Indices studies on fifth instar larval population density requirements in the commercial mulberry silkworm, bombyx mori l.

The final larval instar in the mulberry silkworm, Bombyx mori L. is very decisive period in commercial silkworm rearing. Silkworm larval population density, in the final instar stadium is one of the critical factors for successful commercial cocoon crop. Experiments were conducted with two commercial silkworm hybrids, PM x CSR2 and CSR2 x CSR4 to probe into the optimal larval population density requirements for commercial silkworm cocoon crop during fifth instar silkworm larval period. Four important and directly connected characteristics in the fifth instar larval period, fifth instar larval duration, fifth instar larval growth, fifth instar larval unequal percentage and ripening period after fifth instar larval period were considered in determining the larval population density requirements during fifth instar larval period. Results irrevocably signified that the fifth instar larval population density is directly related to three characteristics studied; fifth instar larval period, fifth instar larval unequal percentage and ripening period while the other character, the fifth instar larval growth (weight) is inversely related. The two commercial silkworm hybrids studied differ in their optimum larval population density requirements during the fifth larval instar period for maximum fifth instar larval growth and minimum fifth instar larval duration, minimal larval unequal percentage and minimal ripening period. For confirmation of the hypothesis, data were analyzed for indexing. Based on all the population density regimes studied and indices analysis as well, the results revealed three fifth instar larval density zones; a. un-economic larval density zone, b. optimum larval density zone and c. loss larval density zone. For PM x CSR2, the fifth instar larval density zone of 80 to 90 number of larvae/feet2 was more suited and designated as optimal fifth instar larval population zone while that for CSR2 x CSR4 was 60 to 70 number of larvae/feet2. Further, critical view revealed that the fifth instar larval density of 80 number of larvae/feet2 and 70 number of larvae/feet2 are to be considered as optimum fifth instar larval population densities for PM x CSR2 and CSR2 x CSR4 silkworm hybrids respectively. Results are discussed on the basis of contemporary Indian commercial silkworm rearing.