Abstract
Nosema ceranae is a pervasive and widespread honey bee pathogen that is associated with colony declines and has recently been shown to infect larval honey bees. In adult bees, Nosema infection is known to alter levels of a key protein, vitellogenin (Vg), which is necessary for egg-laying in queens, brood food production in workers, and proper immune function in all female bees. We therefore tested the effects of larval worker infection on hemolymph Vg titers. In 1-day old adult workers that were infected as larvae with 10,000 (10 K) or 40,000 (40 K) live N. ceranae spores/bee, Vg titers were significantly elevated by + 83% and + 73%, respectively, as compared to controls. At 7 days of adult age, Vg remained significantly elevated (+ 68%) in 10 K treated workers as compared to control workers. Nosema infection decreased total hemolymph protein titers in 1 and 7-day old adult bees (−50% in the 10 K and 40 K treated bees). Bees infected as larvae also had a more queen-like sting morphology. They developed slightly but significantly fewer barbs on their stings (−7% in the 40K-treated bees). Higher Vg levels are associated with younger bees. Thus, elevated Vg levels could delay normal age polyethism and disrupt colony balance.
Highlights
Since 2006, beekeepers have reported unusually high winter colony losses, 22–30% and higher in the USA1,2
deformed wing virus (DWV) is not known to interact synergistically with N. ceranae infection[20], and to date, no studies have investigated the effects of N. ceranae infection alone on honey bee morphology
We focused on hemolymph because Vg occurs in multiple tissues, but Fluri et al.[35] showed that hemolymph Vg titer is well correlated with honey bee age polyethism
Summary
Since 2006, beekeepers have reported unusually high winter colony losses, 22–30% and higher in the USA1,2. Lecocq et al.[15] found that newly emerged adult bees, which were infected with N. ceranae spores and observed for 14 d, exhibited traits of older bees: increased walking and decreased attraction to queen mandibular pheromone. These forward shifts in age polyethism may be adaptive for the colony and limit the spread of infection[24] because foragers have a higher probability of dying outside the nest than nurse bees. Emerged workers have low Vg levels that reach a peak at around 4 days[34] As these nurse bees age, their Vg stores decrease and they gradually transition to becoming foragers[30]. Young adults infected with N. ceranae develop Vg levels that appear age-accelerated
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