PESTICIDAL EFFICACY OF THREE TROPICAL HERBAL PLANTS’ LEAF EXTRACTS AGAINST MACROTERMES BELLICOSUS, AN EMERGING PEST OF COCOA, THEOBROMA CACAO L.

Abstract

ABSTRACT Insecticidal activity of the Phyllanthus amarus, Acassia albida and Tithonia diversifolia leaf crude extracts were evaluated against the workers of Macrotermes bellicosusin vitro. Different concentrations of the aqueous and ethanolic extracts (12.5%, 25%, 50%, 66.7%, and 75%) were tested against M. bellicosus which differed significantly (P < 0.05) from the control and standard (Thiamethoxam–Actara 25 WG). The aqueous extracts of P. amarus, A. albida and T. diversifolia caused 40-56%, 24-60% and 42-88% mortality, respectively after 140 minutes of exposure (MOE) to the extracts. The control resulted in 0% mortality, while the standard caused 100% mortality during the same period of 140 MOE. Similarly, ethanolic extracts of P. amarus, A. albida and T. diversifolia resulted in a significantly (P < 0.05) higher percentage mean mortality of 64 – 91 %, 36.4 – 76 % and 36 – 68 %, respectively. The toxicity ratings of the aqueous extracts ranged between low in 50% concentration of A. albida and very high in 75% concentration of T. diversifolia extracts, whereas, toxicity ratings of ethanolic extracts ranged between moderately low in 50% concentration of A. albida, as well as 12.5 % concentration of T. diversifolia and very high in 75 % concentration of P. amarus. Ethanol enhanced/potentiated the bio-insecticidal activities of some of the plant extracts used in this study. Further studies are needed to be carried out to know the fractional constituents of each plant species that is insecticidal in all the plants used in this study because different active compounds may have different biocidal properties, with different mixtures of the active ingredients so as to maximize the plants’ insecticidal properties.