Battle of the Bugs

Anyone who has tried to rid their kitchen of Argentine ants might well think the species invincible. But these invasive insects now face a formidable challenger: the Asian needle ant.

Argentine ants have invaded six continents and are famous for their enormous colonies. In addition to annoying homeowners around the world, they are pushing out native ants. Recently, the Asian needle ant — another invasive species — moved into the eastern U.S. These ants have smaller colonies, but they are hardly benign: Their sting can cause severe allergic reactions in people.

A research team was studying an Argentine ant infestation at an office park in Morrisville, North Carolina and noticed Asian needle ants in 2008. To track the new invasion, the scientists surveyed the ants each month from 2009 to 2011. Speculating that the newly-arrived insects might be more tolerant of cold weather, the team measured both species’ survival rates in 4-degree and 12-degree Celsius incubators in the lab.

Each year, the number of Asian needle ant clusters tended to rise in March and April, while Argentine ant clusters didn’t increase until about two months later. From 2008 to 2011, the number of sites containing only Argentine ants dropped from 90 to 67, and the number of Asian needle ant-occupied sites rose.

More Asian needle ants also survived in the chilly incubators than the Argentine ants, the team reports in PLOS ONE. The new invaders’ cold tolerance might allow them to get a head start in March and April, when Argentine ant numbers are still relatively low. Roberta Kwok | 12 February 2013

Source: Rice, E.S. and J. Silverman. 2013. Propagule pressure and climate contribute to the displacement of Linepithema humile by Pachycondyla chinensis. PLOS ONE doi: 10.1371/journal.pone.0056281.

Image © Benoit Guenard