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Argentine ants scavenge the remains of a piranha.

Argentine ants scavenge the remains of a piranha.

Mark Moffett/Corbis

Newly discovered insect virus could combat invasive ants

Like colonial Europeans carrying smallpox to the Americas, the tiny brown Argentine ant may be harboring a dangerous virus that’s killing the world’s already vulnerable honey bees. That’s the conclusion of a new study, which also finds that the ants have their own disease to worry about—one that scientists could target to limit the spread of this invasive species.

“I think cataloging the viruses that are widespread in invasive species is very important,” says David Holway, an ecologist at the University of California, San Diego, who was not involved in the study. “The authors have made a good start.”

As its name suggests, the Argentine ant (Linepithema humile) is originally from Argentina. But thanks to the globalization of human society, the invaders have now spread to every continent except Antarctica. They arrived in New Zealand in 1990, for example, probably on a boat or a plane, and have since formed a super colony spanning the nation.

Unlike most ant species, Argentine ants don’t fight with neighboring colonies. Instead, workers move freely from one nest to another, sharing resources and responsibilities over huge ranges. The ants are so successful and their colonies so expansive that they often drive out all other ant species in the area, sending ripples up the food chain that harm lizard and plant populations dependent on the displaced natives. “They are sometimes referred to as the Genghis Kahn of the ant world,” says ecologist Phil Lester at the Victoria University of Wellington in New Zealand. Although all this cooperation and movement makes the insects adaptable, scientist have wondered if this also makes them more susceptible to infectious diseases—a hypothesis supported by recent observations that massive colonies sometimes suddenly collapse with no obvious external cause.

To investigate what sort of viruses naturally infect the Argentine ants, Lester and colleagues extracted RNA from two groups of 30 Argentine ants from two separate nesting sites in Wellington, New Zealand. The team then compared sequences of the purified genetic material to a library of known insect RNA viruses, looking for bits that might be similar. The researchers report today in Biology Letters that they’ve discovered a novel virus—which they’ve named Linepithema humile virus 1 (LHUV-1)—in the Argentine ant population.

LHUV-1 is highly similar to another RNA insect virus called the cricket paralysis virus, and is suspected to be harmful to the ants. Whether the new virus is directly responsible for the observed population collapses is still unclear, but Lester thinks it’s a promising candidate.

Usually the discovery of a novel virus fuels research into cures or prevention, but the Argentine ants an invasive blight: The researchers are hoping to one day use the virus to exterminate the insects by adding it to bait traps to exterminate the ants.

If the virus can be used against the ants, it could be a huge boon for honey bee populations around the world. The team’s RNA analysis also showed that the ants carry the deformed wing virus, which has been implicated in the global honey bee decline. And, according to Lester, there’s plenty of chance for the ants to spread the virus to bees, too. “They raid bee hives. That’s a really good opportunity for the disease to be spread directly, he says. “We also know they forage on [the same] plants, so that’s another opportunity for exchange.”

Holway is more skeptical though, saying there’s no evidence yet of which way the transmission flows. The ants could just as easily be picking up the virus from the bees during the same raids.

As for whether the virus could be used to fight the ants, Holway points out that nobody has even determined whether the virus hurts them. “If there was some species-specific pathogen that knocked out the Argentine ant, I would be extremely happy,” he says. But he notes that pesticides could also be killing the ants, he and points out that whether or not the Argentine ant population is declining as a whole is still contentious.    

Lester’s team plans to investigate whether LHUV-1 also infects and harms other insects. “The host range needs to be determined,” Lester says. “The last thing we want to do is add to the bees’ problem.”