Bacillus thuringiensis protein Cry6B (BGSC ID 4D8) is toxic to larvae of Hypera postica

Insecticidal proteins produced by strains of Bacillus thuringenesis are specific toward target pests. One of the Bt proteins, Cry 1Ac has been used successfully for controlling crop predation by polyphagous pests Helicoverpa armigera. Structurally, Bt proteins consist of three domains; domain I and III are fairly homologous in various Bt proteins while domain II is hypervariable. The hypervariable domain II is believed to be responsible for specificity toward target pest. Successful deployment of Bt proteins requires knowledge of its specificity toward the insect. Various Bt proteins have been characterized for activity against coleopteran pests. Some Bt proteins of class Cry6 have been found to be active against potato weevil. We have evaluated the activity of Cry6B protein (BGSC-4D8) against lucerne weevil, Hypera postica, which is a major pest of forage crop Medicago sativa. Results revealed that the purified Cry6B protein is significantly active against the coleopteran pest with LC₅₀ value 280 ng/μl. The leaves coated with the purified Cry6 toxin were three times less damaged as compared with the negative control.