No specialist pheromone‐ignoring ants in Lasius niger

Abstract

In insect societies, the balance between exploitation of known resources and exploration of new ones is important to ensure sufficient resources. Mass recruiting ants, such as Lasius niger, use pheromone trails to recruit nestmates to a newly discovered food source. Pheromone following, however, shows characteristic non‐following (lapse) rates among different species, with ∼20% of L. niger foragers ignoring pheromone. These characteristic lapse rates might simply be ‘noise’, or they might indicate a subset of specialised explorative foragers, a scouting caste, that consistently ignores pheromone in order to explore. Here we show pheromone ignoring is not a repeatable behaviour in L. niger foragers – ants who did not follow a trail were no more likely to ignore it again an hour later than ants which did follow it. Our findings suggest that there is no subset of specialised pheromone‐ignoring L. niger foragers. This may be due to their moderate colony size and strong reliance on individual memories: species with larger colony sizes or a weaker reliance on private information (i.e. memory) may have specialist non‐followers. Our work raises the question: what is a scout ant? We encourage future research to investigate the presence of a scouting caste in other ant species using our straightforward methodology, as a social information‐ignoring caste may be rarer than expected.

Ants prefer the option they are trained to first

“…2 , compare panels A and B), while pheromone had no significant effect (χ²=0.26, P =0.61). Ants also preferentially chose the left side in the -maze during the test (χ²=14.9, P <0.001), as previously reported ( Koch and Czaczkes, 2021 ). The identity of the odour (lemon or rosemary) did not significantly influence the ants' choices (χ²=1.1, P =0.29), nor were any interactions significant (see ).…”

Conflict interference in an insect.

“…Discrimination between PL and N should thus be easier than between P and L. However, there are two reasons to reject a purely associative account. First, given that P already has innate positive value (it is innately attractive, as can be seen in the first congruent visit, Figure 2C, and in many previous studies [Koch & Czaczkes, 2020]), a purely associative account would predict a blocking effect when P is presented with L, such that the learning of the association between L and reward should actually be weakened. However, in the first incongruent trial, we see random choice, implying that the L association has perfectly balanced out the P effect.…”

“…The preference for a cue rewarded once over no cue in Lasius niger ants is between 70% and 75% (Grüter et al, 2011; Oberhauser et al, 2019). Naïve ants follow pheromone trails on a bifurcation at a rate of circa 75% (Koch & Czaczkes, 2020). Thus, we would expect these two effects to balance each other out in the absence of blocking (as we observe), but not to do so if blocking was taking place.…”

“…This rendered side and pheromone presence uninformative, whereas the lemon odor cue was maximally informative. As ants have a strong innate tendency to follow pheromone trails (Hangartner, 1969;Koch & Czaczkes, 2020;von Thienen et al, 2014), we expect pheromone trails to be strong distractors in this ant version of a conflict task, whereas following the odor cue is referred to as the target response. Trials in which the pheromone and odor cue both were located at the same arm of the Y maze are considered congruent trials, whereas a mismatch of the location of pheromone and odor was considered an incongruent trial.…”

“…Here, we developed a task that mimics the Stroop word-color task in ants. The dominant but irrelevant information source (comparable to the printed word meaning) is provided by a pheromone trail, which ants innately follow at a high rate (Hangartner, 1969;Koch & Czaczkes, 2020;von Thienen et al, 2014). The correct but not innately meaningful response (comparable to the printed color) is provided by a neutral odor cue.…”