Tasks performed by different groups of foragers and regulation of foraging activity in the Mediterranean harvest ant Messor wasmanni (Hymenoptera, Formicidae)

The moment-to-moment tasks performed by an individual can change in response to a shift of internal, e.g. body size or age, and external conditions, e.g. the number of workers currently engaged in another task. For this reason, the term task allocation is replacing the earlier concept of division of labor for describing an invariable association between worker body size and task. In the present study we hypothesized that, in the absence of changing conditions, different sized workers tend to perform different tasks. We also evaluated, using baits, the ability of colonies to regulate foraging activity through interactions between outgoing and returning foragers and the effect of ground temperature on the relative participation of different-sized workers to the foraging activity. Results suggest the existence in large and well-established colonies inhabiting a typical Mediterranean grassland area, of different-sized workers performing different tasks outside the nests. Moreover, we noticed the ability of colonies to adjust the relative participation of different sized foragers when provided with different-sized resources (baits). Finally, we recorded an effect of temperature on the average size of foragers, although no effect on size distribution was found.