Answer: Based on your description, unforunately I am not certain what is happening to your ferns. The typical pests on ferns such as scale and mealy bug would not match the description of small white flying insects (or whitefly), they also would not eat the fern but would cause it dieback or discolor. For this reason, I would suggest you consult with your local Cornell county extension to obtain a more specific identification of the problem and based on knowing that, decide what to do. If a chemical control is needed, they will have the most up to date recommendations on what to use and how/when to use it for best results. I'm sorry I can't be more specific for you long distance.
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