Terpenes and phenylpropanoids for the control of Drosophila suzukii (Diptera: Drosophilidae): Toxicity, oxidative stress, histopathology, and selectivity

Plants' secondary metabolites, in particular terpenes and phenylpropanoids, represent a good source of bioactive molecules for developing biopesticides as an alternative to synthetic pesticides. The great diversity of these classes of biomolecules has not been fully investigated. This work aimed to evaluate the toxicity of five terpenes and four phenylpropanoids to adults, 3rd instar larvae, and pupae of the Spotted wing drosophila, Drosophila suzukii; to evaluate the effect of sublethal exposure to LC50 concentrations of the four most toxic compounds on oxidative stress enzymes and on histological structures of the adult flies; and to evaluate the potential side effects of these compounds on a non-target organism, the earwig Doru luteipes. The results demonstrate that the terpenes L-(-)-carvone and carvacrol and the phenylpropanoids (E)-anethole and (E)-cinnamaldehyde, with respective LC50 s of 3.13, 4.47, 4.22 and 4.60 mM, presented the highest toxicities to D. suzukii adults. These compounds promoted considerable mortality of pupae and deformation in adults. The LC50s of L-(-)-carvone and carvacrol, (E)-anethole, and (E)-cinnamaldehyde also affected the activity of the detoxifying enzymes SOD, CAT, and GST mostly 4 hours after exposure. Histological and histochemical analyses revealed that exposure to these compounds promoted changes in the thickness of the exoskeleton, midgut, and hindgut. Furthermore, the area and density of lipid droplets in the fat body and carbohydrate concentration in muscle fibers and the fat body decreased in treated groups. The terpene carvacrol promoted the most severe histological changes. Finally, the survival and feeding capacity of the non-target organism D. luteipes were not significantly affected by exposure to the selected terpenes and phenylpropanoids making them promising options for controlling D. suzukii. •Five terpenes and four phenylpropanoids were tested on D. suzukii adults and larvae.•Carvone, carvacrol, anethole and cinnamaldehyde were the most toxic.•Terpenes and phenylpropanoids negatively affected SOD, CAT, and GST activities.•Terpenes and phenylpropanoids induced histological and histochemical alterations.