Pupal sexes of the most common mosquito species were determined in the course of biweekly censuses (with replacement) of the contents of 3–7 tree holes from 1980–2003 in Vero Beach, FL. A significant (P < 0.001) male bias was detected over this period for the most abundant species, Aedes triseriatus. No significant deviation from a 1∶1 sex ratio was detected among pupae of Toxorhynchites rutilus or Ae. albopictus, the latter species occurring in this community only since 1991. Although pupae of Ae. triseriatus were recorded during every month of the year, significant male biases were detected only in February–May, August, and December. These results are interpreted in the context of multivoltinism and the previously documented differential sensitivity of male and female eggs of this species to hatching stimuli. Sex-specific responses to hatching stimuli are judged to be present but less pronounced in eggs of Ae. albopictus. Male biases in container Aedes are likely associated with sexual selection, which may also explain seasonal changes in sex ratios, whereby early males compete to mate with high-fecundity females. The overproduction of Ae. triseriatus males may be counterbalanced by increased fitness of females, which are known to predominate in delayed hatches.