Co-occurrence of Lotmaria passim and Nosema ceranae in honey bees (Apis mellifera L.) from six states in the United States

Honey bee populations in the United States have been under stress for the past decade. Although no one cause has been able to explain this, recent studies have shown that multiple interactions among microorganisms may be behind honey bee decline. Several internal parasites may contribute to this, including the trypanosome Lotmaria passim and the microsporidian, Nosema ceranae. This study combined novel data with data from several previous molecular diagnostic surveys for L. passim and N. ceranae to determine co-infection rates of these honey bee parasites. A total of 782 honey bee samples from Arkansas, Oklahoma, Texas, Utah, Mississippi, and Hawaii were analyzed for co-occurrence of N. ceranae and L. passim. Of the 782 samples, 37 (4.7%) were co-infected with both N. ceranae and L. passim, while 110 (14.1%) were infected with N. ceranae alone, and 51 (6.5%) with L. passim alone. Co-infections occurred most frequently in honey bees from Hawaii (11.8%), followed by Utah (2.4%) and Arkansas (1.2%), and no co-infections were observed in samples from Mississippi, Oklahoma, or Texas. Statistical analysis revealed that N. ceranae and L. passim co-occur more frequently than expected in samples from Hawaii and Utah. Infection rates for N. ceranae, L. passim, and co-infections were similar between managed (n = 393) and swarms (n = 73) but were both greater than feral (n = 316) honey bee colonies.