Impacts of antibiotic use, air pollution and climate on managed honeybees in Canada

Antimicrobial resistance is a critical global health threat, significantly exacerbated by the overuse of antibiotics in agriculture. Here we investigate how recent antibiotic regulatory changes have impacted the usage of several level 2 (that is, World Health Organization ‘Watch’ list) antibiotics within the Canadian beekeeping sector. Utilizing national survey data, we examined trends in antibiotic usage and overwintering mortality rates from 2015 to 2023. Our findings reveal a significant reduction in the use of oxytetracycline, tylosin, lincomycin and fumagillin, decreasing from approximately 50% to 25% following regulatory restrictions implemented in 2018. Notably, this decrease was inversely associated with rising overwintering mortality rates, suggesting that withdrawal of antibiotics in the absence of effective alternatives may negatively impact colony health. Furthermore, multivariate analysis accounting for environmental confounders (based on 119,244 data points collected from 234 unique locations across Canada) identified nitrogen dioxide (NO2), a common air pollutant from diesel exhaust, as a strong predictor of mortality. This finding warrants urgent attention given that NO2 can degrade floral odours, rendering them undetectable to honeybees during foraging flights. These results highlight a complex interplay between antibiotic regulation, environmental stressors and honeybee health, emphasizing the need for comprehensive management strategies that mitigate antimicrobial resistance while safeguarding pollinator health.