Identification of Bioactive Plant Volatiles for the Carob Moth by Means of GC-EAD and GC-Orbitrap MS

Abstract

The aim of this study was to validate a workflow that allows structural identification of plant volatiles that induce a behavioral response in insects. Due to the complexity of plant volatile emissions and the low levels at which these bioactive components tend to occur, gas chromatography-electroantennography (GC-EAD) was applied as the prime differentiator technique, i.e., to indicate particular peaks of interest in the chromatogram. In a next step, the analysis was repeated under identical conditions using GC-Orbitrap mass spectrometry (MS). Combining electron impact (EI) ionization and chemical ionization (CI) with the superior spectral resolution and mass accuracy of the technique enabled straightforward identification of these unknowns, with high confidence in a minute amount of time. Moreover, because of the intrinsic sensitivity of the technique, components that occur at trace amounts but may induce disproportional large behavioral responses are evenly well-identified. We were able to positively identify β-caryophyllene as a bioactive compound in female carob moths. Behavioral attraction was negatively correlated with the amount of β-caryophyllene in host fruits. In an oviposition experiment on filter paper, β-caryophyllene was stimulated in the range of 40–100 ng, while concentrations above 200 ng inhibited oviposition.

Plant volatiles play differential roles in pre and post alighting phases in a specialist phytophagous insect

“…Among the olfactively active compounds, behavioral experiments showed that β-caryophyllene had an attractive pre-contact effect on D. radicum females, which supports an important role of this compound in plant-insect interactions as it has been shown attractive to a diversity of generalist and specialist phytophagous insects (e.g. [70][71][72]). However, it is the only VOC which induced pre-or post-contact effect when applied alone, while all three VOC mixtures had such effect.…”

Mass spectometry based untargeted metabolomics in food and health area

“…The collaboration between chemists and biologists, and the introduction of newer analytical techniques, enabled the development of additional approximations to pheromone research or bioactive compounds characterization by untargeted metabolomics (Butcher, 2017;Hefetz, 2019;Li et al, 2018). Most of the studies have focused on the volatile pheromones of different organisms and the employment of GC-MS or GC-HRMS instruments to this aim: in yeast (Ljunggren et al, 2019), insects (Esteves et al, 2017) and plants (Hosseini et al, 2021;Zheng et al, 2021). For more polar pheromones, LC-HRMS was used in marine planktonic diatoms (Fiorini et al, 2020) and nematodes (Falcke et al, 2018;Le et al, 2020),…”