A study of bumble bee (Bombus) populations in North America reveals widespread declines in several species, with some experiencing up to a 96% reduction in abundance and a 23–87% contraction in geographic range over the past 20–30 years. The research, based on a 3-year interdisciplinary study, compared current and historical data from over 73,000 museum records with data from 16,000 specimens collected in nationwide surveys. Declining populations showed higher infection levels of the microsporidian pathogen Nosema bombi and lower genetic diversity compared to stable species. These findings suggest that high pathogen prevalence and reduced genetic diversity are significant predictors of bumble bee decline, although the exact causes remain uncertain. Bumble bees are vital pollinators in temperate ecosystems and have economic importance in crop pollination. Declines in their populations have been reported in Europe and are now spilling into North America, raising environmental and economic concerns. However, large-scale range reductions in North America are not well documented, with many reports being unpublished or limited to local surveys. The study identified four species—B. occidentalis, B. pensylvanicus, B. affinis, and B. terricola—as having experienced significant population declines, while four other species showed stable populations. Declining species had higher infection rates of N. bombi and lower genetic diversity. Genetic analyses revealed that declining populations had reduced gene diversity and were less likely to originate from multiple colonies compared to stable species. The study also found that N. bombi, a microsporidian parasite, is more prevalent in declining species, suggesting it may be a contributing factor to their decline. However, the exact role of N. bombi in bumble bee population declines requires further research. Additionally, genetic factors such as small effective population sizes and reduced gene flow may contribute to the decline, although the study found that genetic differentiation was low among species. The study highlights the need for further research to understand the complex interactions between habitat fragmentation, loss of floral and nesting resources, disease, and climate that may contribute to bumble bee decline. It also emphasizes the importance of conservation strategies to mitigate further losses of pollinator diversity. The findings underscore the urgent need for coordinated efforts to address the status of native pollinators in North America.A study of bumble bee (Bombus) populations in North America reveals widespread declines in several species, with some experiencing up to a 96% reduction in abundance and a 23–87% contraction in geographic range over the past 20–30 years. The research, based on a 3-year interdisciplinary study, compared current and historical data from over 73,000 museum records with data from 16,000 specimens collected in nationwide surveys. Declining populations showed higher infection levels of the microsporidian pathogen Nosema bombi and lower genetic diversity compared to stable species. These findings suggest that high pathogen prevalence and reduced genetic diversity are significant predictors of bumble bee decline, although the exact causes remain uncertain. Bumble bees are vital pollinators in temperate ecosystems and have economic importance in crop pollination. Declines in their populations have been reported in Europe and are now spilling into North America, raising environmental and economic concerns. However, large-scale range reductions in North America are not well documented, with many reports being unpublished or limited to local surveys. The study identified four species—B. occidentalis, B. pensylvanicus, B. affinis, and B. terricola—as having experienced significant population declines, while four other species showed stable populations. Declining species had higher infection rates of N. bombi and lower genetic diversity. Genetic analyses revealed that declining populations had reduced gene diversity and were less likely to originate from multiple colonies compared to stable species. The study also found that N. bombi, a microsporidian parasite, is more prevalent in declining species, suggesting it may be a contributing factor to their decline. However, the exact role of N. bombi in bumble bee population declines requires further research. Additionally, genetic factors such as small effective population sizes and reduced gene flow may contribute to the decline, although the study found that genetic differentiation was low among species. The study highlights the need for further research to understand the complex interactions between habitat fragmentation, loss of floral and nesting resources, disease, and climate that may contribute to bumble bee decline. It also emphasizes the importance of conservation strategies to mitigate further losses of pollinator diversity. The findings underscore the urgent need for coordinated efforts to address the status of native pollinators in North America.