Abstract:Evaluating transgenic Bt maize for resistance to target insect is a key component of research and development as well as the environmental safety assessment of insect resistant transgenic maize. Efficacy of transgenic cry1Ac maize, events BT-X (homozygote) and BT-38, BT-181, BT-43, and BT-105 (segregation populations), expressing Cry1Ac protein, were evaluated both in the laboratory and in the field for controlling the Asian core borer (ACB), Ostrinia furnacalis (Guenée). Enzyme-linked immunosorbent assays was exploited to quantify Cry1Ac protein expressing levels in fresh whorl leaves and silks of transgenic cry1Ac maize plants. The expression levels of Cry1Ac protein were significantly different among the events in the whorl leaves and silks, ranged from 44.07 to 438.00 ng/g fresh weight of the tissue. In addition, the expression level of Cry1Ac protein was significantly low in the silk than in the whorl leaves of BT-X. The survival of larvae fed on whorl leaves of all transgenic cry1Ac maize events, except BT-43, were significantly lower than non-Bt controls, the survival rate ranged from 0.0%-15.3% within 6 or 7 d. However, the survival rate was 62.5% when neonates fed on BT-X silk within 6 d, which was significantly lower than event Bt11 and non-Bt controls. Damage ratings in the field trials indicated that BT-X was highly resistant to ACB. The results demonstrate that transgenic cry1Ac maize events BT-X, BT-181, BT-38 and BT-105 are high toxicity to the ACB and BT-X offers season long protection against ACB in the field.