Belize is a tropical location, so yes.  Fortunately, the prevailing breezes on Ambergris Caye help to keep them at bay!  Sand flies, or noseeums, are tiny creatures that bite like mosquitoes.  When there is little or no breeze, they can come out at dusk.  We recommend that you travel with DEET based insect repellant and you might consider bringing hydrocortisone cream and/or Benadryl to soothe an itch.