Can we make ants kill each other?

Scientists have decoded the words in the secret chemical language of Argentine ants, a discovery that could lead to an environmentally benign pesticide against the insects.

The researchers found special signaling chemicals on the bodies of one aggressive group of ants and then synthesized the chemicals to induce peaceable members of the same species to turn into highly aggressive beasts, perhaps leading them to turn on each other.

The difficult experiments with the hydrocarbons that trigger the ants' silent battle calls were led by University of California at Berkeley evolutionary biologist Neil D. Tsutsui and cost tens of thousands of dollars.

But Brian L. Fisher at the California Academy of Sciences, a leading authority on ants of every tribe, called the discovery "a really novel breakthrough" and said it marks the first successful step in efforts by humans to "understand the entire language that ants use to communicate with each other."

The report by Tsutsui's team was published last week in the British scientific journal BMC Biology.

Almost all Argentine ants in California belong to a genetically distinct group of the species whose members are cooperative and social and form one huge "super colony" that extends from Oregon to San Diego, Tsutsui and Fisher said. Although the ants are viciously aggressive against other species of ants, they are peaceable even when brought together in the lab from different parts of the state, the scientists said.

But in San Diego County exists a tribe whose ants attack each other, and it was there, Tsutsui said, that two postdoctoral researchers in his laboratory, Miriam Brandt and Ellen van Wilgenburg, collected samples to remove the waxlike chemicals that cover the insects' skins.

Those hydrocarbons, the group reasoned, act like pheromones, the airborne substances that serve as chemical signals for mating, aggression and food finding among other insects, as well as vertebrate animals and perhaps even humans.

Chemists at the University of California-Irvine analyzed the chemicals from the San Diego ants and synthesized them so the Berkeley students could apply them to the skins of peaceable ants collected from the same California "super colony" but living as far away as Shasta County.

Tsutsui's team found that the same synthetic compounds "trigger aggression among normally amicable nest mates."

A mixture of five synthetic hydrocarbons greatly increased the attack rate among the normally benign insects, the group discovered.

For their long, difficult and expensive laboratory experiments combining biology and chemistry, the team maintained ants from five different and sometimes genetically identical colonies in California, feeding them three times a week on a diet of sugar water, protein solution and scrambled eggs.

It took the scientists nearly 2,000 separate and carefully controlled trials with the worker ants to establish that their synthetic chemical mixture produced the aggressive behavior, they reported.

Scientists have long known that "chemical signaling" is especially powerful as a means of communication among many insects, and particularly among ants that live in colonies and use the chemicals to recognize each other and their enemies.

But the language of those signals had been a total mystery until Tsutsui's group painstakingly deciphered the complex "cuticular hydrocarbons" from the skins of the ants and showed their power in transforming peace-loving ants into attackers. "Those were remarkable experiments," said Fisher. "They were risky and they could have failed, but they didn't."