Antifeedant and larvicidal activities of Swertia chirata Buch-Ham . ex Wall . against Helicoverpa armigera Hubner and Spodoptera litura Fab

Introduction In a tropical country like India, owing to climatic conditions and its particular environment, agriculture is suffering from severe losses due to pests. The Indian farmers are in need of effective tools to fight against pests [10]. The plant kingdom is the most efficient producer of chemical compounds, synthesizing many products that are used in defence against herbivores. Insect pests are serious limiting factors of food production throughout the world. Helicoverpa armigera Hub and Spodoptera litura Fab are notorious lepidopteran insects causing severe yield loss to several crops as they are polyphagous feeders. Synthetic pesticides have created many problems in the environment and living systems [14, 5]. The deleterious side effects caused by the synthetic pesticides have forced the scientific community to switch over to biological pesticides especially botanicals. Though the use of botanical pesticides is an age old practice in some countries like India, the actual mechanism of action rendered by botanicals is being explored by the scientists and this practice is revived by the farmers as an ecofriendly pest management strategy [3]. World wide attention has been focused on alternative methods to control the pests. Conventional synthetic organic pesticides are handicapped in the green context by their high toxicity, longterm persistence and propensity of bioaccumulation [11]. Some of them induce malignancy in non-target organisms, while most give rise to development of resistance in insect population or cause resurgence of minor/alternate pests [19]. However, pest suppression can be achieved through judicious use of pesticides, crop rotation, destruction of crop residues, change in sowing dates and other practices [15]. Considering the agro-ecosystems with an increase in population and dwindling land resources there is world wide demand for natural insecticides to increase the agriculture production. Due to these problems, a search is going on to discover new, less damaging pest management tools [15]. Microbial and botanical insecticides offer a more natural, environment friendly approach to pest control than synthetic insecticides [9]. No information is available so far on the antifeedant and larvicidal activities of our experimental S. chirata. Therefore the aim of the present work was to study the inhibitory effect of different solvent extracts of S. chirata against the two major lepidopteran pests (H. armigera and S. litura). This is the first report on the antifeedant and larvicidal activity of the solvent extracts of the selected test plant. Materials and methods Collection of plant material Healthy, disease free plants of S. chirata (whole plant) were collected from Darjeeling (West Bengal, India). The species was identified and authenticated by Dr. Jeya Jyothi, Taxonomist, Department of Plant Biology and Biotechnology, Loyola College, Chennai and the voucher specimen (LCH-1002) was deposited at the departmental herbarium. Freshly collected plant was washed thoroughly shade dried and powdered using an electric blender. Preparation of crude extract The plant powder (2 kg) was soaked sequentially in hexane, ethyl acetate, methanol and water in 1:3 ratios (w/v) for 72 h respectively with intermittent shaking. After 72 h the solution was filtered and the filtrate was concentrated under reduced pressure using rotary vacuum evaporator. The filtrate was air dried to yield 25 g of hexane extract, 42 g of ethyl acetate extract, 37 g of methanol extract and 18 g of aqueous extract and stored at 4 O C in air tight containers until further use. Insect culture H. armigera and S. litura larvae were collected from vegetable agro ecosystem outside Chennai, India. S. litura larvae were maintained on the castor (Ricinus communis L.) leaves and H. armigera larvae were maintained on semi-synthetic diet [16]