Pest management through Bacillus thuringiensis (Bt) in a tea-silkworm ecosystem: status and potential prospects.

Bacillus thuringiensis (Bt) is a soil bacterium that forms spores containing crystals comprising one or more Cry or Cyt proteins having potential and specific insecticidal activity. Different strains of Bt produce different types of toxins, affecting a narrow taxonomic group of insects. Therefore, it is used in non-chemical pest management, including inherent pest resistance through GM crops. The specificity of action of Bt toxins reduces the concern of adverse effects on non-target species, a concern which remains with chemical insecticides as well. To make use of Bt more sustainable, new strains expressing novel toxins are actively being sought globally. Since Bt is successfully used against many pests including the lepidopteran pests in different crop groups, the insecticidal activity against Samia cynthia (Drury) (Eri silkworm) and Antheraea assamensis Helfer (Muga silkworm) becomes a concern in the state of Assam in India which is a predominantly tea- and silk-producing zone. Though Bt can be used as an effective non-chemical approach for pest management for tea pests in the same geographical region, yet, it may potentially affect the silk industry which depends on silkworm. There is a need to identify the potentially lethal impact (through evaluating their mortality potential) of local Bt strains on key silkworm species in North Eastern India. This will allow the use of existing Bt for which the silkworms have natural resistance. Through this review, the authors aim to highlight recent progress in the use of Bt and its insecticidal toxins in tea pest control and the potential sensitivity for tea- and silk-producing zone of Assam in India.

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.