Precautions for Roatan & Cozumel-mosquitos, sand flies

I am going to Roatan and Cozumel, in that order, at the end of November.  This will be my first cruise ever.  
Will the insects, flies, mosquitoes be a problem at that time of year?  Any suggestions on the best repellents?  I ask for two reasons, to be prepared and because my friend seems to get a skin rash every fall and doesn't feel like doing anything for weeks.  The last thing I'd want is for either of us to get sick and ruin our vacation.  Please share your personal experiences or articles.  Thanks.

I never noticed a problem but on mission trips to the Dominican I know the nationals gave us a diet high in garlic. My wife indicated this was for insects. So either that will repel them or give you good flavor for them.
 

We had no problem in the beach area of Cozumel but when we got into the jungle we did use the Deep Woods Off.   Lots of mosquito in the area around the ruins.   Buy it before your cruise a small can was about $ 14.00 on the ship.

We visited both of those ports during our May. They weren't a problem, but no place is totally bug free. You're doing the right thing by trying to be prepared. If you're doing excursions that will take you into the wooded areas (we had to hike through the jungle to get to the cave tubing site), zoo or tropical gardens, I'd definitely use some sort of repellant. If you or your friend get bad reactions from bites (I'm hypersensitive and my bites/stings swell up really bad), use a repellant. I use spray, but they have wipes that are even easier and less messy to use. If you don't like chemicals, there are also natural oils & remedies that are effective. 

Have a great trip.