The sap beetles of the genus Nitops (Nitidulidae, Coleoptera) are often found in flowers of columnar cacti like Pilosocereus (Cactaceae). Little is known about the conditions in which these infestations occur and their effects on cacti. The first record of the genus Nitops in northeastern Brazil is presented and different aspects of the ecological interaction between the beetle and columnar cacti of the region are analysed. Quantitative analyses of infestations were performed on 141 samples of flowers, fruits and flower buds collected in the field. A single species of sap beetle, Nitops aff. pilosocerei, was observed in 33% of the flowers (fruits and flower buds did not present infestation). The number of beetles per flower varied from 1 to 126 (average: 12.9 beetles/flower). The male to female ratio was approximately 1:1. Several beetles were found with pollen attached to their exoskeleton. The number of beetles per flower reported is up to 3–4 times greater than other records in the literature. The ecological interaction between beetle and plant is discussed.