A water soluble, fluorescent pigment was aerially applied to caged Culex quinquefasciatus adults in a south Louisiana marshland pasture. Mosquitoes held in cages on 1 m stakes were greater than 90% marked. This number was significantly greater (P less than 0.01) than the number of marked mosquitoes held in cages that were placed in dense vegetation (greater than or equal to 0.5 m high) near the ground surface (70% marked). In a second aerial test with caged Aedes sollicitans in an open, grassy area of the marshland pasture, the pigment marked 100% of the adult mosquitoes held in cages 1 m above the ground and 98% of the caged mosquitoes on the ground surface. Greater than 96% of the adults collected from an emerging population of Ae. sollicitans within the test area were marked as well as 100% of wild caught deer fly adults, Chrysops flavidus complex, in the test area.