Plant taxa visited by the European orchard bee Osmia cornuta (Latreille, 1805) analyzed by metabarcoding through nesting residuals (Hymenoptera, Anthophila, Megachilidae)

Wild pollinator populations are in global decline. Two main factors influence the presence of wild pollinators in a given environment: the availability of nesting resources and the availability of floral resources. However, information on the dietary niches of these insects is lacking, and the protocols set up in this context are often costly and lethal. By studying the species Osmia cornuta (Latreille, 1805), we aimed to find out whether other methods of sampling the flowers visited by this model species were possible —as they were already tested on other Megachilidae species in previous literature. Using metabarcoding, we sought to better define the floral diversity of our model’s diet and how to optimize this definition by combining DNA markers. To do this, we used the inter-cocoon residues of O. cornuta from three nesting tubes of private insect hotels located in the same geographical area. Despite the small number of samples, the results of the present study are consistent with previous articles on this species, which used microscopy or metabarcoding with a single marker: the O. cornuta diet was here composed of 37 taxa including 12 different families. Although further, larger-scale analyses are needed to support these initial descriptive results, it seems that the topology of the floral communities visited by the mason bee O. cornuta can be easily determined by metabarcoding analyses of the residues found in the nesting cavities.