Susceptibility and Selectivity of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae) to Different Cry Toxins

Effectiveness of four Cry toxins (Cry1Ac, Cry1Aa, Cry1Ab, and Cry1C) on Cnaphalocrocis medinalis (Guenee) (Lepidoptera: Pyralidae), collected from paddy fields in Jiaxing, Zhejiang Province, China, was evaluated in the laboratory. Bioassays showed that C. medinalis had different susceptibilities against four Cry toxins. The LC50 values of Cry1Ac, Cry1Ab, Cry1Aa, and Cry1C against C. medinalis were 0.405, 1.111, 1.939, and 1.246 mu g/ml, respectively. Furthermore, the mortality of C. medinalis against different Cry toxins showed different results over time and LT50 values of Cry1Ac, Cry1Ab, Cry1Aa, and Cry1C against C. medinalis were 1.5, 2.3, 1.6, and 2.2 d, respectively. Preference of the larvae to Cry toxins revealed that C. medinalis larvae had no significant feeding preference on leaves without Bacillus thuringiensis (Bacillales: Bacillaceae; [Bt]) toxin compared with those containing Bt toxin. However, different Cry toxins had different attractive abilities to C. medinalis larvae. During 8 h after infestation, C. medinalis larvae preferred the leaves with Cry1Ab (22.4-27.6%) over those with Cry1Ac or Cry1C.