Pathogen spillover from Apis mellifera to a stingless bee.

Pathogen spillover from managed bees is increasingly considered as a possible cause of pollinator decline. Though spillover has been frequently documented, evidence of the pathogen's virulence in the new host or mechanism of transmission is rare. Stingless bees (Apocrita: Meliponini) are crucial pollinators pan-tropically and overlap with managed honeybees (Apis mellifera) in much of their range. Nosema ceranae is the most prevalent disease of adult A. mellifera. We used laboratory experiments and field surveys to investigate the susceptibility of stingless bees (Tetragonula hockingsi) to N. ceranae, infection prevalence and transmissibility via flowers. We found that 67% of T. hockingsi fed sucrose with N. ceranae had detectable spores in their ventriculus, and they died at 2.96 times the rate of sucrose-only fed bees. Five of six field hives harboured bees with N. ceranae present at least once during our five-month survey, with prevalence up to 20%. In our floral transmission experiment, 67% of inflorescences exposed to infected A. mellifera yielded N. ceranae spores, and all resulted in T. hockingsi with N. ceranae spores in their guts. We conclude that N. ceranae is virulent in T. hockingsi under laboratory conditions, is common in the local T. hockingsi population and is transmissible via flowers.