Abstract
Grains are stored worldwide after harvesting for food and seed. During storage grain loss occurs because of insect pests. Stored grain insect pests have long range of hosts, from cereals to dry fruits and legumes. Callosobruchus maculatus (Fabricius) (Chrysomelidae; Coleoptera) and Trogoderma granarium (Everts) (Dermestidae; Coleoptera) are key pests of stored products and can loss 50% of the commodity during storage. Multiple measures have been adopted worldwide to minimize this loss but the problem remains constant. Conventional fumigants are being restricted in application because of development of insecticide resistance in insect pests. Hence, development of a promising tool for sustainable management and food security is required. This study describes development of nano-formulated biopesticides for managing stored product insect pests C. maculatus and T. granarium. Cysteine protease (PeuCP) from Populus euphratica was extracted, purified (by ammonium sulfate saturation prior to gel filtration chromatography), and identified through LC-MS/MS. The molecular interaction of PeuCP with substrate (chitin) was documented via in-silico study. The insecticidal activity of PeuCP was assessed through bioassays against the mentioned stored product insect pests at three concentrations (10, 5 and 2.5 mg/g). Computational analysis showed molecular interaction of PeuCP at five potential sites for ligand (N-acetyl-D-glucosamine) binding in which the strongest site with the highest drug score (Site-1) was located near N-terminus. The insecticidal assays of PeuCP without nano-formulation revealed inhibited population buildup of C. maculatus and delayed life stages development in T. granarium. The growth inhibition of tested insects confirmed the substrate binding of PeuCP. The PeuCP was formulated with Graphene Quantum Dots (GQDs) and Zinc Oxide Nanoparticles (ZnO NPs) for increased insecticidal activity, among which GQDs nanoformulation was more promising. Nanoformulated PeuCP had the potential to control stored grain insect pests as alternative to chemical insecticides.