Toxicity of Bacillus thuringiensis crystal proteins against eri silkworm, Samia cynthia ricini (Lepidoptera: Saturniidae)

• Efficacy of Bacillus thuringiensis (Bt) proteins against Samia cynthia determined.
• Cry1Aa, Cry1Ab, Cry1Ac proteins highly toxic to eri silkworm.
• Castor transgenics harbouring Bt genes should be bioassayed for eri silkworm.

Ten purified crystal proteins of Bacillus thuringiensis (Bt) were tested at concentrations ranging from 2.93 to 3000 ng/cm2 for their toxicity to eri silkworm through protein paint bioassays using castor leaves. Based on LC50 values, Cry1Aa (2.6 ng/cm2) was highly toxic followed by Cry1Ac (29.3 ng/cm2) and Cry1Ab (68.7 ng/cm2). The Cry1Ca and Cry1Ea proteins were moderately toxic to eri silkworm larvae and resulted in 23% and 28% mortality, respectively at the highest concentration tested (3000 ng/cm2). Only reduction in larval weight was observed with Cry2Aa, Cry1Da and Cry9Aa proteins while Cry3Aa and Cry1Ba proteins were found to be nontoxic.

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