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Differential activity and activation of Bacillus thuringiensis insecticidal proteins in diamondback moth, Plutella
R Monnerat1, L Masson, R Brousseau
1Cenargen-EMBRAPA, SAIN-Parque Rural CP, 02372 CEP, 70770-970 Brasilia DF, Brazil.
Abstract:
Whole-crystal preparations from strains HD-1 and HD-133, activated Cry1Ab and Cry1C toxins as well as Cry1Aa, Cry1Ac, Cry1D, and Cry2Aa 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 Cry1Ab and Cry1C, which are both present in HD-133. The Cry1Ab protoxin is activated within 2 days, whereas activation of the Cry1C protoxin occurs between 2 and 5 days. HD-133 is more active than HD-1 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.
Insights
Bacillus thuringiensis (Bt) toxins Cry1Ab and Cry1C are most effective against diamondback moth larvae. Their sequential activation in HD-133 strain enhances insecticidal activity over time.
Area of Science:
- * Molecular biology and entomology, focusing on microbial insecticides.
Background:
- * Bacillus thuringiensis (Bt) produces insecticidal crystal proteins (ICPs) effective against various pests.
- * Different Bt strains and their Cry proteins exhibit varying toxicity profiles against specific insect targets.
Purpose of the Study:
- * To evaluate the toxicity of whole-crystal preparations and specific Cry protoxins from Bt strains HD-1 and HD-133 against Plutella xylostella larvae.
- * To investigate the influence of protoxin activation and solubilization rates on insecticidal efficacy.
Main Methods:
- * Testing of whole-crystal preparations and activated toxins/protoxins against 2nd-instar Plutella xylostella larvae.
- * Monitoring larval mortality at 2 and 5 days post-exposure.
- * Analysis of differential rates of solubilization, activation, and degradation of Cry proteins.
Main Results:
- * Cry1Ab and Cry1C toxins, present in HD-133, showed the highest activity against Plutella xylostella.
- * Cry1Ab protoxin activation occurred within 2 days, while Cry1C activation took 2-5 days.
- * HD-133 demonstrated greater and sustained toxicity compared to HD-1 due to sequential activation of its crystal components.
Conclusions:
- * The differential activation rates and solubility of Bt crystal proteins significantly impact toxicity to diamondback moths.
- * Strain HD-133 exhibits enhanced and prolonged insecticidal activity against Plutella xylostella owing to sequential Cry protein activation.