Effect of Coridothymus capitatus Essential Oil on Chrysanthemum Aphid Behaviour and Survival: Phytochemical Analysis and Antioxidant Potential

Abstract

There is a growing interest in using essential oils with phytoprotectant properties instead of synthetic pesticides to mitigate the risks of insect pesticide resistance, environmental harm, and adverse effects on non-target organisms and human health. This study focused on the effects of Coridothymus capitatus essential oil on host selection, settling behaviour, and survival of Macrosiphoniella sanborni in dual-choice and no-choice tests. The essential oil and methanol extract of C. capitatus were analyzed using Gas Chromatography-Mass Spectrometry (GC-MS) and Liquid Chromatography-Mass Spectrometry (LTQ-LC-MS Orbitrap), respectively. The antioxidant activity was also tested through the radical scavenging assay. The settling inhibitory activity in the dual-choice test increased dose-dependently from 60% to 72% for essential oil concentrations of 0.1 to 0.3% (v/v) for up to 120 min exposure, but decreased thereafter. However, under no-choice conditions, the inhibitory effect after 60 min of exposure was inversely proportional to the concentration but became proportional by the end of the experiment (72 h). After 72 h, both assays produced a mortality rate of 15% to 17%. C. capitatus was classified as a Carvacrol chemotype. Fifteen phenolic compounds were identified in the MeOH extract, and both the extract and essential oil exhibited substantial antioxidant activity. In conclusion, our findings indicate that C. capitatus essential oil affects the behaviour and survival of M. sanborni.

Keywords: DPPH; Macrosiphoniella sanborni; Satureja capitata; Thymbra capitata; Thymus capitatus; essential oil.

Figure 1

Chrysanthemum aphid settling inhibition index (SI%) on chrysanthemum leaf discs treated with C. capitatus essential oil, as determined in a 72 h dual-choice bioassay. Ten adult aphids were applied per treatment. Results are expressed as mean values and standard errors for 40 biological replicates. Asterisks indicate statistically significant differences in aphid numbers on treated and control-untreated chrysanthemum leaf discs (Triton X-100, 0.5%) at p ≤ 0.05 (Wilcoxon’s matched pair signed rank test).

Figure 2

Chrysanthemum aphid settling inhibition index (SI%) on chrysanthemum leaf discs treated with C. capitatus essential oil, as determined in a 72 h no-choice test. Results are expressed as mean values and standard errors for 20 biological replicates, with 10 adult aphids per treatment. Asterisks indicate statistically significant difference between the number of aphids settled on the treated or the control leaf discs (Triton X-100, 0.5%) at p ≤ 0.05 (Kruskal–Wallis Test).

Figure 3

Mortality of chrysanthemum aphids caused by different concentrations of C. capitatus essential oil, as determined by (A) the dual-choice assay and (B) the no-choice assay. Results are expressed as mean values and standard errors for 20 biological replicates, with 10 adult aphids per treatment. Significance was set at p ≤ 0.05 using the LSD test. Different letters indicate significant differences between mean values.