Influence of forestry host plants and rearing seasons on silk gland weight of tropical tasar silkworm, Antheraea mylitta (Lepidoptera: Saturniidae) under Doon valley conditions of Uttarakhand in India

Abstract

Tropical tasar silkworm, Antheraea mylitta is a commercial forest silkworm in India that produces tasar silk, but never experimented in Uttarakhand, a Himalayan state of India. A. mylitta express divergent phenotypic characters under different ecological conditions; so, we studied the effect of seven forest tree species in two rearing seasons on variability in silk gland weight of Daba (bivoltine) ecorace of A. mylitta at Forest Research Institute in Dehra Dun, Uttarakhand during 2012 and 2013. We used two-way completely randomized block factorial design and Post HOC Tukey's HSD test to analyse the collected data and there after carried out multiple regression analysis. Results indicated that silk gland weight differed significantly between rearing seasons (DF=1, F=2333.98, p<0.05), host plants (DF 6, F= 1516.25, p<0.05) and their interactions (DF=6, F=7.10, p<0.05). Higher silk gland weight was found in second rearing season than the first on all the host tree species. Terminalia alata fed A. mylitta larvae showed the highest silk gland weight of 8.03 and 9.47 g in first and second rearing seasons, followed by T. tomentosa (7.19 & 9.01g), T. arjuna (6.8 & 8.08 g) and L. speciosa (6.57 & 7.83 g) fed larvae, respectively. Post HOC Tukey's HSD test indicated that silk gland weight of L. speciosa and T. arjuna fed larvae in both the rearing seasons did not differ significantly. E.I. analysis also confirmed that T. alata, T. tomentosa, T. arjuna and L. speciosa are better in their order of merit than T. bellirica, T. chebula and L. tomentosa. Multiple regression analysis indicates that larval weight gain is a strong predictor (β=1.002, t=346.777, p= <0.05) for the silk gland weight of A. mylitta; however, larval duration had significant negative regression weight (β=-0.270, t=-8.436, p= <0.05) on mean weight of silk gland. IntroductionAntheraea mylitta Drury (Lepidoptera: Saturniidae) is a "tasar silk" producing polyphagous forest insect of India, but it has never been experimented in any Himalayan states of India including Uttarakhand. This is the first study on effect of forest tree species, Rainfall alters functioning of microhabitat, which along with soil and other environmental factor affect foliage quality that consequently reflect distinct impact on performance of insect (Mattson and Haack, 1987).In commercial tasar silkworm rearing, larvae should be healthy and their silk glands should be free from any abnormalities to reduce presence of non-spinning silkworms to zero. In the present work, expression of silk gland weight by A. mylitta larvae reared on seven forest tree species in two rearing season has been analyzed. Materials and Methods Study areaThe study was conducted at New Forest, Forest Research rearing seasons and their interaction on Silk Gland Weight (SGW) of A. mylitta. Silk gland of A. mylitta is an ectodermal organ, which produces liquid silk that forms cocoon fibre. Silk gland become secretory prior to hatching and increase their secretory potential by growing in size during larval life (Aru...