Pollen from urban flora in the ephemeral nests of solitary Megachile bees in three temperate and subtropical cities of Argentina

Abstract

Cities are anthropogenic habitats that are home to many taxonomically diverse groups of bees and contribute to their conservation due to the abundance of flowers and nesting substrates. However, the pollen diet composition of nest provisions for most urban bees in South America is poorly studied and therefore the characteristics of the urban flora needed for their survival remains unknown. Pollen analysis was employed to study the diet composition of the wild solitary bees Megachile infima Vachal, M. pusilla P´erez and Megachile spp. that all nest in urban environments in two eco-regions in Argentina. Nests were found in preexisting small holes within humanmade structures (walls, hosepipes, water taps), natural substrates (hollow stems) or in semi-exposed spaces within four courtyards of three cities. Pollen from brood provisions from these nests were compared with pollen grains from the available flowering plants surrounding the nests. In the temperate city La Plata from the Pampean eco-region, 23 pollen types from 14 families and five unidentified types were present. The most abundant were Styphnolobium japonicum (Fabaceae, Papilionoideae) and Picris echioides (Asteraceae). In the two subtropical cities from the Chaco eco-region, 15 types from eight families and four unidentified types were present, with Phoenix (Arecaceae) and Punica granatum (Lythraceae) being the most abundant. Although bees were polylectic, the presence of pollen in nests was not evenly distributed, which may be related to resource abundance, pollen attributes, and floral morphology. This study provides evidence of forage versatility of Megachile bees on pollen plants from diverse taxonomic origin and status of naturalization, flowering stratum and city microhabitat.