Comparative and Synergistic Influence of Extracts of Two Tropical Plants on the Activity of the Cowpea Weevil, <i>Callosobruchus chinensis</i>

Abstract

The chemical composition of ethanolic extracts of Zingiber officinale rhizome and Moringa oleifera seeds was examined and their individual and combined toxicity assayed against some aspects of the developmental biology of Callosobruchus chinensis . GC-MS revealed forty-one (41) chemical components in ethanolic extract of Z. officinale rhizome and thirteen (13) chemical components in ethanolic extract of M. oleifera seed. 1-(4-Hydroxy-3-methoxyphenyl)-dec-en-3-one (12.40%) and 1-(4-Hydroxy-3-methoxyphenyl) tetradec-4-en-3-one (9.05%) were the most abundant components ethanolic extract of Z. officinale accounting for about 22% of the total oil. Hexadecanoic acid, ethyl ester (22.33%) and 11-Octadecenoic acid, methyl ester (18.09%) were the most abundant components in M. oleifera accounting for about 40% of the total oil. Z. officinale oil was more toxic to C. chinensis than M. oleifera oil (LC 50 : Z. officinale = 24.00 µl; M. oleifera = 38.00 µl). By contrast, the median lethal time (LT 50 ) required to kill 50% of C. chinenesis by extract mixture ( Z . offcinale and M. oleifera ) (36.36 h) was significantly lower (p < 0.05) than those gotten at singular exposure of Z. officinale (64.61 h) and M. oleifera (76.44 h). Thus, the results exemplify the individual applicability of ethanolic extracts of Zingiber officinale and Moringa oleifera as C. chinensis biocide. When combined, the results confirm the synergistic potentials of the oils. This knowledge may facilitate the discovery of components that are essential in the design of an effective cum sustainable biopesticide with multiple modes of actions.