Temporal variability in foliar protein content and trypsin inhibitory levels in two host trees of tropical Tasar silkworm Antheraea mylitta, Drury

Aim: Variation in total soluble proteins and protease inhibitor levels were investigated to determine nutritional and plant defense status in different leaf types of Terminalia arjuna (Roxb.) Wight and Arn., and Schleichera oleosa (Lou.) Oken, two host tree species of the economically important, nonmulberry Tasar silkworm, A. mylitta. Methodology: Quantitative spectrophotometric assays based on diagnostic amidolytic substrates were conducted to assess serine protease inhibitor activities in young, semi-mature and mature leaf types. A microplate quantification assay for total protein estimations was used with leaf types sampled over a year. Efficacy of total trypsin inhibitor and chymotrypsin inhibitor activities detected in T. arjuna (a primary host plant) was further evaluated on gut extracts of fourth instar A. mylitta and Pieris brassicae L. (a Pierid pest of crucifers) to assess the physiological adaptation of larvae to dietary antifeedants. Molecular provenances with rbcL genes were obtained that are available as NCBI accessions #MN460810 for T. arjuna and #MT010554 for S. oleosa. Results: Intra-specific variations were evident in leaf phenology of two tree species. Generally, young leaf type of both tree species had high levels of total protein and trypsin inhibitory activities, while mature leaf type of T. arjuna had low total protein content and trypsin inhibitor levels. Mature leaf type of S. oleosa had low trypsin inhibitor levels during the months of July and August. Midgut proteases of A. mylitta and P. brassicae were significantly more susceptible (p=0.05) to both trypsin and chymotrypsin inhibitors detected in young and semi-mature leaf types of T. arjuna than the mature leaf type. Interpretation: In this study, differential inhibition of digestive proteases in A. mylitta and P. brassicae by protease inhibitors from different leaf types of T. arjuna, suggested adaptation to dietary antifeedants. Such reports on nutritional quality, foliar antifeedants, phenology and host plant utilization are relevant for strategies to domesticate the tropical Tasar silkworm, A. mylitta.