Training Bees have a Mission Cap and a Mission Span. Both affect how many Missions the Bee can complete. (see the chart below for full details).

Mission Cap is the number of Missions the Bee can complete before he retires 

Each Training Bee starts with a Mission Cap of 20.

The Mission Cap is increased each time the Bee is upgraded. Upgrading your Bee's stats will add 10 to the Mission Cap for the upgraded Bee.

Upgradable Training Bee Stats are: Health, Attack, Defense, Agility, Luck, and Capacity.

NOTE: Any rarity upgrade will add 10 to the Mission Cap.

Each successful Hunt or Harvest adds one to the Mission Count

Once a Bee's Mission Count matches his Mission Cap, he will need to be upgraded to add to his Mission Cap.

If he doesn't have any open upgrade slots, he will be retired.

NOTE: Player vs. Player (PvP), Quests, and Breeding do NOT affect the Mission Count.

Mission Span is the number of days a Bee can be active on Missions

A Training Bee will retire once the Mission Span hits 0, even if he hasn't reached the Mission Cap 

NOTE: Mission Span cannot be extended

Starter Bees have a 90 day Mission Span

Hatched Bee have a 30 day Mission Span

Bred Bees' Mission Span is the Queen's Level x 3 (Minimum 30 days, Maximum 60 days)

Retired Training Bees can be converted into shards. This will remove the Bee from your hive.

You will receive 5 Generations Bee Egg shards when converting a Training Bee that has completed at least 60 missions (must be a Certified Beekeeper or have purchased a Season Pass this month to qualify)

You will receive 40 shards for each Bee you convert. The 40 shards are randomly chosen and can be any of the following: Shield, Poison Bomb, Cursed Honey Drop, or Sonar Buzz.

NOTE: Retired Training Bees can still be used to do Quests and PvP.