This valuable study aimed to investigate the larval period duration and its relationship with other biological traits in different breeds and advanced lines of mulberry silkworm (Bombyx mori L.). The study observed a considerable reduction in the duration of larval transition from one instar to another. Thus, in the breeds Parvoz-1 and Parvoz-2, the duration of the transition from the second to third instar decreased by 3.7 hours, whereas in lines 500 and 501, the said duration decreased by 3.4 hours. The larval period shortening was most prominent on day 4 of the fourth instar and on the 7–8 days of the fifth instar. The relationship between the larval period duration and breeding traits revealed an increase in the larval period duration has the complementation of a decrease in phenotypic correlation coefficients (r_p = -0.645 to -0.957) among the proportion of non-viable eggs, egg hatchability, and larval survival. However, an increase in phenotypic correlation coefficients (r_p = 0.859-0.970) was evident between the number of viable eggs, the weight of healthy eggs, the level of larval infection, and cocoon productivity.

Keywords: Mulberry silkworm (B. mori L.), larval period duration, egg productivity, egg hatchability, larval survival, cocoon weight, phenotypic correlation

Key findings: Developing highly productive silkworm (B. mori L.) hybrids with shorter larval periods will contribute to the localization of egg production at the specialized enterprises in Uzbekistan. These measures will increase productivity and improve quality traits of the produced cocoons.