Maternal and cross-stage effects of Metarhizium fungal infection on the malaria mosquito Anopheles coluzzii life-history

BackgroundEntomopathogenic fungi of the Metarhizium genus are widely used as biocontrol agents against harmful insects. These fungi are cost-effective and eco-friendly for vector control, providing an alternative to synthetic chemical insecticides. They have great potential as larvicides against malaria vectors, but their impacts on mosquito fitness have not been fully measured. This study evaluated the effect of Metarhizium fungal strains, locally isolated in Burkina Faso, on the larval survival of the mosquito Anopheles coluzzii, the life history of the emerging adults and on the maternal effects of exposed females. MethodsWe assessed the efficacy of Metarhizium pingshaense (strains S10 and S26) conidia against An. coluzzii larvae. First, larvae were reared in the presence of fungal spores and the survival of the larvae and adults that emerged, their wing length, oviposition rate and blood feeding behaviour were measured. Additionally, we assessed the efficacy of fungal strains S10 and S26 conidia against An. coluzzii adults by spraying them with spore suspensions and assessing the survival of their larval offspring. Survival data was analyzed using Cox proportional hazards model, while other life history traits using generalized linear mixed models. ResultsThe fungal suspension applied to the water in which the larvae were reared caused mortality at the pupae stage. Only a small number of larvae emerged to reach adulthood. Furthermore, at the adult stage, these mosquitoes exhibited reduced survival compared to the control. However, body size and blood-feeding behavior were not affected by the treatment. When fungi was applied to adult females, the number of eggs layed was more abundant in infected group compared to controls, however a lower proportion of larvae successfully developed into adults. ConclusionThe results of this study demonstrate the potential of Metarhizium pingshaense conidia for mosquito larval control. The identified cross-stage and maternal effects showed additional virulent effects of Metarhizium, thus reinforcing the evidence that this biocontrol agent should be part of an integrated vector management. Future work should focus on the molecular mechanism of the fungal infection at the larval stage to improve formulation or genetically engineer the conidia of these strains to make them more virulent.