A Novel Model of Pathogenesis of Metarhizium anisopliae Propagules through the Midguts of Aedes aegypti Larvae

SIMPLE SUMMARY: The mosquito Aedes aegypti is the principal vector of multiple arboviruses including dengue (DENV), zika (ZIKV), and chikungunya (CHIKV) that cause major human disease and suffering. Control is based on the application of synthetic insecticides to reduce mosquito populations. However, the overuse of synthetic insecticides has led to mosquito resistance. Studies on the use of entomopathogenic fungi (EPF) such as Metarhizium anisopliae to reduce mosquito populations are gaining interest as they are ecologically safe and can kill different mosquito life stages. Despite their lethality towards mosquito larvae, their mechanisms of infection are unclear. In this study, we first evaluated the production of blastospores of three M. anisopliae isolates and assessed their effects against Ae. aegypti larvae. We assessed, and describe in detail, the mechanism of infection of one fungal isolate against Ae. aegypti larvae. Overall, our findings indicate that EPF are able to kill mosquito larvae by infecting the insect midgut, disrupting enterocytes, and causing brush border degradation. ABSTRACT: We assessed the effect of the entomopathogenic fungus Metarhizium anisopliae against Aedes aegypti. Conidia of M. anisopliae strains CG 489, CG 153, and IBCB 481 were grown in Adamek medium under different conditions to improve blastospore production. Mosquito larvae were exposed to blastospores or conidia of the three fungal strains at 1 × 10(7) propagules mL(−1). M. anisopliae IBCB 481 and CG 153 reduced larval survival by 100%, whereas CG 489 decreased survival by about 50%. Blastospores of M. anisopliae IBCB 481 had better results in lowering larval survival. M. anisopliae CG 489 and CG 153 reduced larval survival similarly. For histopathology (HP) and scanning electron microscopy (SEM), larvae were exposed to M. anisopliae CG 153 for 24 h or 48 h. SEM confirmed the presence of fungi in the digestive tract, while HP confirmed that propagules reached the hemocoel via the midgut, damaged the peritrophic matrix, caused rupture and atrophy of the intestinal mucosa, caused cytoplasmic disorganization of the enterocytes, and degraded the brush border. Furthermore, we report for the first time the potential of M. anisopliae IBCB 481 to kill Ae. aegypti larvae and methods to improve the production of blastospores.