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 natives Metarhizium pingshaense strains with deltamethrin standard dose in three ways, before, after or simultaneously. These combinations were tested on laboratory insecticide resistant Anopheles coluzzii. Results Therefore, we found that Metarhizium pingshaense and deltamethrin could be combined to achieve greater mortality against a highly insecticide resistance colony of Anopheles coluzzii. When mosquitoes were exposed to both simultaneously, no effect was observed, as expected for an insecticide resistant colony. However, 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). Conclusions These findings suggest that early mosquito infection to Metarhizium pingshaense followed by chemical insecticide exposure synergically improve mosquito control in the laboratory.