Continuing declines in Centris pallida (Hymenoptera: Apidae) male head width in 2025

The head widths of Centris pallida male bees, which have a body size linked alternative reproductive tactics system, have been collected at the Blue Point Bridge field site since 1974, allowing for population-specific analysis of body size changes over time. Prior analyses from 1974-2022 have demonstrated consistent body size declines over the last fifty years, and a reduction in the proportion of the population that has the unique ‘large male’ morphology. In 2025, I collected data on the head widths of foraging, patrolling, hovering, and digging males from May 4 – 11 at Blue Point Bridge. These data corroborate findings in 2022 that show patrolling and foraging male head widths are declining, and that large-morph males are becoming a smaller proportion of the population over time. In addition, several males from this year’s foraging population were the smallest ever recorded at this site. Overall, the data suggest continuing declines in male body size in this population and a reduction in ‘large-morph’ males; though the unusually low level of floral resources, and concomitant low numbers of nesting females, patrolling males, and mating pairs, at the field site this year should be considered when interpreting the 2025 dataset.