(A) NaCl chemotaxis gradient was generated by juxtaposition of two layers of agar solution, the bottom layer contained 50 mM NaCl and the top layer did not contain NaCl, effectively creating a 5 mM/cm linear gradient. (B) CuSO4 chemotaxis gradient was generated by juxtaposition of two layers of agar solution, the bottom layer contained 5 mM CuSO4 and the top layer did not contain CuSO4, effectively creating a 0.5 mM/cm linear gradient. (C) Scoring method used for both chemotaxis assays to soluble chemicals. Animal position was marked on the plate when the assay finished, then chemotaxis indexes (C.I.) were scored according to the formula shown above. (D) Scoring method used for chemotaxis to volatile odorant isoamyl alcohol (IAA). Animal position was marked on the plate when the assay finished, then chemotaxis indexes (C.I.) were scored according to the formula shown above. Spots A and B correspond to the test spots (IAA [10–2]) and spots C and D to the control spots (EtOH). Spot position was defined at 0.5 cm away from the plate edge. Animals were placed in the landing zone (gray dashed circle in the center), those that did not leave the landing zone were excluded from the scoring. (E) Thermotaxis assay was done in 9 cm plates divided into four sections each corresponding to an increasing temperature from left to right. Animals were initially positioned in the landing zone, indicated by a gray dashed rectangle in the center and allowed to navigate through the thermotactic gradient.