night. Forest fragmentation favors increases in both malaria and the occurrence of Plasmodium-infected mosquitoes in peridomestic habitat. The use of insecticide-impregnated mosquito nets can decrease human exposure to infectious Anophelinae and malaria transmission.

Distribution and diversity of mosquitoes and Oropouche-like virus infection rates in an Amazonian rural settlement

Mosquito diversity and disease transmission are influenced by landscape modifications, i.e., vectors and pathogens previously found only in forests are now found close to human environments due to anthropic changes. This study determined the diversity and distribution of mosquitoes in forest environments in order to analyze the potential vectors of Amazonian forest arboviruses. Mosquitoes were collected by 1) vertical stratification from forest canopy and ground areas using Hooper Pugedo (HP) light traps and human attraction and 2) horizontal stratification using HP light traps in peridomicile, forest edge, and forest environments near the Rio Pardo rural settlement, Amazonas, Brazil. A total of 3,750 mosquitoes were collected, representing 46 species. 3,139 individuals representing 46 species were sampled by vertical stratification. Both the Shannon-Weaver diversity index (H’) and equitability (J’) were higher in the canopy than on the ground. 611 individuals representing 13 species were sampled by horizontal stratification. H’ decreased in the following order: forest edge > forest > peridomicile, and J’ was greater at the forest edge and smaller in the peridomicile environment. Moreover, H’ was higher for the human attraction collection method than the HP traps. A total of 671 pools were analyzed by RT-qPCR; three species were positive for Oropouche-like viruses (Ochlerotatus serratus, Psorophora cingulata, and Haemagogus tropicalis) and the minimum infection rate was 0.8%. The composition of mosquito species did not differ significantly between anthropic and forest environments in Rio Pardo. Some mosquito species, due to their abundance, dispersion in the three environments, and record of natural infection, were hypothesized to participate in the arbovirus transmission cycle in this Amazonian rural settlement.

Diversity of mosquitoes (Diptera: Culicidae) collected in different types of larvitraps in an Amazon rural settlement

Anthropogenic environments provide favorable conditions for some species, which is especially true of mosquitoes that present eclecticism at the moment of choice for the site of oviposition. In the present study, the diversity of mosquitoes was assessed by providing plastic containers, bamboo internodes, and tires in a forest, the forest edge, and peridomicile environments in a rural settlement area. Eighteen sampling points were chosen, delimited by a buffer of 200 m, placed in three environments: forest, forest edge, and peridomicile. In each environment, larvitraps were installed, separated by a minimum distance of 7 m and 1 m from the ground. A total of 10,131 immature mosquitoes of 20 species were collected. The most abundant species was Culex urichii (29.5%), followed by Trichoprosopon digitatum (27.1%), and Cx. (Melanoconion) spp. (10.4%). There was a difference in the composition of immature mosquito populations between larvitraps (p < 0.0005), and the plastic container hosted a greater diversity of species, whereas tires presented a greater abundance of individuals. The forest, forest edge, and peridomicile environments were also different with regard to diversity of immature mosquito populations (p < 0.0010). The forest edge was the environment with the greatest diversity of species, followed by the peridomicile and forest environments. In the forest and peridomicile, plastic container larvitraps had the greatest diversity, whereas the forest edge tire presented the largest number of individuals. Further, tire larvitraps collected the largest number of individuals in all environments. Ten species associated with the bamboo internode and tire were identified. The preference of species for artificial larvitraps, such as the plastic container and tire, even in wild environments was noted. These artificial objects may represent a risk factor for the population living in this region, as all vector species found in the study were present in plastic containers and tires.

Diversity of Mosquitoes (Diptera: Culicidae) in the Caatinga Biome, Brazil, from the Widespread to the Endemic

Mosquito fauna in the northeast semiarid region of Brazil, Caatinga biome, are poorly known. Studies on the diversity are scarce and the few surveys available focus on local fauna. In order to understand the ecological pattern of mosquito's distribution, information available from studies from 2008 to 2015 were gathered. A partitioning framework of the beta diversity, the turnover (βJTU) and nestedness (βJNE) components were used to determine dissimilarity among communities. Eighty-two morphospecies were recorded and 47 of the species were not shared between the areas. The most representative genera were Aedes, Anopheles, Psorophora, Haemagogus, Coquillettidia, and Mansonia, which all include species of medical interest. The communities had high rates of variation, and the mechanism of turnover accounted for the observed diversity pattern. Despite differences in collection methods, the observed dissimilarity may be related to the broad environmental heterogeneity of the biome, the intrinsic relationships of the species with their habitats, and the environmental degradation caused by different types of anthropogenic interference. Considering the mosquito species richness and endemicity, the hypothesis that the Caatinga harbor poor biodiversity is rejected. The spatial variation observed is of particular importance and should be taken into account for the knowledge of Caatinga biodiversity.