Abstract
Prior to the beginning of a project to eradicate the melon fly, Dacus cucurbitae COQUILLETT, from Kume Is., a pilot release experiment was made on Kudaka Is. from November 14, 1974. A tentative estimate of the total number of wild melon flies in October was ca. 10, 000. The ratio of sterile to wild males on Kudaka Is. during the study period reached a maximum of 8.23, when we released ten times as many sterile flies as the estimated number of wild flies in each of 9 weekly releases. Percent hatch of eggs collected from loofahs on Kudaka Is. decreased from 55.6 on December 11 to 7.0 on January 14. On the other hand, the percent egg hatch in the control area on the Island of Okinawa was 45.8 to 86.7%. The pupae released from release buckets were seriously attacked by mammalian predators, such as rats and mice. Estimated mortality of pupae by predators increased from 24.7% on the first release to 84.6% in the 4th release. In spite of high pupal mortality, the main reason for the good ratio of sterile to wild males was considered to be the seasonal decline in the wild population. The results obtained suggested that the ability of sterile males to compete with wild males was not so remarkably decreased under fluctuating field conditions.
