Valzano et al. are looking into an alternative malarial control method using symbiosis. A microbe with antimalarial activity could prevent the development of parasites in the mosquito gut, stopping malaria before it was even transferred to humans. Here they find a promising antiplasmodial toxin released from Wickerhamomyces anomalus yeast, referred to as Yeast Killer Toxin, and prove its antiparasitic activity in vitro against Plasmodium berghei.