Dietary shifts in infected mosquitoes suggest a form of self-medication despite benefits in uninfected individuals.

Immune responses protect against infectious diseases but often incur physiological costs, such as oxidative stress. In mosquitoes, these costs may shape behaviours that help regulate oxidative balance, potentially including the consumption of nectar containing bioactive substances such as prooxidants and antioxidants. We investigated whether Anopheles gambiae adjust their preferences for diets with such substances when they are infected with the microsporidian parasite Vavraia culicis. Using sugar solutions supplemented with hydrogen peroxide (a prooxidant) or ascorbic acid (an antioxidant), we assessed the feeding preferences of uninfected and infected mosquitoes at different ages and measured the effects of these diets on oxidative homeostasis, parasite load and lifespan. Infected mosquitoes initially preferred the prooxidant diet, which reduced parasite load and extended lifespan, before shifting their preference towards the antioxidant diet as infection progressed. In contrast, uninfected mosquitoes consistently preferred the unsupplemented sugar, likely to avoid oxidative stress induced by the supplemented diets, which, surprisingly, also increased their lifespan. These results suggest a form of self-medication, despite benefits in uninfected individuals, where mosquitoes dynamically adjust their dietary choices throughout infection. We propose that such dietary strategies may be widespread among mosquitoes, helping them manage oxidative stress, with potential implications for vector-pathogen interactions and the success of biological control programmes.