Abstract：In this study，effects of Bacillus thuringiensis（Bt）broccoli expressing different levels
of Cry1Ac protein on resistance to Cry1Ac-susceptible and Cry1A c-resistant diamondback moth（DBM）
and oviposition behavior were evaluated. The concentrations of Cry1Ac protein in these 3 Bt broccoli
lines were 167 ng·g-1，224 ng·g-1，and 246 ng·g-1 fresh weight，respectively．Untransformed
broccoli plants were used as control．The larval survival rate of diamondback moth on control leaves
was not significantly different between resistant and susceptible DBM. The mortality of Cry1Ac-resistant
DBM was 18% on Bt plants expressing 167 ng·g-1 Cry1Ac protein．The Cry1Ac-susceptible larvae
could not survive on all of the Bt broccoli．There was no significant difference in number of eggs laid by
DBM adults among different Bt broccoli．The development of Cry1Ac-susceptible and Cry1Ac-resistant
DBM on Bt plants was also tested in greenhouse. The results of greenhouse trial were similar to that of laboratory tests.
