Beehive Nucleus

Put it in a beehive and you have bees. Without a nucleus the hive is an empty wooden box; with one, the bees make honeycomb, and the nucleus grows as they do, so the hive yields more the longer it runs. Keep the bees happy and the comb comes faster.

Getting the first one is the slow part. Wild honeycomb can be cooked in a furnace for guaranteed honey, or extracted by hand for honey plus a small chance of a nucleus. So as long as you have no hive running, do not cook your comb.

The other place it goes is a bee grenade. Every jar eats a nucleus your hive could have kept working, so most farmers only throw bees once they have a spare, and recycling an unused grenade only sometimes gives the nucleus back. The honey is worth keeping, too: a jar of honey cuts hunger and radiation.