So nice to have you join our group. You may not be aware but you may get a lot more answers to your questions if you start the thread or question yourself rather then tacking your question on an older thread.
A fresh thread catches more eyes and responses.
But birds nest ferns in my experience do not tolerate pesticides, they can be finicky! A lot of plants are.
With scale insects, aphids and mealybugs, a simple solution of alcohol and water, either applied to a plant with a tissue or cotton swab, can produce wonderful control.
You let the alcohol sit for a few minutes and rinse off. This works well for me. You must be thorough in your treatment because insect populations can explode quickly and re occur.
It may take several treatments to be very effective. Perhaps three in total, a week to ten days apart. The trick is to be observant and catch this early!!