Every spring I re-queen my strongest hives in order to reduce swarming. A colony is less likely to swarm when the queen’s pheromones are strong, and the pheromones are strongest in a first-year queen. In fact, according to most sources, a new queen is the single best deterrent to swarming.
However, it seems ridiculous to take your very best queens, kill them, and replace them with others. And if the new queen is rejected, you are left with nothing.
So a few years ago I started keeping those queens instead of killing them. To do this, I remove the queen along with a frame of brood and a frame of honey and put them in a two-frame nuc. Then I introduce the new queen into the hive. If anything goes wrong with the new queen, I can always re-introduce the old one . . . or I can keep her “in reserve” for some other purpose.
For example, one of the swarms I caught last week appeared to be queenless. The swarm built comb in which it stored only honey, and when I sifted the bees through a queen excluder, I found nothing. So I took one of my reserve queens and introduced her. Once she starts laying the colony will probably supersede her, but without her to get things started, the whole swarm would die.
When I first started saving queens, I wondered what I would do when the two-frame nucs got too populous. But I found that these small colonies tend to expand to fill the available space and then remain constant. When you think about it, they aren’t big enough to swarm or even to abscond. So they just stay small. In the past I’ve kept these “reserve” queens all summer long.
Sometimes I just put a swarm cell, brood, and honey in the small nucs. It seems to take forever, but the bees eventually produce a laying queen and I just leave her there . . . in case. If one doesn’t succeed, I just start another. Since I’m using her only as a backup, it doesn’t really matter how long it takes.