Fig. 2. (A–M) Changes in the amounts of 13 chemicals in three different regions of the central nervous system during successive stages (1–9) in the isolation of long-term gregarious phase locusts (stage 1; darkest grey background) and the gregarization of third generation solitarious locusts (stage 6; white background). Values (mean ± S.E.M.) are the amounts found in the brain (red circles) excluding optic lobes, optic lobes (blue triangles) and the thoracic ganglia (green squares) for final larval instar nymphs at the stages of isolation or crowding indicated on the x-axis. N=9–12 for each point. Note that the values for citrulline are ln transformed. Stages as in Fig. 1.