What biopesticides do farmers use and where do they obtain biopesticides from?

Greetings! I would like to ask what types of biopesticide are used most often by farmers and how to obtain them? Are most available to purchase or do farmers make them? Are biopesticides made in batches so they can occasionally use biopesticides or do make them only when they will need biopesticides?

Thank you for your kind answers.