Parasitismo por moscas phoridae entre castas e entre colônias da saúva atta laevigata (Smith, 1858) (Formicidae) e a fidelidade espacial das operárias às entradas de ninhos

Abstract

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.