Estimation of possible sources for wind-borne re-invasion of Bactrocera dorsalis complex (Diptera: Tephritidae) into islands of Okinawa Prefecture, southwestern Japan

Abstract

The oriental fruit fly and its relatives, Bactrocera dorsalis complex Hendel (Diptera: Tephritidae) were eradicated from the islands of Okinawa Prefecture, southwestern Japan, in 1986. Since just after the eradication, however, re-invasion of B. dorsalis complex has been continuing to date, and the cause of the re-invasion has not been fully analyzed yet. It is believed that there are two possible routes of the re-invasion: wind-borne immigration and importation of infested fruits. This study analyzed the former natural factor by calculating backward trajectories for B. dorsalis complex males caught in monitoring traps from 1986 to 2012. In 65.8 % of the total re-invasion events, trajectories could be traced to at least one of the insect’s native regions: Taiwan (71.8 %), the Philippines (24.3 %) and southern China (3.9 %). In these possible immigration events, the influencing meteorological factors were found to be fronts (44.6 %), typhoons (36.0 %), high-pressure system ridges (12.0 %) and tropical depressions (7.5 %). The number of insects caught per trap was found to greater on the islands near the estimated sources than those further from the sources, supporting the hypothesis of wind-borne immigration of B. dorsalis complex into Okinawa.