In this thesis, we addressed the question how pesticides and pathogen infections affect honey bees at the molecular level and at different developmental stages. Our interest was attracted by the interaction of different pesticides (thiamethoxam, imidacloprid, coumaphos and prochloraz) and the Varroa destructor mite as their simultaneous occurrence in honey bee colonies is almost inevitable. Therefore, the aim of our study was to examine the expression of genes associated with immunity in honey bees using real time polymerase chain reaction method. In the first part of our study we found that pesticides alone alter the level of immune gene expression compared to the control group, and that the expression pattern of studied genes changes with honey bee development. In second part of our study, we examined changes in immune gene expression of honey bees exposed to pesticides and varroa mites. When honey bees were simultaneously exposed to pesticides and varroa mites, their immune system change its expression in comparison to control group and experimental groups exposed to pesticides only. Our results do not show only persistent suppression of honey bee immune system, but also demonstrate increased expression of several immune related genes when honey bees are exposed to studied stressors. The expression of immune genes changes over time, therefore no general pattern of expression has emerged that could be generalized to all of the honey bee studied stressors. Our research is also a good starting point for further research that could examine the interaction and impact of each stressor on honey bees in more detail.