Authors : Hema Dhirwani, Mohan K. Rathod and Manoj M. Rai
Page Nos : 154-155
Description :
Effect of Bt toxin on the development and economic parameters of silk cocoons have been evaluated. Silkworm larvae at second, third, fourth and fifth instars inoculated with Bt spore commercial formulations having 5x107spore /mg. The amount of toxin ingested was about 0.025 mg, 0.050 mg, 0.25 – 0.375 mg, 1.75- 2.00mg and 2.475 – 2.5mg by second, third, fourth and fifth instars respectively. Late larvae ingested large quantity of Bt toxin resulting into acute disease and in the infected forth instar showed involuntary contraction of muscles, paralyzed and distressed. All the stages, second, third, fourth and fifth instars inoculated with Bt toxin exhibited weight loss due to infection during development. The highest mortality (90%) recorded at third instar larvae and lowest in second instar. Two fifth instar inoculated larvae were able to spin the cocoon but enabled to transform into pupa and died. During fifth instar LD50 was 2.38mg, which was approximately 68 times higher than required for second instar. Changes in the total body protein noticed on the second day of inoculation. Inoculation using different doses of Bt toxins, increased protein level drastically to 1.7 times in second, 2.2 times in third, 2.4 times in fourth and 1.7 times (128.3mg) in fifth instar treated as compared to 76.8mg in control.
Keywords: Bacillus thuringiensis, Bt toxin, silkworm, Bombyx mori
