ficus problem is building up

Hi
I have read directions from this group about how to take care of ficus. I have them in a porch where they get all day indirect light, I water them only when the soil is dry and I don't move them around.
The problem is that from the last week their leaves are starting to have some spots. I also have the impression that very little flies fly around them frequently, which I haven't noticed before.
I have 2 pics of a leaf (underside and top side) http://www.flickr.com/photos/7866630@N05/tags/ficus / Flickr scales the image in several sizes. The pic is available in high- res too if needed.
Could somebody give any directions? If more pics or other info is needed, let me know.
Thanks for all the info I have already found in here :-)
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So if I understand correctly you think that this is a problem related to the way I "treat" the plant rather than a sort of malicious parasite or something similar.
Thanks :-)
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