• Nosema ceranae is a major gut parasite contributing to honeybee health decline worldwide • Interactions between N. ceranae and other biotic or abiotic stressors show highly variable outcomes • Co-exposure to pesticides, parasites/pathogens, and environmental stressors can result in synergistic, antagonistic, or neutral effects • Integrating multi-stressor interactions is essential for improving pollinator risk assessment frameworks The western honeybee, Apis mellifera , an essential component of natural ecosystems and a key pollinator for global food production, is increasingly exposed to a wide range of biotic and abiotic stressors that frequently co-occur and interact under realistic environmental conditions. Among these stressors, the microsporidian gut parasite Nosema ceranae is among the most prevalent pathogens in apiaries worldwide and is strongly associated with altered host physiology, impaired individual performance, shortened lifespan, and colony weakening. This review synthesizes current knowledge on the combined effects of N. ceranae infection with pesticides, co-infecting parasites and pathogens, as well as major modulating factors, including nutritional status, climatic conditions and beekeeping practices. Based on both controlled laboratory experiments and semi-field or field studies, the available literature reveals highly variable interaction patterns, ranging from synergistic to antagonistic or neutral effects, depending on the nature, timing, and intensity of the stressors involved. Taken together, these findings highlight the limitations of single-stressor risk assessment approaches and emphasize the need to integrate multi-stress interactions into environmental regulatory frameworks for pollinator protection.
Gilbert et al. (Wed,) studied this question.