_DROSOPHILA_ INNATE IMMUNITY: AN EVOLUTIONARY PERSPECTIVE In response to microbial infections, _Drosophila_ mounts a multifaceted immune response involving humoral reactions that culminate

in the destruction of invading organisms by lytic peptides. These defense mechanisms are activated _via_ two distinct signaling pathways. One of these, the Toll pathway, controls resistance

to fungal and Gram-positive bacterial infections, whereas the Imd pathway is responsible for defense against Gram-negative bacterial infections. Current evidence indicates that recognition

of infectious nonself agents results from interactions between microbial wall components and extracellular pattern recognition proteins. We discuss here evolutionary perspectives on our