Through utilization of quantitative genetic techniques, a strain of cotton boll weevils has been developed that displays improved fitness for use in a sterile insect release control program. The strain has a 14-day post-irradiation survival rate of > 90% and a 10-day post-irradiation mating propensity of about 70% under laboratory conditions. This improved strain was tested under field conditions during the summer of 1987 at Starkville, MS and was compared to a control strain from the Boll Weevil Research Laboratory. It showed a post-irradiation mean survival time increase of 6 days and the males attracted females for at least 5 days longer. The preliminary data obtained from the field indicates that this newly engineered strain could be highly competitive in the field for at least 16 days after release. Further testing under field conditions of the selected strain to effect population control is warranted by these data.