CHEMICAL COMPOSITION, TOXICITY AND BIOCHEMICAL ACTIVITIES OF SOME BOTANICAL EXTRACTS AGAINST THREE MAJOR STORED GRAIN BEETLES

Abstract

The insecticidal, biochemical, toxicological studies and chemical compositions of Clerodendrum capitatum¸ Phyllanthus fraternus, Mitracarpus villosus and Bridelia micrantha crude extracts and sub active fraction for the management of Sitophilus oryzae (L.), Rhyzopertha dominica (F.) and Tribolium castaneum (Herbst) were investigated ambient laboratory conditions. The bioactive chemical composition of the herbal formulation obtained from the various plant extracts active fractions was determined by Gas Chromatography-Mass Spectrometry (GC-MS). Toxicological effects were considered by quantifying liver and kidney enzymes such as aspartate amino transferase (AST), alanine amino transferase (ALT), alkaline phosphatase (ALP), total protein, creatinine and urea respectively. While, phytotoxicity of active extracts on seed germination were equally assayed at 24 and 72 h after treatment exposure time. Results from the study revealed that a total of 14 components representing 97.8% of the formulation were identified from C. capitatum and the main compounds in the formulation were found to be 2-Heptanone, 3-methyl- (33.9 %) and Hexahydrofarnesyl acetone (25.3%) followed by 3-Dodecen-1-al (10.2%) and 8-Methyl-1-undecene (4.9%). The GC-MS analysis of petroleum ether 50%: ethyl acetate 50% active fraction of M. villosus revealed the presence of Methyl 20-methyl-heneicosanoate, Heptadecanoic acid, Tetracosanoic acid, 2-Bromododecane, 7-Hexadecenioc acid and Nonane, 2, 6-dimethyl as the principal chemical compounds. Active fraction of B. micrantha extract revealed that Dibutyl phthalate (96%), 3-Dodecen-1-al (87%), 13-docosen-1-ol (83%) Ethanol-2-(2-butoxyethoxy) (80%), 2-Butenoic acid, 2 propentl (47%), 4-Hydroxyphenylacetic acid (38%) and Phenyl salicylate (30%) were the major constituents out of the eleven bioactive compound identified. The principal compound in the active sub fractions of P. fraternus was methyl palmitate (81.8%) followed by 2, 6-diisopropylnaphthalene (4.3%), 2, 4, 6-trimethyloctane (1.3), 2-pentadecanone, 6, 10.14-trimethyl (2.1%), 4-methoxy-1, 3-butanediol (2.1%), stearic acid (8.2 %) and ethanol, 2 – (-2-ethyoxy) (0.8%). Fumigant activity of sub active fraction of C. capitatum¸ P. fraternus, M. villosus and B. micrantha extracts was found to be concentration-exposure time dependentand highly toxic to mixed age cultures. In general, the repellent activity produced moderate to strong repellence against adult stages of stored grain and varied with insect pests. Toxicological effect show that, there were significant alterations in biochemical indices of AST, ALT, ALP, TP, urea and creatinine in treated animals in comparison to the untreated ones as the concentrations of extracts increased. However, the alteration in treated animal kidney and liver function were neither nephrotoxic nor hepatotoxic. The plant extracts strengthen the non-phytotoxic nature of plant products against seed viability and germination as seeds treated with sub active fraction extracts (50-400 μg seed-1) as it resulted in successful and normal germination within the range of 90 – 97.67% irrespective of the extracts concentration; comparable with seed in control. Antioxidant enzyme system was marked with distinct variations in treated insect species. Superoxide Dismutase (SOD), Catalase (CAT) and Reduced Glutathione (GSH) was significantly elevated with increasing concentration of plant active fractions and exposure period. While, Glutathione peroxidase (GPx) and Glutathione-S-transferase activity (GST) activity was significantly decreased. The active fractions of the various plant extracts significantly inhibited Acetylcholinesterase (AChE) activity with increasing concentrations following 3, 6 and 12 h exposure compared to control. The trend of sensitivity to the plant active fractions was, however, in concentration and exposure period dependent manner. Based on findings from the study, the insecticidal properties exhibited by various plant extracts were due to the volatile chemical compounds identified from the plants. They possess moderately safety index with respects to the liver and kidney functions at concentrations up to 2000 mg/kg body weight of the rats. However, further investigation is necessary to evaluate the effects of the plant extracts active fractions on the organoleptic properties of the stored food grains.