Fire ants’ ‘aphid-ranching’ skills may be key to their successful U.S. invasion

January 3, 2012
By: Steve Byrns

COLLEGE STATION – Like Old West cattle barons in a B-western, red imported fire ants are expanding their range and increasing their herds while laying wholesale waste to the range, according to an expert on the issue.

Dr. Micky Eubanks, a Texas AgriLife Research entomologist at College Station, said the ants are using a practice known as “mutualism” to help them thrive despite the estimated $1 billion Americans pour into controlling them annually.

“Mutualisms play key roles in the functioning of ecosystems,” Eubanks said. “In this case, fire ants protect aphids in exchange for the honeydew that aphids produce and the ants eat. Native ants also do this, however a study by our team recently published in the Proceedings of the National Academy of Science determined that mutualisms involving introduced species such as the red imported fire ant can actually enhance invasion success and ultimately disrupt entire native ecosystems.”

Eubanks said the phenomenon has received relatively little attention in scientific circles prior to this study.

The team, consisting of Eubanks and lead researcher, Dr. Shawn Wilder, Texas A&M University entomologist; Dr. David Holway, Division of Biological Sciences, University of California; Dr. Andrew Suarez, departments of entomology and animal biology, University of Illinois and Dr. Edward LeBrun, Brackenridge Field Laboratory, University of Texas, examined how access to food-for-protection mutualisms involving the red imported fire ant aids the success of this prominent invader.

He said intense competition with other ants and insects in the pest’s native Argentina checks their explosive success there, but in the U.S. the invaders dominate the range, running rough-shod over the native ants while making full use of the aphid “cows’” nourishing honeydew.

The research team found that the carbohydrate-rich substance known as “honeydew”- that sticky fecal substance that drips on your car from aphids feeding on tree leaves – is a magic elixir to the ants. It gives them the energetic edge needed to out-forage native species and conquer new territory.

“Laboratory and field experiments demonstrated that honeydew with its high carbohydrate content dramatically increases fire ant colony growth, a crucial factor of competitive performance,” he said. “We examined colony growth by rearing fire ants with and without honeydew-producing aphids. After seven weeks, laboratory ant colonies with access to honeydew-producing aphids were 20 percent larger than those grown with cotton plants, but no aphids, even though both colonies had all the insect prey they could eat.

“Our findings support the hypothesis that although mutualisms help generate and maintain biodiversity in our native flora and fauna, introduced species such as the red imported fire ant can infiltrate these networks and divert resources for their own success with potentially devastating consequences to their native neighbors.”

For more information on the published work titled: “Intercontinental differences in resource use reveal the importance of mutualisms in fire ant invasions,” go to the Discovery Blog article: or for the complete work, go to:

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