Of 9 dyes fed to workers of Coptotermes formosanus, only oil soluble Deep Black BB and Sudan Red 7B stained the termites sufficiently and were retained long enough to be useful as markers. Workers fed Red 7B, however, absorbed the dye faster, retained the dye longer and had a lower mortality rate than those fed Deep Black BB. Red 7B was found in the fat bodies, mid- and hindguts, muscles, brain, and in the protozoa, but not in Malpighian tubules and tracheal matrix. The density of the termites in the staining chamber seemed to affect the depth of staining and the numbers of protozoa in the termite. The termites stained at a density of 900 individuals per petri dish stained more deeply and better than those stained at 100 individuals per petri dish. Moreover, the numbers of protozoa in the termites stained at the 900 termite density were higher than in termites stained at 100 per petri dish. Red 7B demonstrated all the characteristics required for a suitable marker for C formosanus
