Mimetic host shifts in a social parasite of ants: Behavioural study

We assessed the social status achieved by each form of M. rebeli within colonies of each Myrmica species in a standard bioassay that involved perturbing laboratory ant colonies and recording the order in which the ants' own brood or the mimetic caterpillars were rescued. Groups of 5 butterfly larvae from each region were adopted into matching colonies of niaive French M. schencki and M. sabuleti. Every test colony also contained 5 brood items each of kin ant pupae, large and small larvae, making a total of 20 immature individuals and 20 workers per replicate. Cultures were established in laboratory colonies containing a small moist sponge pad beneath an inverted 6 cm diameter saucer with a notched entrance, under which the ants gathered their brood and M. rebeli. Three hours after the M. rebeli caterpillars had been introduced, we perturbed the experimental colonies by uncovering the brood chamber and relocating it over another pad nearby; we then recorded the order in which the nurse ants rescued their 15 brood items or the 5 M. rebeli and carried them into the new nest. The same experiment was repeated 7 days later, which represents a sufficient period for M. rebeli caterpillars to attain their maximum potential integration with a host society, yet remaining a similar size to when first adopted, i.e. the same size or smaller than the Myrmica pupae and large larvae. The number of replicates for each ant-butterfly combination tested varied due to a lack of some ants and butterfly deaths (especially with unnatural hosts).