Figure 2.

A model for the mechanism of caste differentiation and control in colonies of T. styraci. At the individual level, two factors are involved in soldier differentiation: normal aphids as an inducing cue and soldiers as a suppressing cue. At the colony level, positive and negative feedback is operating to control soldier production: higher density of normal aphids induces soldier production, whereas successive elevation of soldier proportion suppresses further soldier production, whereby investment to soldier production at the colony level is controlled within an appropriate range. In this way, simple responses of aphid individuals to local environmental cues can be integrated into a highly organized regulation of the whole colony.