Third and fourth instars of Wyeomyia smithii were reared in Giemsa stain at 4 concentrations between 4 x 10(-7) and 10(-5) g/liter. The mosquitoes retained the blue mark as adults and remained marked throughout their laboratory life. Concentration of Giemsa significantly affected eclosion success but had no significant effect on mean days to pupation or days as a pupa, male or female adult longevity, per-capita female fecundity or fertility. Larval exposure to low concentrations (4 x 10(-7) or 10(-6) g/liter) of Giemsa stain provides an effective lifetime tag for otherwise indistinguishable laboratory populations.
