Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/5/2005
Publication Date: 11/1/2005
Citation: Toth, M., Csonka, E., Bartelt, R.J., Cosse, A.A., Zilkowski, B.W., Muto, S., Mori, K. 2005. Pheromonal activity of compounds identified from male Phyllotreta cruciferae: Field tests of racemic mixtures, pure enantiomers, and combinations with allyl isothiocyanate. Journal of Chemical Ecology. 31(11):2705-2720. Interpretive Summary: The pheromone of the crucifer flea beetle, a serious pest of canola, rapeseed, and related crops in both North America and Europe, was successfully field tested in Hungary. This pheromone is a group of as many as six natural chemicals from the male beetles that functions by attracting both sexes. Previously, these compounds were identified at NCAUR in Peoria, synthesized, and shown to be attractive in the field in Canada. We now know that the beetle populations on both continents respond similarly. An important property of the pheromone is that it works well only when it is present with another compound called allyl isothiocyanate, which occurs in the host plant, and this chemical was also used in all of the experiments. Further information was learned about the activity of the beetle-related compounds: First, just the most abundant of the beetle-related compounds was as effective as the entire six-chemical blend. Second, an important question about the effect of molecular shape was resolved. The structures of the beetle-related compounds exist in “right-handed” and “left-handed” forms, called enantiomers. The beetles responded well only to the same enantiomers that they actually produce, but having the unnatural enantiomers present as well did not hurt the response. This is important from a practical point of view because a blend of both enantiomers is far easier to synthesize than the pure forms. Third, a number of closely related flea beetle species responded in the experiments also, indicating the existence of complex pheromonal relationships in this group of insects. This research further advances the development of practical, pheromone-based tools for managing pest flea beetles.
Technical Abstract: Four himachalene sesquiterpenes and (+)-'-cadinene, previously identified as possible pheromone components from males of a North American population of Phyllotreta cruciferae Goeze (Coleoptera, Chrysomelidae), were tested for attractiveness in field traps in Hungary. A mixture of the four synthetic racemic himachalenes and (+)-'-cadinene from a botanical source was only slightly active in trapping tests when presented alone, but it significantly increased catches when presented together with the known host-plant derived attractant allyl isothiocyanate; this result was consistent with a previous study in North America. Then in tests with optically pure synthetic compounds, a blend of the himachalene enantiomers present in the male beetles was as attractive as the racemic blend, but a blend of the opposite enantiomers was not active. Through subtraction tests, it was found that the single compound, (5R,5aS)-1,1,5,8-tetramethyl-1,2,3,4,5,6,5a-heptahydrobenzo[1,2-a]annulene (compound A in this study), had the same level of activity as the whole mixture, suggesting this compound is a key pheromone component of the European, population of P. cruciferae. The field results were consistent with electrophysiological (GC-EAD) data. In the course of the tests, catches of P. vittula Redtenbacher and some other minor Phyllotreta spp. showed similar tendencies as those of P. cruciferae, suggesting that the same compounds may be relatively widespread as pheromone components in this genus.