What do Dufor's glands release during reproduction in honeybees?

Dufour's glands are specialized glands found in honeybee queens. During reproduction, these glands play a crucial role in the mating process by releasing pheromones that attract drones. However, the selection of pheromones onto eggs in the vaginal canal specifically points to another function of pheromone activity in the reproductive process.

In the context of mating, queens may utilize pheromones to influence the behavior of drones, but the main role of Dufour’s glands pertains to their involvement in pheromone production and release that can also affect the eggs themselves. Dufour's glands contribute to the queen's ability to signal reproductive readiness and establish chemical communication within the hive, particularly during and after mating.

Therefore, the correct option highlights the direct action of Dufour’s glands in relation to the reproductive system and eggs, showcasing their significant role in honeybee reproduction. Each of the other options discusses different types of pheromones or enzymes that either apply to other circumstances within bee behavior or do not accurately represent the function of Dufour's glands.