Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2006
Publication Date: 11/1/2006
Citation: Zilkowski, B.W., Bartelt, R.J., Cosse, A.A., Petroski, R.J. 2006. Male-produced aggregation pheromone compounds from the eggplant beetle (Epitrix fuscula): identification, synthesis, and field bioassays. Journal of Chemical Ecology. 32:2543-2558. Interpretive Summary: The eggplant flea beetle is an important pest of eggplants and is found throughout most of the United States. Especially damaging in the spring, the beetles can quickly defoliate a field of eggplant seedlings and cause crop failure. Control of these beetles is important but difficult, especially for organic growers. Early detection and monitoring of beetle populations using their pheromone could lead to more efficient and effective control measures, but the pheromone for this species was not known. Therefore, this project was undertaken to discover it. The pheromone was found to be emitted by male beetles, and six male-specific compounds were identified. Four of these, present in minor amounts, were found previously in other flea beetle species. However, the two most abundant compounds were novel for flea beetles and for insects in general. Both were 9-carbon aldehydes with three double bonds and were synthesized in the laboratory. These compounds were tested in traps in eggplant fields in Central Illinois in 2005 and were found to attract both male and female eggplant flea beetles. The use of these compounds in a trapping system could provide an early detection and season-long monitoring tool for the eggplant flea beetle, leading to more timely and effective insecticide applications and organic control options. This research will be of interest to eggplant producers, entomologists studying this species, and to scientists working on pheromones in general. In addition, this project adds important basic knowledge about flea beetles, a large and important family of insects whose chemical ecology it still poorly understood.
Technical Abstract: Volatiles from the eggplant flea beetle, Epitrix fuscula Crotch (Coleoptera: Chrysomelidae), feeding on host foliage were investigated. Six male-specific compounds were detected and were identified through the use of mass spectrometry, nuclear magnetic resonance (NMR) spectrometry, chiral and achiral gas chromatography, high-performance liquid chromatography, gas chromatography-electrophysiology (GC-EAD), and microchemical tests. The two most abundant of the six compounds were (2E,4E,6Z)-2,4,6-nonatrienal (1) and (2E,4E,6E)-2,4,6-nonatrienal (2). The other four compounds, present in minor amounts, were identified as himachalene sesquiterpenes; two of these, 3 and 4, were hydrocarbons and two, 5 and 6, were alcohols. All four sesquiterpenes were encountered previously from male flea beetles of Aphthona spp. and Phyllotreta cruciferae. Synthetic 1 and 2 matched the natural products by gas chromatographic retention times, mass spectra, and NMR spectra. Sesquiterpenes 3-6 similarly matched synthetic standards and natural samples from the previously studied species in all ways, including chirality. Both natural and synthetic 1 and 2 gave positive GC-EAD responses, as did sesquiterpenes 3, 5, and 6. Field trials were conducted with a mixture of 1 and 2, and the baited traps were significantly more attractive than control traps to both male and female E. fuscula. The E. fuscula pheromone has potential for monitoring or controlling these pests in eggplants.