Abstract
Some species of aphids are known as social insects. In social aphids, altruistic individuals called “soldiers” perform colony defense and housekeeping. Tuberaphis styraci, which lives in colonies inside plant galls, is a social aphid with sterile soldier caste. In T. styraci, younger soldiers preferentially perform housekeeping while aged soldiers exclusively perform colony defense, exhibiting a division of labor according to soldier age. We identified two aphid pheromones, corpse-recognition pheromone（linoleic acid） and alarm pheromone （trans-β-farnesene）, and two plant-gall allelochemicals, alarm signal （trans-2-hexenal） and “home sweet home” signal （linalool）, which mediated defense and housekeeping communications in this species. New soldiers preferentially responded to the corpse-recognition pheromone by performing cleaning behavior. Young soldiers chieｆｌｌy responded to the corpse-recognition pheromone and alarm signal by performing cleaning and attacking behaviors. Aged soldiers mainly responded to the alarm pheromone by performing attacking behavior. This age-specific behavioral response can explain the age-dependent division of labor in this species. Notably, when the concentration of each pheromone and allelochemical was elevated in the colony, soldiers were able to perform all kinds of tasks regardless of their age. Combination of alarm signal and alarm pheromone promoted attacking response of soldiers, while “home sweet home” signal inhibited their alarm response and so appeared to relax the aphids and diminish social disruption inside the galls. T. styraci regulated task allocation by utilizing various pheromones and allelochemicals and exhibited a flexible division of labor. Based on these results, we discuss the ecological and physiological mechanisms that coodinate the aphid social system.
