By Josh Lancette
Argentine ants have been marching across the United States for the past few decades, despite the best pest control efforts. However, the authors of a new study published in the Journal of Economic Entomology may have found a better, more environmentally friendly way to stop the procession.
The Argentine ant, Linepithema humile, is an invasive species that has become a major nuisance in California and many southern states. In fact, a 2007 survey published in Sociobiology found that 85% of all urban pest control services in California were focused on the Argentine ant.
One reason why these ants have been so successful is their ability to form super colonies. Each single nest contains hundreds of queens, and this allows the ant to form large colonies very easily and to utilize resources quickly, oftentimes out-competing native ant species and displacing other arthropods.
A common weapon of choice for managing the Argentine ant has been residual insecticide sprays (insecticides that remain effective for a length of time after being sprayed on a surface). However, the downside of this tactic is that the insecticides can find their way into water systems and can harm some beneficial aquatic species.
Another common management technique is baiting, where the ants take food mixed with insecticides back to their colony and then expose other ants to the toxins through “trophallaxis,” the sharing of food. This method is more environmentally friendly, but it can be tricky to perfect because the baits need to be palatable, non-repellent, slow-acting, transferable, and inaccessible to non-ants.
In an effort to improve the baiting technique, a team from the University of California-Riverside decided to try adding ant pheromones to the bait.
They found that baits without pheromones reduced ant activity by 42 percent after four weeks, but baits with pheromones reduced ant activity by 74 percent after four weeks. In other words, adding pheromones dramatically improved the effectiveness of baits.
This result came as a bit of a surprise to the authors.
“We expected the pheromone-assisted gel bait to attract more ants, but the amount of Argentine ant control in homes was quite remarkable,” said Kevin Welzel, the first author on the paper and a graduate student at UCR.
“A good way to explain why the pheromone bait worked better is to think about it like the smell of your favorite food,” Welzel said. “Once you smell your favorite food, you tend to go to the source of the food and you may find it difficult to resist the temptation to consume it. Essentially, we just added an attractive smell to bait that didn’t have an odor. This attractive smell allows the Argentine ants to quickly locate and then consume more of the bait.”
Welzel is optimistic that the findings in this study can positively impact control of the Argentine ant.
“I honestly want to improve the way pesticides are used,” he said. “The Argentine ant is a perfect system to utilize baiting techniques that are environmentally safer. I’m happy that my research has the potential to improve baiting techniques.”
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Josh Lancette is Manager of Publications at the Entomological Society of America.