Virus Prevalence in Egg Samples Collected from Naturally Selected and Traditionally Managed Honey Bee Colonies across Europe

Abstract

Monitoring virus infections can be an important selection tool in honey bee breeding. A recent study pointed towards an association between the virus-free status of eggs and an increased virus resistance to deformed wing virus (DWV) at the colony level. In this study, eggs from both naturally surviving and traditionally managed colonies from across Europe were screened for the prevalence of different viruses. Screenings were performed using the phenotyping protocol of the ‘suppressed in ovo virus infection’ trait but with qPCR instead of end-point PCR and a primer set that covers all DWV genotypes. Of the 213 screened samples, 109 were infected with DWV, 54 were infected with black queen cell virus (BQCV), 3 were infected with the sacbrood virus, and 2 were infected with the acute bee paralyses virus. It was demonstrated that incidences of the vertical transmission of DWV were more frequent in naturally surviving than in traditionally managed colonies, although the virus loads in the eggs remained the same. When comparing virus infections with queen age, older queens showed significantly lower infection loads of DWV in both traditionally managed and naturally surviving colonies, as well as reduced DWV infection frequencies in traditionally managed colonies. We determined that the detection frequencies of DWV and BQCV in honey bee eggs were lower in samples obtained in the spring than in those collected in the summer, indicating that vertical transmission may be lower in spring. Together, these patterns in vertical transmission show that honey bee queens have the potential to reduce the degree of vertical transmission over time.

Seasonal Variability in the Prevalence of DWV Strains in Individual Colonies of European Honeybees in Hawaii

“…The prevalence of DWV was different under different seasons in temperate areas with a higher DWV infection in either September in California [17] or spring in Europe [18]. Due to the warm and relatively stable tropical climate, honeybees are active year-round in Hawaii, and the viral loads and infection prevalence of DWV-A was relatively constant throughout the year.…”

“…However, the relationship "mite, virus, and disease impact" is complex and variable. Among the factors that could potentially affect DWV levels are colony management [14], quantity of natural propolis [15], varroa mite levels [16], and climatic conditions [17][18][19]. In temperate regions, the prevalence and viral loads of DWV vary considerably throughout the year [17,18,20,21].…”

“…Among the factors that could potentially affect DWV levels are colony management [14], quantity of natural propolis [15], varroa mite levels [16], and climatic conditions [17][18][19]. In temperate regions, the prevalence and viral loads of DWV vary considerably throughout the year [17,18,20,21]. The impact of elevated viral loads can be linked to a seasonal susceptibility to disease.…”