Diversity of pollen dispersed by solitary bees to artificial nests in olive groves

We sampled the diversity of pollen dispersed by solitary bees by using bee trap nests in 12 paired olive farms located in 6 localities from Andalusia in 2020. On the one hand, each paired olive farm is constituted by an olive farm with low-intensive herb cover management and an olive farm with intensive herb cover management. The low-intensive management consists of the maintenance of herb cover during most of the year being only removed in late spring by mechanic mowing or cattle. Conversely, intensive management consists of removing the herb cover permanently by using pre-emergence and/ or post-emergence herbicides sometimes in combination with ploughing the ground several times a year. On the other hand, each paired farm in each locality is surrounded by the same landscape complexity. We classified each paired farm in three categories of landscape complexity (simple, intermediate, and complex) according to the proportion of semi-natural area estimated within a 2 km radius buffer around the centroid of each pair of farms. We use 144 bee trap nests in total, using two different materials and four cavity diameters (40× ca. 9 mm bamboo, 20× ca. 12 mm reed internodes, 20× ca. 15 mm reed internodes and 4× ca. 20 mm reed internodes), providing a total of 84 nesting cavities per nest. On each farm, six nests were set in March, matching the period of activity in the phenology of these solitary bees and the flowering plants they pollinate. Bee trap nests were set in different microhabitats (i.e. olive orchard matrix and non-productive areas). Trap nest colonization was monitored monthly, from April to September. For every cavity colonized, samples of three different pollen packs were extracted and dyed using fuchsine. Samples were identified under microscope to species or pollen‐type level.