sGC mutants disconnect taste and aggregation behaviour. The time course of aggregation on the two spots was analyzed with 200 flies. We used a chamber and two spots of grape juice. One spot was complemented with denatonium, conferring a bitter taste (see the drawing in figure 5, and Methods section). (top) The graph represents the time course of the ratio of numbers of flies on grape juice versus denatonium. GC207ca and GC253bv were tested along with the rescue hsp-sGC; GC207. Values are mean ± SEM (n = 10). Statistics for mutants versus genetic background at 10 hours: T value 2.32, P = 0.03, degrees of freedom: 18 (GC253); T value 2.91, P = 0.01, degrees of freedom: 18 (GC207). We observe that rescue (double heat shock: at late third larval stage and 3 day old adult) significantly restores the initial phenotype. (bottom) We tested bitterness recognition by the taste sense organs. Thirty flies were analyzed individually after they had been starved for 5 hours (received only water/agar). They were placed in the chamber and had to choose between two alternatives to feed (grape juice spot or grape juice/quinine spot) (see drawing in figure 5). Flies tended to fly away after proboscis extension when they detected quinine. Arbitrarily, we counted flies feeding for more than 10 seconds on a spot.