I know you use wurmple but I always get dustox.
Some wurmples turn in to silcoon, and some turn into cascoon. cascoon evolves into dustox. silcoon evolves into beautifly. its a 50/50 chance if your going to get a silcoon or cascoon
Beautifly. Go to the petalburg woods and walk around until you see a silcoon. then use an exp. share and level it up to lvl 10.
You may meet Silcoon at Petalburg Woods (10%)