Pesticidal activity of abrus precatorius linn. (fabaceae) against polyphagous field pest spodoptera litura (fab.) (lepidoptera:noctuidae)

Mathivanan Thangarasu, Krishnappa Kaliyamoorthy, Elumalai Kuppusamy

To evaluate the pesticidal activity of antifeedant, ovicidal, oviposition deterrent, and larvicidal activities of hexane, diethyl ether, dichloromethane, ethyl acetate and methanol extract of Abrus precatorius at different concentrations against agricultural polyphagous field pest Spodoptera litura (Lepidoptera:Noctuidae). Antifeedant activities of the selected plant extract were studied using leaf disc no-choice method as described by Isman et al., (1990), with slight modifications. Five replicates were maintained for each concentration and the progressive consumption of leaf area by the larvae after 24h was recorded in control and treated discs using leaf area. The ovicidal activity was determined against S. litura to various concentrations were tested under laboratory conditions and the hatch rates were assessed 120 h post treatment. For oviposition deterrent activity, ten pairs of (adult moths) S.litura were introduced in individual cage. 10% (w/v) sucrose solution with multivitamin drops was provided for adult feeding to increasing fecundity, five replicates were maintained for control and treatments. After 48h, the numbers of eggs masses laid on treated and control leaves were recorded and the percentage of oviposition deterrence was calculated. Twenty five early fourth instar larvae of S. litura was exposed to various concentrations and was assayed in the laboratory by using the protocol of Abbott’s formula (1925); the 24h LC50 values of the A. precatorius leaf extract was determined by probit analysis. The antifeedant activity of Abrus precatorius tested against S. litura fourth instar larvae was determined during a 24 hours test period. All extracts are showed moderate antifeedant activitiy; however, least antifeedant activity was noted in hexane and significant antifeedant activity was observed in methanol extract. In general, the oviposition deterrency is directly proportional to the increase in the concentration and also among the various extracts tested, methanol extract was found to have significant activity than the other solvent extracts. Among five extracts tested, methanol extracts of Abrus precatorius were found to be most significant ovicidal activity 100% at 300ppm concentration. Maximum larvicidal activity was observed in the methanol extract of Abrus precatorius followed by ethyl acetate, hexane, dichloromethane and diethyl ether. The significant larvicidal activity was recorded from the highest concentration of methanol extract at 500 ppm and the least larvicidal activity was recorded from the 100ppm concentration of diethyl ether extract. Lethal concentration, LC50 value of hexane, diethyl ether, dichloromethane, ethyl acetate and methanol extract of Abrus precatorius were 255.91, 266.21, 265.98, 251.84 and 225.76 ppm respectively. The chi-square values are significant at p≤ 0.05 level. Among five solvent extracts, the methanol extract was responsible for strong lethal activity observed against selected pest species. Results of this study show that the selected Indian medicinal plant may be a potent source of natural antifeedant, oviposition deterrent, ovicidal and larvicidal activities against selected important agricultural lepidopteran polyphagous field pest S. litura.

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