Studying the Interaction between Chromobacterium anophelis and the Entomopathogenic Fungus Metarhizium pingshaense in Aedes aegypti, the Dengue Vector in Burkina Faso

Insect-bacteria associations can influence vector competence in multiple ways. Chromobacterium anophelis, a bacterium known to be pathogenic to mosquitoes, may also act as an anti-pathogen by inhibiting the development of other pathogens within mosquitoes. The mechanism behind this inhibition remains unclear, with two hypotheses: the bacterium either boosts the mosquito’s immunity or directly targets other pathogens within the mosquito. The objective of this study is to elucidate the mechanism behind this pathogen-inhibition effect in mosquitoes. Bioassays (assessing longevity, fecundity, and fertility) were conducted on mosquitoes infected with the bacterium and an entomopathogenic fungus, Metarhizium pingshaense, whose hyphae grow on mosquitoes after killing them. The prevalence of hyphal growth was evaluated. The longevity of mosquitoes co-infected with Chromobacterium anophelis and Metarhizium pingshaense was significantly higher than those infected solely with the more virulent microorganism, which was Chromobacterium anophelis. Hyphae were observed on 100% of mosquitoes infected only with the fungus, whereas mosquitoes co-infected with the bacterium exhibited a lower prevalence of fungal hyphal growth. The number of eggs laid by infected mosquitoes was approximately the same, within the typical range (50 - 150). However, the number of larvae observed from co-infected mosquitoes was significantly higher than those produced by mosquitoes exposed to the microorganism that most reduced egg hatch rates. These results align with the hypothesis that Chromobacterium anophelis inhibits the development of other pathogens within mosquitoes by directly targeting them.