Hi, all - posting here because the other threads on this topic seem to have be closed for a while. Anyway . . .
Our tour went, among other places, to M/P and the Amazon. We were not told of any insect attack issues at M/P. However, when we were walking through the ruins near the "plaza" I received bites from a couple of tiny black flies and, after word spread in the bug community, about a dozen more. They did not hurt, but there were tiny rivulets of blood down my ankles.
Although the tour had not recommended any insect repellent my husband had some DEET spray in his day-pack, and after a few sprays the bugs left me alone. I was not (so far as I know) affected in any long-term way, just some tiny scabs that have, a week later, mostly faded away.
No one else else in our group of about a dozen people was targeted; this makes sense as I am always the mosquito (and other bug) magnet! If you are a fellow-sufferer of this condition, I suggest long pants into your socks and/or an application of insect repellent before you go up to M/P.