Fig. 2. Oviposition site preference on menthol in two differently exposed lines.

To test the effect of our experimental design on oviposition-site preference, we compared the preference to P- and M-food (shaded and filled circles, respectively) between two F1 progenies originated from parents (F0; empty circles), which were either (B; exposed line) or not exposed to M-food (A; unexposed line). The menthol preference indices (MPIs; values shown between pairs of circles) were measured between two sites containing either only P-food (no. 1) or P- and M-foods (no. 2). The MPIs of the four F1 sublines (two from unexposed parents  =  nos. 3–4; two from differently exposed parents  =  nos. 5–8) were also measured (n = 8–10). The number of eggs laid by females of each line is shown in Table 1.