Fighting Argentine Ants to Assist ACP Biocontrol

Agriculture officials and researchers in California have drastically reduced populations of HLB-spreading Asian citrus psyllids (ACP) through biocontrol measures. Now they’re working on ways to control other insects that are intent on protecting the ACP — Argentine ants. Mark Hoddle, professor of Extension in biological control at the University of California, Riverside, Department of Entomology, explained the ACP/Argentine ant dynamics in a recent presentation.

Videos from cameras running around the clock in California orchards found that Argentine ants were virtually always present with ACP and attacked and killed the ACP’s natural enemies. Ninety percent of Southern California and coastal orchards in the state are infested with the ants, which feed on the white honey dew that ACP excrete. The ants attack ACP biological control agents to protect the ants’ food source. So, the ants need to be controlled in order for the biological control to be most effective.

Hoddle said insecticidal sprays aren’t very effective at controlling the ants because a majority of the ants are underground at any given time and thus safe from the sprays. He discussed two other ways researchers are trying to improve biocontrol of ACP when Argentine ants are present, as they almost always are.

BAIT BEADS

One method is the use of small, biodegradable hydrogel beads. “We can kill ants by using novel technologies that deliver liquid baits infused with ultra-low concentrations of insecticide,” Hoddle said.

The beads are soaked in sugar water and laced with a slow-acting insecticide. Instead of treating the whole orchard, Hoddle said, “we look for areas in the orchard that have a lot of ant activity” and put the hydrogel beads in those hot spots.

The ants slurp up the sugar water and insecticide and take it to share with other ants in their colony. The method uses a fraction of the insecticide used in spraying.

SPEED BUMPS

Another ant control method being evaluated is the creation of physical barriers clipped on to irrigation lines in citrus orchards. The barriers serve as speed bumps that the ants have great difficulty getting by as they follow the irrigation lines across the orchard floor.

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