Pollen diet assessment and flower association in Melipona orbignyi and recommendations on management and conservation of stingless bees in the Chaco dry forest of South America

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Management and conservation of wild pollinators in forests of the Chaco region of South America is of great interest nowadays as they are pollen vectors that improve the reproductive success of many forest species which are at risk due mainly to forest patch isolation and degradation by human activities. The assessment of the diet of the stingless bee Melipona orbignyi was carried out by comparing different calculations from palynological data being the index of relative importance (IRI) the most complete, objective, and here recommended. This index showed that the order of the four most important pollen resources was Prosopis (IRI = 3354), Albizia inundata (1999), Cynophalla retusa (921), and Solanum type 2 (693), and the value of importance of species (SI) calculated for honey resources showed that they were type Maytenus (SI = 20.79), Prosopis (18.73), Cynophalla retusa (6.72), and Ziziphus mistol (3.32). Three flower types predominated in pollen and nectar provisions: brush flowers, solanoid flowers with poricidal anthers, and generalized small pale flowers, being the former two associated to buzzing. The abundance of the nectarless Solanum in honey samples is discussed. Good forest management practices for pollinator conservation native to the Chaco forest should include the keeping of undisturbed forest patches for nesting and foraging while the surrounding forest resources are managed in a sustainable way. Furthermore, because some threatened plants important for the M. orbignyi diet require gene flow to maintain healthy populations, short distances among the forest patches are needed, a fact that also helps to avoid genetic drift in Melipona colonies. The rational rearing of Melipona orbignyi would be a good practice to be implemented to promote pollination of threatened tree and shrub individuals isolated by forest fragmentation.