Introduction:Declines in honeybee abundance have been observed worldwide during last decades. This is partly due to plant protection agents used in intensive farming, landscaping and infrastructure maintenance. Another type of factors negatively affecting honeybees is the spread of diseases caused by different pathogens and pests. Lately, more focus has been paid to the interactions between different overlapping stressors affecting honeybee health, the combination of these often being more detrimental compared to individual stressors. The most widely used stress-evaluating methods take into account lethal- or motorial changes of the individuals or colonies. Comparatively little honeybee research has examined changes in initial recovery potential and physiological symptoms of toxification. The aim of this study was to examine the combined effect ofNosema apisandN. ceranae(according to a newer classificationVairimorpha apisandV. ceranae), the common causes of nosemosis in the honeybeeApis melliferaL., with the insecticide dimethoate.Methods:In this study, honeybee mortality and metabolic rate were used to assess the combined effects interactions ofNosemassp. and dimethoate.Results:Our results showed that exposure to the low concentration of either dimethoate, either one or both species ofNosemassp as single factors or in the combination had no significant effect on honeybee metabolic rate. The mortality increased with the twoNosemaspp., as well as with infection byN. ceranaealone. The effect of dimethoate was observed only in combination withN. apisinfection, which alone had no effect on individual honeybee mortality.Conclusion:This study demonstrates that the overlapping exposure to a non-lethal concentration of a pesticide and a pathogen can be hidden by stronger stressor but become observable with milder stressors.