Effectiveness of three Bt corn events against feeding damage by the true armyworm (Pseudaletia unipuncta Haworth)

A 3-yr study (2002-2004) was conducted to evaluate the resistance of three Bt corn events to herbivory damage by the armyworm, Pseudaletia unipuncta (Haworth). Resistance was assessed by damage ratings and fresh mass measurements. Greenhouse studies were run in 2002 and 2004, and a field study was conducted in 2003. Hybrids expressing the Cry1A(b) insecticidal protein, Mon810 and Bt176 events, and their near isolines, as well as the TC1507 event, which expresses the Cry1F protein, were evaluated. Bt hybrids suffered less damage in all 3 yr and had higher fresh masses in 2002 and 2003 than the non-transgenic isolines. In 2002 and 2003, hybrids expressing the Cry1A(b) protein were significantly less damaged than the hybrid expressing Cry1F. In both 2002 and 2004, the Mon810 event suffered less damage than the Bt176 event, despite expressing the same Cry1A(b) protein. Bt corn, especially the Mon810 event may be used as an effective method of preventing P. unipuncta herbivory damage in corn. Key words: True armyworm, Pseudaletia unipuncta, Bt corn, Cry1A(b), Cry1F, epistasis