Laboratory-selected Bt-resistant insect colonies are important tools for understanding possible Bt resistance mechanisms, fitness costs, and other resistance characteristics. Here, a laboratory strain (AR) of Helicoverpa zea (Boddie), resistant to the Bt protein (Cry1Ac) found in all commercial Bt cotton varieties in the US, was established by selection with activated Cry1Ac toxin. While conducting Bt Cry1Ac selection experiments, percentage mating success in AR (40.91 ± 5.55) was significantly (p≤0.01) reduced over time with selection compared with the unselected parental strain (SC) (72.76 ± 3.68). AR (0.59 ± 0.09) males produced significantly (p≤0.01) fewer spermatophores than SC (1.24 ± 0.11). Further, reciprocal crosses with AR and SC strains show that both sexes in AR have fitness costs. When F₁ AR was reared on diet containing no Bt protein, they had a significantly (p≤0.05) longer larval (AR: 15.01 ± 0.09; SC: 13.94 ± 0.11) and pupal (AR: 12.02 ± 0.12; SC: 11.39 ± 0.1) period (days). Further, AR (74.38 ± 13.46%) produced significantly (p≤0.05) more malformed adults compared with SC (13.87 ± 1.88%) suggesting the potential importance of refuge crops in delaying field resistance development. Additionally, AR and SC were tested on Bt (DPL 555) and non-Bt (DPL 491) cotton squares. AR outperformed SC on Bt squares in terms of 1) percentage of survivors after four (AR-65.55 & SC-40.00) and seven days (AR-45.55 & SC-23.33), 2) length of survival (AR – 25 & SC – 16 days), and 3) larval instars reached (AR-4^th & SC-3^rd instars). However, AR could not develop to pupation on Bt cotton, even with >150-fold resistance to Cry1Ac toxin (based on artificial diet bioassays). Further, significantly (p<0.05) lower percentage of AR (25%) larvae reached pupation on non-Bt cotton compared with SC (31%). This study shows that there are tremendous fitness costs associated with Cry1Ac resistance in H. zea when feeding on Cry1Ac and on Bollgard^®, and even after selection pressure is removed or tested on non-Bt cotton, fitness costs remain. These results aid in understanding why this major pest of cotton and corn has not yet evolved Bt resistance.