Solenopsis invicta viruses and Kneallhazia solenopsae in Tennessee imported fire ant (Hymenoptera: Formicidae) populations

Multiple pathogens have been identified in red imported fire ants (Solenopsis invicta Buren) in native and introduced ranges, but pathogens infecting black (Solenopsis richteri Forel) or S. invicta × S. richteri hybrids are less studied. Pathogens like Kneallhazia solenopsae (Knell, Allen & Hazard) and Solenopsis invicta virus 3 (SINV-3) negatively impact colony growth and survival and offer augmentative biocontrol potential. The objective of this work was to determine the geography and phenology of K. solenopsae, SINV-1, SINV-2, and SINV-3 pathogens within the Tennessee hybrid-dominated populations. During 2015 to 2016, 62 fire ant-infested counties were gridded (12.1-by-12.1 km), and one colony sampled per grid in warm (July to October) and cool (January to April) periods. Fire ant species were determined by cuticular hydrocarbon and venom alkaloid analysis. Samples were evaluated for pathogens, parasitoids, and social form by molecular analysis. Ant frequencies were hybrid (74.1%), black (25.3%), and red (0.6%). Infection rates were low (9.5% and 1.3% in warm and cool periods, respectively). Parasite prevalence was 4.2% (SINV-1), 1.3% (K. solenopsae), 0.9% (SINV-3), 0.1% (SINV-2), and 0.1% (Pseudacteon). Hybrid colony infection rates were higher (82.2%) than black and red (17.8%) colonies. Polygyne colonies were infrequent (n = 6 of 99) but were more frequently infected (66.7%) than monogyne (11.8%). The most widely distributed pathogen was SINV-1. Higher elevations may negatively influence SINV-1 range expansion. Higher hybridity values (ie more red-like) increased viral infection likelihood, but not Kneallhazia infection. Parasite prevalence was low in Tennessee hybrid-dominated monogyne populations, which may limit their impact on fire ant populations.