Pupal development times and thermal unit requirements, daily adult eclosion patterns, and the durations of phases of emergence of the Mexican rice borer,Eoreuma loftini(Dyar), adult sexes were observed under reversed photoperiodic and thermoperiodic conditions. Female pupae required fewer days and thermal units for development than did males. Both sexes eclosed early in the scotophase; eclosion of adult males and females was complete within ≍ 1.7 and 4.5 h of last light, respectively. Newly emerged males required less time than females to inflate and dry their wings and less time for the entire emergence process (eclosion to wings dried and folded in a normal resting position). The temporal patterns of emergence suggest that efforts to observe emergence in sugarcane fields should be concentrated in the early scotophase. The short duration of the emergence process will limit the time during which newly emerged moths can be identified. Therefore, cage studies of emergence may offer a greater likelihood of success than studies relying on direct observation, especially under the usual conditions of low E. loftini population intensity and high crop biomass.