The previous identification of 2,5-dimethyl-3- (3-methylbutyl)pyrazine as the mandibular alarm pheromone of the little fire ant Wasmannia auropunctata (Roger), has been found to be incorrect. Gas chromatography-mass spectrometry (GC/MS) of ant extracts suggested the correct structure to be the regioisomer 2,5-dimethyl-3-(2-methylbutyl) pyrazine, which was confirmed by comparison with the synthetic pyrazine. GC/MS analysis also revealed the presence of an additional disubstituted alkylpyrazine which was identified as 3-methyl-2-(2-methylbutyl)pyrazine. Headspace sampling of confined ants with SPME and Porapak Q followed by GC/MS analysis showed 2,5- dimethyl-3-(2-methylbutyl)pyrazine as the major volatile released by W. auropunctata workers while 3-methyl-2- (2-methylbutyl)pyrazine was only detected in trace amounts. In laboratory bioassays, W. auropunctata workers were attracted and arrested by both pyrazines, although the results were not always consistent. Synthetic pyrazines generally attracted as many W. auropunctata workers as were attracted to a single crushed ant. However, higher numbers of W. auropunctata were arrested by crushed ant treatments than by synthetic pyrazines in all bioassays but one.
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Acknowledgments We would like to thank Esther Schneider and Janice Nagata for assistance in conducting field experiments and collecting ants; The Shenandoah Valley NMR Consortium housed at James Madison University for use of 1H NMR; Nathan Derstine and two anonymous reviewers for comments and suggestions that improved the manuscript. This project was funded in part by grants from the Hawaii Invasive Species Council Research and Technology Grant Program (Agreement # 58148) and from the Thomas F. and Kate Miller Jeffress Memorial Trust Research Grants Program (Agreement # J-880).
- Alarm pheromone
- Little fire ant
- Wasmannia auropunctata