Submitted to: Journal of Natural Products
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/26/2011
Publication Date: 2/22/2011
Citation: Bartelt, R.J., Zilkowski, B.W., Cosse, A.A., Schnupf, U., Momany, F.A., Vermillion, K. 2011. Male-specific sesquiterpenes from Phyllotreta flea beetles. Journal of Natural Products. 74(4):585-595. Interpretive Summary: Flea beetles are a large group of small insects that are important as crop pests and as biological control agents of invasive weeds. Recently, males of several species in this group were found to emit a number of 15-carbon chemicals with rather complex structures, known as sesquiterpenes. These function as pheromones that attract both sexes ("aggregation pheromones"). Pheromones have become significant tools for monitoring and managing economically important insects; and the current research continued the study of the chemical emissions from flea beetles, in particular, from Phyllotreta striolata and P. pusilla. Both species are significant pests of cabbage-family crops. One previously unknown sesquiterpene was found from P. striolata, and five were found from P. pusilla. Only tiny amounts of the chemicals were given off from male beetles, but a combination of mass spectrometry, nuclear magnetic resonance spectroscopy, molecular modeling, chromatography, and synthetic organic chemistry allowed the structures to be determined. The new information would be of interest to pest management professionals, chemical ecologists, and organic chemists and may open possibilities for new ways to deal with these pests.
Technical Abstract: Flea beetles in several genera are known to possess male-specific sesquiterpenes, at least some of which serve as aggregation pheromones that attract both sexes. In continuing research on the chemical ecology of Phyllotreta flea beetles, six new male-specific sesquiterpenes were identified, one from P. striolata (hydroxyketone 9) and five from P. pusilla (aldehydes 10-12 and 14 and alcohol 13); both species are crop pests. The minute amounts from beetles provided mass spectra and chromatographic data but were insufficient for complete structure determination. However, it was discovered that the new compounds could all be produced by applying organic reactions to previously identified flea beetle sesquiterpenes, and the resulting, larger amounts of material permitted definitive structure analysis by NMR. Molecular modeling was used in conjunction with NMR to define relative configurations of several newly created asymmetric centers. Absolute configurations of natural 9-14 were established by chiral gas chromatography/mass spectrometry. In electrophysiological tests (GC-EAD) conducted with P. striolata, compound 9 was detected with high sensitivity by the beetle antennae, which is consistent with a pheromonal function. The research opens new possibilities for using behavioral chemicals to monitor or manage these pest species.