The leaf-cutter ant Atta laevigata (Smith, 1858) is considered a major pest of major economic
importance in many Neotropical habitats. This species specializes in foraging on monocot and
dicot native and cultivated plants of different biomes throughout South America, resulting in
significant losses due to leaf-cutting activities. Due to the marked polymorphism among
workers and a complex social organization, the colonies of these ants have developed
physical, symbiotic and behavioral mechanisms that allow them to overcome the actions of the
various methods used to manage their populations, making their control difficult and costly. As
an alternative method, an important strategy is the use of the small parasitoid flies of the family
Phoridae (Diptera). The phorids use the leaf-cutting ants Atta spp. as hosts, parasitizing the
adult workers, and thus have the potential to be used in biological control programs of these
species. The present study was conducted to determine the parasitism of A. laevigata worker
castes by phoridae flies between worker castes and between colonies, and to verify the spatial
fidelity of workers to nest entrances. Ants of four castes were collected from the trails and nest
entrances of 18 mature colonies in the field. A total of 21,254 ants were collected on the trails
and 14,649 collected on the mounds. Parasitism on the trails was 5.23% (1,102 foragers and
10 soldiers) and on the mounds was only 0.18% (25 diggers and 2 soldiers). On the trails,
46.2% were attacked by Apocephalus attophilus Borgmeier, 1928, 22.6% by Myrmosicarius
grandicornis Borgmeier, 1928, 16.6% by Eibesfeldtphora erthali (Brown, 2001) and 14.6% by
Apocephalus vicosae, Disney 2000. Only two phorid species, M. grandicornis and E. erthali,
were observed parasitizing burrowers, while only E. erthali parasitized soldiers. This is the first
time that Atta spp. excavators and soldiers have been shown to be parasitized by phorids.
When evaluating parasitism among areas, A. attophilus accounted for the highest proportion
of parasitism of workers collected in PAL (74.44%) and EMB (77.24%), followed by E. erthali
in the same areas. On the other hand, M. grandicornis and A. vicosae were the species with
the highest proportion of parasitism in the UFT area, with 55.4% and 30.63%, respectively.
Among the colonies, parasitism of A. laevigata by phorid species was generally alternating.
When considering parasitism preference with respect to worker size, M. grandicornis (98.41%)
and A. vicosae (94.44%) preferred to parasitize smaller workers, while A. attophilus (61.52%)
preferred to parasitize larger workers, whereas parasitism by E. erthali hardly varied in worker
size preference among colonies. The workers showed fidelity to the trails and to the mounds
in the same nest. And no marked worker was observed transitioning from trails to mound and
vice versa in either of the two bioassays.
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