Effects of Instrumental Insemination and Insemination Quantity on Dufour's Gland Chemical Profiles and Vitellogenin Expression in Honey Bee Queens (Apis mellifera)

Honey bee queens (Apis mellifera) mate in their early adult lives with a variable number of males (drones). Mating stimulates dramatic changes in queen behavior, physiology, gene expression, and pheromone production. Here, we used virgin, single drone- (SDI), and multi-drone- (MDI) inseminated queens to study the effects of instrumental insemination and insemination quantity on the pheromone profiles of the Dufour's gland, and the expression of the egg-yolk protein, vitellogenin, in the fat body. Age, environmental conditions, and genetic background of the queens were standardized to specifically characterize the effects of these treatments. Our data demonstrate that insemination and insemination quantity significantly affect the chemical profiles of the Dufour's gland secretion. Moreover, workers were more attracted to Dufour's gland extract from inseminated queens compared to virgins, and to the extract of MDI queens compared to extract of SDI queens. However, while there were differences in the amounts of some esters between MDI queens and the other groups, it appears that the differences in behavioral responses were elicited by subtle changes in the overall chemical profiles rather than dramatic changes in specific individual chemicals. We also found a decrease in vitellogenin gene expression in the fat body of the MDI queens, which is negatively correlated with the quantities of Dufour's gland content. The possible explanations of this reduction are discussed.