You will be on the hunt for more Pokémon in Pokémon Brilliant Diamond and Brilliant Pearl. Many of them are elusive, and tracking them down can be quite difficult if you don't know the correct locations to look for or where they spawn. Combee is one of these Pokémon, as is its evolved form, Vespiquen. Here's what you need to know about Combee's evolution in Vespiquen into Pokémon Brilliant Diamond and Brilliant Pearl.
Combee does not require an evolution item, friendship level, or learning a certain move. The only thing you need to do for Combee to evolve into Vespiquen is to make sure you catch a female. This is because the male versions of Combee do not become Vespiquen. You must therefore make sure that Combee reaches level 21 and will evolve.
If you have a male version, you won't evolve it, so it's best to release them back into the wild. Thankfully, Combee is relatively common in the Grand Underground. You can find them by exploring the Sunlit Cavern or any cave with grass. If you're having trouble finding Combee, be sure to fill your secret base with more Bug-type statues, increasing your chances of Bug-type Pokémon appearing during your exploration of the Grand Underground.