Propolis can reduce Nosema ceranae infection and enhance the immune response in honey bees, without disrupting the gut microbiota

Honey bees (Apis mellifera) play a crucial role in the environment, being essential pollinators and contributing to agricultural production and natural ecosystem diversity. However, honey bee health is threatened by multiple stressors, including infection by mites, viruses and microsporidia. To defend against invaders, these insects have evolved social and individual mechanisms, including the collection and use of propolis. In this study, we found that under laboratory conditions, the consumption of Ethanolic Extract of Propolis (EEP) reduced the infection level of the pathogen Nosema ceranae and increased the expression levels of immune-related genes (hymenoptaecin or glucose oxidase) in challenged bees, enhancing their immunocompetence. Moreover, it did not affect the diversity and composition of the gut microbiota. Despite these promising laboratory results, the administration of EEP to honey bee colonies under field conditions did not produce a beneficial effect on colony strength or pathogen infection levels. Future studies should be conducted to optimize the method and frequency of applications to maximize potential benefits for honey bee colony health.