Chemical Cocktail Turns Argentine Ants Against Each Other

John Roach
for National Geographic News

September 22, 2006

Scientists are developing a chemical potion that makes mortal enemies of members of a massive Argentine ant gang that has invaded California.

The cocktail, if successful, could pave the way for the return of native ants, which have been driven from the region by the foreign species, says Neil Tsutsui, an evolutionary biologist at the University of California, Irvine.

"If we put enough of a dent in the [Argentine ant] population using this, the native ants may compete more successfully against them and do the final bit of elimination," he said.

Chemical scents on Argentine ant bodies, which are about an eighth of an inch (a third of a centimeter) long, allow the arthropods to recognize friend from foe, Tsutsui says. (Get ant photos, facts, and more.)

He and colleagues are developing and testing varieties of synthetic scents—made up of chemicals known as cuticular hydrocarbons—that make friendly ants smell hostile.

The mistaken identity turns the ants against each other in what amounts to a deadly turf war, Tsutsui says.

The researchers reported preliminary findings last week at a meeting of the American Chemical Society in San Francisco, California.

"With all five compounds initially [created] for testing, the treated ants were attacked by their nest mates," Tsutsui said.

Argentine Invasion

In their native home of South America, Argentine ants are genetically diverse, and their colonies seldom exceed the size of a football field because of turf squabbles, Tsutsui says.

"They waste huge resources fighting other Argentine ant colonies, protecting their colonies from others," he added. "So they are not able to achieve high population densities."

In North America, however, almost all the Argentine ants are related, Tsutsui's research suggests. So the ants work with each other, not against each other.

"This is the key to their success," Tsutsui said. "It allows the population to boom—to grow to an extremely large size and overwhelm other species just by sheer numbers."

Scientists believe the founders of California's Argentine ant gang stowed away on United States-bound cargo ships from South America in the 1890s.

With no need to devote resources to fighting rival gangs—who were left behind in South America—the U.S. invaders quickly multiplied and wreaked havoc on the country's southeast and west coasts.

"In California we now have one huge supercolony [that stretches] from San Diego to north of San Francisco," Tsutsui said (California map).

(Related: "Ant 'Supercolony' in Europe Raises Questions About Getting Along" [April 2002].)

(Some scientists, however, believe the "supercolony" idea is false, arguing instead that the Argentine ants in California are from numerous colonies of genetically distinct ants.)

The Argentine ants have all but ousted the California natives, Tsutsui says. Other critters that eat only native ants, such as the coastal horned lizard, are suffering too.

Homeowners spend gobs of money on sprays and traps in a losing battle to block the invasive arthropods from their food and water.

And farmers routinely see aphids and scale insects—which the Argentine ants protect from parasites in exchange for the insects' sweet secretions—ravage their crops.

Chemical Confusion

Tsutsui and colleagues identified a few small, isolated Argentine ant colonies in California that are distinct from the supercolony. These ants have a different chemical scent.

When the researchers pitted members from these distinct colonies against the supercolony ants, the rivals fought in mortal combat.

Surprised, the researchers compared the chemicals on the bodies of the rival ants and identified 15 compounds that appear to provoke aggression.

The team is now creating these chemical compounds synthetically in the lab and applying them to some colony mates in hopes of starting deadly feuds.

Each artificial chemical has provoked infighting, but the level of aggression differs, suggesting that each scent contributes only a small part to the cues for relatedness.

More closely related ants share more chemicals, and thus behave less aggressively toward each other, Tsutsui says.

"Not only does this research suggest a potential avenue for controlling Argentine ants, it also allows us to gain insight to the evolution of social structure," he said.

Deborah Gordon is a professor of biological sciences at Stanford University in California who was not part of the research team. She says the concept that large differences in hydrocarbons provoke ant feuds is well known.

"The question is, how much will this affect the success of Argentine ants as an invasive species?" she said.

Humans are the greatest help to the invaders, Gordon adds. Houses provide water in the hot, dry summer and warmth in the wet winter.

"It's an open question whether getting [the ants] to fight each other will offset the help we give them," she said.

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