Influence of host plant (Terminalia arjuna)defences on the evolution of feeding behaviourin the tasar silkworm

Abstract

Both under indoor and outdoor rearing conditions, early instars of Antheraea mylitta showed differential preference for eating towards developmentally different leaves of host plant, Terminalia arjuna. Semi-mature leaves were preferred by first, second and third instar of A. mylitta. Nutritional-value study of leaves of different age groups with respect to soluble protein and electrophoretic profile showed that young leaves are nutritionally rich compared to semi-mature and mature leaves. However, growth response and survival of larvae were better on semi-mature leaves compared to young and mature leaves. When analysed, semi-mature leaves showed protease inhibitor activity intermediate between young and mature leaves. This observation suggests optimal defence theory, where young and semi-mature leaves having high fitness and high probability of attack tend to have higher concentration of defence metabolites. Differential inhibition of midgut and bovine proteases by host plant protease inhibitor indicates that the tasar silkworm might have detoxified or evolved proteases that are insensitive to the leaf protease inhibitor of the host plant. Thus the differential feeding behaviour of larvae of tasar silkworm is an adaptation for coexistence of the insect and its host plant.