Genetic and chemical profiling of Solenopsis spp. (Hymenoptera: Formicidae) intercepted in Hawaii

Authors: Ascunce, Marina; Vander Meer, Robert - Bob; CHINTA, SATYA - Foresight Science & Technology; OGURA-YAMATA, CASSANDRA - Hawaii Department Of Agriculture; OISHI, DARCY - Hawaii Department Of Agriculture

Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2021
Publication Date: 4/8/2022
Citation: Ascunce, M.S., Vander Meer, R.K., Chinta, S.P., Ogura-Yamata, C., Oishi, D. 2022. Genetic and chemical profiling of Solenopsis spp. (Hymenoptera: Formicidae) intercepted in Hawaii. Florida Entomologist. 105(1):91-94. https://doi.org/10.1653/024.105.0114.
DOI: https://doi.org/10.1653/024.105.0114

Interpretive Summary: Hawaii is the most isolated archipelago in the world, 4,000 km from the nearest continent. Only half of the insect orders are found in Hawaii. No ants are native to Hawaii; however, there are 60 introduced species and some negatively impact the fragile Hawaiian ecosystems, e.g., the tropical fire ant, Solenopsis geminata. The most destructive fire ant, Solenopsis invictia, has not yet established in Hawaii. Classical taxonomic identification of Solenopsis species is very dificult, thus when Hawaii Department of Agriculture quarantine officials intercepted ants identified as a Solenopsis spp. and possibly S. invicta in 2018 and 2019, some of the collected ant(s)were submitted to USDA-CMAVE, Imported Fire Ant and Household Insects Reseach Unit for further assesment using genetic and chemical analyses. The 2018 sample consisted of one worker ant. The 2019 sample consisted of three worker ants. Fortunately, we have developed very sensitive methods to identify many fire ant species. One uses genetic analyses, and another uses the qualitative and quanitiative analysis of their venom chemistry. Analyses of the 2018 intercepted sample by both methods came to the same conclusion - that this sample was likely S.xyloni, a native to the southern toer of the United States. The 2019 interaction was indentified genetically as most like S. geminata, a tramp species found would-wide in tropical/sub-tropical areas of the world and is already established in Hawaii. The chemistry showed that the intercepted ants were not the highly invasive S. invicta! However, the 2019 ants had an unexpected major venom component, not previously reported. The structure of this component will be the subject of a future publication. For this report, the important point is that neither interception was the dreaded red imported fire ant, S. invitica.

Technical Abstract: Hawaii is the most isolated island archipelago in the world, 4,000 km from the nearest continent. Only half of the insect orders are found in Hawaii. No ants are native to Hawaii; however, there are 60 introduced species and some negatively impact the fragile Hawaiian ecosystems, e.g., the tropical fire ant, Solenopsis geminata. The most destructive fire ant, Solenopsis invicta, has not yet established in Hawaii. Classical taxonomic indentification of Solenopsis species in very difficult, thus when Hawaii Department of Agriculture quarantine officials intercepted ants identifies as a Solenopsis spp. and possibly S. invicta in 2018 and 2019, the collected ant(s) were submitted to the USDA-CMAVE, Imported Fire Ant and Household Insects Research Unit for futher assessment using genetic and chemical analyses. The 2018 sample cosisted of one worker ant. The 2019 sample consisted of three worker ants. In both cases thoraces were used for genetic analyses and the heads and abdomens were used for chemical analyses. The genetic samples were analyzed for the mitochondrial COX1 gene, and the sequences were compared with previously published data from Solenopsis species, including S. geminata, and S. invictia. The 2018 sample was closely related to S. xyloni or S. amblychila, which are natove to the shipment's origin (San Diego, California). The venom alkaloids from abdominal extracts eliminated S. invicta and S. richteri as possibilities. The alkaloid profile qualitatively matched S. geminata and S. xyloni, but quanititatively, S. xyloni was the best match, consistent with the genetic conclusion. The 2019 interception was from a ship of Lithuanian origin. COX1 gene sequences most closely matched S. geminata, a tramp species found would-wide in tropical/sub-tropical areas of the world and is already established in Hawaii. Venom alkaoids from abdomen extracts intially looked like S. geminata; however, the mass spectra of one of the two major componets were previously reported as a major compnent in Solenopsis vemon. The intercepted sample is not S. invicta or S. richteri, but is likely a varient from the S. geminata complex. These are excellent sample of the utility of molecular and chemical tools to identify intercepted invasive ants, even when the number of samples are limited, and morphologival identification is difficult.