Climate strongly influences the geographic distribution and timing of mosquito-borne disease outbreaks. Environmental temperature affects phenotypic traits of mosquitoes including vector competence for arboviruses mediated by changes in infection, extrinsic incubation period and in rates of transmission. Most experiments, however, are done at constant temperatures. In nature, mosquitoes are more likely to experience daily fluctuations in temperature. Here we compare disseminated infection (leg infection) and saliva infection of Aedes aegypti (L.) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) from Florida following oral exposure to an Asian genotype of chikungunya virus emergent in the Americas. We evaluated experimentally the effect of variable temperature regimens on disseminated infection and saliva infection of these Aedes species. Each of three temperature regimes had approximately the same average temperature (27-28°C), but differed in the magnitude of the diurnal temperature range (DTR). The large DTR was 8.0°C (range 23-31°C) and the small DTR was 4.0°C (range 26-30°C) which approximate ranges in different locations of Florida during July-October when risk of transmission is highest. The constant temperature was set at 27°C. Testing three geographic populations of each mosquito species, significant effects on disseminated infection were detected for an interaction between temperature regime and geographic population for both Ae. aegypti and Ae. albopictus. There were no significant treatment effects of temperature, geographic population, or temperature by geographic population interaction on saliva infection for either mosquito species. Constant temperature resulted in a higher viral load in the saliva of Ae. albopictus, but not Ae. aegypti, compared to conditions where the temperature fluctuated.

Mosquitoes often experience intraspecific and interspecific competition among larvae attributable to high densities and nutrient limitation, especially container mosquitoes including Aedes aegypti (L.) and Aedes albopictus (Skuse). Density-dependent effects on larvae impact adult production and adult traits that influence transmission of arboviruses. To improve our understanding of the mechanisms by which density-dependence influences transmission and identify species-specific traits, we tested the hypotheses: 1) Competitive asymmetry in favor of Ae. albopictus over Ae. aegypti translates to altered adult female survival, and 2) Ae. aegypti adult females are more resistant to life-shortening effects of low-humidity conditions than Ae. albopictus. We gauged the relative impact of inter- and intraspecific larval competition on adult survival in high- and low-humidity regimes (77 and 44% relative humidity, respectively). For Ae. albopictus, intraspecific but not interspecific competition usually reduced adult survival under both humidity regimes. For Ae. aegypti, both intraspecific and interspecific competition reduced adult survival. Ae. albopictus adult survival was minimally influenced by interspecific competition with Ae. aegypti, consistent with observations that Ae. albopictus is the superior competitor. A species comparison indicated that Ae. aegypti exhibited a survival advantage relative to Ae. albopictus under both low- and high-humidity conditions. However, similar survival of these Aedes species was observed in some cases depending on conditions experienced in both the aquatic and terrestrial environments. These results demonstrate plasticity in survival rates of dengue and chikungunya vectors and the significance of considering the influence of biological interactions during the immature stages and abiotic conditions during the adult stage.

The effects of microbial biopesticides used for mosquito control on autotrophic microorganisms such as nanophytoplankton are equivocal. We examined impacts of mosquito biopesticides and mosquito larvae on primary producers in two independent experiments. In the first experiment, we examined the effects of a commonly used microbial biopesticide formulation (VectoMax® CG) on a unicellular microalga, Selenastrum capricornatum Printz, under axenic laboratory conditions. The biopesticide treatments included two concentrations (0.008 and 0.016 g liter -1) of VectoMax® CG and two controls (one untreated and another with autoclaved 0.016 g VectoMax® CG liter -1 ) in replicated axenic experimental microcosms. Spectrophotometric analysis of chlorophyll a (proxy for algal biomass) and direct enumeration of algal cells following the treatments revealed no significant effects of the microbial biopesticide on algal population growth during the four-week study. In the second experiment, we tested the effects of different densities of Culex larvae on the population of S. capricornatum. Effects of mosquito larvae feeding on S. capricornatum were significant with a curvilinear relationship between larval density and algal abundance in the water column. Together, these studies demonstrated a lack of direct cytological/toxicological effects of Bacillus-based microbial pesticides on freshwater primary production and support the hypothesis that the reduction in algal primary production previously reported when Bti products were applied to aquatic environments was likely independent of the Bacillus-based larvicidal toxins. Instead, it was likely mediated by microbial interactions in the water column and the trophic cascade effects that resulted from the removal of larval mosquitoes. These studies suggest that mosquito larvae independent of pesticide application can influence primary production. Our method of evaluating biopesticides against small photoautotrophs can be very useful for studying the unintended effects on autotrophic microorganisms of other pesticides, including herbicides and pesticides applied to aquatic environments. Journal of Vector Ecology 42 (1): 51-59. 2017.