A University of California-San Diego study has shown water to be mainly responsible for Argentine ant invasions.
David Holway, an assistant professor of biology who conducted the study with graduate student Sean Menke, found Argentine ants in Southern California need wet soil to live and breed. So residents plagued by indoor infestations might find relief by shutting off or substantially limiting the use of outdoor irrigation.
The scientists say they were able within a matter of weeks to increase the abundance and encourage the spread of Argentine ants by irrigating normally dry land. Once irrigation ended and soil moisture declined, the researchers found, the number of ants returned to pre-irrigation levels.
"This is the first, definitive study that provides unambiguous experimental evidence that soil moisture can control invasions of Argentine ants," said Holway.
The dark-brown ants, are about 3 millimeters in length, are thought to have entered the United States aboard ships carrying coffee from Brazil during the 1890s, then expanded throughout California and the southern parts of the United States.
Holway and Menke report their research in the March 30 issue of the Journal of Animal Ecology.
Copyright 2006 by United Press International
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