Trail pheromones experiments. (Sandra)


Dear Ant Experts,

My lab partner and I designed a foraging experiment for our biology class to determine whether ants (Tetramorium caespitum) have a tendency to follow an established pheromone trail, or find a new food source. Can you provide insight on how to improve our methods?

We used a T-shaped apparatus constructed from PVC pipe with an opening at each end (three openings total). The PVC pipe was cut, allowing an aerial view of the ants when run through . Each arm of the T-shaped apparatus was approximately 6in in length. Food was placed at one opening of a T-shaped maze on aluminum foil. This food consisted of .25 mL of a 5% sugar water solution.A hole was cut into a 3x5 container and attached to the stem T-shaped apparatus. Then substrate from the excavation site, filled half of this container, and an ant was transferred using forceps from the 8x10-holding terrarium to the 3x5 container, which is attached to the maze. This provided a "home base" that ants would return to after food had been discovered. As well the stem of the T-shaped apparatus was lined with substrate. Once placed in the 3x5 container attached to the maze, the ant was allowed to scavenge for the food.Ten ants were run through the maze, separately to establish a trail to a food source.Then, the food source was then switched to the other end of the T-shaped maze. After the trail was established we would run 5 trials of 10 ants each. We would observe whether the ant followed the established path, or choose the path that led to food. Our hypothesis is that ants will always follow the established pheromone trail as long as it is potent and has not dissapated and it will take the proceeding ants less time to arrive at the end where the food originally presided then the first ant.

We ran into some difficulties, when we ran the first 10 ants to establish the pheromone trail. When we were running the ants through the t-shaped apparatus during the trial, they would be reluctant to leave home base, once they did leave home base and got pass the stem of the T-shaped apparatus lined with dirt, it took a substantial amount of time for them to forage around bifurcation. Only one ant that we ran actually arrived at the food, but did not return to the home base, before our class period ended. Other ants that we ran either returned to the home base prematurely (before food was found), or would walk around the food and not acknowledge it was there by eating from it or taking it back to the home base. Do ants need to eat or touch the food to acknowledge that it is there? We had first used grape jelly as a food source but it proved to be too sticky and viscous, because our ants drowned in the jelly. So we changed to a 10% sugar solution, but the ants would drag their appendages in the sugar solution ( while walking around the food) and then they would essentially be crippled, and have difficulty moving. Once they had dragged their appendages in the sugar solution they would try to return to the home base. This is why we diluted the solution to 5%, but the ants run through the T-shaped apparatus would not acknowledge this food source as well. Is there a more appealing food source we could use? Does the species Tetramorium caespitum release multiple pheromones for foraging such a repellent pheromone? How long does is take for the pheromone trail of Tetramorium caespitum to decay? How can we improve our methods, so that we can ensure results which our due in two weeks?

Sincerely,
Sandra


Hi Sandra,

Thanks for your e-mail and the very detailed description of your science project. The problem might be that the ants don't lay pheromone trails. Would it be possible for you to run the experiment for a much longer time and give the ants 1 hour to find the food source and release pheromones? Maybe that would help. Does the PVC tube itself smell, which might confuse the ants?

We have written a previous post here and here that might give you some ideas on baiting experiments. Alternative baits that the ants might work better: smaller drops of sugar solution (I suggest 20%), diluted honey, tuna, ham, dead insects.

Would it be possible that you re-design your experiment and tackle a different question? You could offer different baits simultaneously and test what the ants prefer. Read this post here and here to get some ideas.

The trail pheromone of Tetramorium caespitum has been identified and consists of two components. For the details, click on this link here.

Trail pheromones often decay pretty quickly, within about 10 minutes.

I hope this helps!
Steffi Kautz & the AntAsk Team

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