Abstract
Eusocial insects are exposed to a wide range of pathogens while foraging outside their nest. We know that opportunistic scavenging ants are able to assess the sanitary state of food and to discriminate a prey which died from infection by the entomopathogenic fungus Metarhizium brunneum. Here, we investigate whether a contamination of the environment can also influence the behaviour of foragers, both at the individual and collective level. In a Y-maze, Myrmica rubra ants had the choice to forage on two prey patches, one of which containing sporulating items. Unexpectedly, the nearby presence of sporulating bodies did not deter foragers nor prevent them from retrieving palatable prey. Ant colonies exploited both prey patches equally, without further mortality resulting from foraging on the contaminated area. Thus, a contamination of the environment did not prompt an active avoidance by foragers of which the activity depended primarily on the food characteristics. Generalist entomopathogenic fungi such as M. brunneum in the area around the nest appear more to be of a nuisance to ant foragers than a major selective force driving them to adopt avoidance strategies. We discuss the cost–benefit balance derived from the fine-tuning of strategies of pathogen avoidance in ants.
Highlights
Eusocial insects are exposed to a wide range of pathogens while foraging outside their nest
Foragers that first explored the uninfected foraging area (UFA) were as numerous as those that first headed towards the contaminated foraging area (CFA) (NUFA = ants and N CFA = ants, binomial test: P = 1)
In the few cases (28 out of 287 trips) where the ant visited the two platforms, this prolonged exploration did not result from a redirection of the ants’ activity from the contaminated area towards the uncontaminated one. These trips were as likely to start with a first visit to the UFA (NUFA = 17 trips) as to the CFA (NCFA = 11 trips)
Summary
Eusocial insects are exposed to a wide range of pathogens while foraging outside their nest. Besides the social information mediated by pheromone trails, ant individuals improve their navigational skills over successive foraging trips[21] and may eventually develop a fidelity to stable and rewarding food sites Such a site fidelity has been observed in many different ants such as ponerine ants (Dinoponera quadriceps22), harvester ants (Pogonomyrmex occidentalis[15]; Pogonomyrmex barbatus23), formicine ants (Formica schaufussi[24]; Lasius niger20,25) and myrmicine ants (Myrmica rubra[26]). As regards to the abiotic environment, the soil substrate can modify the collective choice of a foraging r oute[28] and the ambient temperature can influence the running speed and the searching behaviour of foragers[29] Biotic factors such as the presence of predators or competitors are known to act upon ants’ foraging, both at the individual and collective level. Competitors can alter foraging in different ways by either making the ants avoiding the location[31], by increasing recruitment to food[32] or by eliciting no response[33]
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