Phytochemical Composition And Insecticidal Activities Of Some Botanicals On Three Stored Product Pests

ABSTRACT

Ten out of the seven two plants marketed in Lagos State for medicinal and agricultural uses were selected for a study into their insecticidal activity. The ten selected plants Uvaria chamae, Jatropha curcas, Lophira alata, Ageratum conyzoides, Hyptis suaveolens, Alstonia boonei, Plumbago zeylanica, Tephrosia vogelii, Anacardium occidentale and Momordica charantia, were screened in the laboratory for bioactivity against three test insects namely Callosobruchus maculatus (F.), Sitophilus zeamais (Motsch) and Rhizopertha dominica (F.). The dust, ethanolic and aqueous extracts, as well as the oil formulations of the plant species showed that U. chamae, J. curcas, P. zeylanica, T. vogelii and L. alata were the five most toxic and were therefore further screened for elaborate evaluation for their toxicity and efficacy against the three test insects known for infestation of grains in storage. Generally, in the case of all the formulations of the plant species Uvaria chamae was the most toxic followed by Jatropha curcas, Plumbago zeylanica, Tephrosia vogelii, and Lophira alata against the test insects using their 48h LC50 values. Jatropha curcas oil was the most toxic followed by the ethanolic extracts, dust formulation, while the aqueous extracts was the least toxic The 48h LC50 values of Jatropha curcas oil, extracts and dust formulations for S. zeamais were 0.154mg/l, 0.308mg/l and 5.30g/kg respectively. The ethanolic extracts of each test plant species were consistently more toxic to each test insect species than the dust formulations of the same plant species. The 48h LC50 values of the ethanolic extract of U. chamae were 0.17 mg/l, 0.13mg/l and 0.36mg/l, for C. maculatus, S. zeamais and R. dominica while that of the dust formulation was 1.3g/kg, 2.1g/kg and 5.2g/kg respectively. Jatropha. curcas followed a similar trend in all the other plant species. Actellic dust was found to be more toxic than all other plant

species formulations. The toxicity factor of actellic dust when compared with the most toxic of plant dust was 15.0×, 25.8× and 26.7× more toxic for S. zeamais, R. dominica and C. maculatus respectively. TheThe toxicity of toxicity of JJ. . Curcas Curcas oil was comparable with that oil was comparable with that of the synthetic chemical of the synthetic chemical –– actellicactellic.. The efficacy of the oil and extracts reduced with time where the loss in bioactivitybioactivity was 4.7, 5.2, 8.9 and 10 foldwas 4.7, 5.2, 8.9 and 10 folds by the 14th s by the 14th dayday in in J. J. curcas, P.curcas, P. zeylanica, J. curcaszeylanica, J. curcas oiloil and and U. chamaeU. chamae respectivelyrespectively.. Jatropha curcas oil was the most effective in suppressing egg laying followed by the ethanolic extracts J. curcas, U. chamae and P. zeylanica. They all exhibited ovicidal action and reduced progeny development of C. maculatus. The eggs laid decreased with increase in concentration with 14, 19, 24 eggs laid on J. curcas, U. chamae. curcas, U. chamae,, P. zeylanicaP. zeylanica at 1.60mg/l treatment respectively and 95 eggs in the control. the control. Jatropha curcas oil was the most potent against the various life stages of C. maculatus with no adult emergence at 2.00 and 4.00μl/l, while 69 adults emerged in the control. An average of 4, 10, 14 adults emerged on treated cowpea seeds with J. curcas, U. chamae and P. zeylanica at 1.6g/l, while 72 adults emerged in the control. In the hermetic storage of cowpea and maize treatment J. curcas extract protected cowpea and maize grains for four, and three months respectively, while U. chamae and P. zeylanica each protected cowpea and maize grains for three and two months respectively. Chemical analysis showed that P. zeylanica, U. chamae and J. curcas contained alkaloids, tannins, glycosides, saponins, anthraquinone and flavonoids. GC-MS showed that P. zeylanica contained four compounds of which 9, 12, - octadecadienoic acid (z, z) - had the highest percentage occurrence (89.7%). J. curcas contained seven compounds of which 9, 12, - octadecadienoic acid (z, z) - had the highest percentage occurrence (48.1%),while U. chamae contained 11 compounds of which 9 – octadecenoic acid (e) - had the highest percentage occurrence (33.4.1%). Octadecanoic acid and N- Hexadecanoic acid was present in all the three extracts, and may be the main active ingredients in the tested plant species. The bioassay showed that the toxicity was dependent on plant formulations and insect species.