Insecticidal activity of Aguaria salicifolia leaf extracts on cowpea bruchid Callosobruchus maculatus (Coleoptera: Chrysomelidae)

The protection of foodstuffs against insect pests constitutes a serious problem across the world. Synthetic chemical insecticides are the most widely used method for grain protection. Unfortunately, the harmful effects of these insecticides on human health and environment have increased the interest of researchers for botanical insecticides which are recognized as eco-friendly products. Therefore, the efficacy of Aguaria salicifolia Hook. f. ex Oliv. leaf extracts was tested against Callosobruchus maculatus F. on cowpea grain, at the dosage of 2, 4, 8 and 16 g/kg. To estimate the biological activity of leaf powder and aqueous extract, adult mortality, insect population growth reduction, grain damage and weight loss reduction tests were carried out. The repellency effect of A. salicifolia was assessed using the aqueous, methanolic and ethyl acetate extracts. The mortality was recorded at 1, 3, 5 and 6 days post-exposure. All treatments were submitted to four replications, and the experiment was carried out in a completely randomised design in the fluctuating laboratory conditions (Temp. = 23.71 ± 1.03 °C; RH. = 81.38 ± 2.03 %). Overall, all the extracts significantly exhibited insecticidal activities against cowpea bruchids. The highest dosage induced the highest mortality rates; 79.26 % and 84.08 % with aqueous extract and leaf powder, respectively. The different plant extracts considerably reduced insect population, grain damage and weight loss. The complete reduction of C. maculatus population was achieved by aqueous extract of A. salicifolia. The different solvent extracts had repellent property with repellency percentage values ranging from 30 % to 73.75 %. Considering these results, insecticidal products derived from A. salicifolia could constitute an alternative to the chemical synthetic insecticides used against C. maculatus. However, further studies are needed to be carried out concerning the mammalian toxicity and evaluation of suitable formulations of the extracts under field conditions before their promotion for grain protection.