Bay laurel (Laurus nobilis) as potential antiviral treatment in naturally BQCV infected honeybees

• Naturally virus-infected forager honeybees are useful to determine antiviral activity of plant extracts.
• Laurus nobilis extract reduced BQCV virus loads and virus replication.
• Plant extracts are potential antiviral agents improving honeybee health.

Viral diseases are one of the multiple factors associated with honeybee colony losses. Apart from their innate immune system, including the RNAi machinery, honeybees can use secondary plant metabolites to reduce or fully cure pathogen infections. Here, we tested the antiviral potential of Laurus nobilis leaf ethanolic extracts on forager honeybees naturally infected with BQCV (Black queen cell virus). Total viral loads were reduced even at the lowest concentration tested (1 mg/ml). Higher extract concentrations (≥5 mg/ml) significantly reduced virus replication. Measuring vitellogenin gene expression as an indicator for transcript homeostasis revealed constant RNA levels before and after treatment, suggesting that its expression was not impacted by the L. nobilis treatment. In conclusion, plant secondary metabolites can reduce virus loads and virus replication in naturally infected honeybees.

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