Colony-level variation in fire ant foraging activity correlates with mortality in laboratory bait evaluations

Management of invasive ants often relies on toxic baits due to their ability to be shared among nestmates, ultimately leading to colony collapse. Yet, the success of this approach is closely tied to worker foraging activity, which can vary significantly between colonies. However, the effect of intraspecific variation in foraging activity on bait efficacy remains largely unexplored. In this study, we examined how variations in foraging activity influence bait performance in the red imported fire ant (Solenopsis invicta). We hypothesized that colonies with higher foraging activity would remove more bait, resulting in increased worker mortality. Laboratory experiments were conducted using size-standardized colonies under uniform conditions. Foraging activity was measured for each colony using a commercial bait (Amdro®), and both bait removal rate and worker mortality were recorded following exposure. Our results revealed marked variation in foraging activity among colonies. Moreover, foraging activity was a strong predictor of treatment success: colonies with higher activity exhibited greater mortality. In contrast, bait removal rate alone did not consistently correlate with foraging activity or mortality. These findings highlight the importance of accounting for colony-level behavioral differences in bait efficacy studies. Future bait evaluation protocols should consider colony-level foraging behavior to improve accuracy and reproducibility.