Submitted to: Insectes Sociaux
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/23/2010
Publication Date: 3/10/2010
Citation: Showalter, D.N., Troyer, E.J., Aklu, M., Jang, E.B., Siderhurst, M.S. 2010. Alkylpyrazines: Alarm pheromone components of the little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera, Formicidae). Insectes Sociaux. (2010) 57:223-232. Interpretive Summary: The little fire ant is an emerging pest of agriculture in Hawaii and the US mainland. It’s sting are uncomfortable and in large number result in severe reactions. The alarm pheromone of the little fire ant was re-analyzed and found to be identified incorrectly. We used analytical instruments to identify the correct structure of the alarm pheromone and showed that this pheromone had much better biological activity than the previously identified compound. This compound may be useful in delimiting the spread of this invasive pest.
Technical Abstract: 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 alkyl pyrazine 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.