Among fitness-related genes that are in common between Anopheles and Drosophila, we identified an ortholog of serpent (srp), which encodes a GATA transcription factor critical for hematopoiesis in Drosophila, and found that in vivo knockdown in An. gambiae reduced hemocyte numbers and increased malaria parasite infection, suggesting a conserved role in immunity. Here, UCN2 is linked to biological process involved in symbiotic interaction.