Chemical Composition of Five Botanical Powders and Their Insecticidal Activity Against the Rice Weevil, Sitophilus oryzae on Wheat Crop

The rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae) is a key pest of stored cereals in Egypt and elsewhere. The extensive use of synthetic insecticides in its control programs for several decades has led to undesirable effects on humans, the environment and non-targeted organisms. Several plant-based materials have been found to be effective against S. oryzae. The insecticidal performance of botanical powders made from certain parts of Guava, Psidium guajava, Pomegranate, Punica granatum L., Snow thistle, Sonchus oleraceus, Thyme, Thymus vulgaris L.andPurslane, Portulaca oleracea at rates of 1, 2, 4, 6, 8 and 10 g/50 g wheat grains were evaluated against Sitophilus oryzae adults at 3, 7, 10 and 14 days after treatment (DAT). The chemical compositions of the oils extracted from these plant powders were characterized by gas chromatography coupled with mass spectrometry (GC-MS). The major constituents identified in the isolated oils of P. guajava, P. granatum L., S. oleraceus, T. vulgaris L. and P. oleracea powders were caryophyllene (24.34%), 2-furancarboxaldehyde, 5-(hydroxymethyl)- (50.76%), 9-Hexadecenoic acid (13.47%), phenol, 2-methyl-5-(1-methylethyl)- (24.28%) and 9,12-Octadecadienoic acid (Z,Z)- (13.04%), respectively. All the evaluated powders significantly caused S. oryzae adult mortality compared with controls at 3 DAT, even if at the lowest used application rate (1 g powder/50 g wheat grains). The application of P. guajava and T. vulgaris powders at 10 g l/50 g wheat grains showed the highest adult activity, giving the same excellent mortality (93%) at 14 DAT. This was followed by the treatments of S. oleraceus, P. oleracea and P. granatum powders, providing 91, 86 and 70% adult mortality at 14 DAT. These effective plant-based materials could be helpful in lowering chemical pesticides use and should be considered an effective IPM strategy for controlling S. oryzae.