Fire ants: Invaders may hamper vector-borne disease, study says

close up image of a worker fire ant

Image: Wikimedia Commons

Red imported fire ants have earned a bad reputation across the southwest. But according to a new study, the invasive species has made at least one major improvement: The ants may reduce the risk of vector-borne diseases.

Texas A&M scientists, working with a colleague from the U.S. Fish and Wildlife Service’s Attwater Prairie Chicken National Wildlife Refuge, published their work recently in the scientific journal Royal Society Biology Letters.

Their work suggests that predatory arthropods like fire ants may affect the transmission of certain diseases to humans and animals by changing the behavior of both the vector, such as a tick, and a host, such as a rodent.

Co-author Jessica Light, an associate professor and Texas A&M AgriLife Research scientist in the Department of Wildlife and Fisheries Sciences, said the research is the first to shed some positive light on the invasive ant.

“Red imported fire ants are known to predate lots of arthropods, including ticks,” Light said. “They’ve also been shown to change the behavior of small mammals that want to avoid their stings. These small mammals often serve as reservoirs or carriers of tick-borne pathogens that can cause human and animal disease. We wondered if this invasive ant could change the ecosystem in a way to reduce tick-borne disease risk.”

The team specifically looked at the effect of red imported fire ants on small mammals, of which many species are carriers of pathogens or microorganisms such as bacteria and viruses capable of causing disease in humans and animals, she said. They also looked at the ticks that the animals harbor, which are known vectors of these pathogens. And finally, they looked at the pathogens themselves.

“On plots where we experimentally reduced the ant populations, rodents were nearly twice as abundant as they were on sites with the ants, the control plots,” she said. “The rodents were also three times more likely to harbor ticks on plots with reduced fire ants and one species, the fulvous harvest mouse, had a 27-fold increased tick load.

“While testing these ticks for multiple pathogens, we documented one human pathogen, Rickettsia parkeri, which causes a mild form of spotted fever,” she said. “Given that we detected one human pathogen in this ecosystem, the reduced number of ticks and small mammals in areas where ants are in high abundance could scale up to alter disease risk.”

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