Perfluorooctanoic acid exposure induced behavioral and physiological toxicity in Solenopsis invicta (Hymenoptera: Formicidae) without reducing interspecific competitive dominance

Perfluorooctanoic acid (PFOA) is a widespread environmental contaminant. Although its toxicity to aquatic organisms is well known, research on terrestrial arthropods-especially soil-dwelling ants-remains limited. The red imported fire ant (RIFA), (Solenopsis invicta Buren) (Hymenoptera: Formicidae), frequently inhabits soil and is broadly distributed, making it likely to encounter PFOA. This study examined the behavioral, lethal, and physiological effects of PFOA on large and medium RIFA workers. Contact and stomach toxicity experiments showed that PFOA significantly reduced aggregation, climbing, grasping, and crawling over 72 h, with notable mortality at higher concentrations. In contact trials, mortality reached 68.33% (large workers) and 62.50% (medium workers) at 10 mg/g after 48 h, and excavation behavior was markedly inhibited at 0.061-0.61 mg/g. The median lethal concentration (LC50) of PFOA for large workers decreased sharply over time (1660 mg/L on day 3 → 531 mg/L on day 4 → 217 mg/L on day 5). Sublethal colony-level effects emerged by day 21 (28.58%, 30.94%, and 42.55% mortality at 10, 100, and 500 mg/L, respectively). Catalase (CAT) activity increased dose-dependently, indicating oxidative stress (eg from 451 to 2412 U/g in large workers after contact exposure). Despite PFOA exposure (up to 250 mg/L), RIFA maintained higher attack initiation and more intense aggression than Carebara diversa, which suffered 90% to 100% mortality after confrontation in 180 min. Collectively, RIFA exhibits considerable tolerance to PFOA. While PFOA induces sublethal physiological and behavioral impairments, it does not overturn RIFA's competitive dominance, suggesting that environmental contamination alone may not significantly mitigate this ant's confrontation.