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

Abstract

BACKGROUND: Entomopathogenic fungi of the genus Metarhizium are widely used as eco-friendly biocontrol agents against insect vectors, offering a cost-effective alternative to chemical insecticides. While these fungi have demonstrated potential as larvicides against malaria vectors, their impacts on mosquito life-history traits and maternal effects remain poorly understood. This study evaluated the effects of locally isolated Metarhizium pingshaense strains (S10 and S26) on survival, development, reproductive fitness, and maternal effects in Anopheles coluzzii mosquitoes. METHODS: We assessed the efficacy of M. pingshaense (strains S10 and S26) against both larval and adult stages of An. coluzzii. For larval assays, third-instar larvae were reared in water containing 2 × 105 conidia/mL of M. pingshaense. Adult survival, wing length, oviposition rate, and blood-feeding behavior were subsequently measured. For adult assays, female mosquitoes were sprayed with spore suspensions of strains S10 and S26, and survival of their offspring was assessed. Survival data were analyzed using a Cox proportional hazards model, while other life-history traits were analyzed using generalized linear mixed models (GLMMs). All experiments were performed in triplicate to ensure reproducibility. RESULTS: Exposure to fungal suspensions during the larval stage caused significant mortality at the pupal stage (~30%) compared to untreated controls. Adults emerging from treated larvae showed reduced survival (~23%) relative to controls, while wing length and blood-feeding behavior were unaffected. Adult female exposure to fungal spores increased egg-laying compared to controls, but a lower proportion of those larvae developed successfully into adults, demonstrating cross-stage and maternal effects. CONCLUSION: The results demonstrate the potential of M. pingshaense conidia as a biocontrol agent for An. coluzzii larvae, with additional cross-stage and maternal effects that further reduce mosquito fitness. These findings support the inclusion of M. pingshaense in integrated vector management strategies. Future work should focus on elucidating the molecular mechanisms underlying larval susceptibility and optimizing fungal formulations to enhance virulence.