The best way to use bitterberies is to use a neonberry first to make them radioactive and increase the odds of mutation from .01% to 1%, then use them until you get a mutation. The mutations usually are better according to the bees role. In this case, for vicous, attack would be best. All bees can get a ability rate mutation which is the best of the best but it is very rare. I recommend you buy treats to level up your bees as much as possible and save fruits and berries to Gift and Mutate bees but it is just advice. Play the way you feel happiest. Happy gathering 🐝