Entomopathogenic fungi Metarhizium pingshaense increases susceptibility to insecticides in highly resistant malaria mosquitoes Anopheles coluzzii

Background Metarhizium spp. based mosquito control products are among the most investigated and could potentially serve as promising complements to chemical insecticides. However, limited knowledge exists on the implementation of this biocontrol tool in conjunction with primary insecticide-based strategies to achieve synergy. Methods In laboratory bioassays, we combined 10⁷ conidia/ml native Metarhizium pingshaense strains with deltamethrin standard dose in two ways : before and after insecticide exposure. For comparison, some mosquitoes were exposed to deltamethrin or fungi alone. These combinations were tested on laboratory insecticide resistant Anopheles coluzzii. Results We found that Metarhizium pingshaense and deltamethrin could be combined to achieve greater mortality against a highly insecticide resistance colony of Anopheles coluzzii. Specifically, when fungi were applied earlier than deltamethrin, mosquitoes became more sensitive to insecticide with a minimum Lethal Time to kill at least 50% of mosquito population (LT50) less than 8 days. In addition, when deltamethrin exposure was followed by Metarhizium infection, mosquito survival was similar to Metarhizium alone LT50 (LT50 ~11 days). Conclusion These findings suggest that early mosquito infection to Metarhizium pingshaense followed by chemical insecticide exposure synergically increased mosquito susceptibility to the insecticide in the laboratory.