Insecticidal Potentials and Chemical Composition of Essential Oils from the Leaves of Phyllanthus amarus and Stachytarpheta cayennensis in Nigeria

This research evaluated the insecticidal efficacy of essential oils from the leaves of Phyllanthus amarus and Stachytarpheta cayennensis on Periplaneta americana (American cockroach), Schistocerca americana (American grasshopper) and Anopheles gambiae (African malaria mosquito). A gas chromatography-Mass spectrometry (GC-MS) analysis of essential oils was also carried out to determine the active components of the oil likely responsible for the observed Insecticidal properties. Insects were exposed to 0.5g of essential oils as well as the positive control (Raid) for 24 hours and mortality observed and recorded every 4 hours. Both essential oils caused 100% mortality in test insects at different time intervals. P. amarus and S. cayennensis caused 60% and 73% mortality in A. gambiae at 8hours, 60% and 90% mortality in P. americana at 12 hours and 40% and 90% mortality in Schistocerca americana at 16hours. In all cases, S. americana recorded the least mortality among the test insects as compared to the other insects. S. cayennensis oil proved to be more potent than P. amarus oil. The result of the GC-MS analysis carried out on essential oils from both plants revealed the presence of; Decanoic acid, ethylester (Ethyl decanoate) 6.02%, Dodecanoic acid, ethylester (Ethyl dodecanoate) 11.26%, Tetradecanoic acid, ethylester (Ethyl tetradecanoate) 9.22%, Hexadecanoic acid, ethylester (Ethyl hexadecanoate) 10.16%, Phytol 28.52%, 9, 12, 15-Octadecatrienoic acid, rthylester (Ethyl linolenate) 11.34%, Stigmasta-7,25-dien 3-ol 7.95% and Decanoic acid, ethyl ester (Ethyl decanoate) 6.05%, Dodecanoic acid, ethyl ester (Ethyl dodecanoate) 10.89%, Tetradecanoic acid, ethyl ester (Ethyl tetradecanoate) 8.32%, Hexadecanoic acid ethyl ester (Ethyl palmitate) 5.01%, Phytol 8.27%, Linoleic acid, ethyl ester (Ethyl linolenate) 5.79%, 9,12,15-octadecatrienoic acid, ethyl ester (Ethyl linolenate) 5.79%, Vitamin E 8.29%, Stigmasterol 9.38% and beta-Sitosterol 16.67% for S. cayannensis and P. amarus respectively. The result from this study indicates that essential oils from these two plants contain potent insecticidal agents that are available, affordable, and effective in the control of insect pests as against the toxic synthetic chemicals currently in use.