Bacillus thuringiensis cry3Ca1 protein is toxic to the Colorado potato beetle, Leptinotarsa decemlineata (Say)

We expressed the wild-type cry3Aa3 and cry3Ca1 Bacillus thuringiensis genes , which code for insecticidal proteins, in an Escherichia coli expression s ystem. Highly purified preparations of the soluble delta -endotoxins were u sed to perform comparative bioassays with third-instar larvae of the Colora do potato beetle (CPB). Acute mortality data showed that Cry3Ca1 (LD50 = 32 0.1 ng) was 2-fold more toxic than Cry3Aa3 (LD50 = 672.9 ng). We also compa red the chronic effects of sublethal doses of these toxins by measuring the consumption of untreated foliage and monitoring survival and development f or 6 days after intoxication. No significant additional mortality was recor ded, but we found that surviving larvae fed Cry3Ca1 consumed foliage at a s lower rate than the larvae fed Cry3Aa3, suggesting more damage to their dig estive epithelium. This study, the first assessment of the toxicity of cry3 Ca1 in third-instar CPB, suggests cry3Ca1 will prove useful for the control of this important insect pest.