Abstract
The microsporidia Nosema ceranae is an intracellular parasite of honeybees’ midgut, highly prevalent in Apis mellifera colonies for which important epidemiological information is still unknown. Our research aimed at understanding how age and season influence the onset of infection in honeybees and its development in the colony environment. Adult worker honeybees of less than 24h were marked and introduced into 6 different colonies in assays carried out in spring and autumn. Bees of known age were individually analyzed by PCR for Nosema spp. infection and those resulting positive were studied to determine the load by Real Time-qPCR. The age of onset and development of infection in each season was studied on a total of 2401 bees and the probability and the load of infection for both periods was established with two statistical models. First N. ceranae infected honeybees were detected at day 5 post emergence (p.e.; spring) and at day 4 p.e. (autumn) and in-hive prevalence increased from that point onwards, reaching the highest mean infection on day 18 p.e. (spring). The probability of infection increased significantly with age in both periods although the age variable better correlated in spring. The N. ceranae load tended to increase with age in both periods, although the age-load relationship was clearer in spring than in autumn. Therefore, age and season play an important role on the probability and the development of N. ceranae infection in honeybees, bringing important information to understand how it spreads within a colony.
Highlights
The European honeybee, Apis mellifera, currently faces many stressors that affect colony viability such as pesticides, climate change, loss of biodiversity, pests and pathogens
A single honeybee of the 30 bees analyzed in autumn was positive for N. ceranae, which represents a 3.3% of newly emerged bees infected in autumn and a 2.2% among all the newly emerged bees analyzed on day 0
Social organization leads to organizational immunity (Naug and Smith, 2007) whereby the nurse bees and larvae are in the more isolated part of the colony to reduce their contact with pathogens
Summary
The European honeybee, Apis mellifera, currently faces many stressors that affect colony viability such as pesticides, climate change, loss of biodiversity, pests and pathogens (vanEngelsdorp and Meixner, 2010) Among the latter, the microsporidia Nosema ceranae has a detrimental impact on infected colonies (Higes et al, 2008; Emsen et al, 2020). Onset of N. ceranae Infection mellifera in Europe (Higes et al, 2006) and one year later in Asia (Huang et al, 2007) It has since been reported in other parts of the globe (Klee et al, 2007; Chen et al, 2008; Williams et al, 2008; Giersch et al, 2009), becoming a very widespread and prevalent parasite of honeybees. The spores reach the ventriculum where they extrude the polar filament to introduce the sporoplasm into the bees’ epithelial cells in which the parasite completes its cell cycle and reproduces, extending infection throughout the organ and producing severe tissue damage (Higes et al, 2007; Garcıá -Palencia et al, 2010; Maiolino et al, 2014; Panek et al, 2018)
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