Hi There,
My wife and I have been to St John 5 times now and the most important tip is to get off the beach before the mid-afternoon sun drives the noseeums out of the sand. We haven't used any repellent the last 4 trips...get to the beach early and then spend the afternoon sipping on a cold drink at one of the islands' watering holes.
Now if you're a hiker, someone else will have to give you advice. We either relax at the beach or with a nice cold drink at Skinny Legs, Woody's, or Duffy's.
The only trouble we had was on on our first trip while staying in a Maho tent. Went to bed fine, but my wife woke up looking like she had a case of the measels.....probably carried a noseeum into the tent!!!
Enjoy your trip....we return next May.
Kurt

Thanks! Yes, we plan to do some hiking. That scares me about your wife having the little visitor like that! Ugh! We are staying at Cocordia, which is just like the Maho tents. (sister property) I hope I don't wake up like that one morning! 🙂

You should be fine with the 40% DEET. Although I don't vacation on St. John (St. Croix for me) I find myself being bitten by something at all hours and in all places (shops, restaurants, etc.) so I wear a light coating of repellant at all times except by the pool.

For safe measure, I'd recommend calling your physician and asking for a prescription of .05% Diprolene lotion. If you do get bitten this stuff is far, far, far superior to any over the counter remedy. The noseeums and Caribbean mosquitos are sufficiently different from their northern cousins that I find myself itching (I mean REALLY itching) for days unless I use this stuff. YMMV.

The bugs can be a problem in the early am and in the pm. Always use something! I have bad reactions to the bugs and get big welts where I am bitten. Such is the suffering in paradise. I live through it just fine. One other comment.. last year I came in contact with some poison ivy type plant while we were hiking that gave me the typical poison ivy symptoms. If you are going to hike on trails that aren't really cleared well, wear high socks or long pants. It was not fun. Luckily I got exposed only 2 days before we left for home. The plane ride back was very itchy!! This year I am bringing cortisone tabs in case I get exposed again. Cleared me right up last time.

Thanks for all of the advice! We were insect-free! The only time we sprayed ourselves was when hiking in the afternoon at Salt Pond our last full day there (five-night stay). We were always off the beaches by shortly after lunch, as we found it was best to beat the crowds and enjoy empty beaches around 8:00 in the morning! We also took the advice to get a prescription for Diprolene AF 0.05%, and brought the filled prescription along with us just in case...
Thanks again for all of your advice! We thoroughly enjoyed our vacation, and look forward to returning!