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The Rio Grande in Texas is the geopolitical boundary between the United States and Mexico. Considered one of the world’s most at-risk rivers, it has been impacted by intensified management by both countries sharing its watershed. Invasion by Arundo donax (Linnaeus) (Poales: Poaceae), giant reed, has been extensive in the riparian corridor, with potential impacts on native wildlife. A need exists to better understand the ecological communities in these habitats to support strategies for enhancing resources for pollinators. We sampled bee and flowering plant communities monthly over 2 yr along a 3.22 km stretch of the lower Rio Grande in Webb County, TX. Bee and plant richness and abundance were bimodal with peaks in March–April and September in both riparian and upland habitats. The bee community was similar across habitats and sampling dates and dominated by a few common species. Anthophora occidentalis (Cresson) (Hymenoptera: Apidae) and Lasioglossum sp. L (Curtis) (Hymenoptera: Apidae) were indicator species of the riparian habitat, and Halictus ligatus (Say) (Hymenoptera: Halictidae) was an indicator species of the upland habitat. Three plant species were indicator species in riparian habitats, spiny pricklepoppy (Argemone sanguinea Greene) (Papaverales: Papaveraceae), spotted beebalm (Monarda punctata Linnaeus) (Lamiales: Lamiaceae), and Pennsylvania cudweed (Gamochaeta pensylvanica Willdenow) (Asterales: Asteraceae). Analysis showed a positive relationship between bee richness and abundance with flowering plant diversity, increasing bee richness within an optimal temperature range 25−30°C, and higher bee abundance with increased average monthly precipitation. This geographically extensive riparian corridor could be managed using ecological restoration to enhance resources for pollinators.

5The Lower Rio Grande River (LRGR) in Texas is the physical boundary between the United 6 States and Mexico and is considered one of the world's most at-risk rivers due to intensified 7 management of the riparian corridor and human use. Exotic plant invasions have significantly 8 altered the native floral communities because of invasive giant reed, with potential impacts to the 9 native wildlife using resources in the riparian corridor. This study was conducted along a 3.22 10 km stretch of the LRGR in southwestern Webb County, TX to assess bee (Anthophila) 11 communities and their flowering-plant resources among proximal and distal terrestrial upland 12 and river-adjacent sub-corridors. Patterns related to the bee community across the two habitats 13 consisted of low variation and dominance by common taxa, suggesting the riparian corridor 14 could be used as a resource for bee foraging and soil-nesting. Although a lack of community 15 structure similarities among habitats were found, indicator species analysis produced two bee 16 genera that were more common and abundant in the upland habitat. Total number of individual 17 bees and genera collected across 26 dates and 2 years show a bimodal trend, with peaks in 18