Instructions
Go to Floaroma Town, which is north of Route 204. Look for the exit located in the northwest section of town. Leave the town and you will find yourself in Floaroma Flower Fields.
Speak to the only man in Floaroma Flower Fields. Buy 20 bottles of Sweet Honey, which cost 100 PokeDollars each. You will use one bottle of Sweet Honey each time you slather honey on a tree.
Look for a Sweet Honey Tree in the following locations: Route 206, Route 207, Route 208, Route 209, Route 213, Route 214, Route 215, Route 218, Route 221, Route 222, Valley Windworks, Fuego Ironworks and Floaroma Meadow. A Sweet Honey Tree has brown leaves instead of green leaves.
Stand in front of the Sweet Honey Tree and press "A." The game will prompt you to slather honey on the Sweet Honey Tree. Select "Yes."
Return to the Sweet Honey Tree after 12 hours and press "A" to engage in a battle with a Pokemon. The Pokemon may be Aipom, Heracross, Combee, Cherubi, Munchlax or Burmy. Defeat the Pokemon and apply honey to another honey tree if the Pokemon is not a male Burmy.
Use Fire-type Attacks on the Burmy to weaken it. Catch it with a Pokeball. Train the male Burmy to Level 20. It will evolve into a Mothim.