Methoprene (isopropyl (2E, 4E)-11-methoxy-3, 7, 11-trimethyl- 2, 4-dodecadienoate) formulated as Altosid® SR-10 was tested against Culex pipiens L. under simulated field conditions and against Aedes aegypti (L.) in the laboratory. Rates from 0.0027 to 0.27 1b. a.i./A resulted in 90 to 100% emergence inhibition. In the same tests, diflubenzuron (1-(4 chlorophenyl)-3-(2, 6-difluorobenzoyl) urea), formulated as Dimilin® 25% WP, induced 96 to 100% emergence inhibition at rates from 0.003 to 0.03 1b. a.i./A. Also in the same tests, temephos (0,0'-(thiodi-1, 1-phenylene) 0, 0, 0', 0'-tetramethyl bis (phosphothioate)), formulated as 1% Abate® 4E in plaster-of-Paris briquettes, was applied at normal field dosages and resulted in 100% emergence inhibition.