A Picky Generalist: Nesting Females of Pseudaugochlora graminea (Halictidae) are Highly Specialized in an Urban Area

Abstract

Urban areas act as important shelters to support bee populations, but some guilds, such as generalist species, benefit more than others. We aimed to investigate if the floral preferences of a polylectic species would change throughout the years and if gardening practices such as mowing could affect the females’ floral preferences and, thus, the bee-plant interaction networks in an urban area within a medium- sized city in Brazil. Nesting females of Pseudaugochlora graminea (Fabricius) (Halictidae) were collected and had the pollen grains attached to their scopae removed, acetolyzed, and identified in two different periods: March 2019 and March 2022. Only five plant species were identified in samples from 2019, while 13 species were detected in 2022 despite mowing and plant replacements throughout three years. Among the floral sources observed, both exotic and native species were visited by females for pollen and nectar collection. Despite being a generalist species, all interaction networks between P. graminea females and plant species were highly specialized. Females concentrated their pollen gathering on a few plant species, represented by less than ten individuals in the study area. Mowing led to the destruction of the third most important pollen source in 2019. However, plant replacements may have favored females by some nectar sources seedlings. Our findings demonstrate that gardening practices impacted the floral choices of females of a generalist bee species, whose females established highly specialized interaction networks with plants in an urban area.