Differential activity and activation of Bacillus thuringiensis insecticidal proteins in diamondback moth, Plutella xylostella

Whole-crystal preparations from strains HD-1 and HD-133, activated Cry 1Ab and Cry 1C toxins as well as Cry 1Aa, Cry 1Ac, Crys 1D, and Cry 2Aa protoxins were tested for toxicity to 2nd-instar larvae of the diamondback moth, #Plutella xylostella#. Mortality data recorded after 2 and 5 days provided different results that were related to differential rates of solubilization, activation, and degradation of insecticidal crystal proteins. The two most active proteins are Cry 1Ab and Cry 1C, which are both present in HD-133. The Cry 1Ab protoxin is activated within 2 days, whereas activation of the Cry 1C protoxin occurs between 2 and 5 days. HD- 133 is more active than HD- I immediately after infection and remains toxic over 5 days owing to the sequential activation of its crystal components. Solubility properties of crystals and rates of activation of protoxins influence the overall toxicity of HD-1 and HD-133 to the diamondback moth