Asymptomatic presence of Nosema spp. in Spanish commercial apiaries.

Nosemosis is caused by intracellular parasites (Nosema apis and Nosema ceranae) that infect the midgut epithelial cells in adult honey bees. Recent studies relate N. ceranae to Colony Collapse Disorder and there is some suggestion that Nosema spp., especially N. ceranae, induces high mortality in honey bees, a fact that is considered as a serious threat for colony survival. 604 samples of adult honey bees for Nosema spp. analysis were collected from beekeeping colonies across Spain and were analysed using PCR with capillary electrophoresis. We also monitored 77 Andalusian apiaries for 2 years; the sampled hives were standard healthy colonies, without any special disease symptoms. We found 100% presence of Nosema spp. in some locations, indicating that this parasite was widespread throughout the country. The two year monitoring indicated that 87% of the hives with Nosema spp. remained viable, with normal honey production and biological development during this period of time. The results of these trials indicated that both N. ceranae and N. apis could be present in these beehives without causing disease symptom and that there is no evidence for the replacement of N. apis by N. ceranae, supporting the hypothesis that nosemosis is not the main reason of the collapse and death of beehives.