Diversity of Anopheles mosquitoes from four landscapes in the highest endemic region of malaria transmission in Brazil.

Malaria transmission in South America is overwhelmingly located in the Amazon region with limited cases outside that biome. A key factor in the mitigation of malaria transmission is the determination of vector diversity and bionomics in endemic areas. Anopheles mosquitoes were collected in four different landscapes of Cruzeiro do Sul-Acre, the current area with highest malaria transmission in Brazil. We performed adult mosquito collections every three months over two years and associated vector occurrence with local abiotic factors. A total of 1,754 Anopheles belonging to nine species were collected, but only four of them (An. albitarsis s.l. Lynch-Arribalzaga, An. braziliensis Chagas, An. peryassui Dyar and Knab, and An. triannulatus Neiva and Pinto) represented 77.1% of the total. Vector density and diversity was uneven across field sites and collection periods. Higher Anopheles abundance (54.8%) and richness were observed in a deforested palm tree area (IFC), with An. braziliensis the most frequent mosquito (40.5%). Only 7.3% of mosquitoes were collected in the SAB village, but 66.4% of them were An. darlingi and An. oswaldoi, species often regarded as primary and secondary vectors of malaria in the Amazon region. A distinct biting preference was observed between 18:00-19:40. The distance from the nearest breeding site and minimum temperature explained 41.6% of the Anopheles community composition. Our data show that the Anopheles species composition may present great variation on a microgeographic scale.

Lower survival rate, longevity and fecundity of Aedes aegypti (Diptera: Culicidae) females orally challenged with dengue virus serotype 2.

As the pathogenic effects of a parasite on its hosts can strongly influence its epidemiology, we compared the life-histories of dengue virus serotype 2 (DENV-2)-infected and uninfected Aedes aegypti females. Unexposed mosquitoes lived longer than exposed ones, but those infected lived longer than exposed but negative (as assayed by Real-Time quantitative Reverse Transcription PCR [qRT-PCR]) mosquitoes. Infected mosquitoes from a long-established laboratory colony presented more viral RNA copies at death than those from the F1-generation of a field population from Rio de Janeiro. The mortality of infected colony-mosquitoes was independent of the number of viral RNA copies at death, whereas in the field population, longevity decreased with the number of viral RNA copies, suggesting that F1 of field mosquitoes are less tolerant to infection than the laboratory-colony. Infected females had a lower fecundity than controls. F1 of field mosquitoes were more likely to lay eggs than the colony; egg-laying success was strongly affected by mosquito age for both mosquito populations: from 49.28 in the first clutch to 20.7 in the fifth. Overall, DENV-2 reduced Aedes aegypti survival and fecundity, clearly affecting vectorial capacity and consequently transmission intensity.

Influence of the spatial distribution of human hosts and large size containers on the dispersal of the mosquito Aedes aegypti within the first gonotrophic cycle.

It is generally accepted that Aedes aegypti (L.) (Diptera: Culicidae) has a short dispersal capacity, and that displacement can be influenced by the availability of oviposition sites in the surroundings of emergence or release sites. In the present article, we observed the influence of spatial heterogeneity of large containers and human hosts on the cumulative flight direction of Ae. aegypti females during the first gonotrophic cycle, testing the hypothesis that they aggregate in resource-rich areas, i.e. where there are higher concentrations of large containers and/or humans per habitation. We analysed data from pupal surveys and mark-release-recapture experiments (non-blood-fed females were released) carried out in two dengue endemic neighbourhoods of Rio de Janeiro, Brazil: Tubiacanga (a suburb, with a human density of 337 inhabitants/ha) and Favela do Amorim (a slum, with a human density of 901 inhabitants/ha). In both areas, host-seeking females of three different release cohorts showed an overall non-uniform and extensive dispersal from their release point within 1-2 days post-release. At 4-5 days post-release, when many of the released females would be expected to be gravid, in Tubiacanga most mosquitoes were collected in areas with a relatively higher density of containers/premise, independently of the density of residents/house, whereas in Favela do Amorim, almost half of the captured mosquitoes were collected in relatively resource-poorer areas. Although Ae. aegypti dispersal patterns varied between sites, overall the distances travelled from the release point and the cumulative flight directions were correlated with the density of containers and hosts, more markedly in Tubiacanga than in Favela do Amorim.

Body size-associated survival and dispersal rates of Aedes aegypti in Rio de Janeiro.

The daily survival rate of Aedes aegypti (L) (Diptera: Culicidae) is one of the most important parameters in mathematical models of dengue transmission. In this report, we evaluate the effect of adult body size on the survival and dispersal rates of male and female Ae. aegypti, the primary dengue vector in Brazil. Independent of larval diet (i.e. size), the daily survival rate of females recaptured in the field was greater than that of males (smaller: t = 5.617; d.f. = 15; P < 0.05; larger: t = 4.241; d.f. = 16; P < 0.05). Larger males lived longer than smaller males (t = 2.2893; d.f. = 7; P < 0.05), but no size effect was observed for females (t =- 0.086; d.f. = 19; P= 0.932). The daily survival rate of smaller females was similar to that of larger females (0.712 and 0.730, respectively, as calculated by an exponential model, and 0.743 and 0.779, respectively, calculated by a non-linear model), and they dispersed further than larger females (mean distances travelled were 78.8 m and 40.9 m, respectively; t =- 10.22; d.f. = 323; P < 0.05). Adult body size did not influence male dispersal distances (t = 0.904; d.f. = 206; P= 0.367). Given our evidence that smaller females appear to have similar lifespans and evidence from other studies that they bite more frequently during a single gonotrophic cycle than larger females, our results suggest that smaller females have a higher vectorial capacity.