Genetic and Chemical Profiling of Solenopsis spp. (Hymenoptera: Formicidae) Intercepted in Hawaii

Summary Ants intercepted by the Hawaii Department of Agriculture in 2018 and 2019 identified as Solenopsis spp., and possibly S. invicta, were submitted to the United States Department of Agriculture-Agricultural Research Service-Center for Medical, Agricultural and Veterinary Entomology, Imported Fire Ant and Household Insects Research Unit for further taxonomic assessment using genetic and chemical methods. The 2018 sample consisted of 1 worker ant, and the 2019 sample consisted of 3 worker ants. Thoraces were used for genetic assessment and gasters were used for venom analyses. It was determined readily from genetic and chemical analyses that the intercepted ants were not S. invicta or S. richteri. Mitochondrial COX1 gene sequences were compared with previously published data from Solenopsis species. The closest match for the 2018 sample was S. xyloni, which is native to the shipment's origin (San Diego, California, USA). The 2 major alkaloids found were characteristic of the S. geminata species group. In addition, the alkaloid ratio closely matched that of S. xyloni. Therefore, the alkaloid analysis of the 2018 intercepted ant concurs with the genetic data that the ant was an S. xyloni worker. The COX1 gene sequences of the 2019 interceptions most closely matched S. geminata. The corresponding venom alkaloid profile also eliminated S. invicta and S. richteri as possibilities. However, 1 major alkaloid was unusual (Fig. 2) and normally is found only in trace amounts. We suggest the 2019 specimens are an unusual variant of S. geminata.