Determination of Optimum Mulberry Silkworm Larvae Bed Spacing on Feeding Tray using Shelf Rearing Technique

Abstract

Bed spacing is an important silkworm rearing practice to ensure the hygiene of silkworms in order to protect from disease infection and to ensure them good feeding appetite. Different stages of silkworms require different bed space. 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 silkworms, to keep the worms healthy and productive. The treatments used for examining the appropriate bed spacing 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 bed spacing used for examining the mature aged silkworm larvae was 600, 500, 400, 300, 200 and 100 per feeding tray (60cm X 90cm size) using silkworm shelf rearing technique to evaluate the effects of mulberry silkworm bed spacing on different silkworm strains.1^st and 2^nd larval instars 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 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 bed spacing was observed in young, medium and mature silkworm larval stages of silkworm strains. Larval mortality rate was significantly (P < 0.05) reduced when young, medium and mature larval stages of mulberry feeding bivoltine silkworm strains (Korean bivoltine and Kenyan bivoltine silkworm strains) reared in a group of 400 to 1000 worms, 400 to 800 worms and 300 to 500 worms respectively in a 60 cm X 90 cm feeding tray of shelf rearing method. A significant (P < 0.05) reduction of larval mortality was recorded from mulberry multivoltine Vietnamese silkworm strains in a bed spacing of 400 to 1200 larvae for young larval stages, 400 to 1000 larvae for medium larval stages and 300 to 600 larvae for mature larval stages. 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 silkworm strains.

Keywords: bed spacing, silkworm strains, feeding tray, larval instars, larval mortality, shell weight, silk ratio