Many small rather than few large sources identified in long-term bee pollen diets in agroecosystems

Bees provide essential ecosystem services such as crop pollination, but perennial colonies of social species require year-round access to floral resources, especially in resource-poor agricultural landscapes. We investigated pollen resources used by a social bee (Tetragonula carbonaria, Meliponini) in forests and orchards of subtropical Australia. Pollen DNA metabarcoding with the markers rbcL and ITS2 was used to identify hive pollens from 57 colonies collected at seven sites each season over two years. We identified 341 botanical sources of hive pollens from 37 orders, 72 families, 218 genera and 302 species. Interestingly, introduced species (e.g. Ageratum spp. and Raphanus spp.) and wind-pollinated plants (Poaceae, Cyperaceae) were common pollen sources in both orchards and forests. Orchard colonies used a subset of pollen species used by colonies in forests, with many Myrtaceae (Corymbia, Eucalyptus and Melaleuca spp.), Poaceae, Asteraceae, Fabaceae and Proteaceae species found in both land uses. We found T. carbonaria foraged on “many small” rather than a “few large” pollen sources each season, regardless of land use. This suggests stingless bees aim for diversity in pollen diets. As such, land managers and beekeepers should ensure colonies have access to a variety of floral resources year-round. This may be achieved through targeted planting of key families identified in this study (e.g. Proteaceae, Asteraceae, Myrtaceae, Poaceae, Brassicaceae, Araliaceae, Cannabaceae, Arecaceae, Rubiaceae and Sapindaceae) and / or maintaining weeds while they are flowering in the orchard. Land managers may consider planting in unproductive areas such as riparian zones, edges or between crop rows if space is limited.