Monarda didyma Hydrolate Affects the Survival and the Behaviour of Drosophila suzukii

Abstract

Drosophila suzukii (Matsumara) is an herbivorous pest whose control in the field with conventional chemical is particularly difficult and has important drawbacks. Here, we investigated the insecticidal properties of hydrolate from Monarda didyma, scarlet beebalm, an aromatic herb in the Lamiaceae family. The identification of volatile organic compounds (VOCs) by CG-MS systems revealed that thymol (38%) and carvacrol (59%) were the most abundant VOCs in the hydrolate. M. didyma hydrolate did not show fumigant toxicity. Conversely, in contact assays, M. didyma hydrolate showed a LC₅₀ of 5.03 µL mL^-1, 48 h after the application on D. suzukii adults. Expression of detoxification genes increased in flies that survived the LC₅₀ application. Furthermore, toxicity persisted for 7 days after the treatment in the survival evaluation. Artificial diet assays with 100 and 1000 µL mL^-1 of M. didyma hydrolate resulted in a significant decrease in total food intake in both male and female D. suzukii adults. In addition, electropenetrography (EPG) showed that the D. suzukii females' feeding behaviour was altered in hydrolate-treated diets. The hydrolate also caused a significant reduction in the number of eggs laid in two different oviposition assays. Overall, our findings provide a new perspective for the improvement of D. suzukii control strategies through M. didyma hydrolate.

Keywords: Drosophila suzukii; Lamiaceae; Monarda didyma; biopesticide; egg-laying assay; essential oils; hydrolate; monoterpenes; pest control.

Figure 1

Electropenetrography (EPG) setup scheme used to analyse the D. suzukii feeding behaviour on artificial diets.

Figure 2

Total ion chromatogram (TIC) of monoterpenes and other volatile organic compounds present in M. didyma HY.

Figure 3

Effect of M. didyma contact exposure on survival and detoxification enzyme expression. Survival assay of D. suzukii adults after M. didyma HY LC₅₀ exposure (A). Fifteen flies for each biological replicate were scored for survival, and three biological replicates were performed. For survival assay, statistical analyses were performed using the log-rank test. *** p < 0.001. D. suzukii metabolic gene expression levels after 48 h of exposure to the M. didyma HY LC₅₀ (B–H). Data represent means ± SEM of three independent experiments performed in triplicate. n.s. not significant; * p < 0.05, ** p < 0.01 vs. control according to Student’s t-test.

Figure 4

Food intake in D. suzukii adults after 48 h feeding on diet treated with M. didyma HY LC₅₀. (A) Food consumption, measured as µL of diet per hour, of D. suzukii males. (B) D. suzukii females. Data shown are the means ± SEM of four independent biological replicates. * p < 0.05 vs. control according to one-way ANOVA followed by Dunnett’s test for multiple comparisons.

Figure 5

Effect of M. didyma HY on D. suzukii egg-laying. (A) The eggs (mean ± SEM) laid in 48 h by a single D. suzukii female with or without different amounts of M. didyma HY in the diet. * p < 0.05 according to one-way ANOVA followed by Dunnett’s test for multiple comparisons. (B) The schematic representation of the cherry oviposition assay performed with D. suzukii female adults. (C,D) The eggs (mean ± SEM) laid on one cherry with or without 100 µL mL⁻¹ (C) and 1000 µL mL⁻¹ (D) M. didyma HY. n.s. not significant; * p < 0.05 according to Student’s t-test.