Why do Ladybugs Smell Bad?In-vivo Quantification of Odorous Insect Kairomones with SPME and Multidimensional GC-MS-Olfactometry

摘要

Winemakers, small fruit growers, and homeowners are concerned with noxious compounds released by multicolored Asian ladybird beetles (Harmonia axyridis, Coleoptera: Coccinellidae). New method based on headspace solid phase microextraction (HS-SPME) coupled with multidimensional gas chromatography mass spectrometry – olfactometry (MDGC-MS-O) system was developed for extraction, isolation and simultaneous identification of compounds responsible for the characteristic odor of live H. axyridis. Four methoxypyrazines (MPs) were identified in headspace volatiles of live H axyridis as those responsible for the characteristic odor: 2,5-dimethyl-3-methoxypyrazine (DMMP), 2-isopropy1-3-methoxypyrazine (IPMP), 2-sec-butyl-3-methoxypyrazine (SBMP), and 2-isobutyl-3-methoxypyrazine (IBMP). To the best of our knowledge this is the first report of H. axyridis releasing DMMP and the first report of this compound being a component of the H. axyridis characteristic odor. Quantification of three MPs (IPMP, SBMP and IBMP) emitted from live H. axyridis were performed using external calibration with HS-SPME and direct injections. A linear relationship (R~2>0.9958 for all 3 MPs) between MS response and concentration of standard was observed over a concentration range from 0.1 ng L~(-1) to 0.05 μg L~(f-or HS-1SPME-GC-)MS. The methodetection limits (MDL) based on multidimensional GC-MS aproach for three MPs were estimated to be between 0.020 ng L-1 to 0.022 ng L~(Ti-.hnis m e1tvhodoilovgy )ios aplicable for determination of odor-causing chemicals associated with emissions of volatiles from insects.