Mealybug are often found in clusters. Mealybug can be treated with Neem Oil.
Here is a link with more information.
I do think you are describing spores on your fern though, so here is a link with more information and some images that will help you determine
if this is what your plants looks like.
In the case of spores, you will not need to do any treatment, this is naturally occurring.
Here is a link to refresh you on the care requirements.