The results of field cage studies indicated a lower level of competitive fitness in both males and females of a transgenic (EGFP marker gene) pink bollworm (PBW) strain when compared to a non-transgenic mass-reared APHIS strain of PBW. Transgenic male moths had significantly lower response rates to pheromone traps than APHIS strain males after 1, 3, 7 and 10 days on cotton plot field cages. Transgenic female moths placed on mating stations in direct mating competition with non transgenic PBW females had significantly lower mating success when exposed to a population of equal numbers of EGFP and APHIS strain males released 24 hours prior to female placement in the mating stations. Test results suggest that the competitive fitness loss in our transgenic strain of PBW is most likely associated with the transgenic marker gene due to inbreeding depression of the strain, transgene insertion, or EGFP protein expression and/or the production of the protein. Under the conditions of our test and the parameters evaluated, the loss in competitive fitness that was demonstrated by this transgenic strain of PBW reduces its value as a candidate for implementation into the PBW SIT/ Eradication Program as a genetic marker strain for use in a proposed new Program strategy, F₁ sterility.