The solitary egg parasitoidTelenomus heliothidisAshmead recognized its host, the eggs ofHeliothis virescens(F.), (Lepidoptera: Noctuidae), by both chemical and physical cues.T. heliothidisonly accepted hosts between 0.50 and 0.63 mm in diameter, with spherical hosts preferred to spheroidal hosts. Color was not a critical factor in host recognition byT. heliothidis. A minimal area of the host had to be coated by a recognition kairomone to be accepted even if the host were properly shaped. Recognition of both host shape and odor appeared to be by the antennae.T. heliothidisshowed a preference for younger host eggs. This preference was attributed to the change in shape of olderH. virescenseggs.