Honey bees (Apis mellifera L.) inhabiting trees in forests are not managed by humans or treated for pathogens; therefore, many researchers and beekeepers believe that viral, bacterial, and parasitic diseases may lead to their decline. The aim of the study was to evaluate the prevalence of L. passim and Nosema spp. in feral colonies by real-time PCR. This study was performed on twenty-six samples of honey bees inhabiting tree trunks in north-eastern Poland. One sample consisted of sixty worker bee abdomens collected from hollow trees. Honey bees were sampled only from naturally colonized sites. Amplicons of the three evaluated pathogens were detected in twenty of the twenty-six tested samples. A significant correlation was observed between infection with three pathogens (N. apis, N. ceranae, L. passim) (r = 0.84) compared to infection with only two pathogens (N. apis and N. ceranae) (r = 0.49). N. ceranae was the predominant pathogen, but infections with various severity caused by L. passim were also noted in fourteen of the twenty-six tested samples. In view of the general scarcity of epidemiological data concerning coinfections with Nosema spp. and L. passim in honey bees in tree trunks in other countries, further research is needed to confirm the effect of concurrent pathogenic infections on the decline of bee colonies.
