Phorid fly parasitism rates vary between individual colonies of the leaf-cutting ant Atta laevigata

1. Phorid flies are important natural enemies of leaf-cutting ants. Female phorids lay eggs in the worker ants' bodies and the parasitoid larvae feed on the host's internal tissues. 2. Here we investigated the parasitism rates by four species of phorids when attacking individual Atta laevigata colonies at three different field sites in order to further understand the host-parasitoid relationship. 3. There were distinct variations in parasitism rates when comparing phorid species attacking individual colonies. In 13 of the colonies sampled, parasitism by Apocephalus attophilus or Eibesfeldtphora erthali was predominant. However, in four of the colonies, Myrmosicarius grandicornis and Apocephalus vicosae were the predominant species. 4. Variations in parasitism rates by the four phorid species were investigated in relation to the size of the potential hosts that had been collected from the foraging trails of each colony. 5. When correlating the size of potential hosts to phorid species, ants with head capsule widths of >2 mm were predominantly parasitized by A. vicosae and E. erthali. Smaller ants, with head capsule widths of 2 mm or less, were predominantly parasitized by A. attophilus and M. grandicornis. 6. The highest parasitism rates by E. erthali were observed in individual colonies that had the highest proportions of large workers on the trails. 7. Although almost half the size of E. erthali, A. attophilus parasitized both large (head capsule width > 2 mm) and small workers (<2 mm). This was related to the fact that between 1 and 16 larvae can develop within an individual host, depending on host size. 8. M. grandicornis parasitized smaller workers (mean head capsule width = 2 mm) as these phorids are themselves small and only one larva develops within each host. 9. This study demonstrated that the parasitism profiles of individual A. laevigata colonies were related to the size of foragers on the trails.

Automated summary

Phorid flies are important natural enemies of leaf-cutting ants. This study investigates the parasitism rates of four species of phorids on individual colonies of Atta laevigata and finds that the parasitism rates vary with phorid species and the size of the host ants.