Evolution of resistance by insects is the main threat to the long-term use of Bt cotton that produces Bacillus thuringiensis (Bt) toxin(s). Although none of the target pests have yet to develop resistance in the field to Bt cotton, laboratory selection studies with tobacco budworm (TBW), pink bollworm (PBW) and cotton bollworm (CBW) have indicated the inherent capacity of insects to adapt to these toxins. However, attempts to study the evolution of Bt resistance in CBW, Helicoverpa zea have not been as successful as other target pests. Because each species has different resistance characteristics, potentially impacting resistant management strategies, characterizing Cry1Ac resistance in CBW is critical, especially because Bollgard^® does not express a “high dose” against this pest. Additionally, selection experiments cited above were conducted with MVP II, a commercial formulation containing Cry1Ac protoxin inclusion bodies. Because Bollgard^® expresses solubilized Cry1Ac protoxin that is at least partially activated to toxin upon ingestion; we hypothesize that selection using MVP II may not adequately reflect resistance selection occurring in planta. Therefore, we initiated selection experiments using MVP II and Cry1Ac toxin to compare resistance characteristics using these two different selection pressures. A susceptible laboratory strain was established from a colony obtained from Monsanto. The baseline susceptibility (as measured by the molt inhibitory concentration; failure to molt into second instar after 7 days) of this strain to MVP II and Cry1Ac toxin was 26µg/g and 9µg/g diet, respectively. Subsequently, we selected CBW populations resistant to MVP II (MR-strain) or activated Cry1Ac toxin (AR-strain). The selection criterion was only those larvae that had molted into second instar after seven days of exposure to diet containing crystal protein were transferred to normal diet (no-toxin) and reared until pupation. Current resistant ratios for MR and AR strains are 80 fold (after ten generations) and 50 fold (seven generations), respectively. Selection studies indicated quicker resistance development in the AR strain compared to the MR strain; at all three selection regimes conducted to date, the MR strain required a minimum of three generations to achieve 50% survivability compared to two generations in the AR strain. In addition, there appears to be higher fitness costs involved in MR than AR (as measured by % egg hatch and larval survivability and developmental period). Therefore, if the resistant development is quicker when selected using activated toxin (selection in planta), why do not see resistance in field? Hence, further studies of resistance characters like inheritance of resistance, resistance mechanisms etc, are required before drawing any conclusions.