Insecticidal and Histological Effects of Extracts from Leaves of Juglans regia L. Against Sitophilus oryzae (Coleoptera: Curculionidae) Isolated from Soft Wheat in Post-harvest

Abstract

In Algeria, the cultivation of soft wheat (Triticum aestivum Linn.) plays a crucial role in the food chain. However, the crop faces a threat from Sitophilus oryzae (Coleoptera: Curculionidae), which causes substantial economic losses. This study aims to discover novel bioactive compounds derived from Juglans regia Linn., a walnut tree grown in Algeria, to combat S. oryzae. This study focuses on extraction, phytochemical characterization, insecticidal effect against S. oryzae adults, and histological impact. GCMS analysis of the petroleum ether (EPJ) and chloroform (CHJ) fractions indicated the presence of a diverse range of bioactive molecules, including myrtenal (1.17%), eugenol (46.17%), methyl ester (25.84%), lycophyll (5.16%), and hexadecane (1.22%), which are derived from terpenoids, phenols, and fatty acids. LCMS/MS analysis of the ethyl acetate (AEJ) and butanolic (BTJ) fractions identified compounds mainly associated with hydrocinnamic acids, flavonols, flavones, and naphtoquinones, such as 3-caffeoylquinic acid, epi-catechin isomer, kaempferol-3-glucoside, and hydro-juglone derivative. Furthermore, the efficacy of the five extracts (hydromethanolic extract and the four fractions) against S. oryzae adults was evaluated at 625, 315, and 75 µg/mL concentrations over 7 days. EPJ and BTJ demonstrated the highest effectiveness among these extracts, as indicated by their relatively low LC50, LC90, LT50, and LT90 values. These results highlight the potential of EPJ and BTJ, derived from walnut leaves, as biocontrol agents against S. oryzae. Histological analysis of the treated insects revealed significant alterations in various tissues compared to untreated adults. This research gives the first evidence that J. regia grown in Algeria is a promising biocontrol agent against pest beetles in stored soft wheat.