College of Natural Resources, UC Berkeley

Argentine ant genome: Revealing peek at a pervasive pest

January 31, 2011

By Elizabeth Weise, USA TODAY
Photography by: Alex Wild

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The genome of the highly invasive Argentine ant, well on its way to wiping out many native ant species in California, has been sequenced. The effort is part of a consortium of researchers who sequenced the genomes of a total of four ant species.

The researchers found that all the ants, but the Argentine ant (Linepithema humile) in particular, have a tremendous number of genes devoted to taste and smell. The ant lives in a chemical world and their genome shows it. "They're just bristling with these sensors," says Neil Tsutsui, professor at the University of California, Berkeley's Department of Environmental Science, Policy & Management, and an author on three of the papers.

Argentine ants have 367 genes for sensory receptors for odor and 116 for taste, they found. By comparison, the honeybee has 174 genes for odor and 10 for taste, and the mosquito has 79 genes for odor and 76 for taste.

The Argentine ants also have lots of genes that help detoxify harmful substances, 111 such genes, while European honeybees, in comparison, have 46. Tsutsui says knowing where these genes are could help researchers look at pesticide resistance.

Two other ant genomes, the red harvester ant (Pogonomyrmex barbatus) and the red imported fire ant (Solenopsis invicta), as well as the Argentine ant are being published in the Jan. 31 edition of the journal Proceedings of the National Academy of Sciences, The fourth, the leaf-cutter ant (Atta cephalotes), is scheduled for publication in the Feb. 24 issue of the journal PLoS Genetics.

The Argentine ant is small, brown and ubiquitous in California, warmer areas of the U.S., Asia, Australia, South Africa and the Mediterranean. The ants have been in the United States for a long time. They were first observed in New Orleans in the late 1800s and showed up in California in 1970, says Tsutsui.

The ants invade homes and businesses, making long lines of ants as they find food sources and then forage. Humans respond with insecticides that kill other, beneficial insects including spiders and honey bees.

The ants are also a major concern in agriculture because these ants are associated with aphids, mealy bugs and scale insects, caring for them in exchange for the sweet nectar they produce. "Argentine ants love to tend aphids on citrus trees," says Tsutsui.

Finally, these insects kill off other, native ants species that are vital to the ecosystems they inhabit. In California the ants are already edging out between 15 and 20 native ant species, says Tsutsui. "When Argentine ants show up they destroy all the others."

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Photography by: Alex Wild

That's because of an interesting bit of genetics. In their native habitat in South America, each colony is genetically different enough that they consider other Argentine ants to be their enemies. The ants in general are very territorial and aggressive, which keeps their populations down.

However in the United States Argentine ants are genetically similar enough that the millions of colonies here consider themselves to be friends, rather than foes. This means they effectively make up one huge super colony. "You can take ants from San Diego and San Francisco and put them together and they act like best buddies, they groom each other, they take care of each others babies," he says.

This, unfortunately, allows them to devote all their energy and their workers to population growth.

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