Larvae expressing Crei\ChR2^Or24a.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 Or24a-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 acetophenone, but not ethyl acetate, compared to non-activated controls. The increase in response is detected up to 120 minutes after blue light stimulation and lost by 180 minutes. No defects in thermotactic behavior are observed.