Isolating mechanisms are important in maintaining the taxonomic integrity of closely related sympatric taxa. A previous study found strong post-zygotic isolating barriers between two species, Witheringia asterotricha and W. meiantha, of the W. solanacea (Solanaceae) species complex in Costa Rica. This study examines the presence of pre-zygotic barriers between the two species at La Selva Biological Station in Costa Rica. Both species offer pollen and nectar as floral rewards and are visited primarily by solitary or semi-social bees, some of which sonicate (“buzz”) the anthers to discharge pollen. No evidence was found for phenological differences in flowering time between W. asterotricha and W. meiantha, but pre-zygotic factors, such as ethological isolation and possibly fine-scale ecological or geographic barriers, may be responsible for restricting gene flow between the two species.