Waste management in the leaf-cutting ant Acromyrmex lobicornis: division of labor, aggressive behavior, and location of external refuse dumps

BALLARI, SEBASTIAN; FARJI-BRENER, ALEJANDRO GUSTAVO; TADEY, MARIANA

JOURNAL OF INSECT BEHAVIOR

SPRINGER/PLENUM PUBLISHERS

Año: 2007 vol. 20 p. 87 - 98

0892-7553

The social organization in leaf-cutting ants improves the efficiency of some tasks such as foraging. However this also implies some risks, like for example the spread of diseases. The accumulation and handling of waste materials from the fungus culture increases that risk because they harbour microorganisms that are harmful for the ants and their mutualistic fungus. Consequently, leaf-cutting ants should manage their waste in a way that minimizes the risk of infection. We investigated whether in the leaf-cutting ant Acromyrmex lobicornis, waste-worker ants (a) also perform roles in foraging or mound maintenance, (b) are morphologically different than other ant workers, and (c) are aggressively discriminated by other workers ants from its own colony. In addition, we investigated whether the location of external waste piles minimizes their probability of spread to the ant nest. In the filed, we (a) marked with different colours waste-worker, foragers and mound-workers and monitored if these working ants interchange their tasks, (b) measured head width, head length, hind femur length and total length of waste-workers, foragers and mound-workers, (c) forced encounters between waste-workers and foragers, and (d) measured the cardinal orientation of the waste piles in relation to the mound in 100 nests. Waste-workers ants did not perform other function outside the nest; neither foragers nor mound-workers managed the waste. Moreover, waste-workers were smaller than foragers and mound-workers, and were attacked if they tried to ingress to their nest using foraging entrances. The location of external refuse dumps also appears to reduce contamination risks. Waste piles always were down-slope, and often follow the main wind direction. The importance of behaviours such as the division of labour, aggressions against waste-workers and nest compartmentalization (i.e., the orientation of external waste piles) to minimize the spread of pathogens is discussed.