Worker size and geographical distribution of imported fire ant (Hymenoptera: Formicidae) species and hybrid in Tennessee

Authors: PANDEY, M - Tennessee State University; ADESSO, K - Tennessee State University; ARCHER, R - Tennessee State University; Valles, Steven; CALLCOTT, A - Animal And Plant Health Inspection Service (APHIS); BAYSAL-GUREL, F - Tennessee State University; GANTER, P - Tennessee State University; YOUSSEF, N - Tennessee State University; OLIVER, J - Tennessee State University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2019
Publication Date: 3/27/2019
Citation: Pandey, M., Adesso, K.M., Archer, R.S., Valles, S.M., Callcott, A.M., Baysal-Gurel, F., Ganter, P., Youssef, N.N., Oliver, J.B. 2019. Worker size and geographical distribution of imported fire ant (Hymenoptera: Formicidae) species and hybrid in Tennessee. Environmental Entomology. 48(3):727-732. https://doi.org/10.1093/ee/nvz023.
DOI: https://doi.org/10.1093/ee/nvz023

Interpretive Summary: The red and black imported fire ants were introduced into the United States in the 1930s and currently infest about 300 million acres. Fire ants cause approximately $6 billion in damage annually in livestock and agricultural production and pose a serious threat to human health. To improve management of these ants, federal and state agencies have released multiple species of phorid decapitating flies in the U.S. as classical biocontrol agents. Although phorid flies are important biocontrol agents, their effectiveness can be influenced by both species and worker size. Therefore, scientists at Tennessee State University, the USDA-ARS, Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL) and USDA-APHIS (Biloxi, MS) determined the distribution of fire ant species and their hybrid in Tennessee. In addition, they determined if the inter-colony ratio of worker ant sizes varies with geographic region or cuticular hydrocarbon and venom alkaloid values among related species and hybrid status of colonies. An expected impact of the study will be guidance for future releases of suitable classical fire ant biological control agents in Tennessee and other states with variable fire ant populations.

Technical Abstract: Worker size and geographical distribution of red (Solenopsis invicta Buren) (RIFA), black (Solenopsis richteri Forel) (BIFA) and hybrid (S. invicta ' S. richteri) (HIFA) imported fire ants (Hymenoptera: Formicidae) were evaluated in colonies across Tennessee. The fire ant species and hybrid status were determined using cuticular hybdrocarbon and venom alkaloid indices obtained from gas chromatography and mass spectrometry. The HIFA dominated fire ant populations throughout Tennessee. With the exception of a few isolated RIFA samples, HIFA was the only IFA found in east Tennessee and also predominated in middle Tennessee. In west Tennessee, mixed populations of BIFA and HIFA were found. The HIFA population appears to be increasing in prevalence in west Tennessee compared to previous studies. Because of the limited availability of RIFA samples in Tennessee, additional monogyne RIFA were obtained from a Florida site to facilitate ant species size comparisons. The average worker size of monogyne RIFA from the Florida site was significantly smaller than BIFA or HIFA. No statistical differences were detected in the average inter-colonial worker size of BIFA and HIFA. Likewise, no relationships were found for body size of the fire ant workers by geographic location or elevation in Tennessee. Study findings may impact the establishment of size-dependent biological control agents like Pseudacteon phorid flies.