Observations in field trials of boll weevil insecticides indicated a need to investigate patterns of efficacy by boll weevil insecticides at different times after treatment application and for selected exposure times. Laboratory bioassays were conducted in which adult boll weevils were exposed to leaf disks cut from leaves collected from treated plants. These studies investigated patterns of mortality caused by exposure of boll weevils for 6, 12, 24, 48, or 72 h to fipronil, azinphosmethyl, two rates of endosulfan, oxamyl, and a low rate of ULV malathion, at time intervals of 0, 24, 48, and 72 h after treatment application. Mortality continued to increase between observations at 24 to 72 h after initial exposure regardless of duration of the exposure or the insecticide used. However, changes in mortality between observation times were greater for Fipronil, azinphosmethyl, and the high rate of endosulfan than for other materials. When duration of exposure was <12 h mortality was typically reduced, except when initial exposure to insecticides was ≥48 h after application. No material supplied a high level of mortality when initial exposure was at ≥48 h after treatment application. Fipronil, azinphosmethyl, and the high rate of endosulfan supplied high levels of mortality immediately after treatment application, but fipronil demonstrated greater activity than other materials when initial exposure was delayed for 24 h. These results illustrate that consideration of both residual activity and duration of exposure can increase both quality and quantity of information yielded by bioassays.