Abstract
The emergence time of two black-flies, Simulium (Simulium) arakawae and S. (Gnus) bidentatum, were observed in the laboratory by rearing field-caught pupae in Kagoshima, Japan. Under natural condition, most flies of both species were found to emerge during the daylight period with the peak of emergence between 6 : 00 and 12 : 00. There was no sexual difference in emergence time. When pupae were set under continuous light or reversed light-dark cycle conditions, they emerged during the period corresponding to daylight period of normal condition. These results indicate that the emergence pattern is probably controled by the rhythm which was established by the light-dark cycle during larval stage.
