Determination of Dose Specific Susceptibility of Different Larval Instars and Effect on the Cocoon Economic Traits of Bombyx mori L. to Bacillus thuringienesis Var Sotto

Determination of Dose Specific Susceptibility of Different Larval Instars and Effect on the Cocoon Economic Traits of Bombyx mori L. to Bacillus thuringienesis Var Sotto B. Satyanarayana and S. Sankar Naik * Department of Sericulture S. K. University, Ananthapuramu E. mail Id of Corrosponding author sathiserisk@yahoo. in Sericulture is one of the promising means of livelihood, especially for rural people. The sericulture is being practiced in indoor condition and the silkworms are prone to many microbial infections cause different diseases. Among Mulberry silkworm diseases, Bacterial disease caused by Bacillus thuringienesis Var Sotto is causing economic loss to sericulturists. Infection of varied concentrations of B. thuringienesis on different larval instars and effect on cocoon economic traits of silkworm, Bombyx mori L. were studied. Fifteen ml of prepared B. thuringienesis inoculums of different concentrations were smeared evenly on mulberry leaves separately, fed to silkworm larvae of different instars and data was collected. The first instar larvae were more susceptible to bacterial disease which is witnessed with high mortality ranged from 38.33 % to 92.33 %. Whereas, V instar silkworm larvae were relatively less susceptible with low mortality ranged from 7.00 % to 47.67 % at the concentrations ranged from 1 x 10-1 to 1 x 10-8 Cells/ml, respectively. Dose specific mortality indicated that the larvae of same age were more susceptible to the higher concentration of the B. thuringienesis. High LC50 value (1.2 x 10-8 Cells/ml) was observed in case of V instar silkworm followed by IV and III with 1.6 x 10-7 Cells/ml and 2.1 x 10-4 Cells/ml values, respectively. Low LC50 value (3.8 x 10-2 Cells/ml) was observed in I instar silkworm. Silkworms infected in lateral stages manage to complete its life cycle but the cocoon characters are affected significantly. The cocoon characters and interaction of IV instar inoculation and V instar inoculation were significantly effected at Pless than0.01 and Pless than0.05 level, with 1 x 10-7 Cells/ml B. thuringienesis concentration. Bacillus thuringienesis, Bombyx mori, Susceptibility, LC50 value, Mortality