Insects, unlike vertebrates, are widely believed to lack male-biased sex
steroid hormones1. In the
malaria mosquito Anopheles gambiae, the
ecdysteroid 20-hydroxyecdysone (20E) appears to have evolved to both control egg development when synthesized by females2 and to induce mating refractoriness when sexually transferred by males3. Because egg development and mating are essential reproductive traits, understanding how Anopheles females integrate these hormonal signals can spur the design of new
malaria control programs. Here we reveal that these reproductive functions are regulated by distinct sex
steroids through a sophisticated network of
ecdysteroid-activating/inactivating
enzymes. We identify a male-specific oxidized
ecdysteroid,
3-dehydro-20E (3D20E), which safeguards paternity by turning off female sexual receptivity following its sexual transfer and activation by dephosphorylation. Notably, 3D20E transfer also induces expression of a reproductive gene that preserves egg development during
Plasmodium infection, ensuring fitness of infected females. Female-derived 20E does not trigger sexual refractoriness but instead licenses oviposition in mated individuals once a 20E-inhibiting
kinase is repressed. Identifying this male-specific insect
steroid hormone and its roles in regulating female sexual receptivity, fertility and interactions with Plasmodium parasites suggests the possibility for reducing the reproductive success of
malaria-transmitting mosquitoes.