Diary and seasonal foraging activity of the leaf-cutter ant Acromyrmex crassispinus (Forel) in a Chaco Serrano forest from Córdoba-Argentina.

BARRERA, C; BUFFA, L.; VALLADARES, G.

Fortaleza

Congreso; XXI Simposio de Mirmecologia; 2013

Leaf-cutter ants are widely known for their habit of cutting plant leaves and other structures and carrying them to their nests, to serve as substrate for cultivating fungus on which the colony feed. Their foraging activity may show diary and seasonal changes, being influenced by environmental conditions such as temperature and humidity. The present work aimed to characterize the diary and seasonal foraging pattern of Acromyrmex crassispinus (Hymenoptera: Formicidae) in a continuous (over one thousand hectares) area of Chaco Serrano in the Province of Córdoba, in Central Argentina. We randomly selected five nests at the edge (up to 5 m from the tree line) and five in the forest interior (at least 20 m from the tree line). We evaluated foraging activity on these nests by recording, in the morning and afternoon of two consecutive days in each season (from April 2010 to February 2011) the number of ants carrying plant material towards the nest, passing through a fixed point during three minutes of observation. Maximum and minimum air temperature was also recorded in each opportunity. On the spring and summer samplings, we also measured nest temperature and soil temperature near the nest. Data were analyzed by means of ANCOVA, linear regressions, Wilcoxon test and Kruskal Wallis. Along the year, foraging activity was directly related to maximum air temperature (p=0.05) and independent of minimum temperature values, at both interior and edge locations. However, under warm weather (spring-season) foraging activity was inversely related to soil temperature (p=0.05) though independent of nest temperature (p>0.05). In turn, nest temperature was significantly higher than soil temperature (p0.05), but their activity was significantly higher in the forest interior than at the edge (p= 0.013). Moreover, foraging activity was more stable at the interior, showing seasonal differences only at the border (p=0.012) where the highest activity was observed in spring and the lowest in winter. The increased and uniform nest temperature, in comparison with the surrounding ground, could be related to the mound nest structure adopted by A. crassispinus in the region. This type of structure has been proposed to maintain optimal temperature and humidity levels. On the other hand, the continuous foraging activity of this species in the interior (where previous studies recorded higher nest abundance) contrasting with its lower and fluctuating presence at the edges, supports the hypothesis of A. crassispinus representing a possible indicator of forest quality.