A fungus infected environment does not alter the behaviour of foraging ants

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.

Spatial distancing by fungus-exposed Myrmica ants is prompted by sickness rather than contagiousness

“…Overall, our data suggest that the mobility and spatial location of M.rubra foragers is not altered by the chemical and mechanical cues associated with the fungal spores. This goes along with previous observations where M.rubra ants were not repelled by the presence of fungal conidia over prey or on foraged areas and were as prone to retrieve these items inside the nest (Pereira & Detrain 2020b, Pereira et al 2021. Further studies should investigate to which extent this lack of early spatial distancing correlates (or not) with social behaviour such as allogrooming by M.rubra nestmates.…”

Red harvester ants (Pogonomyrmex barbatus) do not distinguish between sorghum head mold symptomatic and asymptomatic seeds

“…Or these changes may be mediated more indirectly by changing soil properties and chemistry (Wagner et al, 1997) or plant communities (Whitford & Ettershank, 1975). While some ants avoid soil with higher densities of entomopathogenic fungi (Huang et al, 2020), other ant genera have also been shown to not avoid foraging in areas even if entomopathogenic fungi are present in the environment (Pereira et al, 2021). Ultimately, understanding how ants interact with a broader range of microbial partners can expand our understanding of their role in agroecological processes in understudied regions.…”

Cross-talk between immunity and behavior: insights from entomopathogenic fungi and their insect hosts

“…Some social insect species, such as the termites Reticulotermes flavipes, M. michaelseni, Zootermopsis augusticollis , and the ants Acromyrmex striatus , and Formica rufa , avoid fungal-infected areas or nestmates (Myles 2002 , Mburu et al 2009 , Liu et al 2019a ). However, other species, such as Myrmica ruba , do not avoid fungal contamination, including M. brunneum found in surrounding areas (Pereira et al 2021 ). In some instances, social insects can detect but react differentially to diseased workers outside versus inside the nest, with health-detectable cues tunable within the social context (e.g.…”