Causes and consequences of microbiome formation in Culex restuans larvae

Authors: SCHWING, CAMERON - University Of Illinois; HOLMES, CHRISTOPHER - University Of Illinois; Muturi, Ephantus; Dunlap, Christopher; HOLMES, JESSICA - University Of Illinois; CACERES, CARLA - University Of Illinois

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Mosquito larvae develop in stagnant water bodies and feed on microbial communities associated with decaying organic matter. Some of the ingested microbial communities colonize the mosquito midgut and contribute to host health. However, the specific microbes that are retained in mosquito midguts and their influence on adult traits remain poorly understood. Larvae of a major vector of West Nile virus were reared under two resource environments (Grass only [G] vs Grass + Nutrients [GN]), two competition types (mosquitoes only vs mosquitoes plus another species of grazer), and two larval densities (high vs. low) to test the hypotheses that these environmental treatments would lead to distinct microbial communities in fourth-instar larvae and influence adult traits. The microbial communities in mosquito larvae were significantly influenced by nutrient enrichment and larval density but not their interactions. Larval samples were mostly associated with bacterial communities from one phylum while water samples were mostly associated with bacterial communities from three phyla. Larvae reared under intraspecific competition in the G treatment had the shortest development time to adulthood and resulted in smaller adults. These findings demonstrate the differences in the free-living and host-associated bacterial communities and confirm a correlation between larval microbial assembly and adult traits.

Technical Abstract: The assembly of host-associated microbial communities is influenced by multiple factors, but the effect of microbiomes on host phenotypes is often not well understood. To address questions of food-web effects on host-microbiome assembly, we manipulated the resource environment (Grass only [G] and Grass + Nutrients [GN]), competition type (intra- and inter-specific), and larval density (high vs. low) for Culex restuans larvae. We predicted the microbial communities in fourth-instar larvae would differ between these environmental treatments and that these treatments would translate into differences in the adult phenotype. Resource environment and density influenced the larval microbiome. The larval microbiome exhibited notable differences compared to the free-living microbial communities. Resource-driven differences in the larval samples can be attributed to Arcobacteraceae being more abundant in larvae reared in the GN treatments relative to those reared in the G treatments and Comamonadaceae being more abundant in the G treatment. Although significant, the difference in community structure between density treatments was difficult to discern. This appears to be driven by Weeksellaceae only being abundant in the high-density, interspecific, GN treatment. Rearing larvae to adulthood resulted in low survival in both resource environments. For the survivors, there was a significant interaction between competition type and resource environment on wing size and time to emergence. Larvae reared under intraspecific competition in the G treatment had the shortest development time to adulthood and resulted in smaller adults. Our results further demonstrate the differences in the free-living and host-associated communities and confirm a correlation between larval microbiome and adult traits.