Abstract: Effects of transgenic Bacillus thuringiensis corn on survival and growth of the beet armyworm, Spodoptera exigua (Hübner) larvae, were evaluated with laboratory bioassay and field tests. Two Bt corn hybrids of events MON810 and Bt11 expressing Cry1Ab toxin and their non-Bt controls were employed. The results showed that the neonates of the beet armyworm could not survive when fed on whorl leaves, tassels and silks separately of the two Bt corns, in laboratory bioassay. A small number of  neonates could survive and develop to pupate when fed on tassels and silks of MON810 and Bt11: the pupation rate is 5.2% and 2.1% with the emergence rate of 2.1% and 1.0% on MON810 and Bt11 tassels; 1.0% and 2.1% larvae pupates without emergence on MON810 and Bt11 silks, respectively. The duration for the larvae from neonate to pupae was 17 d and 28.5 d when fed on silks of MON810 and Bt11, compared with 14.0 d and 16.0 d on the corresponding non-transgenic isogenic controls, respectively. The larvae fed on tassels and silks of Bt corns had significantly lower weights than that fed on non-Bt controls in 7 days after infestation. The weight of the larvae fed on the non-Bt control husks of MON810 and Bt11 was 27.6 and 52.9 times the weights of the larvae fed on MON810 and Bt11, respectively. Development of the beet armyworm larvae fed on Bt corn was significantly delayed. Resistance level of the Bt corn whorl tissues to the 4th instar larvae was low. No significant difference was found in the pupation rate for the 4th instar larvae fed on the whorl leaves of MON810 (71.7%) and its non-Bt control (75.0%), but otherwise for those fed on Bt11 (56.7%) and its non-transgenic hybrid (85.0%). The weights of female and male pupae and the percentage of emergence when the 4th instar larvae fed on the Bt corn were significantly lower than that fed on non-Bt controls. Larval survival rate and the percentage of injured ears when larvae fed on MON810 and Bt11 silks were significantly lower compared with non-Bt controls assayed 10 d after the inoculation of the neonates in the field tests.

Key words: Spodoptera exigua;Bt corn, Cry1Ab toxin, survival rate, developmental period, control efficacy