Abstract
South American fire ants, Solenopsis richteri and Solenopsis invicta, were accidently introduced into the southern USA in the 1900s and 1930s, respectively. The rapid spread and high population densities of S. invicta, and its potent sting, resulted in broad economic impacts and a variety of research efforts. In the 1970s, their venom alkaloids were identified as a complex blend of trans-2-methyl-6-alkyl- and alkenyl-piperidines. Solenopsis geminata is a worldwide tramp species but a native of the southern coastal regions of the USA. It was found to only produce cis- and trans-2-methyl-6-undecyl-piperidines. These alkaloids were considered the Solenopsis ancestral alkaloid profile since they were identified from female sexuals (potential queens) of all Solenopsis species in South and North America. The dramatic modification of alkaloids in Solenopsis invicta was attributed to their response to evolutionary pressure and the lack of change in S. geminata alkaloids due to no response to evolutionary pressure. Here we report the unexpected discovery of 6-undecyl-pyridine, 2-methyl-6-undecyl-pyridine and 2-methyl-6-(1)-undecenyl-pyridine as components of S. geminata worker venom, suggesting that S. geminata like its South American relatives have responded to evolutionary pressures. Our results will stimulate future research on S. geminata populations throughout the tropical/subtropical world.
Highlights
The fire ants, Solenopsis geminata and Solenopsis xyloni, are native to the southern USA and have a long history of human interactions. While they have a significant sting, it was the accidental introduction of two South American fire ants into the southern USA, Solenopsis richteri (1920s) and especially Solenopsis invicta (1930s) (Solenopsis saevissima species complex, Pitts et al 2018), which generated widespread attention
Since all female sexual forms associated with the S. geminata and S. saevissima species complexes produce cis- and trans-2-methyl-6-undecyl-piperidines, these two alkaloids were considered the ancestral type. It was thought S. invicta and S. richteri workers evolved beyond the undecyl-piperidines, while S. geminata species complex workers maintained the ancestral alkaloid blend (Brand, 1978)
The driving force for this research was the unexpected identification of 2-methyl-6-undecyl-pyridine, Fig. 1, peak (3) as the major component from three S. geminata ants intercepted by the State of Hawaii quarantine officials (Ascunce et al, 2021)
Summary
The fire ants, Solenopsis geminata and Solenopsis xyloni (members of the S. geminata species complex, Pitts et al 2018), are native to the southern USA and have a long history of human interactions. Venom alkaloid research was extended to workers of the native fire ants, S. geminata and S. xyloni They produce a mixture of cis- and trans-2-methyl-6-undecyl-piperidines (Brand et al 1972, Fig. 1, compounds 2 and 4), in contrast to the variety of piperidine alkaloids that dominate the two invasive species. Since all female sexual forms (future queens) associated with the S. geminata and S. saevissima species complexes produce cis- and trans-2-methyl-6-undecyl-piperidines, these two alkaloids were considered the ancestral type. It was thought S. invicta and S. richteri workers evolved beyond the undecyl-piperidines, while S. geminata species complex workers maintained the ancestral alkaloid blend (Brand, 1978)
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