Bimodal response in a chemotactic behaviour of Drosophila larvae to monovalent salts

A chemotactic behaviour in Drosophila larvae to monovalent salts was investigated. Larvae showed clear-cut bimodal responses; they preferred low concentration of salts and rejected high. For example, they were attracted to solutions over the range of concentrations of NaCl from 10^?4 M to 10^?1 M but avoided concentrations above 2 × 10^?1 M.The responses to KCl, KBr and Kl showed differences in attraction whereas avoidance thresholds were similar. On the other hand, when the responses to ChCl and ChBr were compared with those to KCl and KBr respectively, only the avoidance responses were depressed. Furthermore, from choice experiments between KCl, NaCl and ChCl, it was shown that cations did not affect the attraction responses.The results observed strongly suggest the existence of two salt receptors (or receptor sites) which act antagonistically on the chemotaxis.