Relationship of imported fire ant (Hymenoptera: Formicidae) integument coloration to cuticular hydrocarbon and venom alkaloid indice

Authors: PANDEY, MANOJ - Tennessee State University; ADDESSO, KARLA - Tennessee State University; Alexander, Lisa; YOUSSEF, NADEER - Tennessee State University; OLIVER, JASON - Tennessee State University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2020
Publication Date: 1/25/2021
Citation: Pandey, M., Addesso, K.M., Alexander, L.W., Youssef, N.N., Oliver, J.B. 2021. Relationship of imported fire ant (Hymenoptera: Formicidae) integument coloration to cuticular hydrocarbon and venom alkaloid indice. Environmental Entomology. 1-7. https://doi.org/10.1093/ee/nvaa184.
DOI: https://doi.org/10.1093/ee/nvaa184

Interpretive Summary: Imported fire ants (IFA) infest over 367 million acres in North America and are still expanding their range annually. The red imported fire ant (RIFA) and the black imported fire ant (BIFA) and their hybrid (HIFA) cause significant damage to crops and the environment and are all regulated by the Federal Imported Fire Ant Quarantine. Applying the appropriate chemical or biological control for IFA requires identifying ants to the species level. However, identifying RIFA, BIFA or HIFA colonies by color can be challenging due to variations in human color perception. Fire ant identification traditionally involves molecular or chemical techniques, but a colorimetric test could allow rapid and low cost identification. Tennessee State University and U.S.D.A. scientists in McMinnville, TN developed a method that rapidly discriminates between RIFA, BIFA, and HIFA using a portable spectrophotometer. This colorimetric analysis may provide a complimentary method to other more time consuming laboratory techniques like chromatograms and molecular methods for the identification of IFA species and subsequent management and control.

Technical Abstract: Red (Solenopsis invicta Buren) (RIFA) and black (Solenopsis richteri Forel) (BIFA) imported fire ants (Hymenoptera: Formicidae) are considered distinct species, but they still have introgression via a reproductively functional hybrid (HIFA). The RIFA and BIFA common names are based on relative coloration. Due to variations in human color perception, identifying RIFA, BIFA or HIFA colonies by color can be challenging. Fire ant identification traditionally involves molecular or chemical techniques, but a colorimetric test could allow rapid and low cost identification. In this study, ant integument coloration was measured by portable spectrophotometer, and color values were compared to cuticular hydrocarbon and venom alkaloid combined species index values. Significant Pearson Correlation coefficients were found for colony species index values versus color attributes of red to green (a*), blue to yellow (b*), chroma (C*), and hue (h*), but not lightness (L*). The RIFA color attributes were distinct from HIFA and BIFA. Likewise, HIFA color attributes were generally distinct and intermediate between RIFA and BIFA; the exception was HIFA with index values closest to BIFA or RIFA, which had coloration similar to BIFA. Color attribute values were not linear with species index value because HIFA color a*, b*, and C* values increased and then decreased as species index value increased, while h* values decreased and then increased. The HIFA a*, b*, C*, and h* attributes also exhibited a sinusoidal pattern as species index increased. Colony coloration may provide a quick technique to supplement molecular or hydrocarbon identification because RIFA color was distinct from BIFA or HIFA. However, coloration of HIFA colonies was more variable with species index and will complicate separations among HIFA genotypes or BIFA.