Land use influences the composition and antimicrobial effects of propolis

Honey bee propolis is a complex, resinous mixture created by bees using
plant sources such as leaves, flowers, and bud exudates. This study
characterized how cropland surrounding apiaries affects the chemical
composition and antimicrobial effects of propolis. The chemical
composition and compound abundance of the propolis samples were analyzed
using Gas Chromatography-Mass Spectrometry (GC-MS) and the antimicrobial
effects were analyzed using the 50% minimum inhibitory concentration
(MIC50) assay against four relevant bee pathogens, Serratia marcescens,
Paenibacillus larvae, Lysinibacillus sphaericus, and Klebsiella
pneumoniae. Propolis composition varied significantly with apiary, and
cropland coverage predicted mean sum abundance of compounds. The apiary
with the highest cropland coverage exhibited significantly higher MIC50
values for S. marcescens and K. pneumoniae compared to other apiaries.
These results demonstrate that agricultural land use surrounding honey bee
apiaries decreases the chemical quality and antimicrobial effects of
propolis, which may have implications for the impacts of land use on hive
immunity to potential pathogens.