Larvae expressing Crei\ChR2^Or42b.PH exhibit an increased preference for blue light compared to controls, resulting in significant suppression of phototaxis. As in controls, the larvae show a photophobic response to white light, and this is enhanced when the Or42b-expressing neurons are activated in blue light for 60 seconds prior to the test. No enhancement is seen when the larvae are stimulated with red light. Activation in blue light also results in an increased response to ethyl acetate, but not acetophenone, compared to non-activated controls. No defects in thermotactic behavior are observed.