Seasonal Differences in Density But Similar Competitive Impact of Aedes albopictus (Skuse) on Aedes aegypti (L.) in Rio de Janeiro, Brazil.

Previous studies have shown that the negative effects of density of Ae. albopictus on Ae. aegypti exceed those of Ae. aegypti on Ae. albopictus for population growth, adult size, survivorship, and developmental rate. This competitive superiority has been invoked to explain the displacement of Ae. aegypti by Ae. albopictus in the southeastern USA. In Brazil, these species coexist in many vegetated suburban and rural areas. We investigated a related, but less-well-studied question: do effects of Ae. albopictus on Ae. aegypti larval development and survival occur under field conditions at realistic densities across multiple seasons in Brazil? We conducted additive competition experiments in a vegetated area of Rio de Janeiro where these species coexist. We tested the hypothesis that Ae. aegypti (the focal species, at a fixed density) suffers negative effects on development and survivorship across a gradient of increasing densities of Ae. albopictus (the associate species) in three seasons. The results showed statistically significant effects of both season and larval density on Ae. aegypti survivorship, and significant effects of season on development rate, with no significant season-density interactions. Densities of Aedes larvae in these habitats differed among seasons by a factor of up to 7x. Overall, Spring was the most favorable season for Ae. aegypti survivorship and development. Results showed that under natural conditions the negative competitive effects of Ae. albopictus on Ae. aegypti were expressed primarily as lower survivorship. Coexistence between Ae. aegypti and Ae. albopictus in vegetated areas is likely affected by seasonal environmental differences, such as detrital resource levels or egg desiccation, which can influence competition between these species. Interactions between these Aedes are important in Brazil, where both species are well established and widely distributed and vector dengue, Zika and chikungunya viruses

Climate normals (1961–1990) for the city of Rio de Janeiro.

<p>Instituto Nacional de Meteorologia—Brazilian National Institute of Meteorology, available at <a href="http://www.inmet.gov.br/" target="_blank">http://www.inmet.gov.br/</a>.</p

Two-way ANOVA for the effect of <i>Aedes albopictus</i> density and season on the mean larval survivorship and developmental progress of <i>Aedes aegypti</i> after 7 days (mean instar).

<p>Two-way ANOVA for the effect of <i>Aedes albopictus</i> density and season on the mean larval survivorship and developmental progress of <i>Aedes aegypti</i> after 7 days (mean instar).</p

Competition experiment results.

<p>Mean (± 2 SE) for competition treatments for mean instar of <i>Ae</i>. <i>aegypti</i> and survivorship after 7 days of experiment in the Autumn, Spring and Summer.</p

Kruskal-Wallis test for significant differences in pupal productivity between Autumn, Spring and Summer colonization period, and Mann-Whitney pairwise comparisons with Bonferroni correction.

<p>Mann-Whitney tests were used for comparisons between <i>Ae</i>. <i>aegypti</i> and <i>Ae</i>. <i>albopictus</i> (overall and in each season).</p

Pupal productivity and Climate data during the colonization period.

<p>Pupal productivity of <i>Ae</i>. <i>aegypti</i> (a) and <i>Ae</i>. <i>albopictus</i> (b), mean daily temperature (c) and daily rainfall (d) during the 30-day period of colonization in the Autumn, Spring and Summer.</p

Relative abundance of the pupal productivity for each mosquito species and mean (standard error) pupae produced per vase at the end of the 30 days period of colonization in the Autumn, Spring and Summer.

<p>Relative abundance of the pupal productivity for each mosquito species and mean (standard error) pupae produced per vase at the end of the 30 days period of colonization in the Autumn, Spring and Summer.</p

Number of 1^st instar larvae of <i>Ae</i>. <i>aegypti</i> and <i>Ae</i>. <i>albopictus</i> used in each density treatment in the three experiments.

<p>Number of 1^st instar larvae of <i>Ae</i>. <i>aegypti</i> and <i>Ae</i>. <i>albopictus</i> used in each density treatment in the three experiments.</p

Larval and pupal productivity during the colonization period defined the Baseline number for the larval manipulation experiments.

<p>Larval and pupal productivity during the colonization period defined the Baseline number for the larval manipulation experiments.</p

Seasonal Differences in Density But Similar Competitive Impact of <i>Aedes albopictus</i> (Skuse) on <i>Aedes aegypti</i> (L.) in Rio de Janeiro, Brazil

<div><p>Previous studies have shown that the negative effects of density of <i>Ae</i>. <i>albopictus</i> on <i>Ae</i>. <i>aegypti</i> exceed those of <i>Ae</i>. <i>aegypti</i> on <i>Ae</i>. <i>albopictus</i> for population growth, adult size, survivorship, and developmental rate. This competitive superiority has been invoked to explain the displacement of <i>Ae</i>. <i>aegypti</i> by <i>Ae</i>. <i>albopictus</i> in the southeastern USA. In Brazil, these species coexist in many vegetated suburban and rural areas. We investigated a related, but less-well-studied question: do effects of <i>Ae</i>. <i>albopictus</i> on <i>Ae</i>. <i>aegypti</i> larval development and survival occur under field conditions at realistic densities across multiple seasons in Brazil? We conducted additive competition experiments in a vegetated area of Rio de Janeiro where these species coexist. We tested the hypothesis that <i>Ae</i>. <i>aegypti</i> (the focal species, at a fixed density) suffers negative effects on development and survivorship across a gradient of increasing densities of <i>Ae</i>. <i>albopictus</i> (the associate species) in three seasons. The results showed statistically significant effects of both season and larval density on <i>Ae</i>. <i>aegypti</i> survivorship, and significant effects of season on development rate, with no significant season-density interactions. Densities of <i>Aedes</i> larvae in these habitats differed among seasons by a factor of up to 7x. Overall, Spring was the most favorable season for <i>Ae</i>. <i>aegypti</i> survivorship and development. Results showed that under natural conditions the negative competitive effects of <i>Ae</i>. <i>albopictus</i> on <i>Ae</i>. <i>aegypti</i> were expressed primarily as lower survivorship. Coexistence between <i>Ae</i>. <i>aegypti</i> and <i>Ae</i>. <i>albopictus</i> in vegetated areas is likely affected by seasonal environmental differences, such as detrital resource levels or egg desiccation, which can influence competition between these species. Interactions between these <i>Aedes</i> are important in Brazil, where both species are well established and widely distributed and vector dengue, Zika and chikungunya viruses.</p></div