Pollen Resources Stored in Nests of Wild Bees Xylocopa ciliata Burmeister and Megachile pusilla Pérez (Hymenoptera: Anthophila) in a Temperate Grassland-Forest Matrix

Pollen analysis was employed to study the diet composition of two wild bees in a patch of temperate grassland invaded by exotic plants. Thirty pollen types from 14 families and two unidentified types were present in the seven samples analyzed. The three samples from Megachile pusilla Pérez were composed of 100% Lotus glaber and the four samples from Xylocopa ciliata Burmeister of abundant pollen (˃5%) of Lotus glaber, Galega offi cinalis, Adesmia bicolor and type Senna-Chamaecrista (all Fabaceae). The latter resource likely foraged out of the park, which could be an evidence to support its pollen preference for Fabaceae. However, a larger number of samples is necessary to identify the specialization status of X. ciliata. The preference for Lotus in this site was due to temporal specialization as M. pusilla was identified as polylectic in its origin area, and this could help to explain its eff ective naturalization in the New World and other areas of the Old World.