Caste differences in behavioral thresholds as a basis for polyethism during food recruitment in the ant,Pheidole pallidula (Nyl.) (Hymenoptera: Myrmicinae)

During foraging, societies of the polymorphic ant, Pheidole pallidula,display several collective patterns which differ in the ratio of recruited majors. The intensity of behavioral stimuli required to induce this majors' recruitment is determined by studying trail-laying and tactile invitations for the following two food recruitments: (I) the slow and weak recruitment of minors, without majors, to a pile of small, individually retrievable fruit flies and (2) the massive recruitment of both minors and majors to large, unretrievable cockroaches. The selective mobilization of majors only to large prey such as cockroaches is due both to their preferential invitation and to their higher behavioral threshold of response to recruiting stimuli. The experimental evidence of caste behavioral thresholds allow us to reconsider behavioral elasticity in the major caste as well as principles of division of labor in ant societies.