Resistance Performances of Transgenic Bt Rice Lines T2A-1 and T1c-19 Against Cnaphalocrocis medinalis (Lepidoptera: Pyralidae)

The transgenic Bacillus thuringiensis (Bt) rice, Oryza sativa L., lines T(2A)-1 and T1c-19 expressing Cry2A* and Cry1C* from 'Minhui 63' (MH63) were evaluated for resistance to newly hatched and third-instar larvae of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), by using detached leaf laboratory bioassays. Both T(2A)-1 and T1c-19 rice showed high C. medinalis resistance; however, the lethal time (LT)50 of larvae fed with T(2A)-1 rice was significantly longer than that of larvae fed with T1c-19 rice, implying T1c-19 rice was more toxic to C. medinalis larvae. Larval mortality after 4 d on nitrogen-free MH63 was 25.5% compared with 2.4% mortality on high nitrogen fertilizer (250 kg N/ha) plants. Larval mortality on high nitrogen T(2A)-1 plants declined by 20% compared with nitrogen-free plants. However, resistance in T1c-19 plants was unaffected by nitrogen fertilizer. C. medinalis moths preferred MH63 at both the seedling and grain milk stages for oviposition but not the T1c-19 and T(2A)-1 Bt rice lines.