Seasonality of Nosema ceranae Infections and Their Relationship with Honey Bee Populations, Food Stores, and Survivorship in a North American Region

Abstract

<i>Nosema ceranae</i> is an emerging pathogen of the western honey bee (<i>Apis mellifera</i> L.), and thus its seasonality and impact on bee colonies is not sufficiently documented for North America. This study was conducted to determine the infection intensity, prevalence, and viability of <i>N. ceranae</i> in >200 honey bee colonies during spring, summer, and fall, in a North American region. We also determined the relationship of <i>N. ceranae</i> infections with colony populations, food stores, bee survivorship, and overwinter colony mortality. The highest rates of <i>N. ceranae</i> infection, prevalence, and spore viability were found in the spring and summer, while the lowest were recorded in the fall. <i>N. ceranae</i> spore viability was significantly correlated with its prevalence and infection intensity in bees. Threshold to high levels of <i>N. ceranae</i> infections (>1,000,000 spores/bee) were significantly associated with reduced bee populations and food stores in colonies. Furthermore, worker bee survivorship was significantly reduced by <i>N. ceranae</i> infections, although no association between <i>N. ceranae</i> and winter colony mortality was found. It is concluded that <i>N. ceranae</i> infections are highest in spring and summer and may be detrimental to honey bee populations and colony productivity. Our results support the notion that treatment is justified when infections of <i>N. ceranae</i> exceed 1,000,000 spores/bee.