Quarantining behaviour in ants: are Myrmica aphid milkers able to detect and get rid of fungus‐contaminated aphids?

Abstract

AbstractFungal infections are highly dangerous for social insects including ants. Close trophobiotic interaction between ants and aphids promotes infection transmission, as aphids can be a disease vector. The ability of ants to detect fungus‐infected aphids and get rid of them is important to the prosperity of both symbiotic partners. However, the diversity of quarantining behaviour among ants is still poorly studied. Here, the behaviour of honeydew foragers of two ant species – Myrmica rubra L. and Myrmica scabrinodis Nylander (Hymenoptera: Formicidae, Myrmicinae, Myrmicini) – was studied in laboratory towards Schizaphis graminum (Rondani) (Hemiptera: Aphididae, Aphidini) aphids contaminated with the generalist fungal pathogen Beauveria bassiana (Balsamo‐Crivelli) Vuillemin (Hypocreales). This fungus attacks a wide range of hosts including aphids and ants. The removal of conidia‐contaminated aphids from the host plant was found not to be typical of the ants studied. Aphid milkers of M. rubra and M. scabrinodis usually displayed non‐aggressive behaviour (tolerance, antennation, honeydew collection, grooming) towards the experimental aphids regardless of whether they were covered with conidia or not. Neither ant species, nor the number of milkers had significant effects on their behaviour towards ‘infected’ aphids. However, some individuals were found to demonstrate quarantining behaviour in full. They quickly detected and removed contaminated aphids, placing them at some distance from the plant. Moreover, in addition to the simple carrying of ‘infected’ aphids down, the more effective technique of dropping them from the plant was noted as well. Ants of the genus Myrmica appear to have a tendency to perform a certain sequence of actions to remove conidia‐contaminated aphids from the plant. It is likely that in larger colonies or under conditions of increased risk of infection with entomopathogenic fungi, some Myrmica ants are able to deploy and actively use the behavioural pattern of quarantining behaviour to increase their viability.