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Local ants wield poison to kill invading Argentine ants


June 8, 2011 - Washington

Argentine ants are showing up all over the world-conquering the entire coastline around the Mediterranean Sea, parts of South Africa, Hawaii, Japan and Australia, as well as the full length of the California coastline-and no native ant species has been known to withstand their onslaught until now.

Now, a group of Stanford University undergraduate students working on a class project have discovered that a native species, the plucky winter ant, has been using chemical warfare to combat the Argentine tide.

The winter ants - named for their unusual ability to function in cold weather, rather than grind to a halt like most insects - manufacture a poison in a gland in their abdomen that they dispense when under extreme duress. One tiny drop applied to an Argentine ant is enough to put an end to it. In laboratory testing, the poison had a 79 percent kill rate.

"This is the first well-documented case where a native species is successfully resisting the Argentine ant," said Deborah M. Gordon, a biology professor at Stanford who specializes in studying ants and taught the three-week summer class in which the students first saw the winter ants wielding their poison.

"I did not believe it at first. This is a group of ants that does not have a sting and you don't see them acting aggressively, but the students were able to show very clearly not just that the winter ants are using poison, but when they use it, how they use it and what the impact is," she said.

The Stanford students began observing the native ants as part of a 2008 short summer class for sophomores called Ecology of Invasions, taught by Gordon. At a variety of locations on the Stanford campus, they started out simply observing and recording ant behavior while visiting each site at the same time every day.

"We were looking at the nest openings of the winter ants and one day it was just winter ants going about their business foraging for food and making trails-just typical ant behavior," said Leah Kuritzky, a student in the class and one of the coauthors.

"The next day we came back and the ground was littered with Argentine ants. There were dead ants all around and there was a lot of fighting around the nest entrances."

In earlier observations, the students had noticed the winter ants occasionally secreting a whitish fluid from their abdomens and, by prodding a few with a paperclip, had figured out that the ants tended to secrete when hassled.

Kuritzky did a chemical analysis of the secretion, using gas chromatography and mass spectrometry. She determined that part of the secretion consisted of a type of hydrocarbon, which many social insects use to carry a colony-specific odor that helps them identify friend from foe.

The findings were published earlier this year in PLoS ONE.

ANI

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