Comparison of larval foraging behavior of Aedes albopictus and Aedes japonicus (Diptera: Culicidae)

Larval Competition between Aedes and Culex Mosquitoes Carries over to Higher Arboviral Infection during Their Adult Stage

The common house mosquito (Culex pipiens) is a native vector for West Nile virus (WNV). Invasive species like the tiger mosquito (Aedes albopictus) and Asian bush mosquito (Aedes japonicus) are rapidly spreading through Europe, posing a major threat as vectors for dengue, chikungunya (CHIKV), and Japanese encephalitis virus (JEV). These mosquitoes share a similar ecological niche as larvae, but the carry-over effects of aquatic larval interactions to the terrestrial adult stage remain largely unknown and their medical relevance requires further investigation. This study examines the context dependency of larval interactions among Aedes albopictus, Aedes japonicus, and Culex pipiens. The survival, development time, growth, and energetic storage were measured in different European populations within density-response (intraspecific) experiments and replacement (interspecific) experiments at 20 °C and 26 °C. Overall, Ae. japonicus was the weakest competitor, while competition between Ae. albopictus and Cx. pipiens varied with temperature. Adults emerging from this larval competition were infected as follows: Culex pipiens with WNV, Ae. albopictus with CHIKV, and Ae. japonicus with JEV. While no JEV infection was observed, mosquitoes experiencing interspecific interactions during their larval stages exhibited higher infection rates and viral RNA titers for CHIKV and WNV. This increased susceptibility to viral infection after larval competition suggests a higher risk of arbovirus transmission in co-occurring populations.

The larval environment strongly influences the bacterial communities of Aedes triseriatus and Aedes japonicus (Diptera: Culicidae)

Mosquito bacterial communities are essential in mosquito biology, and knowing the factors shaping these bacterial communities is critical to their application in mosquito-borne disease control. This study investigated how the larval environment influences the bacterial communities of larval stages of two container-dwelling mosquito species, Aedes triseriatus, and Aedes japonicus. Larval and water samples were collected from tree holes and used tires at two study sites, and their bacteria characterized through MiSeq sequencing of the 16S rRNA gene. Bacterial richness was highest in Ae. japonicus, intermediate in Ae. triseriatus, and lowest in water samples. Dysgonomonas was the dominant bacterial taxa in Ae. triseriatus larvae; the unclassified Comamonadaceae was dominant in water samples from waste tires, while Mycobacterium and Carnobacterium, dominated Ae. japonicus. The two mosquito species harbored distinct bacterial communities that were different from those of the water samples. The bacterial communities also clustered by habitat type (used tires vs. tree holes) and study site. These findings demonstrate that host species, and the larval sampling environment are important determinants of a significant component of bacterial community composition and diversity in mosquito larvae and that the mosquito body may select for microbes that are generally rare in the larval environment.

Cannibalism in temporary waters: Simulations and laboratory experiments revealed the role of spatial shape in the mosquito Aedes albopictus

Cannibalism is a commonly observed phenomenon in arthropod species having relevant consequences for population dynamics and individual fitness. It is a context-dependent behaviour and an understanding of the factors affecting cannibalism rate is crucial to highlight its ecological relevance. In mosquitoes, cannibalism between larval stages has been widely documented, and the role of density, food availability and length of contact between individuals also ascertained. However, although mosquitoes can develop in temporary water habitats with very heterogeneous topologies, the role of the site shape where cannibals and victims co-occur has been instead overlooked. In this paper, we investigated this issue by using a simulation approach and laboratory cannibalism experiments between old (third- and fourth-instars) and young (first-instar) larvae of the tiger mosquito Aedes albopictus. Three virtual spaces with different shapes were simulated and the number of larval encounters was estimated in each one to assess whether the spatial shape affected the number of encounters between cannibal and victims. Then, experimental trials in containers with similar shapes to those used in the simulations were performed, and the cannibalism rate was estimated at 24 and 48h. Our results showed that the spatial shape plays a role on cannibalism interactions, affecting the number of encounters between individuals. Indeed, in the experimental trials performed, we observed the highest cannibalism rate in the container with the highest number of encounters predicted by the simulations. Interestingly, we found also that spatial shape can affect cannibalism not only by affecting the number of encounters, but also the number of encounters “favorable” for cannibalistic events. Temporary waters are inhabited by several species other than mosquitoes. Our results, showing an influence of the spatial shape on cannibalism in Ae. albopictus larvae, add a new critical factor to those affecting ecological interactions in these habitats.

How does competition among wild type mosquitoes influence the performance of Aedes aegypti and dissemination of Wolbachia pipientis?

BACKGROUND

Wolbachia has been deployed in several countries to reduce transmission of dengue, Zika and chikungunya viruses. During releases, Wolbachia-infected females are likely to lay their eggs in local available breeding sites, which might already be colonized by local Aedes sp. mosquitoes. Therefore, there is an urgent need to estimate the deleterious effects of intra and interspecific larval competition on mosquito life history traits, especially on the duration of larval development time, larval mortality and adult size.

METHODOLOGY/PRINCIPAL FINDINGS

Three different mosquito populations were used: Ae. aegypti infected with Wolbachia (wMelBr strain), wild Ae. aegypti and wild Ae. albopictus. A total of 21 treatments explored intra and interspecific larval competition with varying larval densities, species proportions and food levels. Each treatment had eight replicates with two distinct food levels: 0.25 or 0.50 g of Chitosan and fallen avocado leaves. Overall, overcrowding reduced fitness correlates of the three populations. Ae. albopictus larvae presented lower larval mortality, shorter development time to adult and smaller wing sizes than Ae. aegypti. The presence of Wolbachia had a slight positive effect on larval biology, since infected individuals had higher survivorship than uninfected Ae. aegypti larvae.

CONCLUSIONS/SIGNIFICANCE

In all treatments, Ae. albopictus outperformed both wild Ae. aegypti and the Wolbachia-infected group in larval competition, irrespective of larval density and the amount of food resources. The major force that can slow down Wolbachia invasion is the population density of wild mosquitoes. Given that Ae. aegypti currently dominates in Rio, in comparison with Ae. albopictus frequency, additional attention must be given to the population density of Ae. aegypti during releases to increase the likelihood of Wolbachia invasion.

How Diverse Detrital Environments Influence Nutrient Stoichiometry between Males and Females of the Co-Occurring Container Mosquitoes Aedes albopictus, Ae. aegypti, and Culex quinquefasciatus

Allocation patterns of carbon and nitrogen in animals are influenced by food quality and quantity, as well as by inherent metabolic and physiological constraints within organisms. Whole body stoichiometry also may vary between the sexes who differ in development rates and reproductive allocation patterns. In aquatic containers, such as tree holes and tires, detrital inputs, which vary in amounts of carbon and nitrogen, form the basis of the mosquito-dominated food web. Differences in development times and mass between male and female mosquitoes may be the result of different reproductive constraints, which could also influence patterns of nutrient allocation. We examined development time, survival, and adult mass for males and females of three co-occurring species, Aedes albopictus, Ae. aegypti, and Culex quinquefasciatus, across environments with different ratios of animal and leaf detritus. We quantified the contribution of detritus to biomass using stable isotope analysis and measured tissue carbon and nitrogen concentrations among species and between the sexes. Development times were shorter and adults were heavier for Aedes in animal versus leaf-only environments, whereas Culex development times were invariant across detritus types. Aedes displayed similar survival across detritus types whereas C. quinquefasciatus showed decreased survival with increasing leaf detritus. All species had lower values of ¹⁵N and ¹³C in leaf-only detritus compared to animal, however, Aedes generally had lower tissue nitrogen compared to C. quinquefasciatus. There were no differences in the C:N ratio between male and female Aedes, however, Aedes were different than C. quinquefasciatus adults, with male C. quinquefasciatus significantly higher than females. Culex quinquefasciatus was homeostatic across detrital environments. These results allow us to hypothesize an underlying stoichiometric explanation for the variation in performance of different container species under similar detrital environments, and if supported may assist in explaining the production of vector populations in nature.

Contributions of temporal segregation, oviposition choice, and non-additive effects of competitors to invasion success of Aedes japonicus (Diptera: Culicidae) in North America

The mosquito Aedes japonicus (Diptera: Culicidae) has spread rapidly through North America since its introduction in the 1990s. The mechanisms underlying its establishment in container communities occupied by competitors Aedes triseriatus and Aedes albopictus are unclear. Possibilities include (A) temporal separation of A. japonicus from other Aedes, (B) oviposition avoidance by A. japonicus of sites containing heterospecific Aedes larvae, and (C) non-additive competitive effects in assemblages of multiple Aedes. Containers sampled throughout the summer in an oak-hickory forest near Eureka, MO showed peak abundance for A. japonicus occurring significantly earlier in the season than either of the other Aedes species. Despite this, A. japonicus co-occurred with one other Aedes species in 53 % of samples when present, and co-occurred with both other Aedes in 18 % of samples. In a field oviposition experiment, A. japonicus laid significantly more eggs in forest edge containers than in forest interior containers, but did not avoid containers with low or high densities of larvae of A. triseriatus, A. albopictus, or both, compared to containers without larvae. Interspecific competitive effects (measured as decrease in the index of performance, λ') of A. triseriatus or A. albopictus alone on A. japonicus larvae were not evident at the densities used, but the effect of both Aedes combined was significantly negative and super-additive of effects of individual interspecific competitors. Thus, neither oviposition avoidance of competitors nor non-additive competitive effects contribute to the invasion success of A. japonicus in North America. Distinct seasonal phenology may reduce competitive interactions with resident Aedes.

Invasion biology of Aedes japonicus japonicus (Diptera: Culicidae)

Aedes japonicus japonicus (Theobald) (Diptera: Culicidae) has recently expanded beyond its native range of Japan and Korea into large parts of North America and Central Europe. Population genetic studies begun immediately after the species was detected in North America revealed genetically distinct introductions that subsequently merged, likely contributing to the successful expansion. Interactions, particularly in the larval stage, with other known disease vectors give this invasive subspecies the potential to influence local disease dynamics. Its successful invasion likely does not involve superior direct competitive abilities, but it is associated with the use of diverse larval habitats and a cold tolerance that allows an expanded seasonal activity range in temperate climates. We predict a continued but slower expansion of Ae. j. japonicus in North America and a continued rapid expansion into other areas as this mosquito will eventually be considered a permanent resident of much of North America, Europe, Asia, and parts of Hawaii.