Pollinators of Richardia grandiflora (Rubiaceae): an Important Ruderal Species for Bees

Ruderal species may provide pollen and nectar to maintain the pollinators of crops in periods of floral resource shortage. The knowledge about the floral biology of these plant species and their interaction with insects is important for management strategies of agricultural systems. The study was carried out at an experimental research station in two different periods (August 2010-April 2011 and August 2012-January 2013). Floral biology was studied, and the reproductive system and reproductive efficacy (RE) were analyzed using controlled pollination experiments. Furthermore, floral visitors and pollination were identified and quantified. Reproductive success obtained in the open pollination and cross-pollination experiments was higher than those obtained in spontaneous self, hand self, and wind pollination. Richardia grandiflora bloomed throughout the experimental period, and flowers were visited by Coleoptera, Diptera, Hymenoptera, and Lepidoptera, which were observed foraging for pollen and/or nectar. Among the floral visitors, bees were the richest and most frequent group and often contacted anthers and stigmas during visits. Africanized honeybees touched the floral reproductive structures in all visits, and their frequency may be related to changes in the reproductive efficacy between the study periods. Pollinator species of crops cultivated at the experimental research station were frequent bee visitors of R. grandiflora. We demonstrated that R. grandiflora requires cross-pollination and biotic pollen vectors. Among floral visitors, bees are the main pollinators, especially the Africanized honeybees. R. grandiflora can be considered an important ruderal species for maintaining bee pollinator populations at the study site, providing resources during the period that crops are not blooming.