Submitted to: Journal of Chemical Ecology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/15/2004
Publication Date: 3/1/2005
Citation: Cosse, A.A., Bartelt, R.J., Zilkowski, B.W., Bean, D.W., Petroski, R.J. 2004. Identification of the aggregation pheromone of Diorhabda elongata, a biological control agent of saltcedar (Tamarix spp.). Journal of Chemical Ecology. 31(3):657-670. Interpretive Summary: Saltcedar, an exotic invasive weedy tree, is causing up to $285,000,000 of damage per year in water loss due to transpiration and flood damage due to stream channel alteration. The invasion of saltcedar into riparian areas in the Western U.S. has also caused ecosystem damages that are more difficult to quantify, such as decreased habitat quality for wildlife and native plant species, increased soil salinity, and increased fire risk. The control of saltcedar through conventional means has been expensive and of limited success. For this reason, efforts are underway to control saltcedar using the leaf beetle Diorhabda elongata as a biological control agent. We have identified the aggregation pheromone of this leaf beetle; a blend of chemical compounds emitted by male beetles which is used in the attraction of the sexes. This research is a first step towards a pheromone-based trap, one that would attract both sexes of this leaf beetle, and could be a practical saltcedar management tool by following the dispersal of the beetles in the field. A second result of this research is a knowledge base on the chemical ecology of beetle aggregation, dispersal, and host plant selection which will be used in the saltcedar biocontrol program.
Technical Abstract: We have identified the male-produced aggregation pheromone of Diorhabda elongata Brullé (Coleoptera: Chrysomelidae), as a two component blend of (2E,4Z)-2,4-heptadienal (1) and (2E,4Z)-2,4-heptadien-1-ol (2). Existence of the pheromone was demonstrated by gas chromatographic comparison of volatiles collections from male and female beetles feeding on saltcedar foliage and from saltcedar foliage alone. The aldehyde (1) and alcohol (2) were identified by coupled gas chromatographic-electroantennographic detection (GC-EAD), coupled gas chromatographic-mass spectrometric (GC-MS) analysis, and GC and MS comparison with authentic standards. GC-EAD analysis of male volatile emissions showed that the two components were sensed by both male and female antennae. A binary blend of synthetic 1 and 2 was attractive to male and female beetles in the field. Compounds 1 and 2 were also detected at trace levels from feeding females and foliage controls, but amounts from feeding males were 23 to 49 times higher (typically 50-100 ng per day per male for each compound). The amounts of 1 and 2 from female collections did not differ from the uninfested foliage controls. Males began to emit 1 and 2 within several days of setup and continued for at least 30 days. Male and female antennae also responded to a series of compounds collected from saltcedar foliage and beetle-infested saltcedar foliage.