NUTRIENT DYNAMICS AND SUSTAINABILITY OF WILD TASAR SILKWORM ON SAL FLORA

Abstract

Nutrient content in tasar host plant foliage is one of the important factors for sustainability of tasar silkworm, Antheraea mylitta D. Various sericigenous flora is abundantly found in the forests of tropical belt in India for its survivability. An investigation on nutrient dynamics of primary tasar host plants was carried out to understand the sustainability of wild tasar ecoraces on these host plants. Leaf analysis of primary tasar host plants viz. Terminalia arjuna (Arjun), Terminalia tomentosa (Asan) and Shorea robusta (Sal) by following digestion method and using Atomic Absorption Spectrophotometer reveals the fact that there are remarkable differences in intra and inter nutrient contents in the foliage of host plants of Sal and Arjun-Asan. Average nutrient contents viz. N, Fe, Zn and Mn were found more in Sal with significant value of difference in case of Mn ((t-test significance at less than 0.01%) than compared to Asan and Arjun whereas contents viz. K, P, Mg & Cu were found less or with no significant difference. On the basis of chemical analysis of 550 leaf samples of different status and different nutrient level in leaves of primary tasar host plants, it was inferred that survivability and sustainability of all wild eco-races of tasar silkworm depends on the suitable range of nutrient dynamics of its host plant. Concentration of nutrients in plant associated with plant itself was found influenced with plant part, age, leaf position on shoot and type of shoot. Content of Mn in leaf of Shorea robusta found greatly varied within the plant with difference in the height and position of the leaf. Toxic level of manganese content was found in leaves of lower position and lower twigs of the Sal plant whereas the level of this element in leaves of upper twigs and in top position of Sal tree was found in suitable and safe range for tasar silkworm. Tall Sal tree is known to be the origin of all wild eco-races of tasar as it fits both biotic and abiotic factors for tasar silkworm. When tall Sal trees are cut, coppice and dwarf Sal plant develop which does not fit for safe range of essential nutrient content of manganese for tasar insect. Manganese content in leaf of coppice Sal plant of tender, medium and mature was found as 1315.25±123.09, 1560 ± 167.46 and 1923.17±318.01 respectively whereas it was found as 382.25±37.92, 612.42± 51.38 and 712.08±84.00 in tender, medium and mature leaf of tall Sal tree. Mn content in leaf having different maturity level of other two primary tasar host plants, Arjun and Asan was found in the range of 41 ppm to 105 ppm only. Manganese concentration in leaf of coppice plants of Shorea robusta was found in much higher level than compared to other two primary tasar host plants, Terminalia tomentosa and Terminalia. arjuna. The same ecorace when reared in other primary host plants having lower nutrient of N, Fe, Zn & Mn and in lower altitude, survivability of the silkworm and quality and size of the tasar cocoon diminishes. Hence, it is the need of the hour that Sal jungles should be conserved for making dense Sal flora having larger height and size so that important wild tasar silkworm can be conserved in the tropical forests.