Determination of Optimum Eri Silkworm Larvae Population Density in Feeding Tray using Shelf Rearing Technique

Abstract

Population density during the different stages of larval growth and development is one of the crucial issues for successful commercial cocoon crop of silkworms. Using appropriate population density ensures the hygiene of silkworms in order to protect from disease infection and to ensure them good feeding appetite. Different stages of silkworm larvae require different population density or bed space during their growing period in the rearing bed. As worms increase in size, there is overcrowding and overlapping each other that leads to underfeeding, creating a microclimate for disease spread and could also lead to suffocation. Hence, appropriate bed spacing is essential to silkworm larvae, to keep them healthy and productive. The treatments used for examining the appropriate population density of young and medium aged silkworm larvae were 1200, 1000, 800, 600, 400 and 200 per feeding tray (60cm X 90cm size).  Another arrangement of population density used for examining the mature  aged silkworm larvae were 600, 500, 400, 300, 200 and 100 per feeding tray (60cm X 90cm size) using  silkworm shelf rearing technique to evaluate the effects of population density on different larval stages eri silkworm strains. 1^st and 2^nd larval instars/stages as young age, 3^rd and 4^th larval instars as medium age, 5^th larval instar as mature age were considered in the study. Observations on larval mortality, single larval weight, single shell weight, and silk ratio from different eri silkworm strains were carefully noted for each treatment and replications. Three replications were used for each treatment. Statistically significant variation in mean larval mortality rate among population densities was observed in young, medium and mature silkworm larval stages of silkworm strains. Larval mortality rate was significantly reduced when young, medium and mature larval stages of castor feeding eri silkworm strains (Indian eri and Vietnamese eri) reared in a group of 400 to 800 worms, 400 to 600 worms and 300 to 400 worms respectively in a 60 cm X 90 cm feeding tray of shelf rearing method. Bigger Larval weight, bigger shell weight and higher percentage of silk ratio are important cocoon yield quality parameters for silkworm strains. Significant (P < 0.05) variations were observed among population densities for these important variables in all the tested eri silkworm strains.

Keywords: Population density, silkworm strains, feeding tray, larval instars, larval mortality, shell weight, silk ratio