The sugarcane rootscalk weevil borer Diaprepes abbreviates (L.) moves freely among numerous plant hosts within Puertorican agroecosystems. The sweet potato weevil, on the contrary, appears circumscribed to the family Convolvulaceae. The fecundity, life cycle and longevity of the two insects were probed to unveil the biological nature of vagility. Diaprepes fecundity was greatly enhanced by the shift from wild to cultivated hosts, development was not influenced appreciably, and longevity was greater in the sedentary species. It is assumed that vagile populations are briefly boosted by host shifts even ending in expansion thrusts though longevity is not necessarily extended. Undet sedentary conditions populations are generally low but stable.