Trail odors: recognition by insects parasitic on cocoons.

Female parasitic insects in the genera Pleolophus, Endasys, and Mastrus (Hymenoptera: Ichneumonidae) search the ground cover for hosts and avoid areas they have already inspected. Females respond to their own trail odor, and recognition occurs also between conspecific, congeneric, and intergeneric individuals. This is the first direct evidence for recognition between parasitoids at sites other than on the host itself, and between females of different species.