Revealing the Baja California Peninsula's Hidden Treasures: An Annotated checklist of the native bees (Hymenoptera: Apoidea: Anthophila).

To date, the knowledge of bee diversity in the Baja California Peninsula has primarily relied on large, sporadic expeditions from the first half of the 20th century. To address the knowledge gaps, we conducted extensive fieldwork from 2019 to 2023, visited entomological collections in Mexico and USA, and accessed digital databases and community science platforms to compile records. As a result of our field surveys, we identified 521 morphospecies, with 350 recognized as valid species, including 96 new records for the Baja California Peninsula and 68 new findings for Mexico, including the rediscovery of Megachile seducta Mitchell, 1934, ranked as possibly extinct. Additionally, museum visits added 24 new species records for the peninsula, including 12 new to Mexico. Integrating the new and existing records results in a comprehensive checklist that documents 728 species for the peninsula, 613 for Baja California, and 300 for Baja California Sur. Notably, 62 species are endemic to the peninsula, of which 22 are only found in Baja California, and 23 in Baja California Sur. Our findings show a greater bee diversity in northern latitudes, with a sharp decrease to the central and southern peninsula, which corresponds to the geographic distribution of the records. This supports the premise that the Baja California peninsula remains an unexplored area and highlights the importance of conducting studies like the one presented here.