By Lauren Diepenbrock
Red imported fire ants (Solenopsis invicta), commonly referred to as fire ants, are found throughout Florida. This pest infests a broad range of habitats, including urban regions, natural areas and production fields.
In citrus, there are a range of impacts from this pest — from human health to both direct and indirect tree impacts. From a human health perspective, fire ant stings can negatively impact those working in groves, causing a range of symptoms from mild irritation to severe allergic reactions. In terms of tree health, this pest can cause direct damage to tree trunks, including girdling young trees when they build mounds in tree wraps and causing feeding damage to trunks of more mature trees if mounds are built up against trees. The first scenario is more common, especially during hot, dry months when fire ants seek sheltered areas with access to moisture which can be obtained from irrigation or feeding on tree sap.
Additionally, 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. In a study performed in 2021, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers found that fire ants are particularly aggressive defenders of lebbeck mealybugs. If they were excluded from the mealybugs, predators were able to lay eggs in mealybug clusters that would then reduce the lebbeck mealybug population.
Optimal management for 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 colony is below ground. When ants forage for food resources, they bring the items back to the mound to share 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 cooler dawn and dusk times 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 assistant professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.
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