Screening for Bacillus thuringiensis Crystal Proteins Active against the Cabbage Looper, Trichoplusia ni (original) (raw)

2000, Journal of Invertebrate Pathology

Toxicity tests were performed to find among Cry1 and Cry2 Bacillus thuringiensis crystal proteins those with high activity against the cabbage looper. Tests were performed with neonate larvae on surface-contaminated artificial diet. The crystal proteins found to be toxic were, from higher to lower toxicity: Cry1Ac, Cry1Ab, Cry1C, Cry2Aa, Cry1J, and Cry1F (LC 50 of 1.1-4.1, 3.4 -4.4, 12, 34, 87, and 250 ng/cm 2 , respectively). Cry1B, Cry1D, and Cry1E can be considered nontoxic (LC 50 higher than 2500 ng/cm 2 ). Cry1Aa was moderately toxic to nontoxic, depending on the source (LC 50 of 420 ng/cm 2 from PGS and 8100 ng/cm 2 from Ecogen). In vitro binding assays with trypsin-activated 125 I-labeled Cry1Aa, Cry1Ab, and Cry1Ac crystal proteins and brush border membrane vesicles from midgut larvae showed a direct correlation between toxicity and binding affinity. Heterologous competition experiments indicated that Cry1Aa and Cry1F bind, though only at very high concentrations, to the Cry1Ab/ Cry1Ac shared high-affinity binding site.