Phorid parasitoid attack triggers specific defensive behaviours and collaborative responses in leaf-cutting ants

Being social adds another level of defence for organisms: social defences. Beside individual defensive behaviours, social organisms can limit parasite infections by using collective and collaborative behaviours. We evaluated whether the social defence of the leaf-cutting ant Atta cephalotes is specific against phorid parasitoids and the occurrence of collaborative responses depends on the context, i.e. ant activity in foraging trails and number of phorid attacks. We exposed workers to freshly dead specimens of phorids, non-phorid flies or a control without flies in different ant flux conditions and number of attacks and evaluated ant response. We found that workers responded more frequently to phorids than to non-phorid flies and controls suggesting that specific chemical or visual cues of phorids are recognized by leaf-cutting ants triggering a behavioural response. Although the probability of collaborative defences was similar in different ant flux conditions and number of attacks, they occurred more frequently when ants were attacked by a phorid than when they were attacked by the other treatments. Therefore, we demonstrated that leaf-cutting ants differentiate parasitoid flies from other flies, showing a collaborative response against them, in contrast to the other flies and the control, for which almost no collaborative responses were displayed.