The diel activity pattern of Neoetnpheria ferruginea, a harmful fungus fly in the sawdust-based cultivation of shiitake, Lentinula edodes, was studied at 20 degrees C under a photoperiodic regime consisting of a 16-h photophase and an 8-h scotophase. Adult eclosion occurred at photophase in 93% of males and 95% of females. Adult activities showed two peaks: one around when the light was turned off and the other soon after the light was turned on. Copulation occurred mainly around when the light was turned off (40%) or on (40%). These results suggest that the adults are active mainly at dusk and dawn under natural conditions. The duration of copulation was 16.6 +/- 7.7h (mean +/- SD).