Argentine ants (Linepithema humile) (foto) is an aggressive invasive pest species in US. "Argentine ants are one of the most widespread and ecologically damaging invasive species", said biologist Neil Tsutsui.

When Argentine ants enter an area, they eliminate virtually all native species of ants. This damages the ecosystem, affecting species such as the imperiled Coastal Horned Lizard, which feeds exclusively on a few species of native ants. Argentine ants are also a vermin to crops, such as citrus, by protecting aphids and scale insects from potential predators and parasites.

Super colonies have numerous queens and can stretch for hundreds of miles. One colony of Argentine ants is believed to extend almost the complete length of California, stretching from San Diego to Ukiah, 100 miles north of San Francisco. "Although the proliferation of the ants has been slowed in the South and Southeast by the introduction of fire ants, Argentine ants are now the most common ant in California", Shea said.

"In their native South American habitat, Argentine ants are genetically diverse, have territories measured in yards rather than miles and are extremely aggressive toward encroaching colonies, literally tearing one another apart in battle", according to Tsutsui.

But North American colonies are different. They are believed to be descended from a single small population of genetically similar ants. Just one colony reached US in the 1890's aboard ships that docked in Louisiana. The Argentine ants from US essentially "recognize" each other as members of the same clan. "You could take an ant from San Diego and put it in a nest in San Francisco and they would treat them the same as if they are family," said Robert Sulc, graduate student.

"Even though they are just an eighth of an inch long, their sheer numbers have allowed the invasive ants to kick out or kill other ant colonies in California" mentions study team member Kenneth Shea, an organic chemist at the university. The problem is that native ant species have smaller colonies.

Till now, Argentine ants proved to be very resistant to insecticides and trapping. Recently, a team at the University of California, Irvine, may have found a way to stop the spread of environmentally destructive Argentine ants in California and elsewhere in the US.

By altering pheromones on the exoskeletons of these ants, researchers turned typical cooperative behavior into an infighting among the residents of these vast colonies and help check their spread, according to research presented at the 232nd American Chemical Society National Meeting in San Francisco by Shea, Tsutsui and Sulc.

The members of the same colony recognize each other by their pheromones. Because Argentine ants in the California super colony are so interrelated, they have similar pheromones and so, they cooperate.

But in their preliminary laboratory work, Shea and Tsutsui were able to create a slightly altered, synthetic version of one of these pheromones. When wrapped onto experimental Argentine ants, the synthetic pheromones caused untreated nest mates to attack. "Our preliminary results strongly suggest that by manipulating these chemicals on the exoskeleton, one could disrupt the cooperative behavior of these ants and, in essence, trigger civil unrest within these huge colonies," Shea says. "Although further study is needed, this approach, if it proves successful, could enable us to better control this pest."

The chemical treatment was problematic. The team spun an ant into a tube filled with pheromones for 90 seconds to make the chemical stick. "After all that shaking it's a little bit wobbly but usually it's still alive," Sulc said. "Then, we put it back into the Petri dish with ten of its friends from the same colony and then we observe how aggressive they are toward him." "The other ants immediately attacked, using their large mandibles, or jaws, to bite and tear off its legs", Sulc said.

"The final goal of this project would be to recognize the colony markers that distinguish one colony from another," Shea said.

"Once we have an understanding of those markers, then it might be possible to use synthetic mixtures of hydrocarbons to either confuse or confound or otherwise disrupt social behavior."