Fourteen wild species of Arachis (Leguminosae) were investigated under field and laboratory conditions to evaluate their effect on the survival and development of the larvae of Spodoptera litura (Fabricius). All of the species studied were observed to be resistant compared to the susceptible control, Arachis hypogaea (genotype TMV2). Overall, the mortality and development of larvae recorded in the field were similar to those recorded for larvae on excised leaves of the same species in the laboratory. When neonate larvae were exposed to excised leaves of A. batizogaea, A. kemph-mercadoi, A. appresipila, A. paraguariensis, A. stenophyla and A. villosa mortality was greater than 94% compared to less than 20% on TMV2. Third stadium larvae lost weight when exposed to both field plants and excised leaves of eight of the wild species, whereas larvae feeding on TMV2 gained weight. When third stadium larvae were fed pulped leaves they gained more weight than when exposed to intact leaves, except in the case of A. chacoensis and Arachis spp. 30007. A penetrometer was used to determine the relative toughness of the leaves. The leaves of most of the wild species were shown to require a greater biting effort for feeding than the leaves of TMV2. There was a negative correlation between toughness of whole leaves and larval development. Observations of larval behaviour indicated that, overall, larvae were deterred from feeding on the leaves of the wild species. Diets containing the chemical extracts of dried leaves of A. kemph-mercadoi, A. paraguariensis, A. appresipila, A. chacoensis, A. glabrata and A. pseudovillosa resulted in low larval weight gain. The physical quality of the leaves and foliar chemicals are implicated as being responsible for the observed resistance. The implications and potential applications of these results are discussed.