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Fire Ants and Other Burning Problems

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Illustration of a whale and a fire ant on opposite ends of a scale.

At any given point in time, there are about 13,475 million tons of fire ants in the United States. By comparison, a blue whale can weigh about 125 tons, meaning it would take a pod of about 107,800 blue whales to match the weight of all the fire ants here.

ARS Scientists Target Some of America’s Toughest Pests

Nearly a century ago, an unseen invasion began when a handful of non-native ants that had snuck aboard a freighter from South America arrived in Mobile, AL. The world of American insects would never be the same. Fire ants, as the invaders came to be known, have spread inexorably across the entire South, from sea to shining sea, and up the Eastern Seaboard as far as Virginia and into Maryland, wreaking havoc and leaving devastation in their wake.

In a way, fire ants’ scientific name says it all: Solenopsis invicta — the unconquerable. They are omnivores, meaning they view just about everything as an item on a smorgasbord, and estimates put their cumulative economic damages at $8 billion, every year, for everything from crop losses to eating through communications and electrical system components.

In addition to being prolific eaters, fire ants are exceptional breeders. They spread through mating flights that can involve millions of winged females and males that fly about 300 feet in the air and mate; afterward, each newly mated queen will attempt to create a new colony. These mating flights can expand the fire ant’s territory by 6-9 miles per year. However, early on they hitchhiked long distances on nursery stock by people, which prompted USDA to institute quarantine measures on movement of plants from infested to non-infested areas.

Fire ants are known to infest about 350 million acres. Though individually small and light, added together, they weigh in at an impressive 77 pounds of ants per acre. At any given point in time, there are about 13,475 million tons of fire ants in (or under, since about 90% of worker ants live underground) the United States. By comparison, a blue whale can weigh about 125 tons, meaning it would take a pod of about 107,800 blue whales to match the weight of all the fire ants here.

Luckily, a pair of Agricultural Research Service (ARS) scientists are working to reduce the toll the ants have been taking. Bob Vander Meer, research leader at the ARS Imported Fire Ant and Household Insects Research Lab in Gainesville, FL and Man-Yeon Choi, research entomologist at the ARS Horticultural Crops Research Unit in Corvallis, OR, are using a unique receptor interference (“Receptor-i”) technology that they have developed to target fire ants. The technology is environmentally friendly and can also be directed at other existing or emerging invasive pests to provide timely, cost-efficient pest control.

“The fundamental mechanism of Receptor-i is that we can select for bioactive peptides that bind to receptors, thus blocking a specific physiological function,” Choi explained. In other words, the technology blocks some of the ants’ essential biological processes from occurring, rendering them unable to function — or to cause headaches for humans.

Receptor-i takes advantage of a “key and lock system,” in which a specific peptide (the key) binds to and activates a matching receptor (the lock). Neuropeptides are a kind of peptide that activates essential biological functions in target cells, tissues, or organs. “Neuropeptides play critical roles in the normal functioning of insects — from feeding to development; in this case, [binding with receptors called] G-Protein Coupled Receptors (GPCRs),” Vander Meer explained. Neuropeptides and their GPCRs are involved in many of the ant’s essential physiological processes.

Vander Meer and Choi developed a special methodology that tests specific GPCRs with millions of randomly generated amino acid peptides and then determines which peptides are most effective at binding to and blocking the receptors. “These strong binding peptides join with the receptor so that it prevents the natural neuropeptide from binding with the GPCR, therefore ensuring that a critical function does not occur,” Vander Meer explained.

In short, Receptor-i introduces so many keys that most of the locks become overwhelmed. Some of the peptides may irreversibly activate the target GPCR, causing overstimulation and insect malfunction. In either case, Vander Meer said, the GPCR cannot perform its essential physiological task, causing the ant to die or become incapacitated.

Receptor-i yields results more quickly, and at a much lower cost, than high-risk traditional systems that typically take years to “maybe” find an active ingredient, Choi explained. Its innovative qualities lead to rapid identification of strong binding peptide control candidates, which can then be used to target an essential GCPR and neutralize the ants.

Although neuropeptides play essential roles in all insects, Receptor-i is environmentally safe because it affects only targeted species. The delivery mechanism for fire ants would be a bait station that would specifically target the ants and exclude most non-target insects. In addition, the bioactive peptides are biodegradable.

Choi and Vander Meer are optimistic about their results and believe they may hold promise for addressing other invasive pests: soon, they plan to expand their research to the spotted lanternfly, spotted wing drosophila, and pest slugs. — By Scott Elliott, ARS Office of Communications.

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