This article looked at the Argentine ant which is invasive in the US but native to Argentina where this study was conducted. The idea here was to determine if ants abandon toxic bait, a commonly used product in ant control.

The researchers created a sugar solution that has been known to be well accepted by these ants. The toxic solution was made using boric acid as the active ingredient added to that same sugar solution. An important factor in this strategy is that mortality is delayed as is critical for ant baiting to return to the colony. They tested this out in some pre trials, and the ants lived for at least 6 hours after consumption. They also confirmed that the bait being used was palatable to avoid the possibility of distaste rather than avoidance behaviorally.  

The researchers ran two main experiments in this study. The first was day-scale dynamics and spatial extent of trail abandonment and the second was hour scale dynamics of trail abandonment so that's a fancy way of saying they looked at smaller and larger time scales.

 

To begin each experiment, they started by luring the ants into a false sense of security by providing a sugar only solution that was not toxic over a bridge to a set of feeders as seen in the diagram above. They placed this structure right by a known trail of ants that were heading to the nest which is called the trunk trail.  

 

Data collection consisted of measuring ant activity which was the average number of ants crossing the bridge per minute averaged from 3 minutes.  They also measured ant activity on the trunk trail to make sure reduced activity wasn’t a result of the colony dying off.  

For the first experiment, they had two bridge setups 7 meters apart from each other along the trunk trail. They took activity measurements at one hour intervals three times that afternoon. Over the next two days, they took measurements during the mornings and afternoons getting average activity levels for each day’s more active hours. They did this whole thing 5 times on different trunk trails as repetitions.  

This showed that trail abandonment occurred rapidly within about 18 hours of the toxic bait being provided. Fewer ants were found going to the toxic bait at each successive time interval while numbers at the sugar only station remained similar. This means that despite the bait still being palatable, fewer ants went after it as time went on and it was not because they colony had been killed off. 

Based on this result, they continued on to look at a closer temporal scale. To refine the experiment, they had a similar setup with just a few differences. Once the toxic bait was swapped in, the activity measurements were taken every hour from 10am to 5pm. They did all this 6 times on different trunk trails.  

What they found with this closer look was the ant foraging at the toxic bait decreased drastically over just three hours, with a 43% reduction in ants per minute. This increased to 79% reduction by 6 hours. I want to point out that this is all while the regular sucrose bridge did not see a decrease in numbers which indicates that “the ants were not satiated, not killed, and continued actively foraging throughout the experiment.”

With all that said and established, how does this impact using baits to control ants? The 3 hour time frame before foraging was reduced becomes a critical time frame for initial bait placement. Ideal bait placement is important so that as many ants as possible consume the bait before they begin to abandon it. Placing many baits can increase likelihood of more ants running into it.  

The researchers suggest that palatability being separate from abandonment could mean that other ant baits previously thought to be unpalatable were actually just being abandoned and ultimately, adjustments to such baits could be made, making more available products to use.  These experiments were also only tested on one active ingredient so it will be important for such work to be replicated with other common active ingredients.

Article by Ellie Lane

References

Zanola, D., Czaczkes, T.J. & Josens, R. Ants evade harmful food by active abandonment. Commun Biol 7, 84 (2024). https://doi.org/10.1038/s42003-023-05729-7

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