New research from the University of California, Riverside (UC Riverside) reveals that common pesticides cause striking and varied behavioral changes in invasive Argentine ants before they die. These changes, including erratic roaming or clustering near water, can mislead people trying to control infestations. The study highlights how different insecticides affect ant colonies in distinct ways, providing crucial insights for pest management.[bioengineer+2]
Pesticides Trigger Erratic Ant Behaviors
Entomology professor Dong Hwan Choe and his students at UC Riverside conducted the laboratory study. They examined how Argentine ants, a widespread pest in Southern California homes and gardens, responded to two common bait insecticides: thiamethoxam and boric acid. Their findings were recently published in the journal Insects.[bioengineer+2]
The researchers built transparent laboratory colonies, allowing them to observe ants both inside their nests and in foraging areas. They found that both chemicals effectively killed most worker ants, but at different speeds and with sharply contrasting behavioral impacts.[bioengineer+2]
Thiamethoxam Causes Hyperactivity
When exposed to thiamethoxam, a neonicotinoid insecticide, Argentine ants became unusually active. A much larger proportion of ants left their nests and began roaming far beyond their usual foraging paths before they eventually died.[bioengineer+2]
Professor Choe compared this effect to ants being "high on nicotine," explaining that the insecticide compromises their nervous systems. Thiamethoxam acts on nicotinic acetylcholine receptors, overstimulating nerve cells and eventually leading to paralysis. This chemical killed all worker ants in the lab experiments within approximately seven days.[bioengineer+2]
This hyperactivity can create a misleading impression for homeowners. Seeing more ants wandering into visible areas like sinks or windowsills might suggest the infestation is worsening, even though the colony is being progressively weakened.[bioengineer+2]
Boric Acid Leads to Clustering
In contrast, boric acid produced nearly the opposite behavioral response. Instead of increased activity, affected ants largely stopped foraging and retreated into their nests. They gathered tightly together, often near sources of water.[bioengineer+2]
Boric acid is not a neurotoxin like thiamethoxam. It affects multiple parts of the ants' bodies, including the midgut lining, which is vital for digestion and nutrient absorption. It can also damage excretory organs involved in water regulation.[bioengineer+1]
Boric acid killed about 90 percent of worker ants within roughly two weeks in the laboratory settings. The ants' attraction to water after exposure could be linked to a disruption in their internal fluid regulation, though more research is needed to confirm this mechanism.[bioengineer+1]
Implications for Pest Control
These distinct behavioral changes have significant practical consequences for interpreting the effectiveness of ant baiting. If ants suddenly disappear after encountering boric acid, it might seem the colony has been eliminated. However, surviving ants could simply have retreated into the nest, creating a false sense of victory before activity resumes.[bioengineer+1]
Conversely, if ants appear more active and visible after thiamethoxam application, homeowners might mistakenly believe the treatment is failing or making the problem worse. In reality, these ants are poisoned and are nearing death.[bioengineer+1]
Understanding these differences can help pest control professionals and consumers better interpret what they observe after applying ant bait. The findings may also guide manufacturers in designing baits that more effectively exploit the social biology of ants, while potentially reducing risks to non-target species.[bioengineer+1]
Challenges in Colony Elimination
Despite the effectiveness of both chemicals against worker ants, the study noted that neither treatment guaranteed the death of the queen. This poses a significant challenge for long-term ant control. An ant colony can recover from losing large numbers of workers if the queen survives and continues to produce new generations.[bioengineer]
For Argentine ants, this problem is compounded by their extensive networks of interconnected nests and multiple queens. New workers can eventually restore a colony's foraging strength, and nearby colonies can also reinvade treated areas, making complete eradication difficult.The study emphasizes that by linking pesticide exposure to specific changes in movement, nest use, and water-seeking behavior, researchers offer a clearer picture of how insecticides impact ants before fatalities occur.[bioengineer+1]
