Biopesticidal activities of three botanicals (Ageratum conyzoides L., Petiveria alliacea L. and Hyptis suaveolens L. Poit,) against Sitophilus oryzae L

This study was carried out to evaluate the effectiveness of oil extracts from Ageratum conyzoides L., Petiveria alliacea L., and Hyptis suaveolens L. as biopesticides against Sitophilus oryzae in the Entomology Laboratory of Federal University of Technology Akure, Ondo State. The experiments were conducted at a temperature of 28±2°C and a relative humidity of 75±5%. Methanol was used as a solvent to extract the oil from the plants, and different concentrations (0.5%, 1.0%, 1.5%, 2.0%, and 2.5%) of each plant extract were prepared. The results demonstrated that the oil extracts from all three plants had a significant impact on the mortality of Sitophilus oryzae. Among them, the oil extract from Hyptis suaveolens proved to be the most effective, causing 100% mortality of Sitophilus oryzae at 2.0% and 2.5% concentrations within 96 hours of introduction. The LD50 (concentration required to cause 50% mortality) for Hyptis suaveolens was 0.53 (at 96 hours) and 0.36 (at 120 hours), while the LD90 (concentration required to cause 90% mortality) was 4.27 (at 96 hours) and 1.86 (at 120 hours) for Sitophilus oryzae. Furthermore, the oil extracts of all three plants significantly reduced adult emergence of the insects and prevented weight loss in the seeds. These effects were particularly prominent at concentrations of 2.0% and 2.5%. Statistical analysis indicated significant differences (p < 0.05) between the treatments and control groups for all the parameters assessed. In conclusion, the results of this study demonstrated that the leaf extract of Hyptis suaveolens was more effective than the extracts from the other plants in reducing Sitophilus oryzae populations, inhibiting adult emergence, and preventing weight loss in stored grains. Therefore, Hyptis suaveolens can be considered as a valuable addition to the range of botanicals used for Sitophilus oryzae control in food storage.