Corona discharge effects on some parasitical insects of cultured plants

Journalof

ELECTROSTATICS ELSEVIER

Journal of Electrostatics 40&41 (1997) 669-673

C o r o n a discharge effects on some parasitical insects of cultured plants

R. Morara, I. Suarasana, S. Budua, I. Ghizdavub, Monica Poreab, L. Dasealeseuc aTechnieal University of Cluj-Napoea 15, C-Daieovieiu Street, 3400 Cluj-Napoea, Romania bUniversity of Agricultural Sciences of Cluj-Napoea 3400 Cluj-Napoea, Romania cLaboratoire d'Electrostatique et de Materiaux Dieleetriques - CNRS BP 166, 38042 Grenoble Cedex 9, France

The paper presents the results of inter-disciplinary research which demonstrates the effectiveness of a.e. corona diseharges as non-polluting means of annihilating the pests of various cultured plants. The laboratory tests involved the green malt bug ~horodom Humuli) and the common red spider (Tetranicus Urticae). The corona discharge was generated between a grounded plate electrode and a brush-type electrode, connected to a 25 kV, 50 Hz, adjustable high-voltage supply. The electrode system was placed under a 63 I glass bell, in air at atmospheric pressure. The pest annihilation tests were carried out in two ways: direct exposure to the corona discharge and exposure to the ionised air generated by corona. Immediately following the treatements effects upon the insects were at 2, 24, 48, 72, 96 hours, the following effects were observed: paralysis / lack of motion coordination; important reduction of the digestive functions; dehydration; death (60-80% of the exposed insects after 48 hours; up to 99% after 72 hours). The excess of ozone generated in the corona field of application is forseen, especially in destroying the pests of the plants usually cultivated in greenhouses.

1. INTRODUCTION Evidence is mounting that electric fields can exert significant biological effects [1-4]. Although the physical mechanisms influencing the biological functions are only poorly understood at the present time [5], the interaction of the electric field with the living systems is undeniable [6,7]. In the ease of corona discharge fields, the biological effects are partially related to the increase of ozone concentration.in ionised air [8,9]. The present paper alms at analysing the ways in which a.c. corona in atmospheric air could be directly or indirectly employed as a nonpolluting agent for the annihilation of an important group of pests affecting cultured plants. 0304-3886/97/$17.00 © Published by Elsevier Science B.V. All rights reserved.

PII S0304-3886(97)00113-7

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R. Morar et al./Journal of Electrostatics 40&41 (1997) 669-673

2. E X P E R I M E N T A L SET-UP The pest annihilation tests were carried out with the laboratory installation presented in Figure 1. The corona discharge was generated between a 27 cm x 23 cm brush-type electrode consisting of 135 rows of 115 emitting points, each made of 20 mm long x 0.2 mm diameter tungsten wire, and a grounded electrode, made of a 2 mm thick x 32 cm x 28 cm aluminium plate. In all the experiments the electrodes were set under a 41 cm diameter airtight glass bell of 63 dm 3 volume; the inter-electrode distance was 4.0 cm.

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3. M A T E R I A L AND M E T H O D Malt leaves, each infested with 20 to 100 green malt bugs (Phorodom Humuli) and with sporadical individuals of Tetranicus Urticae, were carefully collected and placed on humid sheets of blotting paper at the bottom of several Petri dishes. Two methods of pest annihilation were tested: (1) Direct exposure to the corona discharge. The Petri dishes containing the infested leaves were placed inside an airtight glass bell. The high-voltage U = 10; I 1.5; 13 kV was applied for T = 15, 20, 25, 30 rain. Three replications were performed for each treatment combination (U,T). (2) Exposure to the ionised air generated by corona. The Petri dishes were placed inside the airtight glass bell, but outside the high-voltage electrode system, energised at U = 19, 20, 21, 22 kV for exposure times T = 15 and 30 min. For each treatment combination (T,U), the experiment was repeated three times.

R. Morar et al./Journal of Electrostatics 40&41 (1997) 669-673

671

After exposure, each Petri dish containing infested leaves was covered with a translucent paper and kept in atmospheric air. The pests on the treated leaves were examined under a magnifying glass and a binocular microscope, at t = 2, 24, 48, 72, 96 hours after exposure, and the observations were compared to those performed on non-exposed samples kept under similar conditions.

4. R E S U L T S In all the tests, the exposure of Phorodom Humuli to the corona discharge, or to the ionised air caused the following effects: paralysis / lack of motion coordination; reduction of the digestive functions ; dehydration; death (as shown in Figures 2 and 3). 190

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Figure 2. The evolution in time of the mortality rate for Phorodom Humuli exposed directly to corona discharge.

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R. Morar et aL /Journal of Electrostatics 40&41 (1997) 669-673

The individuals characterised by irreversible deterioration of the vital biological functions (lack of motion when touched) were considered as "dead" at the moment of the examination. The degree of inhibition increased with both the high-voltage level U and the exposure time T. I00

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R. Morar et al./Journal o f Electrostatics 40&41 (1997) 669-673

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5. DISCUSSION Toxicity of ozone to the living matter has already been well documented [10]. In the ca~e of direct exposure to corona discharge, the pests are affected by the combined action of a relatively-intense electric field and of a large quantity of ozone. The high concentration of ozone in air seems to be in itself a sufficiently agresive environmental factor to cause the death of the pests even if not exposed to an electric field. The data given in Figures 2 aad 3 confirm the effectiveness of pest annihilation, measured by mortality rate, increases witl~ the duration of exposure. The aspect of PHORODOM HUMULI pests before and after the treatment in a.c. corona discharge and ionised air shows many damages on the surface o~"the pests. The mortality rate is also affected b y the high-voltage level U. This can be e~sily explained by the increase of ozone concentration with the voltage applied to the electrode system.

6.CONCLUSION Exposure to the ozone generated in a corona discharge may become an effective, alternative to the conventional, chemical methods of pest control. The experiments presented in this paper enabled the developement of a high-voltage supply and of a patent pending ozone generator, with a large field of application in destroy the pests of the plants cultivated in greenhouses.

REFERENCES [ 1] E. Postow and C. Polk (Eds), Handbook of Biological Effects of Electromagnetic Fields. CRC Press, Boca Raton, 1986. [2] R. Morar. Ph.D. Thesis, Polytechnical Institute, Timisoara, 1976. [3] R. Morar, A. Iuga, L. Dascalescu, V. Neamtu and I. Munteanu. Proc. Int. Conf. Mocem Electrostatics, Beijing, 1988, pp. 158 - 160. [4] R. Morar, A. Iuga, L. Dasealescu and I. Munteanu. Proc. Int. Symp. High Voltage Eng., Yokohama, 1993, paper 286. [5] T.S. Tenforde, Proc. Electromagnetic Field Effects Caused by High Voltage Systems, Sapporo, 1994, pp. 311-321. [6] F.S. Barnes. Bioelectromagnetics Supplement, 1 (1992), 67. [7] R. Morar, R. Munteanu, E. Simion, I. Munteanu and L. Dascalescu. Conf. Rec. IEEE / IAS Ann. Meet., Orlando, 1995, pp. 1335 - 1337. [8] F.Schaff. Photonics Spectra, 26 (1992). [9] A.S. Viener, P.A. Lawless, D.S. Ensor and L.E. Sparks. IEEE Trans. Ind. Appl., 28 (1992). [ 10] D. Negoiu. Tratat de chimie anorganica vol. II. Editura Tehnica, Bucuresti, 1973.