Figure 1. Olfactometer.

Individual cockroaches were given a simultaneous choice between two stimulus odours in a glass Y-olfactometer. A pump pushed clean controlled humidified air through the four small vials, the two arms and the starting stem of the olfactometer. Each arm (arms I, II) was connected to two vials placed in a row (vials 1, 2). Vials were either empty (A: clean air), or contained fresh food (F), recently consumed food (NF), non-feeding conspecifics (C), or feeding conspecifics (FC). Choice of the test cockroach for a stimulus odour (odour 1 or 2) was assessed by the total time spent in each olfactometer arm during 5 min tests (see details in Table 1).