Phytochemical screening and insecticidal activity of leaf extracts of Bryophyllum pinnatum and Eucalptus globules against rice weevil (Sitophilus oryzae)

Abstract

Ethanolic extracts of the leaves of Bryophyllum pinnatum and Eucalptus globules were screened for secondary metabolite constituents and insecticidal activity against rice weevil (Sitophilus oryzae). Phytochemical screening of the extracts revealed the presence of alkaloids, flavonoids, saponins, steroids, tannins, phlobatannins and terpenoids in the plants investigated. Phlobatannins and terpenoids were found to be absent in ethanol extract of Eucalptus globules (leaf) while steroidal compounds were absent in Bryophyllum pinnatum (leaf). The extracts of B. pinnatum and E. globules of different concentrations were also investigated for their insecticidal activity against S. oryzae. Average mortality percentage indicated that the extracts caused significant mortality on the targeted insects. The bioassay indicated that the toxic effect of the extracts was proportional to the concentration, and higher concentrations had stronger effects. The observed mortality percentage also increased with increase in time intervals after treatment. The mortality percentage at 0.25, 0.50, 0.70, 1.00 and 1.50 h after treatment (HAT) indicated that 4% solution of the extracts of E. globules and B. pinnatum showed the highest mortality of 37.00% and 35.00% respectively in S. oryzae at 1.50 h after treatment. It could be inferred from the study that extract from E. globules leaf could cause significant mortality compared to extract of B. pinnatum.

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Keywords: Mortality, Phytochemical, Insecticidal activity, Bryophyllum pinnatum, Eucalptus globules, Sitophilus oryzae.