Synergism, biochemical changes and morphophysiological impacts induced by terpenes and phenylpropanoids in Sitophilus...

This study aimed to investigate the insecticidal properties of pure and binary mixtures of L-(-)-carvone, carvacrol, β-citronellol, (E)-anethole, (E)-cinnamaldehyde, p-anisaldehyde, and eugenol on adults of Sitophilus zeamais, an important pest of stored grains. Subsequently, the effects of selected compounds on the activity of oxidative stress-related detoxifying enzymes and digestive enzymes, as well as on the histopathology of S. zeamais adults were evaluated. Finally, the selectivity of these compounds to the non-target pupal parasitoid Tetrastichus howardi was assessed. Carvacrol exhibited the highest insecticidal activity (LC₅₀ = 3.31 μL.mL^-1), followed by (E)-cinnamaldehyde (LC₅₀ = 4.15 μL.mL^-1) and p-anisaldehyde (LC₅₀ = 4.48 μL.mL^-1) meanwhile (E)-anethole showed the greatest synergistic activity in binary mixtures. p-anisaldehyde promoted strong activation of the enzymes catalase, glutathione-S-transferase, and glutathione peroxidase while both (E)-cinnamaldehyde and p-anisaldehyde increased the malondialdehyde content and lipid peroxidation compared to the control. Additionally, p-anisaldehyde strongly inhibited α-amylase activity and increased lipase activity. Moreover, insects exposed to carvacrol, (E)-cinnamaldehyde, and p-anisaldehyde exhibited decreased abdominal muscle fiber thickness, midgut epithelial thickness, midgut regenerative crypt diameter, as well as reduced lipid droplet area and carbohydrate concentration in the fat body. (E)-cinnamaldehyde was the compound that showed the greatest compatibility with the non-target organism T. howardi. Taken together, our findings suggest that these natural compounds promote appreciable insecticidal activity and are alternatives for the control of S. zeamais.