What You Need To Know About Managing Fire Ants

By Lauren Diepenbrock

Red imported fire ants (Solenopsis Invicta), commonly referred to as fire ants, are commonplace throughout Florida. The pest infests a broad range of habitats, including urban sites, natural areas and production fields.

In citrus, a range of impacts from this pest are seen. From a human health perspective, fire ant stings can cause symptoms from mild irritation to severe allergic reactions. Fire ants can cause direct damage to tree trunks, including girdling young trees when they build mounds in tree wraps and causing feeding damage to trunks if mounds are built up against more mature trees. The first scenario is more common, especially during hot, dry months when fire ants seek sheltered areas with access to moisture from irrigation or feeding on tree sap. 

Fire ants have been documented to farm honeydew-producing plant pests including Asian citrus psyllids, lebbeck mealybugs, aphids and scales. When ants farm these organisms, they collect the sugar-rich honeydew from the pest and in return groom and/or protect them from predators. When grooming, ants are generally keeping their “herd” clean of fungal spores that could harm their food source. Similarly, some ants will protect their food resource from other predators.

A 2021 University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) study found fire ants are particularly aggressive defenders of lebbeck mealybugs. If fire ants were excluded from the mealybugs, predators were able to lay eggs in mealybug clusters that would then reduce the lebbeck mealybug population.

Optimal management of fire ants includes the use of well-timed bait applications. Baits take a few days to start showing impacts but are effective in terms of reducing the entire population, including those that you cannot see. At any given time, most of the fire ant colony is below ground. When ants forage for food resources, they bring the items back to the mound where it is shared with the entire colony. Baits take advantage of this behavior and can deliver toxic doses of insecticide to all members of the colony, including the larvae and queen, thereby effectively killing off the next generation.

Baits are most effective when fire ants are actively foraging, generally from spring through fall. Late afternoon to evening applications are often the most effective as ants tend to forage in the dawn and dusk cooler parts of the warm season. Like all insecticides, you must rotate the mode of action and sometimes even the carrier (flakes vs. granules) since fire ants can develop behavioral adaptations to avoid baits that they become too familiar with.

Lauren Diepenbrock is an associate professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.