Behaviours indicating cannibalistic necrophagy in ants are modulated by the perception of pathogen infection level

Abstract

Cannibalistic necrophagy is rarely observed in social hymenopterans, although a lack of food could easily favour such behaviour. One of the main supposed reasons for the rarity of necrophagy is that eating of nestmate corpses carries the risk of rapid spread of pathogens or parasites. Here we present an experimental laboratory study on behaviour indicating consumption of nestmate corpses in the ant Formica polyctena. We examined whether starvation and the fungal infection level of the corpses affects the occurrence of cannibalistic necrophagy. Our results showed that the ants distinguished between corpses of different types and with different levels of infection risk, adjusting their behaviour accordingly. The frequency of behaviours indicating cannibalistic necrophagy increased during starvation, although these behaviours seem to be fairly common in F. polyctena even in the presence of other food sources. The occurrence and significance of cannibalistic necrophagy deserve further research because, in addition to providing additional food, it may be part of the hygienic behaviour repertoire. The ability to detect infections and handle pathogens are important behavioural adaptations for social insects, crucial for the fitness of both individual workers and the entire colony.

Protective behavior or ‘true’ tool use? Scrutinizing the tool use behavior of ants

“…A third possible explanation is that colonies that once experienced prolonged starvation compensate by utilizing food in greater amounts in order to be prepared for another starvation period. A similar phenomenon was described for Formica polyctena foraging on nestmate corpses after a satiation period following feeding stress (Maák et al, 2020). In satiated colonies, the majority of corpses that were offered them were taken back to the nest and consumed in greater quantities than in control (before starvation) colonies.…”

Wood Ants: Important Components of the Forest "Immunity System"

“…Similarly, our results show that the presence of F. polyctena nests reduced the number of infected trees by bark beetles. However, in our scenario, the reduction of this other arthropod groups is the result of an indirect effect of the monopolization of resources and dominance of the red wood ants (47). The complex polydomous system of F. polyctena requires a large amount of food that is provided by foraging in mass (19,72), covering an extensive area of the forest.…”

Wood ants as biological control of the forest pest beetles Ips spp.

“…Our results show that the presence of F. polyctena nests reduced the number of infected trees by bark beetles. In our scenario, the reduction of this arthropod group might be the result of a combination of a direct effect linked with their predation habits and an indirect effect of the monopolization of resources, the aphid colonies (constituting their stable source of carbohydrates, important in maintaining their large colony size), by the red wood ants 66 .…”