Evidence for pollen as a route of virus transmission in the pollinator community

RNA viruses are emerging as a serious threat to honey bee (Apis mellifera) health and are suspected as major contributors to the recent malady, Colony Collapse Disorder. Understanding the transmission of these viruses can shed valuable light on the epidemiology of this syndrome. In addition, the recent detection of some of these viruses from bumble bees as well as in in-hive food reserves of honey bees, suggests a possible wider environmental spread of viruses with potential impact on the overall pollinator community. We studied the distribution of viruses in honey bees, their pollen loads and in other non-Apis hymenopteran pollinators collected from flowering plants. All samples were analyzed with reverse transcriptase-PCR and virus identity was confirmed by sequencing. We report for the first time the molecular detection of picorna-like RNA viruses (deformed wing virus, sacbrood virus and black queen cell virus) in pollen pellets collected directly from forager bees. Furthermore, pollen pellets from some uninfected bees were detected with virus, implicating pollen in virus transmission. These viruses were found in eleven other species of native bees and wasps, expanding the known host range of these viruses and suggesting a possible deeper impact on the health of our ecosystem. Sequence comparisons of viruses isolated from honey bees, pollen and other non-Apis hymenopteran species indicate that the viruses are circulating freely among these species. This study increases our understanding of virus epidemiology and may help explain bee disease patterns and pollinator population decline.