Introduction

The red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychidae), is a major pest of tea, Camellia sinensis in most tea producing countries like India. Since 1960 it had been causing a substantial damage. To warfare the menace from red spider mites different types of acaricides (dicofol, ethion, sulfur, propargite, fenazaquin) are being used. Although the numbers of the pest is vary depending on season but it is present on tea all the year encompassing. To overcome the problem, control measures are been taken by the planters by using the synthetic acaricides (Roy and Mukhopadhyay, 2012). However, the use of synthetic insecticides has led to numerous troubles such as acute and chronic poisoning of applicators and consumers; destruction of wildlife; commotion of natural biological control and pollination; widespread groundwater contamination, potentially intimidating human and environmental fitness; and the evolution of resistance to pesticides in pest populations (Isman, 2006). Additionally, being an export commodity, made tea is under stringent regulatory measures on pesticide residues (Roy et al., 2011).

Application of plant based pesticides in IPM offers numerous advantages over synthetic pesticides. Plants develop these chemicals in comeback to the mutual selection pressure of phytopathogens, insects and other herbivores as well as several of these botanical pesticides are effectual against diseases, nematodes and supplementary organisms in accumulation to phytophagous insects (Singh, 2000). Phytochemicals which occurs naturally wield a broad series of behavioural and physiological possessions on insects and therefore it is tricky for insect pests to build up resistance effortlessly against these pesticides. The production of such products can be dually advantageous for developing countries, where botanical pesticides are most likely to be adopted on a bulky amount (Dev and Koul, 1997).

The current investigation was undertaken to ascertain the bioefficacy of solvent extracts of the selected plants which commonly exist in the locality of tea growing areas of north east India, against O. coffeae under laboratory conditions.

1 Materials and Methods

1.1 Maintenance of red spider mites culture

The red spider mites were collected from North Bengal Regional R&D Centre experimental plots, (26° 54' 0" North, 88° 55' 0" East longitude) Nagrakata, West Bengal, India. The culture of the mites were maintained following the detached leaf culture technique of Helle and Sabelis (1985) with minor modifications under the laboratory conditions (25 ± 2°C, 75 ± 5% RH, and 16L: 8D photoperiod) on a inclined tea cultivar, TV1. From the stash culture, fully developed mites were transferred onto fresh tea leaves (approximately 6 cm²) sited on moistened cotton pads (ca. 1.5 cm wide) in plastic trays (38 × 28 × 5 cm). Shrunken leaves were replaced with fresh ones at 2-3 days intermission.

1.2 Preparation of plant extracts

Fresh and matured leaves of Polygonum hydropiper L., Vitex negundo L., Tithonia diversifolia (Hemsl.) (wild sun flower), Artemisia vulgaris L. and Clerodendrum infortunatum L. were collected locally from nearby areas of North Bengal Regional R&D Centre, Nagrakata, West Bengal (Table 1) (Figure 1  A-E). Each of the plant materials were desiccated under shade and milled by using electric dicer and passed through a 20 mesh sieve and reserved in a 1 kg capability polypropylene container and 500 gm of each plant leaf powder were sent to Entomology Research Institute, Loyola College, Chennai - 600034 for solvent extraction using hexane and methanol following the method of Harborne (1973). The solvent extracts (hexane and methanol) were dissolved in DMSO (dimethyl sulfoxide; an important polar solvent) to prepare 10% stock solution and from the stock solution different test concentrations viz. 1, 0.75, 0.5 and 0.25% were tested against the red spider mites. The extracts were followed by labeled accordingly and prepared for appliance.

1.3 Laboratory ovicidal test

To examine the ovicidal activity of the each plant extracts, 15 gravid females of mites were introduced on TV1 mature fourth leaf from the apex of the shoot for oviposition and set aside overnight in a petri dish. By padding the water soaked cottons leaves the leaves the moisture conditions was maintained. Using a fine brush the mites were removed after 18 h. Under microscope the pre-treatment count was recorded by counting the eggs laid on tea leaves. Leaves where more than 30 eggs were present detached carefully by using a fine needle. For ovicidal effect of each of the plant extract 150 eggs were considered and experiential for five times (30 eggs/experiment). The eggs were subjected to spraying of different concentrations of each plant extracts viz. 1, 0.75, 0.5 and 0.25% (w/v) by using a fabricated atomizer. In case of the control eggs only water was sprayed. For a period of 12 days after oviposition the hatchability was determined for both experimental and control batches of eggs. After this period those eggs that did not hatched were regarded as non-viable (Sarmah et al., 1999) and using the following formula the percent reduction in hatchability was calculated.

1.4 Laboratory acaricidal test

A total 30 nos. of 24 h old healthy mites from the culture maintained under laboratory conditions were released on a detached tea leaf of TV1for laboratory evaluation of each plant extracts. The ultimate reckon of mite population was taken after appropriate settlement of mites (after 4 h) for affirmation on number of mites. Using a fabricated atomizer each concentration of the plant extracts were sprayed on both the sides of leaf. Observations were recorded after 24, 48 and 72 h after treatment and the total numbers of live mites were recorded accordingly. The experiment was repeated five times and the data were statistically analyzed (ANOVA) using a software SPSS 17.

                                                          A

Percent egg mortality = 100 – (------ X 100)   

                                                          B

Where, A: No. of unhatched eggs per treatment; B: Total nos. of eggs per treatment.

2 Results and Discussion
 

2.1 Ovicidal action of plant extracts

The experimental findings showed that, highest mortality was recorded at the highest concentration (1%) among the tested concentrations of methanol extracts of V. negundo and C. infortunatum to the level of 66.7% and 57.45% respectively, where as the methanol extract of A. vulgaris the lowest mortality was recorded (13.3%). In case of hexane extracts the highest mortality was recorded in P. hydropiper (48.5%) and C. infortunatum (34.15%) respectively in the highest dose (1%). The least mortality was observed in A. vulgaris (12.23%) at 1% concentration of hexane extract (Table 2). Almost 20.58% mortality was recorded in 10% aqueous extract of C. infortunatum in red spider mites (Sarmah et al., 1999) where as the in the methanol extract 57.45% mortality was recorded in the present study. Chemical substances of the host plants may block the micropyle region of the egg and hence it prevents the gaseous exchanges and as a result it kills the embryo in the egg. Against Spodoptera litura while screening of 9 different plants with different solvent extracts in relation to ovicidal and ovipositional deterrent activity and diverse responses. Raja et al. (2003) noticed irrespective of the solvents and concentrations used for the extraction. The curtailed blastokinesis and anomalous rupture of additional embryonic membranes in the embryo or uneven penetration of extracts through the egg chorion to remarkable parts of egg at unusual times of the perceptive time could also be related with explanation on inconsistency of morphological possessions (Slama, 1974). Vasanthakumar et al. (2012) evaluated the acaricidal activity of red spider mites using leaf extracts of Vitex negundo, Gliricidia maculate, Wedelia chinensis, Morinda tinctoria and Pongamia glabra and they reported that the aqueous extracts of M. tinctoria and P. glabra had utmost ovicidal activity, ovipositional anticipation and 100% adult mortality. These findings also shows similar results with current work on ovicidal action of the selected plant extracts against the red spider mites.

2.2 Acaricidal activity of plant extracts on adult mites

The result obtained from the leaf disc experiment indicated that, among the five different plant extracts V. negundo and C. infortunatum at 1% concentration of both hexane and methanol were more effective even after 24hrs of treatment (Table 3). After 24 h methanol extract of both the plants and hexane extract of C. infortunatum offered more than 90% mortality at 1% concentrations while in 0.5% dose more than 65% mortality was recorded. Where as in other plants it shows more than 70% mortality after 72 h. Similar properties of Linostoma decandrum Wall (Thymelaeaceae) were recorded by Bora et al. (1998) Radhakrishnan (2014). These laboratory studies warrant trial of the extracts of these plants under field conditions for the development of acaricides towards control of tea red spider mite. Botanical insecticides i.e. products unswervingly obtained from plants are in broad gratitude that numerous plants acquire insecticidal properties, which are in exercise in urbanized countries. All of these botanical insecticides currently comprise 1% of the globe insecticide sell, but annual sales expansion in the sort of 10–15% is exclusively promising (Wink, 1993; Gentry, 1993). The brunt of botanical insecticides is the most conspicuous in the house and backyard sector (Isman, 1995). In recent years plant products are gaining remarkable importances which have substantial prospective as insecticidal compounds (Nattudurai et al 2015). This study reveals V. negundo and C. infortunatum to be most promising plant among all the five plants for the control of mites of tea because of its high adulticidal and ovicidal properties.

This loom would rally round the tea trade in numerous ways (residue free tea, decline in acaricide stack, cost efficiency, consumer pleasure) mainly it will provide the most effective control and unsurprisingly stirring or consequent or pretend with negligible skill, so they are acknowledged by organic certification programmes and by definite purchaser groups along with it is more attuned with biological control process (Weinzierl, 2000; Siakh, 2004). Innate products are disreputably capricious, and so steadiness of the ultimate result will be a lot harder to accomplish. It may be indispensable to settle on both the shelf steadiness of the lively constituent along with its fortune in the surroundings or in flora and fauna. Such type of studies can be convoluted adequate whilst only a particular compound is being tracked, but the attempt requisite tracking numerous alleged active doctrines in a single artifact.

Acknowledgement

The authors are grateful to the Rev.Fr.S.Ignacimuthu, s.j., Director, Entomology Research Institute, Loyola College, Chennai - 600034 for providing solvent extracts for carrying out the work.

Conflict of interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

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