Fasting and chemical signals affect recruitment and foraging efficiency in the harvester ant, Pogonomyrmex vermiculatus

Ants are central-place foragers, their foraging strategies varying from solitary to group foraging. Although the ancestral South American species, Pogonomyrmex vermiculatus, produces alkylpyrazines which attract foragers, this species exhibits solitary foraging behaviour in the field. This restriction was explored by evaluating the effects of fasting and presence of artificially applied trail pheromones on recruitment and foraging of P. vermiculatus. A circular arena connected to the nest at its center was divided into 12 equal sectors with a screen near the peripheral end of each sector. Prey was offered behind the screen in one of the sectors to ants exposed to different periods of fasting. A pyrazines trail was applied or not to the sector with prey. In general, the number of active foragers in the experimental arena depended on experimentation time. Preferential and time-dependent recruitment was observed in the sector with pyrazines. The colonies that used the pyrazines trail discovered the food patch faster and removed prey at a higher rate than colonies not exposed to pyrazines. Collectively, the results show that in Pogonomyrmex species, the ancestral character 'solitary foraging' shows behavioural plasticity when ants are confronted with trail pheromones stimuli and are under fasting stress.