Pro-oxidative challenges and antioxidant protection during larval development of non-mulberry silkworm, Antheraea mylitta (Lepidoptera: Saturniidae)

Abstract

The non-mulberry silkworm, Antheraea mylitta Drury, 1773, is important for the silk industry. Its larvae are phytophagous and pass through five stages (1st–5th instar) during larval development. Cellular events during their development contribute to increased levels of pro-oxidants. Antioxidant defences are, therefore, of critical importance in minimising oxidative damage. Thus, in the present study, stage-specific oxidative challenges and relative levels of antioxidant defences have been assessed during the larval development of A. mylitta. The overall results indicate a progressive decrease in oxidative threat during larval ontogeny. Comparatively high activity of superoxide dismutase (SOD) and catalase (CAT) observed in the 1st instar larvae indicates an adaptive antioxidant response, which could attenuate the elevated oxidative challenges. CAT activity remained unaltered in the midgut during transformation of the larvae from 4th–5th instar, and it was below detection level in serum. Glutathione S-transferase (GST) activity did not exhibit a specific trend; however, it showed tissue specificity in advanced larvae. Glutathione (GSH) content was progressively enhanced during development and exhibited a compensatory function with ascorbic acid (ASA), thus substantiating the role of a GSH–ASA redox couple. Findings of the study imply that early larvae (1st–3rd instar) encounter considerable degrees of pro-oxidative assault and get protection from enzymatic antioxidants. In contrast, advanced larvae receive combined protection from enzymatic and nonenzymatic antioxidants. Therefore, it is assumed that oxidative stress during larval development of A. mylitta is stage-specific and, accordingly, the antioxidant defences are strategic in providing protection to the developing larvae.

Keywords:

• Antioxidant enzymes
• larval progression
• lipid peroxidation
• reactive oxygen species
• tasar silk worm

Acknowledgements

The authors are thankful to Prof. S. K. Dutta, former head, Department of Zoology, North Orissa University, Baripada, India, and Prof. G. B. N. Chainy, former head, Department of Zoology and Biotechnology, Utkal University, Bhubaneswar, India, for the provision of laboratory facilities, which enabled us to complete this work. We thank Mr. Jajati Rout, Senior Technical Inspector, State Silk Board (Baripada, Odisha), for providing the larvae. Financial assistance from the Department of Biotechnology, the Government of India and a DST-PURSE grant (DST-India) to the P.G. Department of Biotechnology, Utkal University, is gratefully acknowledged. We are sincerely grateful to Professor Jatin K. Nayak, Department of English, Utkal University, Bhubaneswar, for copy editing this manuscript.