Field tests were conducted in North Louisiana during 1997 to evaluate the effects of terminating insect control strategies at selected intervals on seedcotton yields. Termination intervals based on cotton plant development used plant mainstem nodes above white flower (NAWF) and heat unit (HU) accumulation. The treatment termination intervals based on crop development rules included NAWF = 5, NAWF = 5 + 200 HU, NAWF = 5 + 350 HU, NAWF = 5 + 500 HU, and NAWF = 5 + 650 HU. The termination intervals based on weather oriented rules used 17 Aug as a final cutout date in Louisiana. Insecticide treatments were terminated at 350, 450, 550, and 650 HU beyond 17 Aug. There was no significant increase in yield from terminating insecticide treatments beyond NAWF = 5 + 350 HU using the crop development rules. Seedcotton yields in the weather-oriented rules test were inconsistent. Also, two tests were conducted to examine the effects of insect-simulated defoliation on seedcotton yield. As defoliation levels increased from 0 to 99% at the NAWF = 5 + 350 HU stage of development, yields consistently declined. Significant yield losses occurred at 99% defoliation levels in the two tests.