As bee populations decline, increasing attention focuses on how local and landscape processes impact the epidemiology of bee pathogens and parasites. Environmental conditions such as habitat loss and urbanization can mediate the transmission of disease through a multitude of ways, including direct influences on pathogen growth and indirect impacts to vector or host physiology and behavior.
While laboratory studies have revealed some of the transmission mechanisms by which floral resources facilitate parasite and pathogen transmission, few studies compare parasite and pathogen incidence from bees in situ. We examined how local and landscape composition, as well as bee community diversity, influence parasite and pathogen loads in bees from 17 urban gardens in central California. At each garden we implemented surveys of local vegetative diversity and classified land-cover categories within 2km. To assess if bee diversity influences disease incidence in Bombus and Apis, we surveyed bee populations. 459 Apis and 204 Bombus were homogenized for RNA and DNA extraction. We used PCR to detect four parasites: Apicystis spp., Crithidia spp, Nosema spp, and Apocephalus borealis. We used MLPA to detect 6 RNA virus targets that cover 10 common bee viruses: ABPV, BQCV, IAPV, KBV, DWV, KV, VDV-1, SPBV, SBV, and CBPV.
Results/Conclusions
We expected that landscapes with fewer land-cover categories and lower bee diversity would correlate with higher parasite and pathogen loads. Because poor quality habitat negatively impacts bee immunity, we expected that bees in urbanized landscapes are more vulnerable to parasites. However, results from the preliminary phase of the study reject this hypothesis for one parasite of bees. Parasitism by the phorid fly A. borealis was first reported in Apis in 2012, but the extent and impact of parasitism is still unknown. We found a 2.16% parasitism rate by A. borealis across both bee species. Percent urban cover within 2km from each site had a significant, negative impact on A. borealis parasitism (p < 0.0001). This means that with increasing urbanization, we saw less parasitism. This result may be emerging if phorid adults are resource limited in urban landscapes; perhaps they lack the pollen and nectar resources that adult phorids require. Another explanation is that, in urban areas, host density is too low for phorids to locate hosts. We will present our work on how different local and landscape characteristics influence each type of parasite and pathogen incidence to towards understanding how urbanization and landscape context drive bee health.