FADD and infection: Ticks and other non-insect arthropods lack genes encoding key molecules, such as transmembrane peptidoglycan recognition proteins that initiate the IMD pathway, and the signaling molecules IMD and FADD (10, 18, 19) Instead, the tick IMD pathway responds to multiple cues such as infection-derived lipids that are sensed by the receptor Croquemort (10, 11, 17) and to cellular stress that is caused by infection (20, 21).