Fig. 1. Procedures of menthol exposure.

Schematic representation of the (A) experimental device used for egg-laying behaviour and (B,C) the two procedures used to expose Drosophila melanogaster wild-type lines to food enriched with 0.1% menthol (M-food). (A) Females laid eggs in a device made with a petri dish covered with a glass dish and containing two egg-laying sites either filled with M-food or with P-food (see Materials and Methods). (B) Lines (issued from parental lines; empty circles) were either continuously raised on plain food (P-food; P-forced line, shaded circles) or on M-food (M-forced line, filled circles). At each generation (from F1 to Fn), flies of the P- and M-forced food were tested for choice between M- and P-food (pairs of circles connected on either side). (C) Lines were established on their preference when tested in dual-choice between P- and M-food. On the left side, eggs laid on P-food were repeatedly used to generate the P-choice line until the Fn generation. In parallel (right side), eggs laid on M-food were used to generate the M-choice line until the Fn generation. Oviposition site preference was measured in the two procedures.