This is not much, since it is just one experience, I realize:
I was there in April/May (years ago) and spent a little over a month snorkeling every day (mostly lighthouse reef, but some Glover's and some cays on the mainland reef). None of us had any problem with pica pica until the last day (natch). We were on... I think Tobacco Cay? (sorry, don't have my log with me). I was wearing my usual outfit of lycra jumpsuit/gloves and during the dive I thought I felt some stingy/itchy around my neck, but wasn't sure if I was just imagining it.
Well, I wasn't. I think it was pica pica. They did pretty much confine themselves to around my neck and a bit at the waist, so there were not TOO many welts, but they did itch ferociously, and last a long time.
We had read that if you get out and douse yourself in vinegar BEFORE you rinse with freshwater (which I guess sort of activates them), that you could nip them in the bud. However, since we had been there so long we never could have carried enough vinegar, and we were in the habit of just hoping and rinsing with fresh water (which did work 99.9% of the time
).
In retrospect, I wish I had rinsed with vinegar THAT time because I did feel some slight stingies during the dive.
I wasn't certified then, but oh would I love to go back. "Even" the snorkeling was spectacular!!
Blue Sparkle