Deterrent Effects of Clary Sage Oil and Two Major Constituents against Drosophila suzukii (Diptera: Drosophilidae)

Abstract

Drosophila suzukii (Diptera: Drosophilidae), spotted-wing drosophila, poses a significant threat to soft-skinned fruit crops in the Americas, Europe, Africa, and Oceania, as well as in Asia. The application of chemical insecticides is the primary control strategy for D. suzukii; however, resistance has developed with the indiscriminate use of chemical insecticides. Essential oils, considered potential alternatives to pesticidal strategies, exhibit potent toxic and sublethal behavioral effects against numerous pests, including D. suzukii. Clary sage oil repels a variety of agricultural and household pests; however, whether it has a repellent effect against D. suzukii remains unknown. Here, we found that clary sage oil exhibited dose-dependent repellency against D. suzukii adults in a T-maze assay, a two-choice assay and a two-choice attraction assay. Also, clary sage oil showed a significant repellent effect against D. suzukii larvae. Next, we explored the chemical constituents of clary sage oil by GC-MS and identified two major constituents, linalyl acetate (40.03%) and linalool (23.02%). Furthermore, the behavioral assays of linalyl acetate and linalool showed that both compounds conferred comparable repellency against D. suzukii adults and larvae. Finally, we found clary sage oil, linalyl acetate, and linalool elicited EAG responses in D. suzukii, especially clary sage oil, suggesting the repellency was mediated by the olfactory system. These findings indicate that D. suzukii shows olfactory-based behavioral avoidance of clary sage oil, linalyl acetate, and linalool. Clary sage oil and its major constituents may be possible alternatives in the management of D. suzukii.

Keywords: EAG; clary sage oil; linalool; linalyl acetate; repellency; spotted-wing drosophila.

Figure 1

Clary sage oil elicited repellency in Drosophila suzukii. (A) Schematic drawing of T-maze assay. (B) Preference index of D. suzukii for clary sage oil in T-maze assay. (C) Schematic drawing of two-choice assay. (D) Preference index of D. suzukii for clary sage oil in two-choice assay. (E) Schematic drawing of two-choice attraction assay. (F) Preference index of D. suzukii for clary sage oil in two-choice attraction assay. (G). Schematic drawing of larval two-choice assay. (H) Preference index of D. suzukii larvae for clary sage oil. Data are plotted as mean ± s.e.m. Dots denote the value of each repeat. Statistical analysis was conducted by using one-way analysis of variance (ANOVA) followed by Tukey’s means separation test in (D,F), and Kruskal–Wallis followed by Nemenyi test in (B,H). Asterisks indicate a significant difference between the preference index of compounds at different dilutions at ** p < 0.01.

Figure 2

Repellency elicited by linalyl acetate in Drosophila suzukii. (A) Preference index of D. suzukii for linalyl acetate in T-maze assay. (B) Preference index of D. suzukii for linalyl acetate in two-choice assay. (C) Preference index of D. suzukii for linalyl acetate in two-choice attraction assay. (D) Preference index of D. suzukii larvae for linalyl acetate. Data are plotted as mean ± s.e.m. Dots denote the value of each repeat. Statistical analysis was conducted by using one-way analysis of variance (ANOVA) followed by Tukey’s means separation test. Asterisks indicate a significant difference between preference indices of compounds at different dilutions at * p < 0.05 and ** p < 0.01.

Figure 3

Repellency elicited by linalool in Drosophila suzukii. (A) Preference index of D. suzukii for linalool in T-maze assay. (B) Preference index of D. suzukii for linalool in two-choice assay. (C) Preference index of D. suzukii for linalool in two-choice attraction assay. (D) Preference index of D. suzukii larvae for linalool. Data are plotted as mean ± s.e.m. Dots denote the value of each repeat. Statistical analysis was conducted by using one-way analysis of variance (ANOVA) followed by Tukey’s means separation test in (A–C) and Kruskal–Wallis followed by Nemenyi test in (D). Asterisks indicate a significant difference between preference indices of compounds at different dilutions at ** p < 0.01.

Figure 4

EAG responses of Drosophila suzukii adults to clary sage oil and its two major constituents. (A) Representative EAG traces elicited by clary sage oil, linalool, and linalyl acetate at 10⁻¹ dilution. (B) EAG responses to clary sage oil, linalool, and linalyl acetate. n ≥ 15 flies. Data are plotted as mean ± s.e.m. Statistical analysis was conducted by Student’s unpaired t-test, and asterisks indicate a significant difference between the response for control and odorants at * p < 0.05 and ** p < 0.01.