Fire ants are a royal pain (literally and figuratively). Chemical pesticides and many other brews have tried to wipe them out, unfortunately without success. They are now colonizing many other countries. But, what is the origin of these new invasions?
The aggressive, stinging fire ants (Solenopsis invicta) are not native to the United States, but rather to a broad swath of South America. They came to the Southern U.S. in the 1930's. Since then scientists have identified eight separate waves of fire ants moving to other countries or regions: Caribbean, Australia, New Zealand, Taiwan, and China, including Hong Kong and Macau.
To track the invasions, an international research team analyzed ants from 2,144 colonies in a total of 75 places in 11 countries, and looked at several kinds of genetic information, including dozens of DNA markers. The genetic make-up of fire ants is complex. Fire ants in their native range in South America revealed 322 distinct genetic types. Only 11 of those types were found in the southern United States, including three that were very rare in the native range.
The populations from the invaded territories noted above had combinations of the three rare variants from those U.S. types, but not the others which are present only in South America. Additionally, the researchers ran computer models of how gene patterns in populations change as invaders move into new territories. The scenarios that fit the data best showed the United States as the source.
The three "rare" U.S. types of fire ants also have an unusual ability to fast, thus making them "fit" as stowaways on ships and planes. Fire ants also produce many queens that can fly off to start new nests. Five thousand or more queens identified with a single large nest have been found in a single day. Thus, once present, colonies can expand rapidly within their new territory.
The research can be found at http://www.sciencemag.org/content/331/6020/1066.abstract.