Insect-Associated Bacteria Boost VOC Emissions, Including Benzenoids, Esters, Hydrocarbons, and Lactone, during Cereal Leaf Beetle Feeding on Wheat

Plant volatile organic compounds (VOCs) constitute part of the signal transmitted between plants, serving as defence molecules that repel plant pests or attract their natural enemies. Insect-associated bacteria are important factors influencing many aspects of plant-insect interactions. In this study, we have undertaken to evaluate the impact of the insect-associated bacteria on the abundance and the content of VOCs emitted from wheat plants damaged by important cereal pest – cereal leaf beetle (CLB, Oulema melanopus), in both larval and adult stages. We assumed that CLB-associated bacteria, as an additional factor, may cause different and higher VOC emissions from plants attacked by insects. VOCs were collected by solid-phase microextraction and analyzed with comprehensive two-dimensional gas chromatography-mass spectrometry. We revealed that CLB-associated bacteria contribute to both the increased number and total peak area of VOCs emitted by plants exposed to CLB, particularly those classified as hydrocarbons, benzenoids, esters, and lactones. This effect is especially pronounced in plants damaged by larvae. Our findings demonstrate that physical damage alone may be sufficient to trigger the release of certain volatiles from plant tissues, but CLB feeding in the presence of its associated bacteria leads to a higher quantity and greater diversity of VOCs emissions.