EN
Nosema spp. spores are extremely resistant to external stress factors and can survive several years without losing the ability for further infection within the insect body. For this reason, combating nosemosis is difficult. Some beekeepers add ethanol to the sucrose solution before the winter to prevent nosemosis infection and to cure already infected colonies. Others feed infected colonies with herbal ethanol extracts. Therefore the aim of this study was to evaluate the ethanol impact on bees infected with Nosema spp. Four groups of uninfected and Nosema spp. infected bees were fed with sugar-water syrup (1:1) supplemented with ethanol at the following concentrations: 10%, 5% and 2.5% and 0% as a control (only a sucrose syrup). Generally, bees consumed 10% EtOH solution in an amount even 50% lower than in other concentrations. The impact of EtOH on the increase of bees’ mortality was observed at a 10% EtOH concentration for healthy bees and even from 5% EtOH concentration for Nosema spp. infected bees. In our study the highest number of Nosema spp. infestation was noticed for bees fed with 5% EtOH and the lowest pH level was also measured for this group of bees. Therefore, a clear correlation was observed between the feeding bees with EtOH, which resulted in the acidification of bees, and the degree of Nosema spp. infestation. A synergistic effect of the ethanol and nosemosis on the rise of the mortality of bees has been observed. The addition of ethanol to sucrose syrup facilitates conditions for the development of nosemosis in honey bees. The strongest effect of ethanol on the level of Noseama spp. infection was observed for the 5% ethanol solutions. Moreover, ethanol at 10% concentration in sugar syrup exerts severe toxic effects even on healthy bees. All these factors induced immune-suppression in bees and enhanced the level of Nosema spp. infestation.