Experimental evidence and meta-analysis indicate the negative effect of nosemosis on the survivorship of honeybees

Nosemosis, caused by microsporidian parasites of the genus Nosema, is considered a significant health concern for insect pollinators, including the most economically significant, the honeybee (Apis mellifera L.). Despite its acknowledged importance, the impact of this disease on honeybee survivorship remains unclear. In this study, we used a standard laboratory cage trial to compare mortality rates between healthy honeybees and those infected with Nosema. We also conducted a systematic review and meta-analysis of existing literature to explore how nosemosis contributes to increased mortality in honeybees tested in such widely used standard trials. Our review and meta-analysis included 50 studies that reported relevant experiments involving healthy and Nosema-infected individuals. We excluded studies that failed to report survivorship curves or information on potential moderators affecting the impact of nosemosis, such as spore inoculation dose, the age of the inoculated honeybees, or factors that may impact energy expenditure. Both our experimental results and meta-analysis revealed a consistent, robust effect of infection, indicating a threefold increase in mortality among the infected group of honeybee workers (hazard ratio for infected individuals = 3.16 [1.97, 5.07] and 2.99 [2.36, 3.79] in the experiment and meta-analysis, respectively). However, the meta-analysis also indicated high heterogeneity in the effect magnitude, which was not explained by our moderators. Furthermore, there was a serious risk of bias within studies and potential publication bias across studies. Our findings underscore knowledge gaps in the existing literature. We stress that laboratory cage trials should be viewed as an initial step in evaluating the impact of Nosema infection on mortality. Complementary field and apiary studies are imperative in search of effective treatment measures to preserve honeybee populations. ### Competing Interest Statement The authors have declared no competing interest.