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Development of insecticide resistance is a serious worldwide challenge for pest management of stored-product insects, as recognized since the FAO Global Survey of the mid-1970s. In this study, we carried out a survey of physiological and behavioral resistance to two organophosphate insecticides (chlorpyrifos-methyl and fenitrothion) in 14 populations of Sitophilus zeamais Motsch. (Coleoptera: Curculionidae) from Brazil and one from Paraguay and investigated if differences in population growth, body size, and respiration rate were associated with the resistance. Concentration-mortality bioassays were carried out and behavioral resistance was studied by recording the walking behavior on filter-paper half-treated with insecticide and determining the distance walked, walking velocity, resting time, and time spent on the treated side of the arena. The instantaneous rate of population growth (r_i) was determined, and …