Walking and foraging activity of Acromyrmex subterraneus molestans (Hymenoptera: Formicidae) at different temperatures

Acromyrmex subterraneus molestans (Hymenoptera: Formicidae) is a leaf-cutting ant species found in the Brazilian Cerrado and the Atlantic Forest and causes serious damages to cultivated plants. Knowledge about its foraging activity could help to improve the integrated pest management of this species and to better understand its ecology. The relationship between ambient temperature and the biomass collected by individuals of one Ac. subterraneus molestans colony was studied in the laboratory. The colony remained in an experimental room at 24°C and its foragers had access to an arena in an incubator set at six different temperatures (10, 16, 22, 28, 34 or 40°C). Fresh leaves of Hibiscus sp. were put in the arena and the flow of ants leaving and returning to the nest, the proportion of ants returning to the nest with a leaf fragment, as well as the dry mass of these fragments, were evaluated during 1 h for each temperature. The head width of foraging ants (laden and unladen) and their running speed were also measured. The rate of biomass collected was almost null at 10°C, increased from 16 to 34°C, and decreased abruptly at 40°C. The size of the workers did not vary across temperatures, and the running speed increased with increasing temperatures but more rapidly for unloaded ants than for loaded ones. The lower flow intensity at 28 and 40°C was somewhat compensated at the individual level by the selection of larger leaf fragments or by an increase in the probability to return loaded to the nest, respectively. The results obtained in this study could improve the management of these ants, allowing to target the most favourable meteorological conditions to apply toxic baits, increase the probability for the baits to be carried to the nest, in addition to reducing their availability to nontarget organisms. Furthermore, they could be used to make predictions on the effects of global warming on the foraging activity of this species.