Estudio de los factores de riesgo asociados a la presencia de la Nosemosis y su impacto en la producción de miel en ambientes sub-tropicales y templados

Abstract

Los microsporidios Nosema apis y N. ceranae son parasitos intestinales muy comunes de A. mellifera alrededor del mundo. Sin embargo, los costos que pueden ocasionar estos microsporidios en las colmenas son muy dispares, en algunos casos se han reportado costos muy altos con infecciones altas y en otros casos las infecciones altas no provocaban altos costos para los apicultores. Por dicho motivo, es difícil saber cuándo y porque las colmenas están experimentando estrés, por tal motivo, es determinante conocer los estresores que operan sobre las colmenas y determinar en qué momentos del año pueden provocar mayores daños sobre las colmenas.El objetivo de este estudio fue identificar los factores de riesgo asociados con la presencia de la Nosemosis y su impacto en la producción de miel. Se evaluó la carga de esporos de Nosema spp. mensualmente en un total de 19 apiarios para determinar el comportamiento estacional de dicho parásito en tres provincias Santa Fe, Chaco y Formosa. En las mismas provincias se analizaron muestras para determinar la especie, ya sea Nosema apis o N. ceranae en 59 apiarios y se realizaron tres muestreos en 65 apiarios durante el transcurso de un año junto con encuestas estructuradas a los apicultores para asociar variables de manejo con el riesgo de alcanzar altas cargas de parasitación. En relación a los resultados del comportamiento estacional, se pudo determinar un patrón similar de comportamiento entre las distintas eco-regiones analizadas, presentando un pico pequeño en mayo, seguido por un pico mayor en julio, las diferencias en las eco-regiones se dieron a causa de las diferentes intensidades, siendo las regiones de Santa Fe Centro y Chaco Semi-árido las que presentaron las mayores intensidad a lo largo del año. Los resultados moleculares indicaron que en las regiones bajo estudio se encuentran presentes ambas especies. Exclusiva infección por N. ceranae en 37.8% de todos los apiarios, mientras que en 26.7% de los apiarios solo estaban infectados por N. apis. El resto, 35.6% de los apiarios, se encontraron coinfectados por ambos Nosema spp. Entre los factores identificados se destacan las diferentes regiones analizadas y la presencia de Varroa destructor en altos y bajos niveles de infestación. Estos resultados brindan respuesta a los apicultores, por un lado, existe un patrón estacional de la parasitosis, los apicultores deberían estar atentos a los momentos en los que se encuentran los picos de cargas altas de Nosema spp. y por otro lado deberían tomar medidas de control de otros patógenos como es el caso del ácaro V. destructor para disminuir el estrés dentro de las colmenas.

Argentina is the second world exporter of honey (13% of the total) and the third producer (contributing with 6%). Our country markets abroad 95% of the honey produced mainly to the UE, the United States and Japan. However, local production has been reduced considerably in recent years, from an average of 84,000 tons to less than 60,000 tons per year in the last two years. The increase in productive activity is threatened by health problems and the advance of the agricultural frontier that reduces plant biodiversity. Among the health problems still unresolved highlight Nosemosis, a disease caused by two species of microsporidiums (Phylum Microspora), Nosema apis and N. ceranae. These agents are commonly found in bees (Apis mellifera) around the world. They are obligate parasites that develop in the intestines of adult bees and generate a considerable reduction in the life of their hosts. The transmission of Nosema in bees is done through the fecal-oral route by means of which the pathogens are spread with the feces of infected individuals to healthy bees by ingestion. Worldwide, a great controversy has been generated about the role that this agent would have in the loss of hives. The objective of this thesis was to determine, through an epidemiological approach, the factors that favor the occurrence of Nosemosis, evaluate the pattern of seasonal behavior of the disease and characterize genetically the populations of Nosema spp. in different ecosystems of Argentina, seeking to determine the real impact on honey production. In the first instance, the number of spores and prevalence of Nosema spp. monthly were estimated over a year in a total of 19 apiaries located in five regions (Santa Fe Sur, Santa Fe Centro, Chaco Húmedo, Chaco de Transición and Chaco Semi-arid) of Santa Fe, Chaco and Formosa provinces to determine the seasonal behavior of the parasite. The results obtained from the sporulation curves in the colony analyzed indicate a characteristic pattern, similar to that reported for the Nosema apis in other regions of the world. This pattern only varies depending on the intensities in each region analyzed, with Santa Fe Sur and Centro and Chaco Semi-arid the regions with the highest sporular levels. In the same regions, samples of bees were collected and analyzed to determine the species of Nosema spp. present in 59 apiaries during the post-harvest period. The molecular results indicated that both species are present in the regions under study Exclusive infection by N. ceranae was recorded in 37.8% of all apiaries, while in 26.7% of the apiaries were only infected by N. apis. The rest, 35.6% of the apiaries, were coinfected by both species of Nosema spp. These results were contradictory with others reported by researchers from other regions of Argentina where it was only possible to obtain positive samples exclusively from N. ceranae. The results also indicated the presence of hives infected purely with N. ceranae in all the regions studied, the presence of hives with exclusive infection with N. apis in regions of subtropical climates and a significantly higher proportion of co-infection in temperate climate regions. These results could account for the possible replacement of N. apis by N. ceranae already reported in other regions. The existence of association between the presence of different species of Nosema spp. and bee haplotypes that were parasitized. The results did not demonstrate the existence of an association between the host haplotype and the parasite species. Finally, to identify risk factors associated with the occurrence of high loads of Nosema spp., three samplings were carried out during one year in 65 apiaries in the previously mentioned regions. Structured surveys were applied to beekeepers with the aim to associate management variables with the risk of high parasitic loads in honey bees. Among the factors identified, the different regions analyzed and the presence of Varroa destructor in high and low levels of infestation, were the most relevant. In the first sampling, post-harvest period, an marked ascending gradient was observed from North to South. Additionally, a positive association was determined between spore counts of Nosema spp. and the levels of infestation with Varroa. Those hives that presented more than 3% of Varroa in the post-harvest period had higher sporular levels of Nosema spp. In the second and third sampling, the autumn and spring period, the highest levels of Nosema spp. were find in South and Center of Santa Fe and in Chaco Semi-arid regions. Regarding the loads of Nosema spp. and the Varroa infestation, the relationship was reversed and it was determined that those beehives that presented more than 1% of Varroa in autumn and spring had the highest sporular levels. This paradoxical situation may be explained because the application of an acaricide product to control Varroa parasitization in 80% of the hives analyzed. On the other hand, management factors associated with high levels of Nosema spp spores were determined in Semi-arid Chaco regions. Those hives whose queens were changed reigns every two years or more had a greater development of parasitism. On the other hand, hives that received a polyvitaminic or pollen supplement had higher sporulation levels.These results provide some answers to beekeepers, there is a seasonal pattern of parasitosis, beekeepers should be attentive to the moments in which peaks of maximum levels of Nosema spp. spores and should take control measures of other pathogens such as the mite V. destructor to reduce stress within the hives. It should be noted that the parasitosis did not have a direct effect on the honey production or on the general state of the hives during the year in which the work was carried out. This could be indicating that despite being found high levels in some regions, the parasite does not get to generate serious damage in the hive.