APPLICATIONS OF INSECT GROWTH REGULATORS IN SERICULTURE AND AS FOOD SUPPLEMENTS

A. Banerji

School of Biotechnology, Amrita Vishwa Vidyapeetham, Amritapuri, Kollam Dist. 690525

Dr. Asoke Banerji

Dr. Asoke Banerji is Distinguished Professor at Amrita School of Biotechnology, Amrita Vishwa Vidyapeetham, Kerala. The main thrust of research activities of Professor Banerji’s group has been directed towards emerging areas of natural product chemistry and Biotechnology. He gave a new direction to the natural product research by purpose-oriented investigation of the plant extracts following reverse pharmacological approach. During the course of research work, an array of natural products belonging to different groups (medicinal as well as other activities) were isolated and characterized. Professor Banerji has several patents to his credit. In addition to medicinal compounds, he has contributed to other areas also such as natural dyes, biopesticides, bioremediation, biotransformation, high-value agrochemicals. As a result of screening of indigenous flora, several insect growth regulators (IGR), both phytoecdysoids and juvenoids, were isolated and characterized. Processes for their preparation in commercial scale have been developed. Some of the isolated phytoecdysoids are being used in the commercial formulations for use in sericulture  isolated. A list of selected publications of Dr. Banerji, provided at the end of this article will give the readers an idea about the span of his work in phytochemistry. 

SUMMARY

Indigenous plant sources of insect growth regulators (both phytoecdysterones and juvenoids) have been identified. Viable methods for their commercial preparations have been established. Optimum doses and timing of application of IGRs for sericulture determined. In addition to sericulture, phytoecdysterones are also useful as food supplement (nutraceuticals) or for fortifying existing health foods/supplements and important biochemical tool for genetic engineering. 

INTRODUCTION

Insect growth regulators (IGRs) such as juvenile and moulting hormones or their analogs (juvenoids and ecdysoids) when used judiciously, have been found to be useful in sericulture industry. In addition, ecdysoids also show a variety of other uses such as insecticidal, as biochemical tool in gene expression studies, as wound healing and anabolic agents ( body building agents with enhancing  protein synthesis), as nutraceuticals and cosmetics (hair growth) IGRs occur in insects in very small amounts and are not practical source for these phytochemicals. However, with the discovery of their occurrence in significant quantities in some plants, IGRs and their analogs became easily available in substantial amounts. As a result, many new bioactivities of ecdysoids and juvenoids were discovered. Besides  use in sericulture, they have found applications in apiculture and aquaculture (prawns). Ecdysoids show remarkable anabolic activities in human and are very much in demand as nutraceuticals (food supplements) including body building agent. Realizing the economic potential of IGRs, bioprospection for these compounds from indigenous plant sources was undertaken. Our survey indicated that a large number plants belonging to different taxa contain IGRs. Our focus was on plants showing insecticidal activities and two main IGRs, viz. ecdysteroids (ecdysterone analogs) and juvenoids (juvenile hormone analogs). Suitable bioassays for each of the activities were established and about 500 plants were screened for IGRs. This resulted in the discovery of several sources of IGRs from different geographical locations.

IGRs IN SERICULTURE

India is one of the largest silk producing countries. Mulberry silk accounts for most of the silk produced in India. Three other species namely, Eri, Tasar and Muga are mainly grown in the north-eastern India. India is also one of the major consumers of silk. Sericulture, the agro-industry of cocoon and silk production is the source of income of several marginal farmers of India. However there is a shortfall of 7000 metric tonnes of silk fibre within the country. The silk production in India needs improvement in quantity as well as quality compared to other silk producing countries. Central Sericulture Research and Training Institute (CSRTI), Mysore has been involved in the improvement of the mulberry seri-technology in a holistic way. However there is considerable scope of improving the varieties of silk produced in north eastern India.

Sericulture is a labour intensive agro-based industry which provides additional income to marginal farmers.  Substantial part of labour in sericulture management goes in the picking up of the mature larvae for mounting. The duration of mounting period is quite variable. Duration of the moulting from beginning to end may vary between 48-72 hours. This implies that labour must be available continuously all through the period (day and night) of moulting. Application of exogenous ecdysoids helps in the synchronization and reducing the time for spinning. Its application hastens the maturation without affecting the quality and yield of silk. Application of ecdysoids synchronizes and   shortens the period of moulting to 18-24 hours. This helps considerably in the management of sericulture and reduces   the cost of labour. Hastening the moulting period also contributes in the reduction in the consumption in the feeding of mulberry leaves without affecting the yield of silk fibre. Use of juvenoids on the other hand, tend to keep the fifth instar silkworm young by extending the larval period and increasing the silk secretion. It postpones the spinning stage by few hours. Thus when applied judiciously, IGRs can contribute significantly in increasing the silk production.

PHYTOECDYSOIDS IN SERICULTURE

Sampoorna-A commercial phytoecdysoid

 Ecdysoids and their analogs (called phytoecdysones) occur in significant quantities in many indigenous plant sources. A simple bioassay based on sclerotization of house fly last-instar larvae was developed. Several hundred extracts from plants were screened following this bioassay. Initiation of the sclerotization within 24 hr of treatment was indicative of presence of phytoecdysoids (PEC). PECs were isolated following activity- guided fractionation of plant extracts and active principles were isolated . More recently, non-biological methods based on chromatographic, spectroscopic and LC/MS methods have been developed in our laboratory for quick identification and quantification of PECs and their analogs. A convenient method for their isolation has been developed (patent pending). Results of our   screening of plant extracts show that  PECs have wide occurrence in plant kingdom.  In collaboration with CSRTI, Mysore, optimum time and dose of application of PEC have been established. Commercially viable sources of PECs have been discovered for possible application in sericulture industry and other applications such as food supplement (nutraceuticals). Commercially viable process for preparation of PEC in large scale has been developed.  Application of PEC  in the farmers fields have established that there is considerable savings in labour cost . In countries like China, Japan, France, IGRs are in regular use in sericulture.

PHYTOECDYSOIDS AS NUTRACEUTICAL

Amrutha- a commercial phytoecdysoid

Formulations with PECs as active constituents have found use as health promoting products. PECs do not have adverse effects on human health even at gram levels.  They show   anabolic activities and are useful constituents in many commercial food preparations. They are useful adjunct for fortifying many of the currently used beverages and food supplements. They are popular in many countries as natural body building agents. In addition they show a variety of biological applications such as molecular switches, and have potential use in researches on gene expression and related studies.

JUVENOIDS (JH)

The juvenile hormone (JH) activity of plant extracts/isolated compounds were determined using 5^Th instar nymph of red cotton bugs (Dysdercus koenigii).  Juvenoids are analogs of insect juvenile hormones. Several compounds, showing JH activities have been found in many common plants.  Application of JH’s to silk worm prolongs the larval period.  Synthetic JH analogs are in use in sericulture industries in countries such as Japan, China. There is no commercial Indian source for juvenoids.

Samrudhi- a commercial  juvenoid

Imported synthetic JH analogs are expensive. Hence there is a need for identification of cost effective JH formulation for improving silk productivity. Several sources JH analogs from plants have been identified in our laboratory and isolation and characterization of the active principles have been carried out. Eco-friendly economic process for their preparation has also been developed by our laboratory. Based on existing information, it can be predicted that use of IGRs will give a boost to sericulture industry.

PROSPECTS OF USE OF IGRs IN INDIA

IGRs are in use in many countries in sericulture, aquaculture and apiculture. They are in great demand for body building formulations and cosmeceutical preparations. Indian farmers have realised the beneficial effects of IGRs and some preparations have appeared in the market. As a result of our studies several plant –based sources for PECs and JHA have been discovered. Protocols for their application have been developed. Detailed information on the sources, quality control and applications of indigenous IGRs is available for commercial exploitation. Entrepreneurs interested in the commercial exploitation of these products for sericulture, food supplement or as biochemical tool are welcome to contact me at Amrita School of Biotechnology, Amrita Vishwa Vidyapeetham. banerjiasoke@gmail.com or mobile +91 9895527851. 

Select list of publications of Dr. A. Banerji

1.    A. Banerji, G. J. Chintalwar and M. S. Chadha,  Isola­tion of Ecdysterone from Indian Plants, Phytochemis­try,  10, 2225 (1971)

2.     A. Banerji and G. J. Chintalwar, Phytoecdysones and Flavonol Glycoside from  Sesuvium   portulacastrum, Indian J. Chem.,9, 1029 (1971).

3.     A. T. Sipahimalni, A. Banerji and M. S. Chadha,  Biosynthesis and Interconversion of Phytoecdysones in  Sesuvium portulacastrum L. J. Chem. Soc. Chem. Commun., 692 (1972).

4.   A. Banerji and G. J. Chintalwar, Biosynthesis of Bakuchiol, A Meroterpene from Psoralea corylifolia  Phytochemistry, 22, 1945 (1983).

5.   A. Banerji and G. J. Chintalwar, Biosynthesis of Bakuchiol from Cinnamic and p-Coumaric      acids. Phytochemistry, 23, 1605 (1984).

6.      N. K. Joshi, K. M. Lathika, A. Banerji and M. S. Chadha,  Effects of Plumbagin on Prothoracic glands of Dysdercus cingulatus      in "Endocrinological Fron­tiers in Physiological Insect Ecology" (Eds. F. Seh­nal, A. Zabra and D.L. Denglinger) Technical Universi­ty Press, Wroclaw (Poland) pp. 69 (1988).

7.   N. K. Joshi, K. M. Lathika, A. Banerji and ,  M. S. Chadha,  Effect of plumbagin on Growth and Development of Red Cotton Bug, Dydercus Koenigii, Proc. Indian Natn. Sci. Acad., B54, 43 (1988).

8.   V. Ramakrishnan, G. J. Chintalwar and A. Banerji, Environmental Persistance of Diallyl Disulphide, an Insecticidal Principle of Garlic and its Metabolism in  Mosquito,  Culex pipens Quinquifaciatus Chemosphere, 18, 1525 (1989).

9.    A. Banerji and G. J. Chintalwar, Fate of Leucine in the Biosynthesis of Bakuchiol, a  Meroterpene from  Psoralea corylifolia.  Indian J. Biochem. Biphys., 26  394 (1989).

10.  D. L. Luthria, V. Ramakrishnan, G. S. Verma, B. R.  Prabhu and A. Banerji,  Insect Antifeedants for  Atalantia racemosa.  J. Agric. and  Food Chem. 37, 1435 (1989).

11.  57. N. K. Joshi, K. M. Lathika, V. Ramakrishnan, A. Ba­nerji and  M. S. Chadha,  Plumbagin-Induced Inhibition of Ovary Development in  Dysdercus cingulatus.  in "Regulation of Insect   Reproduction IV', Eds. M. Tonner, T. Soldan, B. Bennettova,  Academia Publishing House of the Czechoslovak Academy of  Sciences Praha, pp. 287 (1989).

12.  A. Banerji, Radiosynthesis of 35S-Labelled Bioactive Compounds and their Metabolics, Proceedings of nation­al symposium on nuclear techniques in the study of pesticides in food agriculture and environment,  The University of Acultural Science, Hebbal, Bangalore Feb. 8-10, 1989.

13.  A. Banerji, Insect control by biotechnical procedures - Lessons from plant kingdom, in “Insect  Chemical Ecology” (Ed. I. Hrdy), Academia Praha, pp. 235.

14.  A. Banerji,  Biotechnical Potential of Natural Products,  Bioelectrochemistry and Bioenergetics, 27, 105 (1992).

15.  A. Banerji, Insect Plant Interactions:  Natural Insect Control Agents, Recent Advances in Insect Physiology and Toxicology, 41, Ed. G.T. Gujar, Agricole Publishing Academy, Delhi, (1993).

16.  A. Banerji in Role of Allelochemicals in the Ecodynamics of Insects and Plants. "Biochemical Perspectives in Chemical Ecology of Insects", ed. T. N. Ananthakrishnan, Oxford & IBH Publishing Co., New Delhi, 000 (1995).

17.  G. R. Shivakumar, K. V. Anantha Raman, K. Venkata Rami Reddy, S. B. Magadum, R. K. Datta, S. S. Hussain. A. Banerji and S. K. Chowdhury, Effect of Photoecdysteroids on Larval Maturation and Economic Parameters of the Silkworm, Bombyx mori.,  Indian J. Seric., 34, 46, (1995).

18.  G. R. Shivkumar, K.V.A. Raman, S.B. Magadum, R.K. Datta, S.S. Hussain, A. Banerji and S.K. Chowdhary, Effect of Phytoecdysteroids on  the Spinning, Cocoon and Reeling Parameters of the Silkworm, Bombyx mori L., Allelopathy Journal, 3, 71, (1996).

Note: To read another related article on phytojuvenoid published earlier in this journal, CLICK HERE