U.S. imports fire ant enemies

South American fire ants reside on more than 300 million acres of U.S. soil.

November 30, 1999
Web posted at: 12:16 p.m. EST (1716 GMT)

By Environmental News Network staff

Natural enemies of the fire ant are being imported from South America to combat the invasive pests in the United States, report scientists focused on eradicating the critters. Fire ants reside on more than 300 million acres across 12 states and Puerto Rico.

"We believe imported fire ants have flourished in the United States because they have no natural enemies here. We're trying to change that by working with state cooperators to introduce natural enemies," said David Williams, a scientist with the U.S. Department of Agriculture Agricultural Research Service.

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It is thought that fire ants came into the United States in the 1930s as castaways aboard ships from South America. The pests are known for their aggressive behavior, nasty stings and huge mounds. Their prolific breeding has allowed them to displace many native ants.

The ants attack anything that disturbs their colonies, making them a threat to small children who have slow reaction to the ants' sting. The ants can also cause potholes by undermining roads and can destroy electrical contacts.

Researchers, who have had no luck eradicating the pests, have turned to the ants' natural enemies from South America as a means to control them. These include a disease-causing microorganism and a decapitating fly.

These tiny flies lay eggs in fire ants that cause the ants' head to fall off.

The microorganism, Thelohania solenopsae, infects ant colonies and causes disease. The worker ants probably transfer the pathogen to the queen through food exchange. The disease reduces her weight, she lays fewer eggs and the colonies get smaller, said Williams.

The microorganism does not harm plants or native ant species. After several years of testing, it has only been found in red and black imported fire ants.

"Since our first release in 1998 in Florida, Thelonia has spread to more than 75 percent of the colonies we're monitoring," said Williams. "But it will take longer to see a major impact."

The other notable enemy is a fly, Pseudacteon tricuspus which pierces an ant's outer cuticle and deposits an egg underneath. The egg quickly hatches into a fly maggot that moves into the ant's head. When the maggot is mature, it releases an enzyme that causes the ant's head to fall off.

"One female phorid fly usually contains a hundred or more torpedo-shaped eggs, so she can make multiple attacks," said Sanford Porter, an entomologist at the Agricultural Research Service.

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