Antibacterial and antifeedant activities of Spilanthes acmella leaf extract against Gram-negative and Gram-positive bacteria and brinjal fruit borer,Leucinodes orbonalis larvae

Objective:To evaluate the antibacterial and antifeedant activities of dichloromethane,acetone and aqueous extracts of Spilanthes acmella(L.)(S.acmella)Murr against selected bacterial strains and larvae of Leucinodes orbonalis Guen.Methods:Solvent extracts were tested against pathogenic microbes using disc diffusion method and fruit disc no-choice method for antifeedant activity.Results:The study revealed that dichloromethane extract of S.acmella leaf showed broad spectrum antibacterial activity against all the tested bacteria.Maximum zone of inhibition was observed in dichloromethane leaf extract of S.acmella against Escherichia coli[(18.9±0.34)mm]followed by Staphylococcus aureus[(18.6±1.31)mm],Proteus vulgaris[(17.2±0.68)mm],Bacillus subtilis[(17.0±0.76)mm]and Klebsiella pneumonia[(16.4±1.55)mm]at 5 mg/disc concentration.The aqueous extract was moderately inhibited the tested bacteria at all the concentrations.Dichloromethane extract showed good antifeedant activity against Leucinodes orbonalis(68.88%)when compared to acetone(60.80%)and aqueous(45.48%)extracts at 5%concentration.The preliminary phytochemical analysis showed the presence of alkaloids,terpenoids,phytosterols,saponins,steroid,tannins and phenolic compounds.Conclusions:The study suggests that the dichloromethane leaf extract of S.acmella could be used to develop a novel herbal formulation to control pathogenic bacteria and agricultural pests.

Phytopesticidal effects of Spilanthes acmella(L.)Murr.leaves on three economically important lepidopteran insect pests

Objective:To evaluate the antifeedant and larvicidal activities of dichloromethane(DCM),acetone,dimethylsulfoxide(DMSO)and aqueous extracts of Spilanthes acmella(S.acmella)leaves against Earias vitella,Helicoverpa armigera and Spodoptera litura.Methods:DCM,acetone,DMSO and aqueous extracts were studied using fruit and leaf discs no-choice method at 0.625%,1.25%,2.5%and 5%concentration.Results:All the extracts showed antifeedant and larvicidal activities against all the tested insects.However,maximum antifeedant activity was detected in DCM extract of S.acmella against all tested pest,followed by acetone,DMSO and aqueous extracts at 5%concentration.The leaves extract of S.acmella also showed larvicidal activity;maximum larval mortality was observed in DCM extract against Helicoverpa armigera(48.88%),Spodoptera litura(44.88%)and Earias vitella(75.11%)followed by acetone,DMSO and aqueous extracts at 5%concentration.Conclusions:DCM extract of S.acmella could be further purified to develop a formulation for eco-friendly pest control agent.