The impacts of pathogen prevalence and landscape composition on propolis production in honey bees

Propolis is a sticky substance made by honey bees, Apis mellifera, composed of plant resins and balsams, bee-derived wax, and salivary gland secretions. The plant resins and balsams, gathered by foragers, vary with the geographic region, collection time, and vegetation availability, and propolis production, which influences honey bee health via its content of phytochemicals with antimicrobial or immunoregulatory properties, is influenced by environmental factors and disease. Throughout the seasons, the prevalence of different pathogens fluctuates, with fungal pathogens more prevalent during the spring and viral pathogens more prevalent during the fall. Coinciding with changes in pathogen prevalence, honey bees may alter their resin foraging behavior to produce propolis with greater antifungal, antiviral, or antibacterial properties during a particular season. We hypothesize that the chemical composition of propolis will change across the growing season and depend on landscape composition. We identify changes in propolis chemical composition due to landscape composition by placing colonies across landscapes varying in the abundance of forested areas, as trees are the primary source of resin for propolis. We inventory the total phytochemical content of resins by identifying both non-volatile and volatile chemical components using GC-MS and SPME/GC-MS analysis, respectively. Additionally, we hypothesize that there is seasonal variation in the antimicrobial properties of propolis, and these properties correspond to pathogen prevalence throughout the year. We test for seasonal variation by feeding bees infected with two bee pathogens, Nosema ceranae and Israeli Acute Paralysis Virus (IAPV), with sucrose solutions containing propolis extracts from each season and measuring survivorship.