Avirulence gene mapping in the Hessian fly ( Mayetiola destructor ) reveals a protein phosphatase 2C effector gene family

First-instar Hessian fly larvae (A) use their microscopic mouthparts (m) to introduce secreted serine/threonine protein phosphatases (B) into wheat cells. These effectors presumably modulate wheat signal transduction pathways that alter seedling growth and development. (C) Susceptible seedlings (S) are stunted, but seedlings that detect the presence of an effector induce effector-triggered immunity (R) and grow normally.