Effect of plant extracts and essential oils on major Lepidopteran pests of cruciferous crops
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Date
2018-10
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College of Post Graduate Studies in Agricultural Sciences, Central Agricultural University , Imphal
Abstract
Vegetable production is an important source of income to the farmers of NE region. The lepidopteran pests are one of the most important constraints in vegetable production. Leaf defoliators, Spodoptera litura, Plutella xylostella and Pieris brassicae are three important pests attacking cruciferous plants. Fresh eggs of the major defoliating insect pests on vegetables viz., leaf eating caterpillar, S. Litura (Fabricius), the large cabbage white butterfly, P. brassicae (Linnaeus) and the diamondback moth, Plutella xylostella (Linnaeus) were collected from the unsprayed vegetable field of Division of Crop Protection (Entomology), ICAR Research Complex for NEH Region, Umiam, Meghalaya, during the year 2017-18 and further reared inlaboratory for different experiments on castor, cabbage and knol khol plants, respectively. Plant extracts from different plants viz., Vitex negundo, Curcumaangustifolia, Parkia roxburghii and Fleminga vestita were collected from Division of Crop Protection (Entomology). Essential oils viz., Cymbopogon citratus, Piper nigrum, Mentha piperita, Occimum basilicum and Rosmarinus officinalis were collected from ICAR, Umiam and some are purchased commercially. The test insects were exposed (In contact and oral toxicity) to plant extracts/oils in 2nd instar larval stage (i.e. most active feeding stage). Toxicity test were conducted by standard protocols: Topical application technique: Direct contact (fixed dose) (Mclaughlin et al., 1998) and Leaf dip method: Oral toxicity (Hoskins and Craig., 1962). Concentrations of the extracts were determined on the basis of preliminary experiments on the test insects. Seven concentrations (including control) of each extract were tested against test insects.Overall results revealed that, in topical application technique, LC50 value of O.basilicum was observed to be 0.09 per cent and V. negundo 1.99 per cent, against the caterpillars (2nd instar) of S. litura at 72 hrs; whereas it was found to be 0.28 per cent and 1.59 per cent on P. xylostella, respectively. In case of P. brassicae, LC50 of Pipernigrum oil and V. negundo extract was observed to be 0.02 per cent and 0.71 per cent. When the caterpillars of S. litura, P. brassicae and P. xylostella were topically treated with sub-lethal doses, the significant variation was observed in larval and pupal weight, their duration, per cent pupation and adult emergence. Inverse relationship was found in leaf area consumption by the caterpillars on different extracts. Food consumption was significantly reduced in treated larvae of the two pest species (S. litura and P.brassicae) compared to untreated larvae in control. From the present study, it can be concluded that, n-hexane fraction of Vitex negundo and essential oils of Ocimumbasilicum and Piper nigrum are most effective against major cruciferous defoliators and thus, they can be formulated and further evaluated for their potential under field conditions in organic farming.