Correlated effects of selection in honey bees on viral load of deformed wing and chronic bee paralysis viruses

Today honey bee colonies are facing increasing pressure from viral pathogens, particularly from the deformed wing virus (DWV) and chronic bee paralysis virus (CBPV). Both viruses contribute to the global decline in colony health and survival worldwide. This study explores the effect of genetics on the viral load of the two viruses (DWV and CBPV). Results are based on 69 colonies belonged to an Italian breeding population selected for honey production, hygienic behaviour and docility. DWV was detected in all colonies, with varying viral loads, whereas CBPV was detected in 18.8% of the colonies. The same colonies were further evaluated for two varroa-related traits: phoretic mite load and varroa growth rate. Results showed a genetic effect on the levels of CBPV viral load, suggesting genetic differences in susceptibility. In contrast, DWV viral loads did not vary significantly among lines however moderate correlations with both varroa growth rate and phoretic mite load were identified, confirming the role of the varroa mite in DWV transmission.