Investigating incidences of European foulbrood and other pathogens in highbush blueberry-pollinating honey bees

Blueberries are Canada’s top fruit crop export, with cultivated blueberries occupying 75,000 hectares of land. In 2016, Canada produced more than 200,000 metric tonnes of blueberries, valued at $400 million. British Columbia produces the majority of Canadian cultivated highbush blueberries (Vaccinium corymbosum), which are mostly pollinated by honey bees originating from British Columbia and Alberta. Recent reports indicate a decline in honey bee colony health, particularly an increase in European foulbrood (EFB) frequency, after colonies return from pollinating blueberries. Our goal was to investigate the honey bee colony health status following blueberry pollination, with an emphasis on EFB infections.

For this study we examined five blueberry-pollinating apiaries and one non-blueberry apiary across three time points (start, end, and postblueberry pollination). We observed a greater increase in EFB-like symptoms in the blueberry-pollination apiaries compared with the nonblueberry-pollinating apiary. Field observations showed all blueberry-pollinating apiaries experienced an increase in EFB-like symptoms following blueberry pollination. Laboratory analysis incorporated the novel technique of droplet digital PCR (ddPCR) to obtain absolute
quantitation of EFB infection in honey bees across pollination time points. Molecular techniques confirmed field diagnosis of EFB-like symptoms in 77% of the samples. Colonies in blueberry-pollinating apiaries experienced a modest increase in Varroa infestations relative to the non-blueberry pollinating apiary, however Varroa levels did not increase in all blueberry-pollinating apiaries over time. We are also investigating Nosema spore counts and species to further evaluate honey bee health.

The observed increased incidence in pathogens following blueberry pollination indicates that beekeepers’ observations merit further investigation to determine the exact variable(s) that are affecting bee health. These studies will guide management strategies to ensure the sustainability of healthy honey bee colonies that are able to continue pollinating blueberries and other agricultural crops.