Native to South America, Argentine ants were introduced to California in 1905. Today, 90% of Southern California and coastal orchards are infested with ants. Some trees experience up to 1 million ant visits per day.
Ivan Milosavljević, Citrus Research Board (CRB) entomologist, presented that information in a June 17 webinar that was part of CRB’s Grower Seminar Series. His presentation was titled “Argentine Ant Management Innovations in Citrus Orchards.”
Milosavljević said that Argentine ant populations begin to build up in California from May to July, so that is a good time to apply controls. Populations are highest from July through October. These ants can be problematic in Florida citrus groves, too.
Argentine ants trade protection for honeydew, a sugary waste excreted by Asian citrus psyllids (ACP) and other insects. Milosavljević’s research shows ant presence on trees triples ACP densities and reduces Tamarixia radiata parasitism by 50%.
He is working to create a synergistic integrated pest management program for ants and sap-feeding insects that includes automating ant monitoring to target control efforts.
Ant counts can be automated with infrared sensors and the Internet of Things, said Milosavljević. These techniques are currently still under development.
Irrigation lines act as super highways for ants. “We can predict with 85% accuracy the number of ants ascending tree trunks based on the number of ants running on irrigation lines,” said Milosavljević.
His work also includes developing sustainable and effective hydrogel controls. There are two types of hydrogels, seaweed-based and polyacrylamide. The hydrogels have been in development for seven years. Milosavljević said he is hopeful growers will have these tools available for use soon.
Both seaweed-based and polyacrylamide hydrogels are biodegradable bait stations with ultra-low insecticide concentrations. For both types, his research showed .0001% thiamethoxam and .01% spinosad effectively controlled Argentine ants at 5 to 10 gallons of gel per acre with minimal to no off-target effects.
Seaweed-based hydrogels are exempt from registration as adjuvants, and a label amendment of a 24(c) for insecticide use in citrus is in progress. Polyacrylamide hydrogels are pending registration. According to Milosavljević, the regulatory path has been challenging for polyacrylamide hydrogels, but active efforts are ongoing from the Citrus Research Board, California Citrus Quality Council and California Citrus Mutual.
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