# First Test of a Potential Biological Control Agent of Argentine ants (Linepithema humile)

## TL;DR

Researchers tested a fungus that can kill Argentine ants, a harmful invasive species, and found one strain to be highly effective in the lab.

## Contribution

This is the first study to test biological control using fungi against Argentine ants.

## Key findings

- Beauveria bassiana Li053 caused over 80% mortality in Argentine ants within 2–5 days.
- Higher spore concentrations increased the speed and extent of ant mortality.
- Fungal infection was confirmed in 87–92% of dead ants, validating the method's effectiveness.

## Abstract

Argentine ants are a major invasive species worldwide, forming massive supercolonies that threaten native wildlife, damage crops indirectly by protecting sap-feeding insects, and harm beehives and irrigation systems. Traditional control efforts using synthetic chemicals have had limited success and are unsustainable. Biological control—using natural enemies—offers a safer alternative, but has never been tested against this species until now. We isolated six strains of entomopathogenic fungi from Argentine ants in their native range and tested them in the laboratory on ants from four distinct native colonies. One strain, Beauveria bassiana Li053, more consistently caused over 80% mortality, killing half the ants within 2–5 days. Higher spore concentrations led to quicker and greater final mortality. These findings show strong potential for biological control of Argentine ants. Such a method is environmentally friendly, more specific to the target species, safer for beneficial insects and humans, and sustainable over time.

The Argentine ant (Linepithema humile), listed among the world’s 100 worst invasive alien species, is notoriously difficult to control due mainly to its formation of large, expansive supercolonies. Despite the drawbacks of chemical control, biological alternatives have not been previously explored for this species. In this study, we evaluated six native entomopathogenic fungal strains against Argentine ants from four behaviorally distinct supercolonies, identified through aggression assays and collected from both urban and natural sites within the species’ native range. Ants were inoculated with 1 × 108 conidia/mL using three methods: topical application, spray, and immersion. Mortality was recorded over 14 days, and the cause of death was confirmed by fungal outgrowth from cadavers. Among all strains, Beauveria bassiana Li053 consistently induced high mortality across all supercolonies and inoculation methods, with LT50 values between 2 and 5 days and final mortality rates exceeding 80%. Fungal infection was confirmed in 87–92% of cadavers. Dose–response assays revealed that higher conidial concentrations accelerated and increased mortality, with an LC50 estimated at 1 × 106 conidia/mL. These results demonstrate that B. bassiana Li053 is a promising candidate for the biological control of L. humile and merits further evaluation under field conditions.