UCR research shows how Argentine ants have been a successful invasive species

Courtesy of Mike Lewis, Center for Invasive Species Research

A recent UCR research paper, “Verification of Argentine Ant Defensive Compounds and Their Behavioral Effects on Heterospecific Competitors and Conspecific Nestmates,” explores how Argentine ants have been able to fight against other ants and become a successful invasive species. The research was conducted for about three years by UCR Entomology Assistant Cooperative Extension Specialist and Assistant Professor Dr. Dong-Hwan Choe, US Department of Agriculture (USDA) chemist Kamlesh Chauhan, All Things Bugs founder Aaron Dossey, Shao Hung Lee (Dennis) and Ph.D student Kevin Welzel.

Argentine ants are hypothesized to have been introduced by intercontinental trade. These species of ants have existed in California, particularly Southern California, for more than 100 years, where they cause problems ranging from urban infestations to agricultural concerns such as threatening citrus orchards.

Argentine ants have been a concern to citrus orchards due to their mutualistic relationship with citrus orchard pests. The citrus pests create a sugary waste called honeydew, which, when deposited on the citrus leaves, form sooty mold. The ants then consume some of the honeydew and in return, protect the pests.

“As a result from that protection, pest population grows to high levels,” said Dr. Matthew Daugherty, agriculture extension specialist and principal investigator in the UCR Department of Entomology.

The Argentine ants were analyzed on a hypothesis formed through previous researchers’ observations of ant behavior. Argentine ants were observed raising their abdomen to face a competing ant, who would suddenly become irritated and disoriented. Based on this behavior, it was hypothesized that the competing ants were affected by the Argentine ants excreting two compounds called dolichodial and iridomyrmex from their abdomen. The research tested this hypothesis by placing different species of ants with Argentine ants. “Once we saw the Argentine ant was behaving aggressively towards the other ants, we would take a sample from the air scene,” explained Lee.

The researchers hope to use this new information to better improve insecticides. The goal is to modify these two compounds to create an insecticide that attracts the Argentine ants while repelling native ants. Currently, the use of sugary baits, which contain 25 percent sugar solution and 0.0001 percent of pesticide, are used to control the Argentine ant population. The ants drink the bait, but since there is a low amount of pesticide present, it does not kill them instantly. This gives the ants time to bring the poison back to the queen inside the colony. However, this method not only reduces the population of the invasive species, but unintentionally affects the native species as well.

New, suggested alternative controls include the introduction of phorid flies. These flies drill into an ant’s neck, depositing eggs which hatch, becoming maggots that consume the ant’s brain. However, using the information gained in the research project, the Argentine ant’s own biology could be used to control their own population.

While Dr. Choe does not currently have any future research on Argentine ants in progress, Choe will continue to study Argentine ants and other ants since “the ant diversity in Riverside and other parts of southern California is slowly changing” due to biological or environmental factors.

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