Abstract: Consumption and utilization of the 5th instar larvae of Mythimna separata (Walker) feeding on the leaves of transgenic Bacillus thuringiensis corn were assayed in the laboratory. Two Bt corn hybrids with events MON810 and Bt11 expressing CryIAb protein and their nonBt controls were employed in the bioassays. Results showed that the survival rate of the 5th instar larvae of M. separata was significantly lower when fed on MON810 and Bt11 leaves. The food ingestion was 88.1 mg and 115.4 mg, respectively, when larvae fed on MON810 and Bt11, whereas 653.6 mg and 715.4 mg when fed on non-Bt corn DK647 and NX4906 separately, at 4th day. The larvae exhibited an average weight loss of 12.2 mg and 7.4 mg when fed on MON810 and Bt11 leaves, and showed an average weight gain of 100.4 mg and 119.9 mg when fed on two non-Bt controls at 3rd day. The efficiency of conversion of ingested food (ECI) and efficiency of conversion of digested food (ECD) by the larvae feeding on the two Bt corn leaves were significantly lower than by the larvae feeding on non-Bt corn hybrids. This indicated that the Bt corn significantly restrained the feeding, food consumption and utilization of the 5th instar larvae of M. separata. However, the approximate digestibility (AD) by the larvae was much higher when fed on Bt corn leaves than on non-Bt corn controls, and a possible explanation is that the digestion function of the larvae fed the Bt corn leaves was restrained as a result of the toxication by Bt toxin.

Key words: Mythimna separata; Bt corn, CryIAb protein, food ingestion, food utilization