Tutl mutant larvae displayed normal phototaxis behaviors. (A) A schematic diagram of the phototaxis assay. Briefly, the arena is divided into four quadrants, and two of which are covered with black paper. The arena is then illuminated with a light source from above. (B) The performance of larvae in phototaxis assay was examined (four trials). Performance index (PI) was estimated as follows: PI = (number of larvae in two dark quadrants - number of larvae in two bright quadrants) / (number of larvae in two dark quadrants + number of larvae in two bright quadrants). There were four trials for each genotype, n=20 per trial. p>0.05, one-way ANOVA test. Error bars represent SEM.