BIOLOGICAL CONTROL OF MYLLOCERUS SUBASCIATUS GUERIN INFESTING BRINJAL (SOLANUM MELONGENA L.) USING BACILLUS THURINGIENSIS SSP.TENEBRIONIS

In Karnataka and other neighbouring states of South India, Coleopteran pest Myllocerus subfaciatus infesting brinjal (Solanum melongena L.) has assumed a major pest status often resulting in 100% crop loss. Chemical control methods are not ecofriendly and have several problems of resistance development and residual toxicity. Therefore, biological control methods were tried to control the insect. To start with methods were standardized to rear the insect in the laboratory. Insecticidal crystal protein was extracted from Bacillus thuringiensis ssp. tenebrionis grown on the sporulation medium. The specific activity of the insecticidal protein in 50 ml 48 h old culture containing 10^-9 cells was 2.5 µg mL-1. Bioassay was standardized in replicated sets to test the insecticidal property of the toxic protein on Myllocerus larvae by soil drenching and root dip methods. In the soil drenching procedure, the freshly emerged larvae from the egg were transferred to the pots containing the brinjal seedlings, which was treated with 10 mL of 10² to 10^-4 ng/ mL concentrations of Bt toxins. In the root dip method, the root tissue of known size treated with the same concentrations of Bt toxins and dried in air were fed to the larvae. Suitable controls were compared. Mortality was recorded after 24 hours. Lethal concentration of Bt was determined by Probit analysis. The LC₅₀ values were 2.69 ng mL^-1 and Fiducial limit was 1.4-511 ng mL^-1. In the root dip method LC₅₀ value was 44.936 ng mL^-1 and Fiducial limit was 20.4-110.5 ng mL^-l . Bt toxins (25 ng/mL concentrations) was also tested in Myllocerus infested field of brinjal ‘Purple Long’plants in 5m x 5m replicated plots by soil drenching. The toxin from Bacillus thuringiensis ssp. tenebrionis was effective against Myllocerus subfasciatus infesting brinjal crop.