Bioethics in India: Proceedings of the International Bioethics Workshop in Madras: Biomanagement of Biogeoresources, 16-19 Jan. 1997, University of Madras; Editors: Jayapaul Azariah, Hilda Azariah, & Darryl R.J. Macer, Copyright Eubios Ethics Institute 1997.
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88. Biologically Active Plant Extracts Against Euproctis Fraterna

M.S.Nalina Sundari
Department of Zoology, University of Madras, Chennai 600 025


Introduction

Pesticides have the potential for contaminating the environment and they have resulted in many complex problems. The development of resistance by insect pests and the pollution caused by the pesticides call for the discovery of less hazardous alternatives. A new approach which has captured world wide attention is the use of plant products to control pest populations. In India, limited studies have been made to identify plants whose extracts possess juvenile hormone like activity on insects. Studies in this field led to the discovery of three different plants namely, Catharanthus roseus, Datura metel and Eucalyptus globulus the extracts of which showed promising juvenile hormone effects.

Materials and methods

The plant parts were thoroughly dried at room temperature in shade and were then pulverized in a grinder. 25g of dried and powdered material was extracted in Soxhlet apparatus using acetone as the solvent for 8 hours at 55oC. Different concentrations of the plant extracts of known weight were prepared in distilled water after dissolving the weighed amount of the extract in acetone. Distilled water with 1 ml of acetone forms the control solution. Newly moulted third instar larvae were separated into different containers and were fed ad libitum with castor leaves soaked in different concentrations of plant extracts. They were maintained in the same concentrations till pupation. The percentage of juvenile hormone activity of plant extracts were then calculated using the formula adopted by Williams and Slama (1966) and Bransly Williams (1971).

Results

The manifestations of the morphogenetic activity of juvenile hormone in insects are to maintain immaturity, promote supernumerary moulting, prevent normal pupation and produce larval-pupal or pupal-adult intermediates. The plant extracts produced various morphological deformities in E. fraterna. Depending on the doses used, the extracts affected larval and pupal development. Based on the morphological deformities, the following categories were recognised; supernumerary larvae, larval pupal intermediates, deformed pupae, pupal adult intermediates and adultoids.

Application of the extract of C.roseus leaves showed greater JH like activity while the activity was only 30.0%, 33.2% and 28.8% by the extracts of flowers, seeds and roots of C.roseus. More number of supernumerary larvae were produced in the extract of C.roseus leaves treated insects than other plant extracts tested.

The extracts of D. metel have insecticidal and antifeedant properties, but it showed only a little JH like activity. However, in case of D. metel flower extracts, 50.0% of JH activity was obtained at the concentration of 1200 ppm. Supernumerary larvae were also obtained when treated with flower extracts.

The extracts of E. globulus also showed promising Juvenomimetic activities. 63.2% of JH activity was obtained at the concentration of 1000 ppm of E. globulus leaves extract. However, the extract of E. globulus seeds showed only insecticidal properties rather than juvenile hormone like properties, when we increase the concentration above 700 ppm. mortality was more pronounced than juvenile hormone like activities.

Table 1 : Juvenomimetic activity of the extracts of C.roseus on E.fraterna
Part of plant Concentration of Number of insects falling in rates of JH Activity
used the extract (ppm) 0 1 23 4 5(%)

Leaf
400

600

800

1000

11

17

3

0

21

3

2

3

10

2

0

5

4

7

9

3

2

15

21

17

2

6

16

22

28.4

47.2

73.6

80.0

Flower400

600

800

1000

30

15

7

9

9

16

13

3

7

9

4

2

3

3

5

5

1

3

11

20

0

4

10

11

14.4

30.0

52.0

62.8

Seed200

400

600

800

27

21

19

12

11

11

10

7

5

8

5

4

2

6

4

5

4

2

9

18

1

2

3

4

19.2

25.2

33.2

48.8

Root400

600

800

1000

26

23

15

10

10

9

7

5

8

4

4

12

2

4

4

12

3

7

12

15

1

3

7

8

19.6

28.8

44.8

56.4

Table 2: Juvenomimetic activities of the extracts of the D.metel on E.fraterna
Part of plant Concentration of Number of insects falling in rates of JH Activity
used the extract (ppm) 0 1 23 4 5(%)
Flower800 19 46 126 336.4
1000 7 1112 162 240.4
1200 6 94 215 550.0
1400 3 84 256 454.0

Discussion

Most of the plant extracts tested produced morphological deformities in E. fraterna and those deformities were very similar to those caused by the action of JH analogues. The extract of C.roseus showed distinct juvenile hormone like activity of E. fraterna. The extracts of flowers of D. metal showed varying degrees of juvenomimetic activities on E. fraterna. The presence of juvenile hormone like activity in the extracts from plants such as C.roseus, E. globulus, C. aurantium, D. regia etc., provides as has been pointed out by Deshpande et al. (1974) & Chokalingam and Nalina Sundari (1988), additional support to the possibility of insect plant interactions in the course of evolution. They also pointed out that subsequent production of certain secondary metabolites by these plants can influence various physiological processes in insects resulting in growth inhibition or general toxicity.

The degree of juvenile characters retained by supernumerary larvae and pupae of E. fraterna was found to be dependent on the dosages of the extracts applied. In all the plant extracts, the juvenomimetic effect showed a proportional increase with the increase in dosage up to a certain level only. Beyond that level mortality was more pronounced than the juvenomimetic effect. Secondary metabolites accumulated in the woody parts of the plant also known to exhibit JH activity (Prabhu et al. 1973).

Hence, from the present study, it is clear that we can successfully use plant products in the control of insect pests. They have considerable advantages over chemical pesticides, which have residual action and hazardous effects on non target organisms, and to which the insects have developed resistance. The striking features of these biocides are biodegradability, feasibility of low cost production, and amenability to genetic engineering approaches for amplification of production. Therefore, they show promise as potential insecticides as alternative to chemical larvicides.

Table 3: Juvenomimetic activities of the extracts of E.globulus on E.fraterna
Part of plant Concentration of Number of insects falling in rates of JH Activity
used the extract (ppm) 0 1 23 4 5(%)
Leaf400

600

800

1000

33

23

9

5

8

10

19

8

7

6

11

2

2

7

6

7

0

4

2

15

0

0

3

13

11.2

23.6

32.8

63.2

Flower1600

1800

2000

2200

21

4

3

5

11

7

3

6

7

9

10

6

9

26

27

21

2

2

4

7

0

2

3

6

20.4

48.4

54.0

55.2

Seed200

400

600

700

35

29

14

12

10

11

10

9

2

6

4

5

2

3

19

21

1

1

3

2

0

0

0

1

9.6

17.6

34.8

38.0

Root1400

1600

1800

2000

18

17

8

7

15

14

21

8

4

5

13

0

11

10

4

7

2

3

2

18

0

1

2

10

25.6

28.4

30.8

60.4

Acknowledgement

My grateful thanks are due to Dr. Jayapaul Azariah, Professor and Head, Department of Zoology, University of Madras, for providing facilities. I am also grateful to UGC for Research Associateship.

References
Bransly Williams, W.R. (1971) : Juvenile hormone activity of ethyl farnesoate dihydrochloride with the cotton stainer Dysdercus cardinals Gerst. Bull. ent. Res., 61 : 41-47.
Chockalingam, S & M.S.Nalina Sundari (1988) : Juvenomimetic activities of some plant extracts on the lepidopteran pest, Porthesia scintillans. Geobios, 15(4) : 183-184.
Deshpande, R.S., P.R.Adhikary & H.P.Tipris (1974) : Juvenile hormone like activity of some Indian herbaceous plants. Indian J.Exp.Biol., 12 : 572-575.
Prabhu, V.K.K., M.John & B.Ambika (1973) : Juvenile hormone activity in some South Indian plants. Curr. Sci., 42 : 725-726.
Williams, C.M. & K.Slama (1966) : The Juvenile hormone III. Effect of the "Paper factor" on the growth and metamorphosis of the bug. Pyrrhocoris apterus. Biol. Bull., 130(2) : 247-253.


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