EVALUATION OF TWO COLEOPTERANS, SITOPHILUS ORYZAE (L.) AND ORYZAEPHILUS SURINAMENSIS (L.) SURVIVAL ON PLANT EXTRACT TREATED RICE CULTIVARS IN NIGERIA

Abstract

Food production is very vital to the growth of any nation. Rice is a staple food for people living in rural and urban communities. One of the major threats against availability of rice is insect pest infestation in which both primary and secondary insect pests are involved. Although various synthetic chemical insecticides had been used against insect pests of rice but the effects of their residue on the health of rice consumers call for altinative save insecticides for food preservation. There is a need to search and screen for viable botanicals without harmful health effects on consumers. Therefore, this study assessed the impact of botanicals as a preservative for rice cultivars in southwestern Nigeria. Four kilograms each of eleven rice cultivars were collected in five states within southwestern Nigeria (Ekiti, Oyo, Ogun, Ondo, and Osun). Identified rice samples were assessed for proximate and heavy metal contents. Susceptibility tests of the rice cultivars were carried out by introducing rice weevil (Sitophilus oryzae) and saw-toothed grain beetle (Oryzaephilus surinamensis). Gas Chromatography/Mass Spectrometry (GC/MS) was used to check the array of biochemical compounds in the rice samples. Methanolic extracts from three plant materials (Agerantum conyzoides, Petiveria alliacea, and Hyptis suaveolens) were tested for potential control of the two insect pests. Ten Sitophilus oryzae and Oryzaephilus surinamensis were introduced separately into 10 g of the rice samples. Methanolic extract from the A. conyzoides, P. alliacea, and H. suaveolens leaves were introduced in different concentrations (0.5, 1.0, 1.5, 2.0 and 2.5) % for the period of 24, 48, 72, 96, and 120 hours. The solvent (methanol) was used as the control (0.0%). The most potent plant extracts were tested for acute toxicology effects on albino rats. The albino rats were grouped into four cohorts (four rats in a cohort) (control, 1, 2, and 3). The different cohorts were treated with the plant extract at 400mg/kg, 600mg/kg, and 1200mg/kg, while the control cohort was treated with normal saline. The extract was administered orally for 14 days. Toxicological effects were assessed using haematological parameters, as well as biochemical and histopathology of the Liver and kidney. Results obtained from this study revealed the range proximate composition of the rice cultivars as; moisture content 5.25 – 8.10 %, Crude fat 0.45 – 2.00%, Crude Protein 3.10 – 6.74, Ash 0.35-2.36, Crude fat 4.51-14.41; while Carbohydrate is between 71.54 and 79.10%. Among the heavy metals determined from the rice samples were Zinc (0.49 – 2.55), Manganese (0.07-1.62), Copper (0.02-0.21), and Nickel (0.03-0.08), with traces of Cadmium (0.01) in some of the rice cultivars, lead was not detected in all the rice samples. Hyptis suaveolens was more potent in controlling Sitophilus oryzae and Oryzaephilus surinamensis than Ageratum conyzoides and Petiveria alliacea. The value of haematological parameters was low in albino rats treated with the control (normal saline) compared with those treated with different concentrations of the extract of Hyptis suaveolens. Biochemical indices of the Liver, kidney, and serum showed normal function. The value of Aspartate Aminotransferase (AST), Alanine Aminotransferase (ALA), Creatinine urea, Alkaline Phosphatase (ALT), and Total Protein decreased compared to the control. The histopathology of the Liver across the groups showed moderate dilation of sinusoids and normal hepatocytes and intracellular infiltration in group one (400mh/kg bwt), mild architectural damage with slight sinusoids dilation, ballooning of some hepatocytes, necrosis and karyolysis in group two (600mg/kg bwt), while those in group three (1200mg/kg bwt) generally showed normal structure which is similar to the control. Also, compared to the control group, kidneys in group one (400mg/kg bwt) showed mild tubular injury with congestions, and animals in group two (600mg/kg bwt), showed a reduced number of bowman capsules and more tubular inflammations. In contrast, those in group three (1200mg/kg bwt) showed severe tubular inflammations with little or no obvious functional nephrons. This study demonstrates the potential safety of a methanolic extract of Hyptis suaveolens to the Liver and kidney at low concentrations but may have a greater capacity for hepatoxicity and nephrotoxicity at higher concentrations. Hyptis suaveolens is not only potent medicinally but also as a potent insecticide against stored product insect pests. H. suaveolens treated stored products are safe at a lower concentration since no severe damage was recorded on the vital organs.