Pheromone and morphometric features of honey bee (Apis mellifera) queens from around the globe

Canada imports approximately 300,000 honey bee queens annually to support the beekeeping industry, in addition to producing queens domestically during the short rearing season. Most imported queens (>80%) originate from the U.S., with additional contributions from Italy, Australia, and Chile, each with a ~5% market share. We conducted morphometric analysis and pheromone profiling of domestic (n=55) and imported (n=40) queens representing all four dominant source countries, including “vaccinated” (transgenerational immune-primed, or TGIP) and non-TGIP queens from the U.S., to compare their physical and pheromonal quality. Imported queens had lower morphometric scores than domestic queens, and this difference was driven by smaller ovary size (a plastic, likely inconsequential metric exhibiting transient changes due to temporary confinement). Pheromone scores did not differ among domestic and imported queens, but varied substantially within each group. Non-reproductive morphometrics (e.g., head width and wing length) were significant positive predictors of pheromone abundance, whereas reproductive morphometrics (e.g., ovary size and spermatheca width) were not. Queen size, therefore, has a stronger relationship with pheromone production than fecundity, possibly as a consequence of larger queens possessing larger pheromone source glands. TGIP queens had lower pheromone scores than non-TGIP queens, and this pattern was not driven by pre-existing morphological differences. Whether morphometric and pheromone differences lead to differences in acceptance rates and queen performance was not assessed, nor was the comparative benefit of immune-priming even if pheromone differences are persistent. Based on the measured variables, Canadian queens are high-quality and efforts to expand the domestic queen market are worthwhile.