The Drosophila immune response after attack by parasitoids. (a) The parasitoid Asobara tabida stabs a second instar Drosophila melanogaster larvae with her ovipositor and inserts a single egg. (b) The parasitoid egg is susceptible to nonself recognition by membrane-bound and noncellular pattern recognition proteins in the larval hemolymph. (c) Hemocyte proliferation and differentiation is triggered, and the blood cells aggregate around the parasitoid egg. (d) The hemocytes form a multilayered capsule around the parasitoid egg and melanin is deposited on the capsule. (e) The parasitoid egg dies when it becomes fully melanized.