Evaluation of Matured Larval Weight and Larval Duration of New Breeding Lines of Bombyx mori L

Abstract

We planned to conduct this study with the main aim to develop bivoltine breeds for our tropical climatic conditions by 
using silkworm breeds with known genetic backgrounds (KA, NB18 and PM) in various hybrid combinations and 
incorporating them over generations, followed by backcrossing and adequate selection of different generations with the 
objective of profitability and productivity. The isolated Bivoltin lines (R1 and R2) were reared with their parental races at 
different times of the year to evaluate their stability in the expression of commercial traits. For the present breeding 
program, the purebred Bivoltine Kalimpong-A (KA), which spin white oval cocoons, New Bivoltine18 (NB18) white 
cocoons with rotating dumbbells and Multivoltine Pure Mysore (PM), the yellow pointed cocoons of the mulberry 
silkworm Bombyx mori L., Selected. One-way and three-way crosses were made using the above three breeds. The first 
single cross comprised KA females and PM males. The second unique cross comprised NB18 females and PM males. 
Selection was performed at the egg, larva, pupal, and cocoon stages over the course to determine the desired traits. The 
offspring of F from the respective crosses were backcrossed with their respective bivoltine males to improve commercial 
traits. Heterosis in the F1 generations of crosses, including NB18 and PM, was determined by the mean score of the parents 
(MPV) and the best score of the parents (BPV). A significant test for heterosis was performed using a standard ANOVA 
table. Based on the results of our study, it was found that the performance of the characters, viz. The weight of mature 
larvae and the duration of the larvae over generations do not simply increase or decrease regularly, but fluctuate 
irregularly. The reason for this variation may be due to random genetic drift, sampling errors in estimating generational 
means, selection pressures, and environmental factors. Therefore, inbreeding variations due to random drift and sampling 
errors could be reduced by increasing the number sampled and selected.