Comparison of different matrices for the detection of honey bee pathogens: results from a Norwegian study

Honey bee colonies can be infested by a range of pathogens, resulting in considerable morbidity and mortality. Detection and identification of pathogens in bee colonies is thus essential in apiculture, and various matrices are used for screening for pathogens within a colony, including hive debris, bees, and the combs. Previous investigations have explored using honey as a non-invasive sample material for detection of pathogen DNA, but have rarely compared the results with those from molecular analysis from other matrices. In this study, samples of bees, honey, and hive debris from beekeepers in Norway were investigated for several pathogens: Acarapis woodi, Crithidia mellificae, Lotmaria passim, Ascosphaera apis, Nosema apis and Nosema ceranae. For all sample types and all pathogens, pathogen-specific qPCR was used for detection, with microscopy methods also used for A. woodi and Nosema spp. Honey was the most difficult matrix to work with in the laboratory, and detection seemed to be lower than in hive debris or bees, depending on pathogen. While hive debris seems to be the optimal matrix for investigating honey bee colonies for Nosema spp. and A. apis, for L. passim bee samples provided the most positive results, and with lower Cq values. qPCR was significantly more sensitive for detecting Nosema than microscopy, and also provides the species information. None of our samples were positive for A. woodi or C. mellificae, but A. apis and Nosema spp. occur widely among apiaries in southern Norway, with N. apis being the predominant Nosema species.