Ananda Mukhopadhyay

Field efficacy of a biopesticide prepared from Clerodendrum viscosum Vent. (Verbenaceae) against two major tea pests in the sub Himalayan tea plantation of North Bengal, India

The toxicity of four concentrations (1, 5, 10 and 20% w/v) of an aqueous extract from the weed, Clerodendrum viscosum Ventenat (Verbenaceae) was investigated under field conditions of the North Bengal University, Darjeeling, West Bengal, India for managing two major pests of tea, Camellia sinensis (L), namely the tea mosquito bug, Helopeltis theivora Waterhouse, (Heteroptera: Miridae) and the tea red spider mite, Oligonychus coffeae Nietner, (Acarina: Tetranychidae). Four field trials, two for red spider mite and two for tea mosquito bug, were conducted during April–May 2008 and October–November 2009 following a Randomized Block design. The aqueous extract of C. viscosum effectively and significantly reduced the mite population as well as infestation of tea mosquito bug by 68–95% and 73–86%, respectively, and their bioefficacy is comparable to synthetic and neem pesticides. No phytotoxic effect (score 0–5% and grade 1) was observed in the tea bushes sprayed with different doses of aqueous extract of C. viscosum in the field. Made tea samples were taint free. Organoleptic test revealed leaf-infusions and liquor strength as good, scoring 6.5–7.0 on a 10 point scale. Availability and distribution of this weed (C. viscosum) in and around tea-growing areas of sub Himalayan region, along with its processing for the feasibility of including C. visosum extracts in the current IPM programme is discussed.

Insecticide resistance mechanisms in three sucking insect pests of tea with reference to North-East India: an appraisal

Tea is prepared from the tender leaves and buds of Camellia sinensis (L.). In sub-Himalayan tea plantations of North-East India, different management practices are followed to protect the tea crop against different sucking insect pests such as Helopeltis theivora (Hemiptera: Miridae), Empoasca flavescens (Homoptera: Cicadellidae) and Scirtothrips dorsalis (Thysanoptera: Thripidae). Most plantations are managed conventionally through the use of different organo-synthetic insecticides, whereas some are managed organically by using herbal and microbial insecticides. In conventional tea plantations, organo-synthetic insecticides of different functional groups (organochlorines, organopho- sphates, synthetic pyrethroids and neonicotinoids) are routinely applied round the year to keep the sucking insect pest populations under control. A variety of defence mechanisms, including enzymatic detoxification systems (carboxylesterases, glutathione S-transferases and cytochrome P450 monooxygenases), physiological tolerance and behavioural avoidance, protect insect herbivores from these hazardous compounds. Insect pests have evolved mechanisms to degrade metabolically (enzymatically) or otherwise circumvent the toxic effect of many types of chemicals synthesized as modern insecticides. The extent to which insects can metabolize and thereby degrade these toxic or otherwise detrimental chemicals is of considerable importance for their survival in an unfriendly chemical environment. These mechanisms continue to evolve as insects attempt to colonize new plant species or encounter newer molecules of synthetic insecticides. The level and type of detoxifying mechanisms differs greatly, which, therefore, results in varying toxicity among different stages, species and populations. Variation in detoxifying enzyme activity is responsible, in part, at least for the selective toxicity of different insecticides, the development of resistance to insecticides and the selection of host plants. Overexpression of these detoxifying enzymes, capable of metabolizing insecticides, can result in higher levels of metabolic tolerance/resistance to synthetic insecticides.

Baseline susceptibility of Oligonychus coffeae (Acarina: Tetranychidae) to acaricides in North Bengal tea plantations, India.

ABSTRACT Among various biotic stresses that tea plants face, mite attack, especially from the tea red spider mite (Oligonychus coffeae, Acarina: Tetranychidae), has been a major challenge in recent years. The difference in relative toxicity of different commonly used acaricides to O. coffeae was observed in plantations of the tea-growing region of North Bengal, India. This study indicated that the relative susceptibility values (50% lethal concentration; LC50) of O. coffeae to different acaricides varied with region. O. coffeae populations of West Terai and South Terai showed less susceptibility to all acaricides tested compared with those from the Eastern Dooars. Populations of the Central Dooars, Western Dooars, and North Terai showed intermediate levels of susceptibility to different acaricides against O. coffeae. Ethion had the lowest efficacy to the pest in all tea-growing regions in North Bengal. Effective field dosages of these acaricides were compared with LC95 values, and a significant decrease in the susceptibility of the test population to ethion and dicofal was observed. As yet, there was little change for the newly introduced acaricides like fenazaquin, fenpropathrin, and propargite, which were effective at doses lower than the recommended dose.

Development of resistance to endosulphan in populations of the tea mosquito bug Helopeltis theivora (Heteroptera: Miridae) from organic and conventional tea plantations in India

The tea mosquito bug Helopeltis theivora (Waterhouse) is an important economic pest of tea in India. The development of resistance in H. theivora populations obtained from a conventional plantation and an organic plantation was studied in the laboratory for five generations, and associated changes in life cycle traits were assessed. Selection using sub-lethal concentrations of endosulphan resulted in a 4.4-fold increase in insecticide resistance ratio from the F1 to the F5 generation in the H. theivora population from the conventional plantation. By the F5 generation, nymphal duration was higher and fecundity was lower in the endosulphan-selected strain than in the non-selected strain from a conventional plantation and the susceptible strain from an organic plantation. These findings have practical implications for insecticide resistance management of this important sucking pest of tea.

The red spider mite, Oligonychus coffeae (Acari: Tetranychidae): its status, biology, ecology and management in tea plantations

Oligonychus coffeae Nietner (Acari: Tetranychidae), the red spider mite (RSM), is a major pest of tea (Camellia sinensis) in most tea-producing countries. Nymphs and adults of RSM lacerate cells, producing minute characteristic reddish brown marks on the upper surface of mature leaves, which turn red in severe cases of infestation, resulting in crop loss. The pest is present on tea all the year round, although numbers vary depending on season. Their number increases as the weather warms up and decreases markedly once rains set in. Under optimal conditions there may be 22 overlapping generations in a year. Parthenogenesis is known to occur; consequently, all mite stages can be found at a given time. Their infestation is mainly confined to the upper surface of the mature leaves and could readily be identified by the bronzing of the leaf. There are several naturally occurring insect predators, such as coccinellid and staphylinid larvae, lacewing larvae, and mite predators, most importantly species of the families Phytoseiidae and Stigmaeidae. Integrated management has been adopted to control this mite pest, involving cultural, mechanical, physical, biological and chemical methods. This review collates the most important works carried out on biology, ecology and management of O. coffeae. Also the scope of future studies for better management of this regular mite pest of tea is discussed.

Host-based life cycle traits and detoxification enzymes of major looper pests (Lepidoptera: Geometridae) of tea from Darjeeling Terai, India

Three polyphagous looper caterpillars, Buzura suppressaria Guenée, Hyposidra talaca Walker and Hyposidra infixaria Walker, have established themselves as severe pests of tea [Camellia sinensis (L.) Kuntze] in the plantations of sub Himalayan West Bengal (Terai region). Schima wallichii (DC.) Korth. is a naturally occurring alternative host of all these looper species. To gain an insight into looper and host plant relationships, the present work contemplates studies on host preference, host-based life cycle traits and levels of detoxification enzymes, such as general esterases (GEs) and glutathione S-transferases (GSTs). From the study, host-induction of feeding preference was evident in all the three looper species. Hyposidra spp. exhibited similar post-embryonic development periods both on tea and S. wallichii, whereas B. suppressaria reared on tea needed a longer development period than on S. wallichii. Tea-reared caterpillars of Hyposidra spp. were significantly heavier, having higher quantities of GEs and GSTs than S. wallichii-reared ones. B. suppressaria, however, exhibited similar body weights on tea and S. wallichii. While GST level was higher in tea-reared B. suppressaria, its GE quantity was higher on S. wallichii. Although tea was found to be a more suitable host for Hyposidra spp., the host S. wallichii proved marginally better than tea for supporting B. suppressaria. However, all the three looper species could utilize the foliage of tea and S. wallichii successfully. So S. wallichii trees can act as a sylvan reservoir of the looper species, prompting their possible invasion of tea plantations and thus making management of looper pests in tea more difficult.

Bioefficacy assessment of Melia azedarach (L.) seed extract on tea red spider mite, Oligonychus coffeae (Nietner) (Acari: Tetranychidae)

Aqueous seed extract of Melia azedarach (L.) was evaluated against tea red spider mite, Oligonychus coffeae (Nietner), in relation to mortality of adult mites, viability of eggs and subsequent adult emergence and oviposition deterrence in the laboratory, and the extract underwent field evaluation in terms of per cent reduction of the mite population. Direct spray methods were used in the laboratory with concentrations of 1%, 2%, 4%, 6%, 8% and 10%. Mortality of O. coffeae was dependent on both concentration and time (56.4% mortality on the first day; 95.6% mortality by the seventh day). The viability of eggs was reduced significantly compared with untreated mites eggs. Significant reduction in adult emergence and increased duration of total developmental period were noted. Deposition of eggs by adult mites on treated leaf surface was decreased significantly compared with the control. No phytotoxic effect (score 0–5% and grade 1) was observed in the field when tea bushes were sprayed with different doses of aqueous seed extract of M. azedarach. The made tea samples were taint free. An organoleptic test scored both leaf infusions and liquor strength as good, scoring 6.5–7.0 on a 10-point scale. The availability and distribution of this plant (M. azedarach) in and around the tea-growing areas of the sub-Himalayan region, along with its processing for economic utility and inclusion in the current integrated pest management program, is discussed.

Chemical-based integrated approaches for the management of tea red spider mite, Oligonychus coffeae Nietner (Acari: Tetranychidae) in tea plantations of sub-Himalayan North Bengal, India

The tea red spider mite, Oligonychus coffeae Nietner (Tetranychidae), is considered one of the main phytophagous mite pests of tea plants in north-east India. To reduce the amount of synthetic chemicals in tea, a strategy of using optimal rates and effective spray practices has been developed. In laboratory tests, the 50% lethal concentration (LC50 in parts per million (ppm)) values of ethion, dicofol, profenofos, propargite, fenpropathrin, fenazaquin and abamectin were 687.18, 534.04, 241.684, 90.256, 12.549, 4.319 and 2.405, 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, dicofol and profenofos was observed. There was no change for the newly introduced acaricides like fenazaquin, fenpropathrin, propargite and abamectin, which were effective at doses lower than the recommended dose. Of all the acaricides tested, abamectin was the most toxic and ethion was the least toxic. On the basis of LC50 values, the descending order of ovicidal toxicity of the acaricides tested to O. coffeae eggs was fenazaquin, followed by profenofos, propargite, fenpropathrin, ethion, dicofol and abamectin. The data obtained in this study may be used as a tool in integrated pest management strategies that can effectively control the pest.

Fitness traits of insecticide resistant and susceptible strains of tea mosquito bug Helopeltis theivora Waterhouse (Heteroptera: Miridae)

We compared the biological traits of insecticide resistant and susceptible field populations of tea mosquito bug Helopeltis theivora Waterhouse. The insecticide resistant population of the conventional Tea Estate “Chuapara” of the Dooars, Jalpaiguri, differed significantly from the susceptible strain of the organic Tea Estate “Makibari” of Darjeeling. Both these tea plantation areas are located in the northern part of West Bengal, India. Adverse changes in biological and developmental traits were observed mainly in: (i) reduction in oviposition period; (ii) fecundity; and (iii) prolongation of nymphal and total developmental period. However, all other parameters such as pre‐ and post oviposition periods, egg incubation period, hatchability and adult longevity were not significantly different. These results clearly demonstrated that only certain fitness components in the resistant strains appear to be adaptively changed and lowered.

Insecticide susceptibility and activity of major detoxifying enzymes in female Helopeltis theivora (Heteroptera: Miridae) from sub-Himalayan tea plantations of North Bengal, India

Despite the continuous use of synthetic insecticides during the last two decades, the tea mosquito bug Helopeltis theivora Waterhouse still exists as the most destructive pest of tea in North East India. The susceptibility levels of the female sucking bug collected from conventional (synthetic insecticide treated: Terai and Dooars plain regions) and organic (synthetic insecticide untreated: low-altitude Darjeeling region) tea plantations of the northern part of West Bengal to two synthetic insecticides, quinalphos and cypermethrin, and the activity of three principal detoxifying enzymes were assayed. Compared with the susceptible Darjeeling population, the Terai and Dooars populations showed a resistance factor at the lethal concentrations for 50% level ranging from 547- to 2680.87-fold and from 3810- to 7480-fold for quinalphos and cypermethrin, respectively. General esterases (GEs), glutathione S-transferases (GSTs) and cytochrome P450-mediated mono-oxygenases (CYPs) also showed an increased activity in the Terai and Dooars populations compared with those fromDarjeeling. Defence enzyme activity was enhanced by 15.4- and 17.6-fold for GEs, 1.8- and 1.9-fold for GSTs and 2.1- and 2.4-fold for CYPs in the synthetic insecticide-treated H. theivora populations when compared with the untreated Darjeeling populations. Electrophoretic analysis for GEs showed a higher level of expression for esterase I–VI isozymes in the Terai and Dooars populations when compared with that in the Darjeeling populations. This study reveals a reduced efficacy of quinalphos and cypermethrin against field populations of H. theivora, possibly due to enhanced activities of GEs, GSTs and CYPs. The findings may be used in developing integrated resistance management strategies that can help in the effective control of this major tea pest.