In recent years, honeybees (Apis mellifera) have been strangely disappearing from their hives, and strong colonies have suddenly become weak and died. The precise aetiology underlying the disappearance of the bees remains a mystery. However, during the same period, Nosema ceranae, a microsporidium of the Asian bee Apis cerana, seems to have colonized A. mellifera, and it's now frequently detected all over the world in both healthy and weak honeybee colonies. For first time, we show that natural N. ceranae infection can cause the sudden collapse of bee colonies, establishing a direct correlation between N. ceranae infection and the death of honeybee colonies under field conditions. Signs of colony weakness were not evident until the queen could no longer replace the loss of the infected bees. The long asymptomatic incubation period can explain the absence of evident symptoms prior to colony collapse. Furthermore, our results demonstrate that healthy colonies near to an infected one can also become infected, and that N. ceranae infection can be controlled with a specific antibiotic, fumagillin. Moreover, the administration of 120 mg of fumagillin has proven to eliminate the infection, but it cannot avoid reinfection after 6 months. We provide Koch's postulates between N. ceranae infection and a syndrome with a long incubation period involving continuous death of adult bees, non-stop brood rearing by the bees and colony loss in winter or early spring despite the presence of sufficient remaining pollen and honey.

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Honeybee colony collapse is a sanitary and ecological worldwide problem. The features of this syndrome are an unexplained disappearance of adult bees, a lack of brood attention, reduced colony strength, and heavy winter mortality without any previous evident pathological disturbances. To date there has not been a consensus about its origins. This report describes the clinical features of two professional bee-keepers affecting by this syndrome. Anamnesis, clinical examination and analyses support that the depopulation in both cases was due to the infection by Nosema ceranae (Microsporidia), an emerging pathogen of Apis mellifera. No other significant pathogens or pesticides (neonicotinoids) were detected and the bees had not been foraging in corn or sunflower crops. The treatment with fumagillin avoided the loss of surviving weak colonies. This is the first case report of honeybee colony collapse due to N. ceranae in professional apiaries in field conditions reported worldwide.

The biological cycle of Nosema spp. in honeybees depends on temperature. When expressed as total spore counts per day after infection, the biotic potentials of Nosema apis and N. ceranae at 33°C were similar, but a higher proportion of immature stages of N. ceranae than of N. apis were seen. At 25 and 37°C, the biotic potential of N. ceranae was higher than that of N. apis. The better adaptation of N. ceranae to complete its endogenous cycle at different temperatures clearly supports the observation of the different epidemiological patterns.Biotic potential represents the maximum reproductive capacity of a population under optimum environmental conditions. Thus, a species fulfilling its biotic potential would exhibit maximal exponential population growth, thereby augmenting the possibilities of transmission of the species. A wide range of factors affects the biotic potential of each species, and among the external factors, temperature clearly influences the life cycles of most parasitic species (4).Nosemosis is a common worldwide disease of adult honeybees (Apis mellifera) that is caused by microsporidia (19). Nosema apis was the only agent known to produce this disease in A. mellifera until N. ceranae was identified in this host in 2005, in Europe (11) and Taiwan (12). Both these microsporidia infect and multiply in the ventricular cells of A. mellifera, and they can be found under different environmental conditions in both the northern and southern hemispheres (17, 13). Significantly, N. ceranae seems to be more pathogenic than N. apis in caged worker bees (10, 18), and it has recently been related to significant losses of bees and colony collapses under field conditions (17,8).Due to the lack of comparative studies of the factors affecting parasite virulence, trials were designed to determine the influence of temperature on the biotic potentials of both microsporidia. Only the deleterious effect of high exogenous temperature on spores of N. apis has been checked previously (16).In this work, purified N. apis and N. ceranae spores with a minimum viability of 99% (tested with 4% trypan blue) were obtained from experimentally infected honeybees always maintained at 33°C as described previously (9). The spores were counted using a hemocytometer chamber (19), while the Nosema species identification was confirmed by PCR (17).The experimental infection of bees was carried out as described previously (10). Briefly, young Nosema-free honeybees were starved for 2 h and fed 2 l of 50% sucrose solution containing 100,000 viable N. ceranae or N. apis spores. Honeybees were anesthetized with CO 2 , and later, a droplet of the spore solution was administered to each honeybee by touching a micropipette to its mouthparts until the entire droplet was consumed. The bees that did not consume the entire droplet were discarded. Uninfected control bees were fed 2 l of 50% sucrose solution alone.Three trials were carried out for 1 week each at three different temperatures (25, 33, and 37°C). Each trial included four replicate cages ...

Nosema ceranae is a hot topic in honey bee health as reflected by numerous papers published every year. This review presents an update of the knowledge generated in the last 12 years in the field of N. ceranae research, addressing the routes of transmission, population structure and genetic diversity. This includes description of how the infection modifies the honey bee's metabolism, the immune response and other vital functions. The effects on individual honey bees will have a direct impact on the colony by leading to losses in the adult's population. The absence of clear clinical signs could keep the infection unnoticed by the beekeeper for long periods. The influence of the environmental conditions, beekeeping practices, bee genetics and the interaction with pesticides and other pathogens will have a direct influence on the prognosis of the disease. This review is approached from the point of view of the Mediterranean countries where the professional beekeeping has a high representation and where this pathogen is reported as an important threat.