Intra- and inter-specific variation in alarm pheromone produced bySolenopsisfire ants

Abstract

Some fire ants of the genus Solenopsis have become invasive species in the southern United States displacing native species by competition. Although the displacement pattern seems clear, the mechanisms underlying competitive advantage remain unclear. The ability of ant workers to produce relatively larger amount of alarm pheromone may correspond to relative greater fitness among sympatric fire ant species. Here we report on quantitative intra-specific (i.e. inter-caste) and inter-specific differences of alarm pheromone component, 2-ethyl-3,6-dimethylpyrazine (2E36DMP), for several fire ant species. The alarm pheromone component was extracted by soaking ants in hexane for 48 h and subsequently quantified by gas chromatography-mass spectrometry at single ion monitoring mode. Solenopsis invicta workers had more 2E36DMP than male or female alates by relative weight; individual workers, however, contained significantly less pyrazine. We thus believe that alarm pheromones may serve additional roles in alates. Workers of Solenopsis richteri, S. invicta, and hybrid (S. richteri × S. invicta) had significantly more 2E36DMP than a native fire ant species, Solenopsis geminata. The hybrid fire ant had significantly less 2E36DMP than the two parent species, S. richteri and S. invicta. It seems likely that higher alarm pheromone content may have favored invasion success of exotic fire ants over native species. We discuss the potential role of inter-specific variation in pyrazine content for the relationship between the observed shifts in the spatial distributions of the three exotic fire ant species in southern United States and the displacement of native fire ant species.

Electrophysiological Responses of Eighteen Species of Insects to Fire Ant Alarm Pheromone

“…The most likely explanation is that alkylpyrazine compounds are not only confined to S. invicta . For example, EDP has been identified as the alarm pheromone of several other ant species in the genus of Solenopsis [40], and alkylpyrazines have also been found in other ant species, such as Wasmannia auropunctata [41] and Aphaenogaster rudis [42] in the subfamily Myrmicinae, Myrmecia gulosa [43], in the subfamily Myrmiciinae, Calomyrmex splendidus [44] and Notoncus ectatommoide [45] in subfamily Formicinae, and Linepithema humile [46], I. purpurreus [47], I. nitidus, I. rufoniger , and Dolichoderus clarkia [48] in subfamily Dolichoderinae. Alkylpyrazines are also commonly seen in the subfamily Ponerinae.…”

Comparative Cutaneous Water Loss and Desiccation Tolerance of Four Solenopsis spp. (Hymenoptera: Formicidae) in the Southeastern United States

“…The identity of each species was confirmed by gas chromatography of hexane extracts of ca. 50 workers using both venom alkaloid and cuticular hydrocarbon characters, [ 32 , 55 , 56 ] following the methodology in Hu et al [ 57 ]. Ants were used for experiments within the same week they were collected.…”

HPLC Separation of 2-Ethyl-5(6)-methylpyrazine and Its Electroantennogram and Alarm Activities on Fire Ants (Solenopsis invicta Buren)

“…2-Ethyl-3-methylpyrazine (99%) and deuterated chloroform were purchased from Acros Organics (Geel, Belgium). EDMP (2-ethyl-3,6-dimethylpyrazine) was synthesized as described in Hu et al [ 49 ].…”