Characterization of Pinus spp. needles by gas chromatography and mass spectrometry: Application to plant-insect interactions

Abstract

The pine processionary moth Thaumetopoea pityocampa (Lepidoptera: Notodontidae) is considered as the most destructive pine defoliator in the Mediterranean area. Host species appear to influence the distribution and population dynamics of the defoliator, but the mechanisms responsible for its performance are not yet understood. Tree resistance/susceptibility might be due to either the presence of some compounds present in the needles, or to specific volatile components emitted by the host trees. In this context, the characterization of the chemical composition of the needles from different pine species is an important tool to decode the process of host tree selection and performance by T. pityocampa. The chemical composition of the needles of P. pinea, P. pinaster, P. halepensis, P. nigra, P. brutia, P. patula, P. radiata, P. taeda, P. elliotti, P. kesiya, P. sylvestris and P. eldarica was investigated. Headspace solid-phase microextraction and steam distillation extraction were used to collect the volatile fractions, and resin acids were solvent extracted and derivatized before analysis. Samples were analyzed using one-dimensional gas chromatography (1D-GC), enantioselective multidimensional gas chromatography (MDGC) with heart- cutting transfer mode, comprehensive two-dimensional gas chromatography (GC × GC) and mass spectrometry(GC/MS) with different mass analyzers. The potential of mass spectrometry using field ionization as ionization mode, was also evaluated. Results showed that the analytical capabilities of 1-D-GC are partially limited by the separation power of the columns. The high sensibility and the absence of peak skewing of the time of flight mass analyzer, with the use of automated peak finding and deconvolution algorithms, allowed for the detection of trace components with qualitative full spectra and the extraction of true mass spectra from coeluting compounds, promoting their reliable identification and thus significantly improving results obtained by 1D-GC/MS, using a quadrupole mass analyzer