Abstract
Persistent exposure to mite pests, poor nutrition, pesticides, and pathogens threaten honey bee survival. In healthy colonies, the interaction of the yolk precursor protein, vitellogenin (Vg), and endocrine factor, juvenile hormone (JH), functions as a pacemaker driving the sequence of behaviors that workers perform throughout their lives. Young bees perform nursing duties within the hive and have high Vg and low JH; as older bees transition to foraging, this trend reverses. Pathogens and parasites can alter this regulatory network. For example, infection with the microsporidian, Nosema apis, has been shown to advance behavioral maturation in workers. We investigated the effects of infection with a recent honey bee pathogen on physiological factors underlying the division of labor in workers. Bees infected with N. ceranae were nearly twice as likely to engage in precocious foraging and lived 9 days less, on average, compared to controls. We also show that Vg transcript was low, while JH titer spiked, in infected nurse-aged bees in cages. This pattern of expression is atypical and the reverse of what would be expected for healthy, non-infected bees. Disruption of the basic underpinnings of temporal polyethism due to infection may be a contributing factor to recent high colony mortality, as workers may lose flexibility in their response to colony demands.
Highlights
The economic and ecological importance of honey bees (Apis mellifera) as pollinators of many cultivated and native plants make them an important system for studying the effects of illness at both the individual and colony or social levels
Many pathogens and parasites are common and widespread in non-symptomatic, or apparently healthy, colonies [5]. This burden emphasizes the buffering capacity of honey bee societies, but makes it difficult to state with confidence the impact a specific factor has on colony health
Nosema ceranae had a negative effect on lifespan (z = 3.97, n = 363, p,0.0001; Figure 1)
Summary
The economic and ecological importance of honey bees (Apis mellifera) as pollinators of many cultivated and native plants make them an important system for studying the effects of illness at both the individual and colony or social levels. For the U.S the outcome of this health crisis has been losses of nearly one-third of colonies annually since 2006 [3]. This recurring level of death may be unsustainable for the beekeeping industry, and could debase the value of crops and other products requiring pollination [4]. Many pathogens and parasites are common and widespread in non-symptomatic, or apparently healthy, colonies [5]. This burden emphasizes the buffering capacity of honey bee societies, but makes it difficult to state with confidence the impact a specific factor has on colony health. We relied on this research background to explore mechanisms that could interfere with worker behavior following exposure to a single specific pathogen, Nosema ceranae, considered to be a factor in colony decline [1]
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