Viral infections in queen bees
New customers often raise concerns about their queens’ prolificacy and ask us about possible causes. Rearing queens, regardless of line or subspecies, is highly specialised work. Supplying them to others also carries ethical responsibilities concerning genetic material and the possible transmission of viruses and diseases. We therefore pay close attention to our breeding operations, particularly hygiene and health management, to provide professional customers with healthy, high-quality queens expressing the selected traits.
This study supports the proposed relationship between viral infection and symptoms of queen failure, suggesting that a trade-off between reproduction and immunity is partly, but not entirely, responsible for these effects.
With their long lives and exceptional reproductive output, social insect queens have escaped the classic trade-off between fecundity and lifespan. Evidence for a trade-off between fecundity and immunity, however, has been inconclusive, partly because pathogen effects are rarely separated from immune activation. We conducted parallel laboratory and field virus-infection experiments to investigate this trade-off in honey bee queens (Apis mellifera) and understand how these widespread stressors affect their health.
Queens injected with infectious viruses had smaller ovaries and were less likely to resume egg laying than controls, while queens injected with UV-inactivated viruses showed an intermediate phenotype.
In the field, heavily infected queens had smaller ovaries, and infection significantly predicted poor colony reproductive performance. Immune responses were similar in queens receiving live or inactivated viruses, and many of the same immune proteins were negatively associated with ovary mass in field queens. Two parallel infection experiments further supported the relationship between viral infection and the poor queen performance reported by beekeepers, while exploring a possible reproduction–immunity trade-off.
In the cage experiment, queens injected with infectious viruses had significantly smaller ovaries and were significantly less likely to lay after infection. Queens injected with inactivated viruses had slightly smaller ovaries but no difference in laying ability.
In parallel, both experimental groups showed a similar immune response, indicated by increased immune-related expression. Inactivated or dead viruses and bacteria can also trigger immune responses, a principle used in some vaccines.
Across all three study groups, higher virus levels were associated with smaller ovaries and fewer eggs. The field experiment became correlational rather than manipulative because experimental infection unexpectedly failed to alter total viral load measured at the end. Nonetheless, total viral load, irrespective of group, was negatively associated with ovary mass and positively associated with supersedure cells, suggesting that viral infections affect queen productivity and possibly workers’ perception of queen quality.
The study connects ovary mass, an indicator of fertility, with reproductive effects such as egg laying and colony-level effects such as relative brood quantity. Previous work found that the reduced ovary mass of queens caged for shipping returned to normal only after time back in colonies. Oogenesis is more severely impaired in queens caged outside a colony than in those caged inside one, probably because queens receive better nutrition within colonies.
Our findings indicate that viral infections produce the field symptoms that concern beekeepers. A trade-off between immunity and reproduction partly, but not entirely, governs these effects. Attempted or premature supersedure is a commonly cited sign of queen failure that we have now shown to be directly correlated with queen viral infections.
The acute effects of experimental infection were amplified in our laboratory studies, where nutritional stress was probably an exacerbating factor, compared with the field trial, where colonies with abundant food could provide better queen nutrition. Forage shortages and nutritional stress can also occur in the field, and our data suggest that viral infection effects on queens may worsen under these conditions.
This work provides further evidence linking viral infections with symptoms beekeepers identify in poorly performing field queens. It highlights the inseparable relationship between queen health and colony environment and the importance of managing virus levels in beekeeping to improve colony health.
Adapted from: “Common viral infections inhibit egg laying in honey bee queens and are linked to premature supersedure”
Abigail Chapman et al. (2024)
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