Altering ant uniforms

From San Francisco, at a meeting of the American Chemical Society

The chemical coat that an invasive ant species relies upon to recognize its kin may someday serve to turn family into foe, reports a team of chemists and behavioral ecologists from the University of California, Irvine.

The Argentine ant is now found in Mediterranean-type climates throughout the world. Its success as an invader rests partially in behavior not displayed back home (SN: 4/20/02, p. 245: Available to subscribers at European Union for Ants: Supercolony reigns from Italy to Portugal). In Argentina, the ants (Linepithema humile) form small, territorial colonies. A colony’s fights with other colonies over food and space keep its numbers in check, explains behavioral ecologist Neil D. Tsutsui.

However, in their adopted homes, most of the insects live in supercolonies, in which far-flung ants identify each other as nestmates. Therefore, the ants can collectively turn their aggression toward defeating native species. One such supercolony resides along much of the California coast.

The ants recognize nest mates by smell. They detect hydrocarbons in a waxy coating that covers each insect’s exoskeleton. Tsutsui and his colleagues asked which of the 80 to 100 chemicals on the exoskeleton act as recognition cues.

“If you can find the chemicals that these ants use to recognize and attack members of different colonies, maybe you can think of a tricky way to get these chemicals on the exoskeletons of [same-colony] ants so they can kill each other off,” Tsutsui says.

The team extracted the waxy coats of ants from the California supercolony and from four smaller colonies in the state. Then, the researchers compared the hydrocarbons among the groups to look for those that differed between colonies but not within a colony.

The researchers picked out 15 chemical candidates. So far, they’ve synthesized five of them and have tested how the chemicals affect the ants.

The team spiked individual ants with one of the five synthesized chemicals, then placed each insect back with its nest mates. In every colony, ants attacked a former mate with an altered coat, although not every chemical led to aggression in every colony, says Tsutsui.

The researchers are now synthesizing and testing the remaining candidates. Their goal is to learn more about the mechanisms behind the ants’ recognition of each other, Tsutsui says.