Gautam Handique

Use of plant extracts for tea pest management in India

India is the second largest producer of black tea in the world. The biggest challenge for tea growers of India nowadays is to combat pests and diseases. Tea crop in India is infested by not less than 720 insect and mite species. At least four sucking pests and six chewing pests have well established themselves as regular pests causing substantial damage to this foliage crop. Various synthetic pesticides are widely used for the management of tea pests in India. Applications of such large quantity of pesticides could cause various problems such as development of resistance, deleterious effects on non-target organisms such as insect predators and parasitoids, upsetting the ecological balance, and accumulation of pesticide residues on tea leaves. There is a growing demand for organic tea or at least pesticide residue free tea in the international market which affects the export price. There is also a higher emphasis of implementation of new regulations on internationally traded foods and implementation of Plant Protection Code (PPC) for tea by the Government of India. This necessitates a relook into the usage pattern of synthetic pesticides on this crop. There are various non-chemical interventions which are being worked out for their sustainability, compatibility, and eco-friendly properties which can gradually replace the use of toxic chemicals. The application of plant extracts with insecticidal properties provides an alternative to the synthetic pesticides. Botanical products, especially neem-based products, have made a relatively moderate impact in tea pest control. Research has also demonstrated the potential of 67 plant species as botanical insecticides against tea pests. The majority of plant products used in pest management of tea in India are in the form of crude extracts prepared locally in tea garden itself, and commercial standardized formulations are not available for most of the plants due to lack of scientific research in the area. Apart from systematic research in this area, to facilitate the simplified and trade friendly registration procedures with quality assurance of the products, there is an increasing need of regulatory authority and national norms in India.

Aqueous extracts of Duranta repens (Verbenaceae) as an alternative to control tea red spider mite, Oligonychus coffeae (Acari: Tetranychidae)

We evaluated an aqueous extract of Duranta repens L. in the laboratory against the tea red spider mite, Oligonychus coffeae Nietner, to determine its effect on adult mortality, viability of eggs, oviposition deterrence and repellent properties. We also evaluated the same extract in the field to determine its effect on mite populations. The direct spray method was used in the laboratory at concentrations of 2, 4, 6, 8 and 10 g/l. Mortality of O. coffeae was dependent on both concentration and time after application. Deposition of eggs by adult mites on treated leaf surfaces decreased and the viability of eggs was also reduced. Its bioefficacy was comparable to that of the commonly used commercial neem oil formulation (azadirachtin 0.03EC). In addition, different concentrations of the aqueous extract of D. repens also exhibited repellent properties against adult mites. In the field, the application of the aqueous extract of D. repens reduced the mite population and its bioefficacy was comparable to that of the synthetic pesticide Propargite 57 EC. No phytotoxic effect was observed when tea bushes were sprayed with different concentrations of D. repens. Tea samples were taint free. Treatment of plants with the extract did not affect the quality (appearance of liquor, flavour, taint and taste) of made tea. Availability and distribution of this plant in and around tea growing areas of Assam, along with its processing, and the possibility of including D. repens extracts in the current IPM programme are discussed.

Potential of Nyctanthes arbor-tristis L., Phlogacanthus thyrsiformis Nees and Sapindus mukorossi L. as novel acaricides of natural origin

Aqueous extract of three indigenous medicinal plants viz., Nyctanthes arbor-tristis L. (Oleaceae), Phlogacanthus thyrsiformis Nees (Acanthaceae) and Sapindus mukorossi L. (Sapindaceae) was evaluated in the laboratory against the tea red spider mite, Oligonychus coffeae Nietner (Tetranychidae) to determine its effect on adult mortality, viability of eggs, oviposition deterrence and repellent properties. The direct spray method was used in the laboratory at concentrations of 2, 4, 6 and 8 g/l. Mortality of O. coffeae was dependent on both concentration and time after application. Deposition of eggs by adult mites on treated leaf surfaces decreased significantly and the viability of eggs was also significantly reduced. In addition, different concentrations of the aqueous extract of these chosen plants also exhibited repellent properties against adult mites. Among the chosen plant extracts, S. mukorossi registered highest mortality in both adults and egg forms, whereas P. thyrsiformis showed significantly higher repellence property against O. coffeae. The plant extracts caused no mortality to the adults and 4th instar larvae of Stethorus aptus, a natural predator of O. coffeae and no significant change in predatory efficiency was recorded in comparison with untreated control. Availability and distribution of these plants in and around tea growing areas of Assam, along with the feasibility of processing, may be thus included in the current IPM programme in tea.

Clove Oil Efficacy on the Red Spider Mite, Oligonychus coffeae Nietner (Acari: Tetranychidae) Infesting Tea Plants

The tea red spider mite, Oligonychus coffeae Nietner (Tetranychidae), is an economically important pest of agricultural and ornamental crops and considered one of the major pests of tea plants in North-east India. In view of increasing resistance recorded in insect and mite pests against pesticides, a study was conducted to determine the acaricidal, antiovipositional, repellent and ovicidal activities of clove oil (an essential oil from the clove plant, Syzygium aromaticum L. Merr. & Perry: Myrtaceae) against tea-red-spider-mite. Mortality of O. coffeae varied with the concentrations and the duration of exposure time of the mites after application of oil. Rate of deposition of eggs by mites on treated leaf surfaces as well as the viability rate of eggs decreased significantly. In addition, certain concentrations of clove oil have been proved effective against adult mites.

Faunal Composition of Scarab Beetles and Their Hosts in Assam

Field investigations were conducted in the Instructional cum Research Farm and Horticultural Orchard of Assam Agricultural University, Jorhat, to monitor the population of foliage-feeding scarab beetles on eight different host plants during 2010–2012. The highest numbers of beetles were collected from sthal-padma (Hibiscus mutabilis) (1579 numbers) followed by agar (Aquilaria malaccensis) (1526 numbers) and guava (Psidium guajava) (1348 numbers). The lowest number was found on jute (Corchorus sp.) (370 numbers). The host plants, viz., rose (Rosa chinensis), ber (Ziziphus jujuba), Silikha (Terminalia chebula), and Soalu (Litsaea polyantha) recorded 1143, 1143, 1065, and 930 beetles, respectively. The present investigation also revealed 13 numbers of new host plants of scarab beetles, viz., devil tree (Alstonia scholaris), albizia (Albizia odoratissima), dalchini (Cinnamomum zeylanicum), cocoa (Theobroma cacao), indigo (Indigofera zollingeriana), mango (Mangifera indica), Assam lemon (Citrus lemon), green gram (Vigna radiata), jamun (Syzygium cumini), rain tree (Samanea saman), mast tree (Polyalthia longifolia), jackfruit (Artocarpus heterophyllus), and drumstick (Moringa oleifera). Through scouting 20 species of scarab beetles were recorded, of which, Sophrops iridipennis, Anomala perplexa, Anomala dussumieri, and Adoretus renardi are new records from Assam.

Toxicity of Three Plant-Based Oils Against Oligonychus coffeae (Acari: Tetranychidae)1

There has been an increasing trend to reduce the dependence on conventional chemical insecticides with the implementation of the Plant Protection Code (PPC) for tea production by the government of India. Naturally derived plant products or botanicals are viable alternatives for pest management in tea plantations (Roy et al. 2016, Appl. Microbiol. Biotech. 100: 4831–4844). However, preparation of such botanicals is time consuming as well as labor intensive in terms of collection and drying of such plant materials. Thus, use of commercially available plant-based oils may represent a novel class of crop protectants which are readily available in the market as their preparation is reasonably easy and less time consuming. The effectiveness of plant-derived oils in control of arthropod pests in different crops is well established (Isman 2006, Annu. Rev. Entomol. 51: 45–66) and many have been documented to be effective against insect and acarine pests (Isman 2000, Crop Prot. 19: 603–608). They are also selective in having little to no impact on natural enemies and pollinators, which does not occur among conventional insecticides (Digilio et al. 2008, J. Plant Interact. 3: 17–23). The advantage of plant-based oils is that they contain complex mixtures of monoterpenes, phenols, and sesquiterpenes which not only repel insects and mites but also have fumigant and contact toxicity (Koul et al. 2008, Biopest. Int. 4: 63–84). In tea production, a few plant-derived oils have demonstrated promising results against crop pests, primarily the red spider mite, Oligonychus coffeae Nietner (Barua et al. 2015, Proc. Zool. Soc. doi: 10.1007/s12595-015-0147-6; Roy et al. 2015, Acta Phytopath. Entomol. Hungarica 50: 127–138; Roy et al. 2016, Proc. Nat. Acad. Sci. India Sec. B: Biol. Sci. doi: 10.1007/s40011-016-0734-y). Identification and evaluation of such natural insecticides is necessary so that tea producers may have a variety of choices of products for effective pest management. Hence, the

Geographical variation in susceptibility of tea red spider mite, Oligonychus coffeae (Nietner) (Acari: Tetranychidae) to commonly used acaricides in tea plantations of Assam, north east India

ABSTRACT The tea red spider mite, Oligonychus coffeae, is one of the most destructive pests of tea in the world which is mainly managed by chemical acaricides. In the present study, concentration-mortality responses of O. coffeae from eight tea geographical populations along with a laboratory susceptible strain against five acaricides, viz., ethion, dicofol, propargite, fenazaquin and fenpropathrin were assayed based on standard leaf-dipped method. Although observed levels of susceptibility varied between populations and acaricides, population from Cachar region registered a high LC50 value to most of the acaricides evaluated. Almost all of the tested field populations had developed high to very high level of resistance to ethion and dicofol, with resistance ratios ranging from 13.58 to 134.27-fold. Fenazaquin and propargite were very effective against O. coffeae in all tested populations, while fenpropathrin showed minor variation in their susceptibility. Significant positive correlation was only observed between the LC50 values of ethion and dicofol (r = 0.95, P = 0.005) suggesting the potential for cross-resistance. These results indicated that control failure was associated with resistance to ethion and dicofol therefore reinforcing the need of resistance management program and offered useful information about alternative acaricides to control O. coffeae.

Susceptibility to acaricides and detoxifying enzyme activities in the red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychidae)

Susceptibility of red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychidae), collected from conventionally-managed (synthetic acaricide usage) versus an organicallymanaged (no acaricide usage) tea plantations in Assam, India, to five synthetic acaricides was determined in laboratory bioassays. Activity of three principal detoxifying enzymes of these mite populations was also assayed. The median lethal concentrations (LC50) of ethion, dicofol, propargite, fenpropathrin, and fenazaquin were 1049.75, 599.21, 232.03, 11.44, and 6.75 ppm, respectively. Field rates of these acaricides were compared with 95% lethal concentration (LC95 in ppm) values, and a decrease in the susceptibility of the test population to ethion, propargite, dicofol and fenpropathrin was observed. There was no change for fenazaquin which was effective at lower doses than the recommended dose. Of all the acaricides tested, fenazaquin was the most toxic and ethion was the least toxic. General esterases (GEs), glutathione- S-transferase (GST), and cytochrome P450 monooxygenases exhibited a higher activity in mite population from the conventionallymanaged tea plantation as compared with the activity in mites from the organicallymanaged tea plantation. These findings may be helpful in the selection of acaricides and in developing resistance management strategies for an effective management program for this major tea pest.

Ecology and management of the black inch worm, Hyposidra talaca Walker (Geometridae: Lepidoptera) infesting Camellia sinensis (Theaceae): A review

Abstract The black inch worm, Hyposidra talaca (Walker) (Geometridae: Lepidoptera) has earned considerable importance as a defoliator during last decade in north east India. Characteristic features of H. talaca, such as switching from wild plants to Camellia sinensis, and completion of 6–8 generations in a year without winter diapause appear to be the major reasons for persistence of the defoliator on C. sinensis. There are reports on the aggressive infestation of the pest on C. sinensis than on alternate host plants and development of high tolerance/resistance to certain insecticides. Till date, more than one hundred alternate host plants have been recorded for H. talaca, but with very few natural enemies. To manage this pest chemically, synthetic pesticides are widely used. Integrated management is recently being encouraged wherein cultural, mechanical, physical, biological and chemical methods have been contemplated. This review collates the work and literature on the ecology of H. talaca and offers an analysis of the problems encountered in managing the defoliator in tea plantations. Further, future directions for better management of H. talaca are suggested.

Antenna morphology and sensilla microstructure of the male and female scarab beetle, Lepidiota mansueta Burmeister (Coleoptera: Scarabaeidae)

Abstract Studies on Lepidiota mansueta Burmeister were conducted to describe and compare the external morphology of the antenna and its sensilla of male and females. Distinct variations were observed in antennal segments between the sexes with males possessing longer scape, pedicel, flagellum and lamellar club segments. Variation was also seen in the antennal sensilla, with males possessing three different types of sensilla while the females possessed seven types of sensilla. Sensilla trichodea (TRS), sensilla placodea (PLAS) type I and sensilla placodea (PLAS) type II were common in both sexes while sensilla chaetica (CHS), sensilla auricilica (AUS) type I, sensilla auricilica (AUS) type II and sensilla auricilica (AUS) type III were found only in females.