Background: There are four species of fire ants found in the United States in addition to the most common, Solenopsis invicta. Reactions have been reported from stings of each of these species, but large numbers of insects and adequate amounts of venom for study are very difficult to obtain.
Methods: Venom was obtained, the purified allergens were isolated, and the complete amino acid sequences were determined for two of the three allergens from S. richteri. Skin testing and RAST studies were performed on patients with reactions to native fire ant stings and analyzed in comparison with clinical history.
Results: The structures of S. richteri allergens have a high degree of similarity to S. invicta allergens. The Sol 2 allergens are less related to each other than either the Sol 1 (phospholipase AB) or Sol 3 (antigen 5) allergens. Patients sensitized to native species of fire ants react primarily to the Sol 1 and Sol 3 allergens, whereas those originally sensitized to S. invicta also react significantly to the Sol 2 and Sol 4 allergens. Some patients are initially sensitized to S. invicta and have life-threatening reactions to stings of native species. The tropical fire ant, S. geminata, has become a serious problem in some areas of the Pacific and South Asia, especially Okinawa and Guam.
Conclusions: The venoms from all of the species of fire ants examined appear to be highly cross-reactive. S. invicta imported fire ant venom extracts are probably sufficient for diagnosis and may warrant a clinical trial for immunotherapy of allergic reactions to venoms of any of the other four species.