A selection experiment was conducted in Colombia using a field population of the tobacco budworm Heliothis virescens. Profenofos, thiodicarb, cypermethrin and a-cypermethrin were applied to third instar larvae for 13 generations. Bioassays were conducted to measure the development of resistance. The resistance factors after a 13 generation pressure were respectively 2 for profenofos, 21 for thiodicarb, 748 for cypermethrin and over 2000 for a-cypermethrin.